Journal of Colloid And Interface Science (v.343, #1)
Electrical and morphological properties of conducting layers formed from the silver–glass composite conducting powders prepared by spray pyrolysis
by D.S. Jung; H.Y. Koo; Y.C. Kang (pp. 1-6).
Silver–glass composite conducting powders used as a new material for electrodes were prepared by spray pyrolysis. Composite conducting powders had a core–shell structure, which was the same as that of glass-coated silver powders.Ag–glass composite powders with various glass contents and excellent conducting properties were prepared by spray pyrolysis. Irrespective of the glass content, all the prepared powders were found to comprise spherical particles with nonaggregation characteristics. The crystal structure of the powder particles resembled that of pure Ag particles, irrespective of the glass content. Conducting layers formed from pure Ag did not melt even when sintered at 400°C. On the other hand, conducting layers formed from composite powders containing 3 and 5wt% glass melted when sintered at 400°C. The optimum glass content of the composite powders was 3wt% at sintering temperatures of 400 and 450°C. However, the optimum glass content decreased to 1wt% when the sintering temperature was increased to 550°C. The lowest specific resistances of the conducting layers formed from the composite powders were 5.3 and 2.3μΩ-cm at sintering temperatures of 400 and 550°C, respectively.
Keywords: Silver; Conducting powder; Spray pyrolysis; Electrode material
Constructions of silver nanowires and copper oxide microrings by a surface-formation technique
by Teng-Yuan Dong; Chen-Ni Chen; Ching-Wen Wang; Wei-Ting Chen; Chiao-Pei Chen; Shu-Fan Lin; Shuchen Hsieh; Chiung-Wen Hsieh; Jenn-Ming Song; In-Gann Chen; Hsien-Tse Tung; Tzu-Hsuan Kao (pp. 7-17).
A simple method to form silver nanowires and copper oxide ring-shaped microstructure and solid-body dandelion-like spherical microstructure by thermal reduction of corresponding aqueous AgNO3 and Cu(NO3)2 droplets with TiO2 nanoparticles which were spin-coated on different matrices is described.We demonstrate a simple method to synthesize silver wires by thermal reduction of aqueous AgNO3 droplet with catalytic anatase TiO2 nanoparticles which were spin-coated on Si wafer. Structural characterization of the silver wires shows that the nanowires grow primarily along the [011¯] direction. SEM image of the silver wires clearly shows the catalytic TiO2 nano-cluster attached to the end of the each silver wire. Since the process was surfactant-free, the silver nanowires prepared by our method retain the excellent electrical conductivity. The intrinsic resistivity calculated from the current–voltage curve for a wire with 12880.41nm2 cross-section area was 18.72μΩ cm, which is about 11.6 times higher than that of bulk silver (1.61μΩcm). Our simple method can be also applied to generate CuO with ring-shaped microstructure by using ITO conducting glass as matrix. We have found that the size and reproducibility are well-controllable. A single phase of CuO ring-shaped microstructure with outer diameters ranging from ∼13 to 17μm and inner diameters ranging from ∼1.4 to 3.3μm was obtained. The composition of CuO microring was confirmed by thin-film XRD and XPS analyses.
Keywords: Silver; CuO; TiO; 2; Nanowires; Nanorods; Microrings; Thermal decomposition
One-step preparation of PS/TiO2 nanocomposite particles via miniemulsion polymerization
by Yanfei Wu; Yang Zhang; Jiaxi Xu; Min Chen; Limin Wu (pp. 18-24).
Raspberry-like PS/TiO2 nanocomposite particles have been prepared through a one-step method based on miniemulsion polymerization. The polymerization of styrene and sol–gel reaction of tetra-n-butyl titanate occurred simultaneously inside droplets.This paper presents a one-step method to fabricate PS/TiO2 nanocomposite particles via miniemulsion polymerization technique. In this approach, styrene (St) and acetylacetone (Acac) chelated tetra-n-butyl titanate (TBT) were confined in the miniemulsion droplets with the aid of cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and co-stabilizer hexadecane (HD). During the polymerization of St, TBT diffused towards the surface of the miniemulsion droplets owing to its hydrophilicity and yielded TiO2 particles via a sol–gel process. With the electrostatic interaction between the positively charged CTAB and negatively charged Ti-OH, TiO2 particles were coated onto the PS cores to form PS/TiO2 nanocomposite particles.
Keywords: PS/TiO; 2; Nanocomposite particles; Miniemulsion polymerization
CTAB promoted synthesis of Au nanorods – Temperature effects and stability considerations
by Richard Becker; Bo Liedberg; Per-Olov Käll (pp. 25-30).
TEM images of CTAB stabilized Au nanorods synthesized at four different temperatures. The mean aspect ratio fluctuates with increasing temperature; it decreases, then increases and finally decreases again, due to entropy and CTAB solubility. The use of CTAB in the washing medium after centrifugation considerably increases the stability of the Au nanorods.A systematic study is performed of the influence of surfactant and temperature on the aspect ratio and monodispersity of Au nanorods, synthesized by a seed-mediated growth technique in water using cetyltrimethylammonium bromide (CTAB) as surfactant. The changes in aspect ratio with temperature show an “anomalous” behavior, where the aspect ratio first decreases with increasing temperature, reaching a minimum at about 55°C, and after that increases again reaching a maximum at about 80°C. A physical explanation of the observed behavior is proposed. It has also been studied how the CTAB concentration in the cleansing water used in the post-synthesis treatment of the samples affected the stability of the gold suspension. It was found that without the presence of a surfactant such as CTAB in the washing medium, only very few centrifugations can be carried out without considerable loss of product. Characterization of prepared samples was performed with UV–Vis and TEM.
Keywords: Aspect ratio; CTAB; Gold; Nanorods; Stability; Synthesis
Aqueous dispersions of silica shell/water-core microcapsules
by Michael O’Sullivan; Brian Vincent (pp. 31-35).
SEM of dried water-core/silica shell microcapsules.The preparation is described of water-core/silica-based shell particles, from W/O emulsion droplets, by adding alkoxysilanes to the oil-continuous phase, to form the shell by an interfacial condensation reaction at the W/O interface. In order to form relatively thick (and hence stronger) shells, it is found necessary to use a mixture of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEODMS), rather than TEOS alone. It is suggested that, in the former case, trans-shell diffusion of the alkoxysilane monomers (from the oil side) and water molecules (from the aqueous side) can continue, as a result of the higher permeability of the shells to these small molecules, thus allowing the interfacial condensation reaction to continue, even when the reaction would have ceased for a harder shell, having a much lower permeability, as occurs when TEOS alone is used. A successful method of transferring the water-core/silica-based shell particles from oil into water is described, based on the direct centrifugation of the particles from an upper oil phase (containing the dispersed particles initially) into a lower aqueous phase placed beneath, which contains a surfactant capable of adsorbing onto the particles and making them water-wetted.
Keywords: Core–shell particle; Water-cores; Silica shells; Microcapsule
Small angle scattering model for Pickering emulsions and raspberry particles
by Kjersta Larson-Smith; Andrew Jackson; Danilo C. Pozzo (pp. 36-41).
The present work derives an analytical small angle scattering model for Pickering emulsions and raspberry particles.Pickering emulsions, raspberry particles and other colloidal particle complexes are often characterized using small angle scattering techniques. The present work derives an analytical scattering model that accounts for the self-correlation of a spherical core and surface adsorbed particles as well as the particle–particle and core–particle correlation terms characteristic of Pickering emulsions and raspberry particles. It is shown that contrast matching of the scattering length density is not essential to obtain meaningful information as long as the scattering contrasts of all phases are precisely known. The derived equations are useful for analyzing data and planning experiments for Small Angle Neutron Scattering (SANS) and Small Angle X-ray Scattering (SAXS) involving these colloidal systems.
Keywords: Pickering emulsions; Emulsions; Scattering; SAXS; SANS; Colloids; Raspberry particles
Stability analysis of an encapsulated microbubble against gas diffusion
by Amit Katiyar; Kausik Sarkar (pp. 42-47).
Mechanisms for unstable equilibrium for an inelastic encapsulation (a) and stable equilibrium for an elastic encapsulation (b).Linear stability analysis is performed for a mathematical model of diffusion of gases from an encapsulated microbubble. It is an Epstein–Plesset model modified to account for encapsulation elasticity and finite gas permeability. Although bubbles, containing gases other than air, are considered, the final stable bubble, if any, contains only air, and stability is achieved only when the surrounding medium is saturated or oversaturated with air. In absence of encapsulation elasticity, only a neutral stability is achieved for zero surface tension, the other solution being unstable. For an elastic encapsulation, different equilibrium solutions are obtained depending on the saturation level and whether the surface tension is smaller or higher than the elasticity. For an elastic encapsulation, elasticity can stabilize the bubble. However, imposing a non-negativity condition on the effective surface tension (consisting of reference surface tension and the elastic stress) leads to an equilibrium radius which is only neutrally stable. If the encapsulation can support a net compressive stress, it achieves actual stability. The linear stability results are consistent with our recent numerical findings. Physical mechanisms for the stability or instability of various equilibriums are provided.
Keywords: Epstein–Plesset; Contrast agent; Ultrasound imaging; Bubbles; Dissolution; Interfacial rheology; Stability
New anthracene–tetrathiafulvalene derivative-encapsulated SWNT nanocomposite and its application for biosensing
by Min Song; Xuemei Wang; Wei Liu; Jinglin Zuo (pp. 48-51).
A novel anthracene–tetrathiafulvalene derivative has been synthesized and immobilized on single-walled carbon nanotubes through non-covalent sidewall functionalization.In this study, a novel anthracene–tetrathiafulvalene derivative has been synthesized and immobilized on single-walled carbon nanotubes through non-covalent sidewall functionalization. The new anthracene–tetrathiafulvalene (TTF) derivative-encapsulated SWNT nanocomposites were characterized using SEM, TEM, and Raman spectra and were utilized for biomolecular recognition. Our observations demonstrate that the new anthracene–TTF derivative-encapsulated SWNT nanocomposites can readily facilitate the biosensing and sensitive detection of DNA, which could be further explored for promising applications in bioelectronics and biosensors.
