Journal of Colloid And Interface Science (v.339, #1)
Spatial and temporal control of surfactant systems
by Xiaoyang Liu; Nicholas L. Abbott (pp. 1-18).
Surfactant-based systems can be used for reversible control of both bulk and interfacial properties of aqueous surfactant systems, as well as in situ manipulation of the interactions of surfactants with macromolecules.This paper reviews some recent progress on approaches leading to spatial and temporal control of surfactant systems. The approaches revolve around the use of redox-active and light-sensitive surfactants. Perspectives are presented on experiments that have realized approaches for active control of interfacial properties of aqueous surfactant systems, reversible control of microstructures and nanostructures formed within bulk solutions, and in situ manipulation of the interactions of surfactants with polymers, DNA and proteins. A particular focus of this review is devoted to studies of amphiphiles that contain the redox-active group ferrocene – reversible control of the oxidation state of ferrocene leads to changes in the charge/hydrophobicity of these amphiphiles, resulting in substantial changes in their self-assembly. Light-sensitive surfactants containing azobenzene, which undergo changes in shape/polarity upon illumination with light, are a second focus of this review. Examples of both redox-active and light-sensitive surfactants that lead to large (>20mN/m) and spatially localized (∼mm) changes in surface tensions on a time scale of seconds are presented. Systems that permit reversible transformations of bulk solution nanostructures – such as micelle-to-vesicle transitions or monomer-to-micelle transitions – are also described. The broad potential utility of these emerging classes of amphiphiles are illustrated by the ability to drive changes in functional properties of surfactant systems, such as rheological properties and reversible solubilization of oils, as well as the ability to control interactions of surfactants with biomolecules to modulate their transport into cells.
Keywords: Surfactants; Active control; Self-assembly; Redox-active surfactants; Light-sensitive surfactants; Spatial and temporal control; Ferrocene; Azobenzene; Photosensitive
Ternary [Al2O3–electrolyte–Cu2+] species: EPR spectroscopy and surface complexation modeling
by Ioannis T. Papadas; Chariklia Kosma; Yiannis Deligiannakis (pp. 19-30).
EPR spectroscopy of ternary [Al2O3–electrolyte–Cu2+] species.Cu2+ binding on γ-Al2O3 is modulated by common electrolyte ions such as Mg2+,SO42-, andPO43- in a complex manner: (a) At high concentrations of electrolyte ions, Cu2+ uptake by γ-Al2O3 is inhibited. This is partially due to bulk ionic strength effects and, mostly, due to direct competition between Mg2+ and Cu2+ ions for theSO− surface sites of γ-Al2O3. (b) At low concentrations of electrolyte ions, Cu2+ uptake by γ-Al2O3 can be enhanced. This is due to synergistic coadsorption of Cu2+ and electrolyte anions,SO42- andPO43-. This results in the formation of ternary surface species (SOH2SO4Cu)+, (SOH2PO4Cu), and (SOH2HPO4Cu)+ which enhance Cu2+ uptake at pH<6. The effect of phosphate ions may be particularly strong resulting in a 100% Cu uptake by the oxide surface. (c) EPR spectroscopy shows that at pH≪pHPZC, Cu2+ coordinates to oneSO− group. Phosphate anions form stronger, binary or ternary, surface species than sulfate anions. At pH≫pHPZC Cu2+ may coordinate to twoSO− groups. At pH≪pHPZC electrolyte ionsSO42- andPO43- are bridging one O-atom from the γ-Al2O3 surface and one Cu2+ ion forming ternary [ γ-Al2O3/elecrolyte/Cu2+] species.
Keywords: Electrolyte; EPR; Cu; 2+; Ternary species; Phosphate; SO; 4; 2; -; Synergistic; Ionic strength; FITEQL; γ; -Al; 2; O; 3
Effects of fluorination modification on pore size controlled electrospun activated carbon fibers for high capacity methane storage
by Ji Sun Im; Min Jung Jung; Young-Seak Lee (pp. 31-35).
Fluorine played an important role in guiding methane gas into carbon silt pores via the attractive force due to the high electronegativity.Electrospun carbon fibers were prepared as a methane storage medium. Chemical activation was carried out using potassium carbonate to develop the pore structure, which can provide sites for the uptake of methane, and then fluorination surface modification was conducted to enhance the capacity of storage. Chemical activation provided a highly microporous structure, which is beneficial for methane storage, with a high specific surface area greater than 2500m2/g. The pore size distribution showed that the prepared samples have pore sizes in the range of 0.7–1.6nm. The effect of fluorination surface modification was also investigated. The functional groups, which were confirmed by XPS analysis, played an important role in guiding methane gas into the carbon silt pores via the attractive force felt by the electrons in the methane molecules due to the high electronegativity of fluorine. Eventually, the methane uptake increased up to 18.1wt.% by the synergetic effects of the highly developed micropore structure and the guiding of methane to carbon pores by fluorine.