Keywords: Nanocomposites; SWNTs; Anthracene–tetrathiafulvalene derivative; Sensors; DNA
A simple method for preparation of Ag nanofilm used as active, stable, and biocompatible SERS substrate by using electrostatic self-assembly
by Renming Liu; Minzhen Si; Yipu Kang; Xingfa Zi; Zhenquan Liu; Deqing Zhang (pp. 52-57).
SEM micrograph of Ag nanofilm obtained by electrostatic self-assembly. The nanofilm is used as active and biocompatible SERS substrate in the analysis of biological macromolecules. The stability of the surface is checked by recording SERS relative intensity of sodium citrate at different times.A new SERS-active Ag nanofilm on the surface of a glass slide has been prepared by a low-cost electrochemical strategy using polyvinyl alcohol (PVA) at a proper voltage. The two-dimensional morphology of the Ag nanofilm has been examined by scanning electron microscopy (SEM). The average size of the aggregated particles on the surface of the Ag nanofilm is up to ca. 200±50nm, which is much larger than that of PVA-protected Ag colloidal nanoparticles (PVA–Ag CNPs, 45±8nm). Meanwhile, many nano-scale regions with average sizes of ca. 300±50nm are formed between the adjacent Ag nanoparticles. By the SERS measurements of human serum (HS) and hemoglobin (Hb), this Ag nanofilm is shown to be an excellent SERS substrate with good stability and biocompatibility. As the fabrication process of this SERS substrate is simple and inexpensive, this method may be used in large-scale preparation of substrates that have been widely applied in Raman analysis. In addition, this SERS-active Ag nanofilm can serve as a novel SERS substrate in biochemical analysis due to the biocompatibility.
Keywords: Surface-enhanced Raman scattering (SERS); Ag nanofilm; Human serum; Hemoglobin; Electrostatic self-assembly
Effect of total organic carbon content and structure on the electrokinetic behavior of organoclay suspensions
by B. Bate; S.E. Burns (pp. 58-64).
Zeta potential as a function of total organic carbon content, varying the length of one carbon chain.This experimental investigation measured the zeta potential of the clay mineral, montmorillonite, which was modified with six different quaternary ammonium cations. The organic cations were chosen to quantify the effect of cation functional groups, including chain length and cation size, on the resulting zeta potential; each of the six cations were exchanged onto the clay surface at three levels of total organic carbon. The zeta potential of the unmodified and the organically modified clays was measured as a function of pH, and in all cases, became less negative as the total organic carbon was increased and as the length of the attached carbon chain was increased, indicating that the organic cations were more strongly bound within the particle’s shear plane as total organic carbon content was increased. Measured zeta potential was also less negative for all clays tested (including unmodified montmorillonite) as pH was decreased. When compared on the basis of total organic carbon content, increasing the length of one carbon chain in the quaternary positions was a more effective method of neutralizing surface charge than was increasing the overall size of the cation (i.e., increasing the chain length in all quaternary positions).
Keywords: Montmorillonite; Organobentonite; Quaternary ammonium cation; Zeta potential
Control of the morphology and size of magnetite particles with peptides mimicking the Mms6 protein from magnetotactic bacteria
by Atsushi Arakaki; Fukashi Masuda; Yosuke Amemiya; Tsuyoshi Tanaka; Tadashi Matsunaga (pp. 65-70).
Magnetite synthesis using peptides mimicking the Mms6 protein from magnetotactic bacteria resulted in the formation of uniformsized cubo-octahedral crystals with a narrow size distribution.Mms6 is a dominant protein that tightly associates with the surface of bacterial magnetites in Magnetospirillum magneticum AMB-1. The protein has previously been shown to mediate the formation of uniform magnetite crystals of cubo-octahedral morphology consisting of (111) and (100) crystal faces with a narrow size distribution during chemical magnetite synthesis. In order to understand the role of this protein in chemical magnetite synthesis, magnetite formation was investigated using synthetic peptides mimicking the Mms6 protein. Particles that were synthesized in the presence of short peptides harbouring the C-terminal acidic region of Mms6 exhibited a spherical morphology with circularities of 0.70–0.90 similar to those of bacterial magnetites and particles formed in the presence of the Mms6 protein. In contrast, a rectangular morphology with circularities of 0.60–0.85 were obtained when other peptides were used for synthesis. The results indicated that the C-terminal region of the Mms6 protein has significant control over the morphology of magnetite crystals in the chemical synthetic method. This method can, therefore, be useful as an alternative method of controlling the size and morphology of magnetite crystals under ambient conditions.
Keywords: Biomineralisation; Biomimetic material; Peptide; Nanoparticle; Magnetotactic bacteria; Magnetic particles
Hydrothermal synthesis and luminescent properties of YVO4:Ln3+ (Ln=Eu, Dy, and Sm) microspheres
by Fei He; Piaoping Yang; Na Niu; Wenxin Wang; Shili Gai; Dong Wang; Jun Lin (pp. 71-78).
YVO4:Ln (Ln=Eu3+, Dy3+, Sm3+) microspheres with uniform morphologies were successfully prepared via a simple hydrothermal route using N, N-dimethylformamide as the solvent and polyvinylpyrrolidone as protective agent.Rare-earth ions (Eu3+, Dy3+, Sm3+) doped YVO4 microspheres with uniform morphologies were successfully prepared via a simple hydrothermal route using N, N-dimethylformamide (DMF) as the solvent and polyvinylpyrrolidone (PVP) as protective agent. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and the kinetic decays were employed to examine the resulting phase formation, particle morphology and luminescent properties. The XRD results reveal that all the doped samples are of high crystallization which are assigned to the pure tetragonal phase of YVO4. Additionally, the DMF/H2O volume ratio and the concentration of PVP both have obvious effects on the morphologies and sizes of the as-synthesized products. The sample prepared at 180°C for 24h with the DMF/H2O volume ratio of 3/1 and 0.4g/L PVP concentration exhibits uniformly spherical shape with the diameter of 1–2μm. Upon excitation by ultraviolet radiation or low-voltage electron beams excitation, the YVO4:Ln3+ (Ln=Eu, Dy, and Sm) samples show strong light emissions with different colors from the doped Ln3+ ions. These phosphors exhibit potential applications in the fields of fluorescent lamps and light emitting diodes (LEDs).
Keywords: Hydrothermal synthesis; DMF; PVP; Luminescence; YVO; 4
Avalanches of coalescence events and local extensional flows – Stabilisation or destabilisation due to surfactant
by Deniz Z. Gunes; Xavier Clain; Olivier Breton; Guy Mayor; Adam S. Burbidge (pp. 79-86).
In a concentrated emulsion, avalanches of coalescence events can occur by the repetition of capillary relaxation. Higher surfactant concentrations can allow for stabilisation by thread formation and break-up.From two-drop collision experiments, it is known that local extensional flow favors coalescence. Recently, Bremond et al. used microfluidic methods to evidence this point. Similarly, we used specific microfluidic geometries to impose sudden extensional flow, following drop collision under controlled conditions, and coalescence events were recorded with a high-speed camera. In this study we focus on the effect of surfactant on the coalescence, or stabilisation against it, between drops flowing apart due to either imposed external flow or capillary forces related to drop shape relaxation. Coalescence can be induced even when drops are initially separated by an intersticial lubricating film by far thicker than the critical thickness for rupturing under the action of Van der Waals forces. This is particularly relevant to avalanches of coalescence events, in flowing or even quiescent emulsions or foams. When non-ionic surfactant was used, it was observed that small concentrations apparently enhance coalescence in extension. But at higher concentrations it provides stabilisation through a specific mechanism of thread formation and rupture; the stabilisation mechanism can be complex.
Keywords: Emulsion; Foam; Coalescence; Stability; Drop; Microfluidic; Avalanche; Extensional; Instability; Concentrated; Thread; Destabilisation; Collision; Surfactant
Aqueous foam stabilized by plate-like particles in the presence of sodium butyrate
by Qian Liu; Lingyu Luan; Dejun Sun; Jian Xu (pp. 87-93).
SEM images of foams stabilized by butyrate anions-modified LDH particles at low and high sodium butyrate concentrations. The initial sodium butyrate concentrations are (a) 25mM (b) 100mM.The addition of salt promotes the adsorption of layered double hydroxide (LDH) particles onto the air–water interface, but stable foams cannot be prepared from LDH dispersions at all the concentration of NaCl or sodium acetate. We generated stable foams using positively charged plate-like LDH particles in the presence of sodium butyrate. The effects of adding sodium butyrate to LDH on the particle zeta potential, adsorption behavior and the adsorption of modified particles at the air–water interface were studied. At a fixed LDH particle concentration, adding of a trace amount of sodium butyrate maximizes flocculation of the aqueous particle dispersion. Foams prepared under this condition of particle dispersion are most stable to coalescence and halt completely disproportionation. Also, the size of the bubbles is the smallest. The bubbles are stable when drying at 80°C with little change in size. Laser-induced fluorescent confocal micrographs and scanning electron microscopy observations clearly confirm the adsorption of LDH particles on the foam surfaces, and the bubbles are armored by an interfacial particle multilayer.
Keywords: Foam stability; LDH; Sodium butyrate
Aggregation behavior of a chiral long-chain ionic liquid in aqueous solution
by Xin-Wei Li; Yan-An Gao; Jie Liu; Li-Qiang Zheng; Bin Chen; Li-Zhu Wu; Chen-Ho Tung (pp. 94-101).
Aggregation behavior of a surface active long-chain chiral ionic liquid, S-3-hexodecane-1-(1-hydroxy-propan-2-yl) imidazolium bromide, in aqueous solution are investigated.The synthesis of a chiral long-chain ionic liquid (IL), S-3-hexadecyl-1-(1-hydroxy-propan-2-yl)-imidazolium bromide ([C16hpim]Br), is presented. The adsorption and aggregation of this surface active IL in aqueous solution is described. The critical micelle concentration (cmc) measurement suggests that the chiral IL has superior capacity for micelle formation compared to traditional ionic surfactants. The relatively larger hydrophilic head group of the IL results in a larger maximum surface excess concentration ( Γmax) and a smaller minimum molecular cross-sectional area ( Amin). Electrical conductivity studies show a small degree of counterion binding to these micelles, which may increase the electrostatic repulsions between the hydrophilic heads of adjacent surfactant molecules. Both factors of the hydrophilic headgroup size and electrostatic repulsion in [C16hpim]Br micelles lead to a looser packing of the surfactant molecules in the micelles. As a result, a higher micropolarity and smaller mean aggregation number is observed. Moreover, the looser micellar packing of the [C16hpim]Br molecules results in a unusual upfield shift of the proton NMR signals in the hydrophobic chains after micelle formation.1H NMR and 2D ROESY spectroscopic analyses confirm a chiral arrangement of the micelles. Chiral IL micelles may have potential applications in the stereochemical recognition of surfaces or of biological structures.
Keywords: Chiral ionic liquid; Aggregation behavior; Micelle
Influence of surfactant structure on the contribution of micelles to Ostwald ripening in oil-in-water emulsions
by Suwimon Ariyaprakai; Stephanie R. Dungan (pp. 102-108).
Possible mechanisms of micelle-enhanced transport during Ostwald ripening of emulsions.The rate of Ostwald ripening was measured, using light scattering, in 2wt.% and 10wt.% decane-in-water and dodecane-in-water emulsions. Sodium dodecyl sulfate and several nonionic ethylene oxide dodecyl ethers—surfactants with tails containing 12 carbons, but with various headgroups—were used to form the emulsions. Emulsions were formed with sufficient quantities of the surfactant to saturate the droplet interfaces. The influence of surfactant micelles in the continuous phase was then explored by adding 1–5wt.% surfactant to the water. The increase in the average droplet radius in the absence of micelles was found to agree qualitatively with Lifshitz–Slyozov–Wagner theory for the different surfactant types. The addition of micelles increased the rate of Ostwald ripening, by factors between 2 and 50, depending on the type and concentration of surfactant. However, there was no systematic correspondence between the increased rate and the equilibrium solubilization capacity of the micelles, nor was the rate decreased with increased strength of repulsive interactions between micelle and the droplet interface. It is proposed that the complex influence of surfactant on Ostwald ripening kinetics may depend on the ability of micelles to become supersaturated with oil—i.e., to incorporate solute temporarily above their equilibrium solubilization capacity.
Keywords: Abbreviations; C; 12; E; m; poly(ethylene oxide) dodecyl ether; cmc; critical micelle concentration; EO; ethylene oxide; LSW; Lifshitz–Slyozov–Wagner; SDS; sodium dodecyl sulfate; Tw 20; Tween 20Nonionic surfactants; C; n; E; m; Emulsion stability; Supersaturation; Coarsening; Disproportionation; Solubilization
Hierarchically imprinted polymer substrates for enhanced attachment of Escherichia coli
by Fengxiang Zhang; Hongzhe Li; Xin Wang; Hong Yee Low; Xu Li (pp. 109-114).
Hierarchically patterned polymer substrate significantly enhances E. coli attachment as compared with purely micro- or nano-patterned surfaces. Escherichia coli ( E. coli) detection is important for ensuring human health and public security. One critical step in most detection methods is to have the E. coli cells attach to the substrate or transducer of a biosensor before they can be detected and/or identified. In this context, a chemical or physical enhancement effect arising from the substrate will help to achieve a high sensitivity of bacterial detection. This work makes use of hierarchically imprinted surface structures to demonstrate such effect using quartz crystal microbalance (QCM). Specifically, hierarchical structures are imprinted on polystyrene coated resonance crystals of QCM; such crystals, after incubation in an E. coli suspension of reduced concentration (1×104colony forming units/mL), exhibit improved resonance frequency shifts, which are 1–2 orders of magnitude higher than those without the hierarchical structures. The enhancement effect is attributed to the enlarged surface area of the substrate and the way it immobilizes the bacteria. As revealed by scanning electron microscopy, the hierarchical substrates immobilize the E. coli cells by both trapping them in the micro-trenches and having them adhere to the nano-protrusions, while the single-level imprinted structures accommodate the cells mainly in the trenches or over the protrusions, instead of both.
Keywords: Hierarchical structure; Attachment; Escherichia coli; Enhanced
Comb-like polymer blends of poly(oxyethylene)s with CH3-terminated and CF3-terminated alkylsulfonylmethyl side chains: Effect of terminal CF3 moiety on the surface properties of the blends
by Eun-Ho Sohn; Byoung Gak Kim; Jae-Seung Chung; Jong-Chan Lee (pp. 115-124).
The effect of polar CF3-end groups on the surface properties of comb-like polymer blends was studied.The surface properties of comb-like polymer blends of poly(oxyethylene)s having CH3-terminated and CF3-terminated alkylsulfonylmethyl side chains were studied. These side chains were found to be well oriented on the surface of the blends, while being phase separated, forming various surface morphologies composed of holes, islands, or connected islands, because of their immiscibility resulting from their different polarities. The domain size of each polymer on the blend surface was found to be almost linearly proportional to the bulk compositions of the mixture, and the CF3-terminated alkylsulfonylmethyl side chain domains were found to be located in the lower region of the surface. The polar CF3-terminal groups in the lower regions were deemed to control the surface properties, because the contact angles and stick–slip behaviors of the blends containing more than 40mol% of poly(oxyethylene) with CF3-terminated side chains were almost identical.
Keywords: Comb-like polymer; Blend; Trifluoromethyl; Surface property; Wettability
Controlling the morphology of electrospray-generated PLGA microparticles for drug delivery
by Begoña Almería; Weiwei Deng; Tarek M. Fahmy; Alessandro Gomez (pp. 125-133).
PLGA microparticles of different morphologies were obtained by affecting the sequence of onset of polymer entanglements and Coulomb fission in electrospray-generated droplets.We developed a well-controlled method to generate PLGA microparticles of different morphologies using the electrospray drying route. By judiciously selecting polymer molecular weight, concentration, and solution flow rate, we can control the order in which polymer entanglements and Coulomb fission occur in the droplets and their relative importance, and subsequently govern the morphology of the resulting polymer particles. We show that spherical, monodisperse particles are generated when sufficiently strong polymer entanglements set in the evaporating droplets before they undergo any Coulomb fission. On the other hand, tailed and elongated particles are obtained if the Coulomb fission occurs first and if the droplets/particles are sufficiently evaporated to freeze in their irregular shape. Strictly spherical particles are unachievable for polymer solutions below a critical concentration, because the onset of Coulomb fission always sets in prior to the development of a sufficiently entangled polymer network. An extension of a simple model, originally used to determine the onset of electrospinning of polymer solutions, adequately predicts when non-spherical particles are produced. We conclude by demonstrating the scale-up of this approach to the synthesis of polymer particles using a compact, microfabricated, multiplexed electrospray system, which would make it suitable for practical applications.
Keywords: Electrospray; Controlled drug delivery; Morphology; Entanglements; Coulomb fission; Multiplexing
Porosity evolution of VP-DVB/MCM-41 nanocomposite
by Radoslaw Zaleski; Wojciech Stefaniak; Malgorzata Maciejewska; Jacek Goworek (pp. 134-140).
Evolution of mean diameters and relative volume of free spaces observed by Positron Annihilation Lifetime Spectroscopy (PALS) in PVP-DVB/MCM-41 composite during outgassing for (a) 13h, (b) 40h, (c) 95h, (d) 230h.The porous structure of nanostructured vinylpyrrolidone-divinylbenzene (VP-DVB)/MCM-41 composite was characterized using N2 adsorption at 77K and positronium annihilation lifetime spectroscopy (PALS), atomic force microscopy (AFM) and Raman spectroscopy. Positron annihilation lifetime spectra were measured during outgassing procedure. The voids of differentiated dimensions were detected in the composite material. The number of free volumes and their dimensions depend on the degree of evacuation of volatile components from the samples.
Keywords: VP-DVB; MCM-41; Nanocomposite; PALS
One-pot preparation of thermoresponsive silica-poly( N-isopropylacrylamide) nanocomposite particles in supercritical carbon dioxide
by Chengwei Wang; Jing Wang; Wei Gao; Jiqing Jiao; Huajie Feng; Xin Liu; Liuping Chen (pp. 141-148).
Thermoresponsive silica-poly(N-isopropylacrylamide) nanocomposite particles were prepared through a one-pot approach in supercritical carbon dioxide.Inorganic/polymer nanocomposite silica-poly( N-isopropylacrylamide) (SiO2-PNIPA) was successfully synthesized through a one-pot approach in supercritical carbon dioxide (scCO2). All raw materials, N-isopropylacrylamide (NIPA), vinyltriethoxysilane (VTEO), tetraethoxysilane (TEOS), initiator 2,2′-azobisisobutyronitrile (AIBN), crosslinker N,N′-methylenebisacrylamide (MBAM) and hydrolysis agent acetic acid (AA) were introduced into one autoclave and the parallel reactions of free radical polymerization and hydrolysis/condensation occurred simultaneously in the reaction mixture with scCO2 as solvent. The obtained novel composite particles were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The swelling ratios ( SR) and lower critical solution temperatures (LCSTs) of the prepared thermoresponsive microspheres were investigated by swelling tests and ultraviolet–visible (UV) spectrophotometry, respectively. TEM images demonstrated that well-dispersed particles with diameter less than 100nm were formed. The composite microgels exhibited higher LCSTs than poly( N-isopropylacrylamide) (PNIPA) microgels did. The in vitro release simulation of the particles in situ impregnated with ibuprofen indicated that SiO2-PNIPA composites could improve the drug releasing effect of the microgels as controlled drug delivery systems.
Keywords: Silica-poly(; N; -isopropylacrylamide) (SiO; 2; -PNIPA); One-pot preparation; Thermoresponsive; Supercritical carbon dioxide
Fast proton conduction in hydrogen bonded microheterogeneous systems: Bis(2-ethylhexyl)phosphoric acid/N-methyl formamide liquid mixtures
by Pietro Calandra; Marco Passarello; Angela Ruggirello; Vincenzo Turco Liveri (pp. 149-154).