Keywords: Methane storage; Carbon; Electrospinning; Fluorination; Pore size control
Carboxylated core–shell particles: I. A system showing hindered swelling behavior
by Aileen E. Lozsán R.; Manuel S. Romero-Cano (pp. 36-44).
Carboxylated core–shell particles shows different swelling behavior depending of the sample preparation route and their final shell conformation changes the behavior of salt-induced swelling.We study the swelling behavior of carboxylated core–shell particles. It is well-known that these particles swell with increasing pH due to the electrostatic repulsion between carboxylate groups. Our results reveal that the swelling behavior is affected by the preparation method. We find that the swelling is promoted in those particles which were initially in a highly swollen state (pH⩾10). However, the swelling is hindered for those particles which were not previously in this trigger pH. In the hindered systems, a compact conformation of the polymer shell is induced by hydrophobic attractions between the non-charged segments which compete against the swelling driving force. In addition, an interesting hysteresis behavior emerges when promoted systems are subjected to a heating–cooling cycle; a new stable system appears with a less extended polymer shell conformation. Furthermore, salt-induced swelling experiments corroborate not only polymer restructuring but also assembly among carboxylate groups which affects their ionization grade.
Keywords: Core–shell particles; Weak polyelectrolyte; Swelling; Electrostatic interaction; Hydrophobic interaction; Carboxyl poly(acid)
A simple route to interpenetrating network hydrogel with high mechanical strength
by Qunwei Tang; Xiaoming Sun; Qinghua Li; Jihuai Wu; Jianming Lin (pp. 45-52).
A two-step method is developed to synthesize interpenetrating network hydrogels with high mechanical strenght and toughness.A simple two-step method was introduced to improve the hydrogel mechanical strength by forming an interpenetrating network (IPN). For this purpose, we synthesized polyacrylate/polyacrylate (PAC/PAC), polyacrylate/polyacrylamide (PAC/PAM), polyacrylamide/polyacrylamide (PAM/PAM) and polyacrylamide/poly(vinyl alcohol) (PAM/PVA) IPN hydrogels. The PAC/PAC IPN and PAC/PAM IPN hydrogels showed compressive strength of 70 and 160kPa, respectively. For the PAM/PAM IPN and PAM/PVA IPN hydrogels, they exhibited excellent tensile strength of 1.2 and 2.8MPa, and elongations at break of 1750% and 3300%, respectively. A strain relaxation was also observed in the case of PAM series IPN hydrogels. From FTIR, TGA and SEM measurements, we confirmed that physical entanglement, hydrogen bonds and chemical crosslinking played major roles in improving hydrogel strength and toughening. The two-step technique contributes to the understanding of ideal networks, provides a universal strategy for designing high mechanical strength hydrogels, and opening up the biomedical application of hydrogels.
Keywords: Hydrogel; Interpenetrating network; Two-step method; Mechanical strength; Strain relaxation
Influence of iron oxide nanoparticles on the rheological properties of hybrid chitosan ferrogels
by Rebeca Hernández; Vanessa Zamora-Mora; María Sibaja-Ballestero; José Vega-Baudrit; Daniel López; Carmen Mijangos (pp. 53-59).
The elastic modulus increase induced by iron oxide nanoparticles is counterbalanced by the disruption of hydrogen bonding responsible for the formation of chitosan hydrogels in alkali media.Magnetite nanoparticles have been successfully synthesized in the presence of chitosan using an in situ coprecipitation method in alkali media. This method allows obtaining chitosan ferrogels due to the simultaneous gelation of chitosan. The chitosan concentration has been varied and its effects on the particle synthesis investigated. It has been demonstrated that high chitosan concentrations prevents the formation of magnetite due to the slow diffusion of the alkali species through the viscous medium provided by chitosan, instead iron hydroxides are formed. The presence of magnetite nanoparticles increases the elastic modulus which results in a reinforcement of the chitosan ferrogels. This effect is counterbalanced by the disruption of hydrogen bonding responsible for the formation of chitosan hydrogels in alkali media.
Keywords: Chitosan; Rheology; Ferrogels
Interactions between bioactive ferulic acid and fumed silica by UV–vis spectroscopy, FT-IR, TPD MS investigation and quantum chemical methods
by T.V. Kulik; N.A. Lipkovska; V.N. Barvinchenko; B.B. Palyanytsya; O.A. Kazakova; O.A. Dovbiy; V.K. Pogorelyi (pp. 60-68).