The insertion of N-methyl formamide (NMF) into bis(2-ethylhexyl)phosphoric acid (HDEHP) liquid crystals leads to the formation of a local network allowing fast proton mobility.Structural and dynamical properties of bis(2-ethylhexyl)phosphoric acid (HDEHP)/N-methyl formamide (NMF) liquid mixtures in the whole composition range have been investigated by Fourier Transform Infrared spectroscopy (FT-IR), X-rays Diffraction (XRD), and AC complex impedance spectroscopy. Driven by hydrogen bond interactions among HDEHP PO4H group and NMF CO and NH groups, and also by steric effects among the HDEHP alkyl chains, the system microstructure is mainly characterized by the coexistence of spatially separated hydrophilic and hydrophobic nanodomains showing local organization and short-range order. The evolution of this structural feature with system composition has been highlighted by FT-IR and XRD. On the other hand, the thermally activated proton mobility within these hydrophilic domains, as pointed out by AC complex impedance measurements, emphasizes the occurrence of a percolating behaviour characterized by percolation threshold at zero. Due to fast proton conduction across the interconnected network formed by the polar groups, some samples showed very high room-temperature conductivity up to 10−3Scm−1.
Keywords: Fast proton conduction systems; Microheterogeneous liquid mixtures; Bis(2-ethylhexyl)phosphoric acid; N-methyl formamide
Optically switchable organic hollow nanocapsules
by Ying Wu; Xiaozhong Qu; Liyan Huang; Dong Qiu; Chengliang Zhang; Zhengping Liu; Zhenzhong Yang; Lin Feng (pp. 155-161).
The strong photoswitchable fluorescence of the poly(methyl methacrylate-methacrylated spiropyran) nanocapsules can be reversibly switched between “on” and “off” by alternating irradiation of ultraviolet (365nm) and visible light (>450nm).Hollow nanocapsules with both photoswitchable-fluorescent and reversible-photochromic properties are synthesized via a one-pot non-templating microemulsion copolymerization using methyl methacrylate and methacrylated spiropyran as co-monomers. The strong photoswitchable fluorescence of the nanocapsules are switched between “on” and “off” by alternating irradiation of ultraviolet and visible light, which causes the reversible photoisomerization between spiropyran and merocyanine in the nanocapsules. The distribution of spiropyran/merocyanine in a nanocapsule is mostly incorporated inside the wall of the nanocapsule, with only about 17.7% on the surface of the wall. This confinement is the reason of the unusually strong fluorescence of the merocyanine form yielded by the UV radiation. For the same reason, the photochemical stability of the chromophores is increased compared to those in the solution of water/DMF mixture.
Keywords: Nanocapsules; Spiropyran; Photoswitchable; Fluorescent
Cement–epoxy/water interfaces – Energetic, thermodynamic, and kinetic parameters by means of heat-conduction microcalorimetry
by Antonio R. Cestari; Eunice F.S. Vieira; Andréa M.G. Tavares; Marcos A.S. Andrade Jr. (pp. 162-167).
The cumulative heat release curves at epoxy–cement/water interfaces were well fitted to the multistep Avrami kinetic model.Hydration phenomena at cement/water interfaces drive the characteristics of oil-well cement slurries. In this study, new epoxy-modified cement slurries were synthesized. The slurries characterization has suggested the presence of low amounts of portlandite in the slurry with the higher content of polymerized epoxy resin. The hydration processes of the cement slurries were studied by heat-conduction microcalorimetry. The energetic and enthalpic hydration data were all exothermic in nature. The cumulative heat release curves have shown the presence of multilinearity of the kinetic processes. The hydration microcalorimetric data were well fitted to the multistep Avrami kinetic model. It was found that the epoxy-modified cement slurries present a good potential to be used in environmental-friendly oil-well operations.
Keywords: Cement/water interfaces; Oil-well cement slurries; Epoxy resins; Microcalorimetry; Thermodynamics; Kinetics
Phase transition behaviors of poly(N-isopropylacrylamide) microgels induced by tannic acid
by Gang Chen; Catherine Hui Niu; Ming-Yu Zhou; Xiao-Jie Ju; Rui Xie; Liang-Yin Chu (pp. 168-175).
Isothermal phase transitions of poly(N-isopropylacrylamide) microgels are induced by tannic acid molecules in aqueous solutions at 25°C (below the lower critical solution temperature).Effects of tannic acid (TA) on the phase transition behaviors of monodisperse poly(N-isopropylacrylamide) (PNIPAM) microgels in aqueous solutions are systematically investigated. Monodisperse PNIPAM microgels are prepared through a microfluidic approach. The isothermal phase transition behaviors of PNIPAM microgels induced by TA in aqueous solutions are studied at 25°C. The results show that there exist significant isothermal phase transition phenomena for PNIPAM microgels induced by TA, and the dynamic phase transition rate and the equilibrium shrinking degree of PNIPAM microgels in TA solutions are dependent on the TA concentration. The higher the TA concentration, the faster the isothermal shrinking rate of PNIPAM microgels induced by TA. There exists a critical TA concentration for the isothermal phase transition behavior, below which the equilibrium shrinking degree of PNIPAM microgels becomes larger with increasing the TA concentration, while above which the equilibrium shrinking degrees of PNIPAM microgels remain almost the same. The adsorption of TA molecules to PNIPAM polymer networks leads to slight shift of the low critical solution temperature to higher temperatures when the TA concentration in solution is lower than 10−5mol/L.
Keywords: Poly(N-isopropylacrylamide); Tannic acid; Microgels; Phase transition; Hydrogen-bonding; Hydrophobic interaction
Effect of water chemistry on calcium carbonate deposition on metal and polymer surfaces
by Zhen Wu; Jane H. Davidson; Lorraine F. Francis (pp. 176-187).
The formation of calcium carbonate on the surfaces of polypropylene and copper tubes was studied by exposing tubes to a laminar flow of room temperature distilled water, supersaturated with respect to calcite. Three water chemistries were used: a control (pH 9.3), one with lower supersaturation but similar pH as the control, and one with higher pH (pH 11) but similar supersaturation as the control. The accumulation of calcium carbonate with time was characterized along with the microstructure and the crystal structure of the deposits. On both tube materials, the amount of calcium carbonate deposited per unit surface area increased with time. At any given time, the accumulation was significantly less when the low supersaturation water was used. For all three water chemistries, more calcium carbonate formed on polyproplyene as compared with copper, with the greatest difference between the two noted for the higher pH water. The deposits consisted of discrete particles and particle clusters, the number and size of which increased with time. Calcite was the dominant polymorph for deposits on copper. On polyproplyene, the deposits were a mixture of calcite, vaterite and aragonite with aragonite dominating except at low supersaturation. A simple model for the mass accumulation of particulate-based deposits with time is presented and the factors responsible for the differences between materials are discussed.
Keywords: Calcium carbonate; Scale formation; Nucleation; Induction time; Supersaturation
Adsorption of Basic Violet 14 in aqueous solutions using KMnO4-modified activated carbon
by Qianqian Shi; Jian Zhang; Chenglu Zhang; Wei Nie; Bo Zhang; Huayong Zhang (pp. 188-193).
KMnO4-modified activated carbon.In this paper, an activated carbon was prepared from Typha orientalis and then treated with KMnO4 and used for the removal of Basic Violet 14 from aqueous solutions. KMnO4 treatment influenced the physicochemical properties of the carbon and improved its adsorption capacity. Adsorption experiments were then conducted with KMnO4-modified activated carbon to study the effects of carbon dosage (250–1500mg/L), pH (2–10), ion strength (0–0.5mol/L), temperature, and contact time on the adsorption of Basic Violet 14 from aqueous solutions. The equilibrium data were analyzed by the Langmuir and Freundlich isotherms and fitted well with the Langmuir model. The pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to evaluate the kinetic data and the pseudo-second-order kinetics was the best with good correlation.
Keywords: KMnO; 4; -modified activated carbon; Typha orientalis; Basic Violet 14; Adsorption equilibrium; Adsorption kinetics
Adsorption of non-ionic surfactants on hydrophobic and hydrophilic carbon surfaces
by M. Soria-Sánchez; A. Maroto-Valiente; A. Guerrero-Ruiz; D.M. Nevskaia (pp. 194-199).
Adsorption isotherms on oxidized graphite (GTox) and oxidized activated carbon (NTox).The adsorption from aqueous solutions of a series of non-ionic surfactants (TX-114, TX-100, TX-165 and TX-305, where the ethoxylation degree is increasing in the series) on a non-microporous carbon surface, that is a high surface area graphite (GT), and on a mainly microporous activated carbon (NT) has been comparatively studied. Also the initially hydrophobic GT and NT surfaces have been modified by oxidation treatments in order to achieve partially hydrophilic carbon materials (GTox and NTox samples). The adsorption results reveal that for GT sample below the critical micellar concentrations (cmc) of surfactants practically the whole surface is covered by monomers. For NT there are steric hindrance limitations, so the surfactant molecules are adsorbed only on micropores of sizes larger than 8Å. When oxygen surface groups are introduced on the carbonaceous surfaces, the adsorption behaviour is again different for both materials. Thus, for GTox the adsorbed amounts below the cmc decrease probably due to withdrawal effect of the oxygen surface groups. On the contrary, the adsorbed amounts above the cmc slightly increase with regard to bare graphite, possibly due to an improved formation of micelles. In the case of NTox the adsorbed uptakes below and above cmc increase remarkably in comparison with NT sample, which can be explained by some specific interactions of the surfactants molecules with oxygen surface groups inside the micropores.
Keywords: Activated carbon; Graphite; Adsorption; Polyoxyethylenic surfactants; XPS
Marked enhancement of photocatalytic activity and photochemical stability of N–doped TiO2 nanocrystals by Fe3+/Fe2+ surface modification
by Fan Dong; Haiqiang Wang; Zhongbiao Wu; Jinfeng Qiu (pp. 200-208).
High photocatalytic activity and reusability are two major factors that should be considered for photocatalyst applications. Our result indicates for the first time that Fe3+/Fe2+ modification can not only improve the photocatalytic performance but also long term stability of N–doped TiO2 nanocrystals.N–doped TiO2 (N–TiO2) nanocrystals with anatase and rutile mixed phases were prepared by partial oxidation of TiN. The samples were further modified by Fe-ions through incipient wetness impregnation method. The as-prepared samples were characterized by XRD, TEM, XPS, Raman, EPR, UV–vis DRS, and PL in detail. The results indicated that Fe mainly existed as Fe3+/Fe2+ ions on the catalyst surface. The addition of small amounts of Fe-ions to N–TiO2 nanocrystals caused several times enhancement of the photocatalytic activity under visible, UV and UV–vis light irradiation in degradation of gaseous toluene. The optimized Fe-ions content in this investigation was 0.02 wt.%. EPR and PL clearly showed that Fe3+/Fe2+ redox cycle facilitated electron/hole charge separation, and contributed to the enhanced photocatalytic performance. Moreover, the photochemical stability of N–TiO2 nanocrystals under visible light was improved due to the stabilization of nitrogen atoms in TiO2 lattice by surface Fe-ions modification. The N–doped TiO2 nanocrystals without Fe-ions modification suffered from a gradual deactivation due mainly to the loss of lattice-nitrogen during the photocatalytic reaction. The way to modification of nonmetal-doped TiO2 nanomaterials brought new concept in enhancing the photocatalytic performance from the viewpoint of practical application.
Keywords: N–doped TiO; 2; Visible light; Photocatalytic activity; Photochemical stability; Redox cycle
Synergistic effect of silicate clay and phosphazene-oxyalkyleneamines on thermal stability of cured epoxies
by Yu-Min Chen; Yi-Lin Liao; Jiang-Jen Lin (pp. 209-216).
The thermal stability of epoxy nanocomposites was found to be synergistically affected by the coexistence of phosphazenes and silicate platelets.Amine substitution of hexachlorocyclophosphazene (HCP) with poly(oxypropylene)diamines (POP) afforded HCP–POP adducts which were subsequently intercalated into a layered silicate clay. The relative thermal stabilities of the epoxies cured with the phosphazene-amines and the intercalated clays were studied. The organoclays, with the confined HCP–POP from 400 and 2000g/mol Mw amines, are nongelled products when using 1/6M ratio of HCP/POP starting materials in tetrahydrofuran solvent. The intercalation of HCP–POP polyamine salts into sodium montmorillonite afforded the HCP–POP-embedded organoclays with an expanded interlayer silicate spacing (2.4–5.1nm) from the original 1.2nm spacing (X-ray diffraction). The effect of silicate clays was evaluated by blending the HCP-POP/clay hybrids into a two-component epoxy system (diglycidyl ether of 4,4′-isopropylidenediphenol (BPA) and a diamine) and fully cured to form solid materials. The distribution of the exfoliated silicate platelets in the matrix was analyzed by transmission electronic microscopy (TEM). Thermal gravimetric analysis (TGA) indicated an enhanced thermal stability for the HCP/clay epoxy nanocomposites, with a delayed weight-loss pattern (temperature of weight loss at 10% ( T10wt.%) from 360 to 385°C and temperature of weight loss at 85% ( T85wt.%) from 598 to 696°C), compared to the pristine epoxies. By comparing these epoxies with different amounts of phosphazene and/or silicates, the TGA revealed a synergistic effect for the presence of both phosphorous and silicate components. Furthermore, the epoxies had improved physical properties such as hardness (from 3H to 5H) and surface adhesion (observed by scanning electron microscope (SEM) on fracture surface).
Keywords: Silicate clay; Montmorillonite; Poly(oxypropylene)amines; Phosphazene; Organoclay; Thermal stability
Structures of D2 layers on LiF(001)
by J.N. Dawoud; I.I. Fasfous; S.M. Hamzeh; D.B. Jack (pp. 217-224).
D2 (160) molecules distributed over a (16×16) patch of LiF(001) surface, where the (+) sign represents the cationic Li+ site, and (−) sign represents the anionicF − site.Classical Monte Carlo (MC) simulations of D2 molecules physisorbed on LiF(001) surfaces are reported and show a series of interesting commensurate structure forms, viz., p(2×2) → p(8×2) → p(4×2), with coverages Θ=0.5, 0.625, and 0.75, respectively, and are stable up to 8K. These structures are consistent with recent helium atom scattering (HAS) results (the p(4×2) is not observed) in terms of coverage and stability, but disagree in terms of symmetry. The p(2×2) structure contains two D2 molecules per unit cell, with each molecule lying parallel to the plane of the surface directly above every other cationic site. For the p(4×2) structure, there are two kinds of adsorption sites: a parallel site, as in the case of p(2×2), and a tilted site, where the D2 molecules sit between cationic and anionic sites with the molecular axis directed toward the anionic site, with a tilt angle of θ∼63°. Perturbation theory calculations show that the adsorbed D2 molecules are azimuthally delocalized and hence the structures are indeed c-type. Our calculations also indicate that o-D2 and helicoptering p-D2 species prefer cationic sites, compared to cartwheeling p-D2 species.
Keywords: Physical adsorption; Deuterium; Quantum delocalization; Potential energy surface; Monte Carlo simulation
High adsorption selectivity of ZnAl layered double hydroxides and the calcined materials toward phosphate
by Hongmei He; Hongliang Kang; Shulan Ma; Yongxiang Bai; Xiaojing Yang (pp. 225-231).
A high selectivity toward phosphate and reusability were exhibited by the calcined ZnAl–CO3 LDHs at different temperatures.The selective adsorption of phosphate ions was investigated onCO32-, Cl−, andNO3--type ZnAl layered double hydroxides (LDHs) and the calcinedCO32--type LDH at 200, 400, 600 and 800°C, respectively. The calcined LDHs andNO3--type LDH showed high selectivity toward phosphate ions, while the Cl−-type LDH shows selectivity toward bothSO42- and phosphate ions. TheNO3--type LDH selectively adsorbed phosphate ions mainly through ion exchange. The calcined samples possibly proceed through ligand complexation or electrostatic attraction between phosphate ions and hydrated ZnO formed after calcination, although the structural memory effect was observed for the samples calcined below 600°C with the formation ofCO32--type LDH. Adsorption/desorption behaviors indicated that the calcined samples had good stability and reusability.
Keywords: ZnAl-LDH; Calcined ZnAl-LDH; Adsorption; Selectivity; Phosphate
An XPS study for mechanisms of arsenate adsorption onto a magnetite-doped activated carbon fiber
by Shujuan Zhang; Xiao-yan Li; J. Paul Chen (pp. 232-238).
As3d spectra of the RACF and MACF after As(V) adsorption under various pHs.The surface and bulk structures of a newly developed carbon-based iron-containing adsorbent for As(V) adsorption were investigated by using X-ray diffraction (XRD), field emission scanning electronic microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). XRD patterns of the adsorbents indicated that the modified activated carbon fiber (MACF) was a simple mixture of the raw activated carbon fiber (RACF) and magnetite. After modification, a porous film was formed on the surface of the MACF with nano-sized magnetite on it. The As(V) uptake on the MACF was highly pH dependent and was facilitated in acidic solutions. XPS studies demonstrated that the surface oxygen-containing functional groups were involved in the adsorption and that magnetite played a key role in As(V) uptake. The dominance ofHAsO42- in surface complexes and the pH effect on As(V) uptake demonstrated that the monoprotonated bidentate complexes were dominant on the surface of the MACF. No reduction of As(V) was observed on the surface of the ACFs.
Keywords: Arsenate; Activated carbon fiber (ACF); Adsorption; Magnetite; X-ray photoelectron spectroscopy (XPS)
Electrokinetic properties of hydroxyapatite under flotation conditions
by Dušica R. Vučinić; Dragan S. Radulović; Slaven Đ. Deušić (pp. 239-245).
Proposed mechanisms of interactions of hydroxyapatite surface with oleate species present in the solution at different pH (concentration of Na-oleate ⩽1×10−4molL−1).The effect of calcite supernatant, calcium, and carbonate ions on the hydroxyapatite (HA) zeta potential without and in the presence of sodium oleate (1×10−4molL−1) was examined within the pH range from 4 to 12. The interpretation of results was based on the HA surface and oleate solution chemistry, and on some floatability tests. HA, with different positive and negative surface sites formed depending on its solubility and pH, had a negative zeta potential over the whole pH range. This mineral is not naturally floatable (flotation recovery, 5%< R<18%). The oleate ions (Ol−), present in a very low concentration in an acidic medium (pH from 4.8 to 6), chemisorb individually on HA surface centersCa+,HPO4Ca+, andOH2+, increasing the negative zeta potential of the mineral. Within the pH range from 7 to 9, the dominant oleate species Ol− ion and ion–molecule complex,H(Ol)2-, adsorbed on HA by head groups toward the solid and associated due to chain–chain interaction in hemimicelles, made the HA surface with zeta potential about −22/−23mV, and more floatable ( R=80–100%) than in 4R=15–35%) or in pH>9.3. The HA surface is less negatively charged in calcite supernatant than in water from pH 6.6 to 9.2 due to the adsorption on HA negative surface active centers(HPO4-andPO42-) of the Ca2+,CaHCO3+, and CaOH+ ions (present in the calcite supernatant), producing more surface sitesHPO4Ca+,PO4Ca,HPO4CaOH, andPO4- CaOH, and new centersHPO4CaHCO3 andPO4- CaHCO3. In the presence of 1×10−3molL−1 CaCl2, the HA sample has positive zeta potential, the same as calcite from the same deposit, up to IEP at pH 11.25. Carbonate ions (1×10−3molL−1 Na2CO3) do not affect the HA zeta potential. However, a possible process can be the ion-exchange reaction between bicarbonate (or carbonate) and some anion from the surface sites formed on HA. The obtained values of the HA zeta potential with the collector (1×10−4molL−1 Na-oleate) added into hydroxyapatite/calcite supernatant suspensions corroborate the weak chemisorption of Ol− andH(Ol)2-. The likely processes in this system also are the ion-exchange reactions onHPO4CaOH andPO4- CaOH,HPO4CaHCO3 andPO4- CaHCO3 between oleate ion and surface hydroxyl and bicarbonate ions, surface and bulk precipitations of calcium oleate, Ca(Ol)2, and the surface and bulk precipitations ofCa[H(Ol)2-]2 over the pH range from 7 to 9. Calcite supernatant does not influence natural floatability of the mineral. However, calcite supernatant depresses the hydroxyapatite flotation in the presence of 1×10−4molL−1 Na-oleate (pH 9, R∼50%), a likely result of the weak chemisorption due to the steric effect of heterogeneous HA surface formed in calcite supernatant, Ca(Ol)2 andCa[H(Ol)2-]2 surface and bulk precipitations.
Keywords: Hydroxyapatite; Electrokinetic potential; Flotation; Calcite; Oleate
Silica encapsulation of n-octadecane via sol–gel process: A novel microencapsulated phase-change material with enhanced thermal conductivity and performance
by Huanzhi Zhang; Xiaodong Wang; Dezhen Wu (pp. 246-255).