Interaction between ferulic acid and silica results in the formation of different energetically favorable surface complexes, which ratio depends on the way of ferulic acid loading (adsorption, mixing or co-milling).The interactions of bioactive ferulic acid with fumed silica were studied by UV/vis spectroscopy, FT-IR, TPD MS techniques and quantum chemical methods. It was found that surface complexes may form through phenol or carboxyl group of ferulic acid depending on its coverage value. The structure of surface complexes and mechanisms of the ferulic acid chemosorption on the silica surface are discussed. The kinetic parameters of the chemical reactions on silica surface are calculated. The mechanisms of thermal transformations of the ferulic chemosorbed surface complexes are proposed.
Keywords: Ferulic acid; Fumed silica; Adsorption; TPD MS; FT-IR; Electronic spectra
Polyelectrolyte mediated formation of hydroxyapatite microspheres of controlled size and hierarchical structure
by Yongsheng Wang; Meer Saiful Hassan; Poernomo Gunawan; Raymond Lau; Xin Wang; Rong Xu (pp. 69-77).
Hydroxyapatite microspheres of good uniformity, different size and hierarchical structure are formed via polyelectrolyte(PSS)-mediated hydrothermal synthesis. The flower-like porous microspheres are potential carriers of drug for biomedical applications.The understanding of the role of polyelectrolytes in the synthesis of inorganic materials could provide effective routes towards design of advanced materials. In this study, negatively charged poly(styrene sulfonate) (PSS) is employed as a modifier in hydrothermal synthesis of hydroxyapatite (HA). The results indicate that both the morphology and particle size could be well controlled by adjusting the PSS concentration. The presence of PSS (within the range of 0–9.6wt%) modified the growth pattern of HA crystallites and results in particles from the ribbons to microspheres. The building units of various microspheres change from nanofibers to nanorods or nanoplates. Along with that, the microspheres become smaller and more compact at higher PSS concentrations. The adsorption of PSS onto certain crystal faces as well as the complexing effect of PSS with Ca2+ can be considered as the controlling factors which determine the influence of PSS on the growth mode. The drug release study indicates that the flower-like HA microspheres can be possibly used as effective carriers for biomedical applications. The present synthesis method is simple and controllable, and can provide a convenient route to synthesize uniform HA microspheres with different sizes and hierarchical structures.
Keywords: Hydroxyapatite; Polyelectrolytes; PSS; Microspheres
Synthesis and characterization of the water-soluble silica-coated ZnS:Mn nanoparticles as fluorescent sensor for Cu2+ ions
by Bohua Dong; Lixin Cao; Ge Su; Wei Liu; Hua Qu; Daixun Jiang (pp. 78-82).
The silica-coated ZnS:Mn nanoparticles (QDs/SiO2) are water-soluble and have selective fluorescence sensitivity to Cu2+, which are employed as a novel fluorescent sensor for the determination of Cu2+.Silica-coated ZnS:Mn nanoparticles were synthesized by coating hydrophobic ZnS:Mn nanoparticles with silica shell through microemulsion. The core–shell structural nanoparticles were confirmed by X-ray diffraction (XRD) patterns, high-resolution transmission electron microscope (HRTEM) images and energy dispersive spectroscopy (EDS) measurements. Results show that each core–shell nanoparticle contains single ZnS:Mn nanoparticle within monodisperse silica nanospheres (40nm). Photoluminescence (PL) spectroscopy and UV–vis spectrum were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnS:Mn nanoparticles, the silica-coated ZnS:Mn nanoparticles have the improved PL intensity as well as good photostability. The obtained silica-coated ZnS:Mn nanoparticles are water-soluble and have fluorescence sensitivity to Cu2+ ions. Quenching of fluorescence intensity of the silica-coated nanoparticles allows the detection of Cu2+ concentrations as low as 7.3×10−9molL−1, thus affording a very sensitive detection system for this chemical species. The possible quenching mechanism is discussed.
Keywords: Quantum dots; Fluorescence; Quenching mechanism; Sensor; Silica
Multifunctional nanoparticles/silica microsphere assemblies using polyglycidyl methacrylate shells as supports
by Zheng Wang; Zhihui Zhao; Junhu Zhang; Zhaoqiang Li; Yuan Gao; Chunlei Wang; Hao Zhang; Bai Yang (pp. 83-90).
Nanoparticles/SiO2 microsphere assemblies were prepared, and integration of magnetic and fluorescent properties was achieved through varying the proportion of different nanoparticles assembled.A general method to prepare functional (or multifunctional) nanoparticles/silica microsphere assemblies is reported in this article. A thin shell of polyglycidyl methacrylate is grafted on the surface of silica through surface-initiated atom transfer radical polymerization technique. And then, various types of nanoparticles, including water-soluble CdTe quantum dots, Au nanoparticles and oil-soluble Fe3O4 nanoparticles are assembled on silica microspheres, respectively, or simultaneously. The properties of the assembled nanoparticles are well retained in the nanocomposite assemblies, and the controllable integration of magnetic and fluorescent properties can be achieved through varying the proportion of different nanoparticles assembled on nanoparticle/silica microsphere.