A novel microencapsulated phase-change material based on an n-octadecane core and a silica shell was synthesized via a sol–gel process for enhancement of thermal conductivity and performance.A novel microencapsulated phase-change material (PCM) based on an n-octadecane core and an inorganic silica shell was designed to enhance thermal conductivity and phase-change performance. These silica microcapsules were synthesized by using TEOS as an inorganic source through a sol–gel process. Fourier transform infrared spectra confirm that the silica shell material was successfully fabricated onto the surface of the n-octadecane core. Scanning electronic microscopy images suggest that the silica microcapsules exhibit a spherical morphology with a well-defined core–shell microstructure. Furthermore, the silica microcapsules synthesized at pH 2.45 display a smooth and compact surface. These microcapsules also present a large particle size range of 7–16μm. Wide-angle X-ray scattering patterns indicate that the n-octadecane inside the silica microcapsules still retains a good crystallinity. Thermogravimetric analysis shows that these silica microcapsules are degraded in two distinct steps, and have good thermal stability. The silica-microencapsulated n-octadecane can achieve good phase-change performance, high encapsulation efficiency, and good antiosmosis property by controlling the loading of core material and acidity of the reaction solution during the sol–gel process. The thermal conductivity of the microencapsulated n-octadecane is also significantly enhanced due to the presence of the high thermal conductive silica shell.
Keywords: Silica microcapsules; n; -Octadecane; Sol–gel process; Thermal conductivity; Phase-change performance
Oxide surface modification: Synthesis and characterization of zirconia-coated alumina
by Cleocir José Dalmaschio; Valmor R. Mastelaro; Pedro Nascente; Jefferson Bettini; José Luiz Zotin; Elson Longo; Edson Roberto Leite (pp. 256-262).
Diagrams built from the proposed model for surface modification of oxide for a coating composed of ZrO2 and experimental results obtained by XRD for the coating of aluminas.Four aluminas were used as supports for impregnation with a zirconium oxide with the aim to achieve a coating, without phase separation, between support and modifier. The supports were impregnated with different concentrations of zirconium aqueous resin, obtained through the polymeric precursor method. After impregnation the samples were calcined and then characterized by XRD, which led to identification of crystalline zirconia in different concentrations from each support used. Using a simple geometric model the maximum amount of surface modifier oxide required for the complete coating of a support with a layer of unit cells was estimated. According to this estimate, only the support should be identified below the limit proposed and crystalline zirconium oxide should be identified above this limit when a complete coating is reached. The results obtained from XRD agree with the estimated values and to confirm the coating, the samples were also characterized by EDS/STEM, HRTEM, XPS, and XAS. The results showed that the zirconium oxide on the surface of alumina support reached the coating in the limit of 15 Zr nm−2, without the formation of the ZrO2 phase.
Keywords: Surface; Coating; Dispersion; Catalysis; Ceramics
Competitive adsorption involving phosphate and benzenecarboxylic acids on goethite—Effects of molecular structures
by Malin Lindegren; Per Persson (pp. 263-270).
Phosphate adsorption on α-FeOOH in the absence (in black) and the presence of benzenetricarboxylates highlighting the strong dependence on the molecular structure of the competing ligand.The competitive adsorption between phosphate and either one of seven benzenecarboxylates (benzoate, phthalate, trimellitate, trimesoate, hemimellitate, pyromellitate, and mellitate) on the surfaces of fine-particulate goethite ( α-FeOOH) was investigated as a function of pH. The series of ligands contained molecules with an increasing number of functional groups as well as three structural isomers of the tricarboxylates. Thus, the effects of both the number of carboxylate groups and the relative positions of these groups on the competitive efficiency toward phosphate were probed in this study. Quantitative adsorption experiments in batch mode and infrared spectroscopy were collectively used to evaluate the competitive adsorption reactions. Under the conditions probed, mono- and dicarboxylates had no detectable effect on phosphate adsorption whereas the ligands containing three or more carboxylate groups were able to partially outcompete phosphate. However, the pH dependency and the extent of these competitive effects were strongly dependent on the structure and composition of the benzenecarboxylate. The collective results showed that it was the competition for hydrogen-bonding surface sites rather than inner sphere surface sites that primarily determined the outcome of the competitive adsorption experiments, and it was the ability of the organic ligand to act as hydrogen-bonding acceptor and/or donor in various parts of the pH range that also determined the competitive pH dependency. The importance of H-bonding for the competitive adsorption between phosphate and benzenecarboxylic acids suggested that H-bonding interactions contributed substantially to the stabilities of both the adsorbed benzenecarboxylates and the phosphate ions and that these interactions were structurally specific; i.e., they were sensitive to the locations and the directional properties of the H-acceptor and H-donor surface sites.
Keywords: Phosphate; Benzenecarboxylic acid; Competitive adsorption; Infrared spectroscopy
Nanostructured multilayer TiO2–Ge films with quantum confinement effects for photovoltaic applications
by Abdul Faheem Khan; Mazhar Mehmood; Muhammad Aslam; Syed Ismat Shah (pp. 271-280).
The graph of conductivity vs. annealing temperature.Multilayer TiO2–Ge thin films have been deposited using electron beam evaporation and resistive heating. The thickness of the TiO2 layers is 20nm, while the thickness of the Ge layers varies from 2 to 20nm with a step of 2nm away from the substrate. These films were characterized by studying their optical, electrical, and structural properties. The films were annealed at various temperatures up to 500°C for 2h. The films are amorphous up to an annealing temperature of 400°C, although Raman spectra suggest short-range ordering (and adjustments). The films annealed at 450 and 500°C exhibit X-ray reflections of Ge and anatase TiO2. Illumination in sunlight increases the conductivity of the as-deposited and annealed films. The band gap of the amorphous films changes from 1.27 to 1.41eV up to 400°C; the major contribution is possibly through direct transition. Two band gap regimes are clearly seen after 450 and 500°C, which have been assigned to an indirect band gap at about 1.2eV and a direct band gap at about 1.8eV. Conductivity of the multilayer films has been higher than that of pure Ge film. The conductivity increases with annealing temperature with abrupt increase at about 380°C. The results imply that the TiO2–Ge multilayer films may be employed as heterojunctions with tunable band gap energy as related to quantum confinement effects.
Keywords: Multilayer TiO; 2; –Ge thin films; Photoconductivity; Impedance spectroscopy; Quantum confinement effects; Raman spectroscopy; Heterojunction
Study of molecular arrangement of organized molecular films of charge–transfer complexes containing 1,3-dithiole-2-thione-4,5-dithiolate by in-plane and out-of-plane X-ray diffractions
by Yoko Tatewaki; Shuji Okada; Ryosuke Itagaki; Takayoshi Nakamura; Atsuhiro Fujimori (pp. 281-290).
Accurate structural analysis of conductive organized molecular films for alkylammonium–M(dmit)2 are carried out by in-plane and out-of plane X-ray diffractions.We investigated the molecular arrangement and surface morphology of organized molecular films of alkylammonium–M bis(1,3-dithiole-2-thione-4,5-dithiolate) ((dmit)2, M=Ni, Au, and Pd) charge–transfer complexes using the surface pressure–area ( π– A) isotherm, polarized visible spectroscopy, in-plane and out-of-plane X-ray diffractions (XRD), and atomic force microscopy (AFM). Since Langmuir–Blodgett films of alkylammonium–M(dmit)2 generally exhibit superconductivity, it may be possible to develop novel electronic molecular devices on the subnanometer scale. In the bulk state, several alkylammonium–M(dmit)2 molecules could not form a highly ordered layered structure along the c-axis and a subcell structure of the alkyl chain in the ab-plane; however, almost all molecules formed a layered structure in the film multilayers. Monolayers of alkylammonium–M(dmit)2 molecules on the water surface were extremely condensed. Out-of-plane and in-plane XRD measurements revealed that over a long period, systematic changes occurred in the two-dimensional lattice structure of alkylammonium–M(dmit)2 molecules and not in their bulk state. These structural changes appear to be caused by enhancement of the van der Waals interaction among long hydrocarbons and the π– π interaction among (dmit)2 units arranged two dimensionally. In addition, both the molecular arrangement and the structural morphology of the films showed dependence on the hydrocarbon chain length, number of long alkyl chains, and kind of central metal. In particular, the molecular arrangement of materials having didecyl chains changed drastically and (dmit)2 units were highly oriented in the ab-plane. Such structural formations are suggested to significantly influence the stacking of functional dmit units presiding over the conductive properties.
Keywords: Alkylammonium–metal(dmit); 2; Layer structure; Two-dimensional lattice; Molecular arrangement; Surface morphology
Bubble formation on a submerged micronozzle
by Saeid Vafaei; Dongsheng Wen (pp. 291-297).
The work reveals detailed characteristics of bubble formation on a micrometer-sized nozzle, such as an instantaneous variation of contact angles as shown here, through experimental and analytical studies.This work investigates detailed formation of air bubbles on a submerged micrometer-sized nozzle. The experimental study is conducted on a submerged nozzle of radius of 55μm under low gas flow rate conditions (0.015∼0.83ml/min). The bubble formation is recorded by a high-speed optical camera and detailed characteristics of bubble formation such as the variations of instantaneous contact angles, bubble heights and the radii of contact lines are obtained, which shows a weak dependence on the flow rate under the conditions of current work. Using experimentally captured values of the height of bubble and the radius of contact line, the Young–Laplace equation is solved, which is found to be able to predict the bubble evolution quite well until the last milliseconds before the detachment. A force analysis of bubble formation reveals that the observed variations of contact angles and other characteristics during the bubble growth period are associated with the relative contribution of surface tension, buoyancy force and gravitational force.
Keywords: Contact angle; Surface wettability; Young–Laplace equation; Bubble formation
Evolution of surface area-to-volume ratio for a water meniscus evaporating between contacting silica spheres
by R.E. Cutts; S.E. Burns (pp. 298-300).
Modeled geometry of water meniscus evaporating between two contacting silica spheres.An experimental investigation was performed under isothermal conditions to quantify the rate of evaporation of water from a receding pendular meniscus connecting two silica spheres. Optically based measurements were used to determine the relevant meniscus dimensions, and the meniscus was modeled using a toroidal approximation. The rate of change of meniscus surface area and volume was then predicted using mathematical modeling software. The results demonstrated that once the meniscus transitioned from a relatively flat surface to one with an increasing radius of curvature, the rate of change of the ratio of surface area-to-volume was relatively constant over the range of water contents that were observable using the optical investigation techniques implemented in this study. Comparison of the flux of water from the meniscus surface demonstrated that the evaporation of bound water was four orders of magnitude slower than evaporation from a free water surface.
Keywords: Evaporation; Receding meniscus; Silica; Toroidal approximation; Torous; Wetting fluid
Fabrication of conductive metal lines by plate-to-roll pattern transfer utilizing edge dewetting and flexographic printing
by Moon Kyu Kwak; Kyu Ho Shin; Eung Yeoul Yoon; Kahp Y. Suh (pp. 301-305).
By exploiting edge dewetting and flexographic printing, conductive silver line patterns of 20μm width are transferred onto 300mm-diamter aluminum cylinder with high pattern fidelity and physical integrity.We present a simple flexographic printing method mediated by edge dewetting for potential applications to roll-to-roll or plate-to-roll pattern transfer. By controlling dewetting of a thin, conductive ink material under conformal contact with a patterned elastomeric mold (e.g., polydimethylsiloxane, PDMS), the liquid ink layer is broken and then selectively wets the protruding part of the mold with high fidelity. Subsequently, a thin photoresist layer that is coated on 300mm-diameter aluminum cylinder is brought in contact with the ink-coated PDMS mold, resulting in a plate-to-roll pattern transfer without collapse or merging of neighboring features. Using this method, conductive silver lines are fabricated on the cylindrical surface with the resolution of ∼20μm and the sheet resistance less than ∼4.3Ω after 10 repeated transfer cycles.
Keywords: Dewetting; Pattern transfer; Printing; Flexography; PDMS
Leveling of thin films of colloidal suspensions
by Benson Tsai; Marcio S. Carvalho; Satish Kumar (pp. 306-313).
Convection, diffusion, adsorption, and desorption of colloidal particles all infuence the leveling of thin liquid flms.We present an analysis of leveling in thin films of colloidal suspensions. The colloidal particles are assumed to be much smaller than the film thickness and influence the film rheology through a concentration-dependent viscosity and bulk diffusivity. A system of coupled nonlinear partial differential equations based on lubrication theory is used to describe the film height and the particle concentrations in the bulk and at the film surface. Linear stability analysis is applied to develop expressions for leveling rates in a number of limiting cases. It is found that for soluble particles, there exist regimes where increasing the Marangoni number slows down leveling at both short and long times, in contrast to the case of insoluble particles. Nonlinear simulations show that the linear theory accurately predicts leveling times even for large amplitude disturbances, and that the presence of a concentration-dependent viscosity and bulk diffusivity speed up leveling. The results of this work should be useful for estimating leveling rates in coatings laden with colloidal particles, and also in coatings containing soluble surfactant.
Keywords: Leveling; Thin films; Colloidal suspensions
A disjoining pressure study of foam films stabilized by mixtures of a nonionic (C12DMPO) and an ionic surfactant (C12TAB)
by Enda Carey; Cosima Stubenrauch (pp. 314-323).
A disjoining pressure study of foam films stabilized by mixtures of a nonionic (dodecyldimethyl phosphineoxide, C12DMPO) and an ionic surfactant (dodecyl trimethylammonium bromide, C12TAB).This work is a continuation of a previous study [ Langmuir 23 (2007) 5315–5323] of aqueous foam films stabilized by surfactant mixtures consisting of a cationic and a nonionic surfactant. In both studies a thin film pressure balance was used to investigate the disjoining pressure Π as a function of the film thickness h. With the resulting Π– h curves the surface charge densities q0 of the foam films were determined by fitting them with the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Our previous study demonstrated that mixing the nonionic surfactant β-dodecylmaltoside (β-C12G2) and the cationic dodecyl trimethylammonium bromide (C12TAB) allows one to tune q0 and thus the type of foam film. In the present study the nonionic surfactant dodecyldimethyl phosphineoxide (C12DMPO) instead of β-C12G2 was used and C12DMPO/C12TAB mixtures in a concentration range from 0.1 to 2.0cmc were studied at mixing ratios of C12DMPO:C12TAB=1:0, 50:1, 1:1, 1:50, 0:1. The results are compared with those of the β-C12G2/C12TAB mixture and are discussed in terms of surface charge densities.
Keywords: Thin liquid foam films; Disjoining pressure; Mixtures of nonionic and cationic surfactants; Dodecyldimethyl phosphineoxide; Dodecyl trimethylammonium bromide
Patterning of J-aggregated dyes using directed self-assembly on micro- and nanopatterned templates fabricated from phase-separated mixed Langmuir–Blodgett films
by Satoshi Watanabe; Hirobumi Shibata; Shin Horiuchi; Reiko Azumi; Hideki Sakai; Masahiko Abe; Mutsuyoshi Matsumoto (pp. 324-329).
Nanowires of dyes have been fabricated on patterned templates prepared from phase-separated mixed LB films, the patterns of which can be tuned by adjusting intermolecular interactions between the film-forming molecules.We report a useful technique for the deposition of dyes in the form of J-aggregates using directed self-assembly on the micro- and nanopatterned templates fabricated from the phase-separated mixed Langmuir–Blodgett (LB) films. The patterns of the mixed LB films can be tuned by adjusting the intermolecular interactions between the film-forming molecules. We used the mixed LB films containing silane coupling agent for the fabrication of micro- and nanopatterned templates, taking advantage of the difference between the surface free energy of the patterned regions and that of the self-assembled monolayers of the silane coupling agent. Atomic force microscopy showed that dyes were deposited by casting, spin-coating and the LB technique in accordance with the patterns of the original mixed LB films. Emission spectroscopy revealed that J-aggregates were formed in the patterned films. We succeeded in obtaining nanopatterns of a cyanine dye in the form of J-aggregates on the templates.
Keywords: Phase separation; Mixed LB films; J-aggregate; AFM; Line tension; Dipole–dipole interaction
β-Lactoglobulin aggregates in foam films: Effect of the concentration and size of the protein aggregates
by Bénédicte Rullier; Monique A.V. Axelos; Dominique Langevin; Bruno Novales (pp. 330-337).
Top view of foam films (bulk concentration 1g/L) containing 50% protein aggregates for: (a)R h=35nm (b)R h=71nm; (c)R h=117nm and (d)R h=197nm. A pressure ramp is applied (10Pa per 10min) and, for all images, the final pressure is 100Pa.Single foam films made from mixtures of nonaggregated proteins and protein aggregates have been studied using a thin film balance apparatus. Their features (heterogeneity, stability and resistance to pressure change) are dependent on the aggregate size and on the ratio between nonaggregated proteins and protein aggregates. A phase diagram of these foam films has been drawn and a correlation of the structural properties of foam film and stability of real foams has been found. In particular, the formation of a gel-like network within the foam film coincides with the stability of the corresponding 3-D foams.
Keywords: Protein aggregates; Foam film; Foam stability
van der Waals interaction energy and disjoining pressure at small separation
by Lee R. White (pp. 338-343).
Scaled van der Waals energy (blue) and disjoining pressure (green) for the finite wavenumber cutoff approximation, compared to the corresponding classical Lifshitz theory results (red, purple) for dodecane/air/dodecane.The divergence of the van der Waals interaction energyE132(L) between plane half-spaces 1 and 2 separated by medium 3 as the separation distance L tends to zero is naively thought of as due to the overlap of the atomic polarization centers. It follows that it may therefore be prevented by properly allowing for the finite size of the atomic species which would prevent the overlap. The distance cutoff model is a simple example of such a modification. The present paper demonstrates that this is not ultimately the origin of the divergence and, that although finite atomic dimensions would alleviate the embarrassment, non-overlap does not properly address the thermodynamic restriction that pertains to the interaction energy. By allowing in an albeit approximate way for the wavelength dependence of the material dielectric response functionsε(iξ,k) which arise naturally in the modern Lifshitz theory for this interaction, a form for the van der Waals energy and the corresponding disjoining pressure may be derived which obey the thermodynamic constraint and remove the divergence asL→0. The energy and disjoining pressure in this new model are compared with the classic non-retarded results and the length cutoff model.
Keywords: van der Waals interaction; Distance cutoff; Wavenumber cutoff; Dielectric response function; Contact force
Mesoporous zirconium phosphate from yeast biotemplate
by Xiuying Tian; Wen He; Jingjie Cui; Xudong Zhang; Weijia Zhou; Shunpu Yan; Xianan Sun; Xiuxiu Han; Shanshan Han; Yuanzheng Yue (pp. 344-349).
Mesoporous zirconium phosphate with high specific surface area (217.64m2g−1) was prepared using yeast cells as templates.Mesoporous zirconium phosphate has attracted increasing interest due to its extraordinary functionalities. In particular, great progress has been made in the synthesis of mesoporous zirconium phosphate using traditional approaches. However, synthesis of mesoporous zirconium phosphate using yeast as biotemplate has not been well studied so far. Here, we show that zirconium phosphate with a mesoporous structure has been synthesized under ambient conditions using yeast as biotemplate. The derived samples were examined by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), thermogravimetry/differential thermal analysis (TG/DTA), fourier transform infrared spectroscopy (FTIR), and N2 adsorption–desorption isotherms. A biotemplated mesoporous zirconium phosphate, possessing a specific surface area (Brunauer–Emmett–Teller, BET) of 217.64m2g−1, a narrow pore distribution centered at 2.7nm, and pore volume of 0.24cm3g−1, was obtained. We discover that amide carboxyl groups of yeast play an important role in the chemical interaction between protein molecules and zirconium phosphate nanoparticles. Interestingly, an air electrode fabricated using mesoporous zirconium phosphate exhibits remarkable electrocatalytic activity for oxygen reduction reaction (ORR), compared to that of the electrolytic manganese dioxide (EMD) air electrode employed commercially, which has important applications in fuel cell technologies.
Keywords: Zirconium phosphate; Mesoporous structure; Biotemplate; Electrocatalytic property
Consideration of polydispersity in the evaluation of the dynamic mobility of concentrated suspensions
by S. Ahualli; F.J. Arroyo; A.V. Delgado (pp. 350-358).
An illustrative proof of the feasibility of this complete cell model accounting for polydispersity of concentrated suspensions shows an accurate description of the results: two inertial relaxations in the frequency spectrum of the dynamic mobility.Many practical uses of electroacoustic methods for the characterization of disperse systems involve concentrated and/or polydisperse suspensions. While the effects of particle concentration have been well described experimentally and theoretically, similar studies considering a wide size distribution of the dispersed particles are lacking. This is not a minor point, as these methods are based on the action of alternating fields (either electric or acoustic) on the systems and the characteristic frequencies and amplitudes are largely determined by the particle geometry. In this work, we first evaluate the effect, on the dynamic (or ac) mobility, of changing the size distribution in the suspension. It is found that the inertia (also called hydrodynamic) relaxation of the mobility is shifted toward lower frequencies, and that the overall mobility spectrum is smoothed when the size polydispersity of the suspension increases. The results theoretically obtained are subsequently used for fitting experimental mobility data corresponding to two alumina samples, in a wide range of particle concentrations and ionic strengths. It is demonstrated that a complete model accounting for polydispersity leads to a better description of the results; very significantly, this can be done by using the zeta potential as the only fitting parameter, and forcing this parameter to be determined only by the ionic strength, and not by the volume fraction.
Keywords: Dynamic mobility; Polydispersity; Concentrated suspension; Zeta potential
Improved enzymatic activity of Thermomyces lanuginosus lipase immobilized in a hydrophobic particulate mesoporous carrier
by Malin H. Sörensen; Jovice B.S. Ng; Lennart Bergström; Peter C.A. Alberius (pp. 359-365).
Interfacial activation of fluorescently-tagged lipase’s active site via hydrophobic interaction with the hydrophobilized mesopore walls which it is immobilized in.Lipase from Thermomyces lanuginosus has been immobilized within particulate mesoporous silica carriers, with either hydrophilic or hydrophobic supporting surfaces, produced by the newly developed emulsion and solvent evaporation (ESE) method. The Michaelis–Menten model was used to calculate the parameters related to the enzymatic activity of lipase i.e. the turnover number,k cat, and the specific activity. The specific activity was improved by immobilization of lipase onto the hydrophobic support, compared to lipase immobilized onto the hydrophilic support and lipase free in solution. The enhanced enzymatic activity of lipase onto a hydrophobic support was attributed to interfacial activation of the Thermomyces lanuginosus lipase when it is attached to a hydrophobic surface and a reduced denaturation. Confocal scanning laser microscopy (CLSM) studies, of fluorescently tagged lipase, showed that leakage of the lipase from the mesoporous particles was limited to an initial period of only a few hours. Both the rate and the amount of lipase leached were reduced when the lipase was immobilized onto the hydrophobic support.
Keywords: Lipase; Mesoporous; CLSM; Particulate; Carriers; Enzymatic activity; Supporting surfaces
Influence of calcium and silica on hydraulic properties of sodium montmorillonite assemblages under alkaline conditions
by Andrew S. Kinsela; Alice Tjitradjaja; Richard N. Collins; T. David Waite; Timothy E. Payne; Bennett C.T. Macdonald; Ian White (pp. 366-373).
Additions of calcium and silica resulted in complex changes to tactoid assemblages influencing the hydraulic properties of Na-montmorillonite under alkaline conditions.A sodium-washed montmorillonite was exposed to calcium and silica under alkaline conditions in order to gain insight into possible interactions of engineered clay barriers and cementitious leachates found in many waste storage facilities. The changes in physico-chemical properties of the material were investigated using a combination of dead-end filtration, electrophoresis and scanning electron microscopy. The results show minimal differentiation between unaltered Na-montmorillonite samples at the two pH values tested (9 and 12), with the structure of the resulting assemblages arising from repulsive tactoid interactions. The addition of calcium (50mM) greatly decreases the size of the structural network, and in doing so, increases the hydraulic conductivity ∼65-fold, with the effect being greatest at pH 12. Whilst the addition of silica alone (10mM) produced little change in the hydraulic properties of montmorillonite, its combined effect with calcium produced alterations to the structural assemblages that could not be accounted for by the presence of calcium alone. The likely binding of calcium with multiple silanol groups appears to enhance the retention of water within the Na-montmorillonite assemblage, whilst still allowing the fluent passage of water. The results confirm that polyvalent cations such as Ca2+ may have a dramatic effect on the structural and hydraulic properties of montmorillonite assemblages while the effects of solutions containing both silicate and calcium are complex and influenced by silica–cation interactions.
Keywords: Montmorillonite; Clay; Hydraulic conductivity; Calcium; Silica
Mechanism of heavy metal uptake by a hybrid MCM-41 material: Surface complexation and EPR spectroscopic study
by Panagiota Stathi; Kostas Dimos; Michael A. Karakassides; Yiannis Deligiannakis (pp. 374-380).
Cd inhibits access to the MCM-41 pores.A novel hybrid MCM-41-based material was synthesized by incorporation of AEDTC [ N-(2-aminoethyl)dithiocarbamate] in the MCM-41 pores. The derived MCM-41⊗AEDTC material possesses high AEDTC loading 35% [w:w], and a well-defined array of regular mesopores with a specific surface area of 632m2/g. Heavy metal, Cd, Pb, Cu, and Zn, uptake was studied in detail at physiological pH values 6–8, by a combination of analytical and electron paramagnetic resonance (EPR) spectroscopic techniques. The analytical data show a significant improvement, i.e., 200–500%, for Pb, Cu, and Zn uptake by the MCM-41⊗AEDTC hybrid vs the unmodified MCM-41. In contrast, Cd shows an exceptional behavior: (a) Cd uptake by MCM-41⊗AEDTC is very low. (b) Competitive metal uptake experiments reveal that Cd ions cause a characteristic inhibition of Cu or Pb uptake by the MCM-41⊗AEDTC while Cd binding itself always remained low. The present findings are analyzed by a combination of surface complexation modeling and EPR spectroscopy. Accordingly, in the MCM-41⊗AEDTC the sulfur atoms of AEDTC provide strong binding sites for metal binding, with a stoichiometry [ SAEDTC]:[Metal]=1:1. Cd inhibits accessibility of Cu or Pb ions in the AEDTC sites.
Keywords: Hybrid; MCM-41; Dithiocarbamate; Heavy metals; Pb; Cd; Cu; Zn; Adsorption; SCM; FITEQL; EPR
Electrochemical charge of silica surfaces at high ionic strength in narrow channels
by Moran Wang; André Revil (pp. 381-386).
Electrical potential and charge distribution near solid surfaces in the electrical triple-layer model. The symbol M represents the metal cations and A the anions.We present a theoretical framework to calculate the electrochemical charge on silica surfaces in contact with high-ionic-strength solutions in narrow channels. Analytical results indicate that the contribution of the adsorbed metal cations to the total surface charge is not negligible when the salinity is larger than 1mM. The electrical triple-layer model is proved much better than other models for high ionic strength. The charge regulation caused by the double-layer overlap in narrow channels will reduce the surface charge density but increase the zeta potential on silica surfaces.
Keywords: Electrical triple-layer; Electrochemical charge; Charge regulation; High ionic strength
Peptide-based spherulitic films—formation and properties
by Noam Sidelman; Yuri Rosenberg; Shachar Richter (pp. 387-391).
Spherulitic films from peptide nanotube forming peptides can be induced to form on flat solid surfaces. This process requires elevated levels of environmental humidity. The image shows a characteristics Maltese cross pattern observed in spherulites viewed using polarized-light microscopy.Peptide nanotube-based spherulitic films are a recently discovered phenomenon, which was demonstrated in the case of the self-assembled diphenylalanine peptide nanotubes. Here we show that the film-formation method can be implemented with other peptides. We also demonstrate that a critical physical parameter, an elevated level of environmental hydration, is required for film growth. A possible formation mechanism is suggested. The optical, morphological and mechanical properties of these films are characterized and are found to be substantially different from those of non-spherulitic deposits.
Keywords: Spherulites; Films; Peptide nanotubes
Monodisperse alginate microcapsules with oil core generated from a microfluidic device
by Ping-Wei Ren; Xiao-Jie Ju; Rui Xie; Liang-Yin Chu (pp. 392-395).
Monodisperse alginate microcapsules with oil core are generated from a microfluidic device.A microfluidic approach is developed to fabricate monodisperse alginate microcapsules with oil cores, which have the potential to be a brand-new type of vehicles for encapsulating, storing and/or transferring lipophilic drugs or active ingredients/chemicals. The alginate microcapsules with oil cores are generated in a microcapillary microfluidic device using monodisperse oil-in-water-in-oil (O/W/O) double emulsions as templates. All the as-prepared alginate microcapsules and the encapsulated oil droplets are satisfactorily spherical. Both the alginate microcapsule size and the thickness of alginate membrane can be easily controlled by modulating the dimensions of microfluidic device and the flow rates of solutions, because the outer diameter of the O/W/O double emulsion templates and the size of their inner oil cores can be controlled independently by adjusting the inner diameters of emulsification tubes and the flow rates of different solutions. The as-fabricated monodisperse micro-egg-like core–shell alginate microcapsules with oil cores may open new possibilities for engineering novel functional materials.
Keywords: Microcapsules; Alginate; Membranes; Microfluidics; Hydrogel; Template synthesis
In situ precipitation of magnetic fluid encapsulated in giant liposomes
by Grégory Beaune; Christine Ménager (pp. 396-399).
Brown and spherical precipitate of magnetic fluid inside giant liposome.It is well known that adding salt to a colloidal solution stabilized by electrostatic repulsions can induce its destabilization. When this colloidal solution is encapsulated inside liposomes an in situ precipitation can be induced by slightly modification of the environment: application of a magnetic field in the case of magnetic particles or increase of the temperature. It has been shown in a previous study that magnetic liposomes exhibit strong deformation under magnetic field. In this case the precipitation can be induced after their elongation under magnetic field and liposomes keep their shape even if the magnetic field is cut off. The following study is motivated by the desire to use the salt effect to precipitate magnetic nanoparticles inside giant liposomes.
Keywords: Liposomes; Magnetic nanoparticles; Magnetic fluid; Precipitation; Vesicles
by Arthur Hubbard (pp. 400-400).