Keywords: Core–shell; Polyglycidyl methacrylate; Composite silica microsphere; Nanoparticle assembly
Freeze–thaw stability of water-in-oil emulsions
by S. Ghosh; D. Rousseau (pp. 91-102).
The freeze/thaw stability of water-in-oil emulsions is strongly influenced by the sequence of crystallization events (i.e., dispersed vs. continuous phase or vice versa) and the solid–liquid behavior of interfacially-bound surfactants.Factors influencing water-in-oil emulsion stability during freeze/thaw-cycling, namely interfacial crystallization vs. network crystallization and the sequence of crystallization events (i.e., dispersed vs. continuous phase or vice versa), are assessed. We show that destabilization is most apparent with a liquid-state emulsifier and a continuous oil phase that solidifies prior to the dispersed phase. Emulsions stable to F/T-cycling are obtained when the emulsifier crystallizes at the oil–water interface or in emulsions where the continuous phase crystallizes after the dispersed aqueous phase. The materials used are two food-grade oil-soluble emulsifiers – polyglycerol polyricinoleate (PGPR) and glycerol monostearin (GMS) and two continuous oil phases with differing crystallization temperatures – canola oil and coconut oil. Emulsion stability is assessed with pulsed field gradient NMR droplet size analysis, sedimentation, microscopy and differential scanning calorimetry. This study demonstrates the sequence of crystallization events and the physical state of the surfactant at the oil–water interface strongly impact the freeze–thaw stability of water-in-oil emulsions.
Keywords: Emulsion; Freeze–thaw; Stability; Coalescence; Sedimentation; Microstructure
Comparison of surface properties between kaolin and metakaolin in concentrated lime solutions
by K.L. Konan; C. Peyratout; A. Smith; J.-P. Bonnet; S. Rossignol; S. Oyetola (pp. 103-109).
Surface adsorption of calcium and hydroxyl ions onto kaolin and metakaolin in concentrated lime solutions.The surface adsorption of calcium hydroxide onto kaolin and metakaolin was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clays to calcium hydroxide solutions of various concentrations. Both clays adsorb calcium and hydroxyl ions but differently. Kaolin adsorbs calcium hydroxide not only at the edges of the clay particles but also onto the basal faces. The adsorbed hydrated calcium ions form a layer on the clay particle surfaces, preventing further dissolution of the clay mineral platelet. Metakaolin shows high pozzolanic activity, which provides the quick formation of hydrated phases at the interfaces between metakaolin and lime solutions. The nature of the hydration products has been investigated using X-ray diffraction (XRD) and differential thermal analysis (DTA). The most important hydrated phases like CSH (hydrated calcium silicate) and C2ASH8 (gehlenite) have been identified.
Keywords: Kaolin; Metakaolin; Hydrated phases; Lime
Micro-structure differences in kaolinite suspensions
by Marek S. Żbik; Ray L. Frost (pp. 110-116).
SEM micrographs of Georgia KGa-1 kaolinite show mostly edge-to-face platelet orientation.SEM observations of the aqueous suspensions of kaolinite from Birdwood (South Australia) and Georgia (USA) show noticeable differences in number of physical behaviour which has been explained by different micro-structure constitution. Birdwood kaolinite dispersion gels are observed at very low solid loadings in comparison with Georgia KGa-1 kaolinite dispersions which remain fluid at higher solids loading. To explain this behaviour, the specific particle interactions of Birdwood kaolinite, different from interaction in Georgia kaolinite have been proposed. These interactions may be brought about by the presence of nano-bubbles on clay crystal edges and may force clay particles to aggregate by bubble coalescence. This explains the predominance of stair step edge-edge like (EE) contacts in suspension of Birdwood kaolinite. Such EE linked particles build long strings that form a spacious cell structure. Hydrocarbon contamination of colloidal kaolinite particles and low aspect ratio are discussed as possible explanations of this unusual behaviour of Birdwood kaolinite. In Georgia KGa-1 kaolinite dispersions instead of EE contact between platelets displayed in Birdwood kaolinite, most particles have edge-to-face (EF) contacts building a cardhouse structure. Such an arrangement is much less voluminous in comparison with the Birdwood kaolinite cellular honeycomb structure observed previously in smectite aqueous suspensions. Such structural characteristics of KGa-1 kaolinite particles enable higher solid volume fractions pulps to form before significantly networked gel consistency is attained.
Keywords: Clay aggregates; Kaolinite micro-structure; Georgia kaolinite; Birdwood kaolinite; Colloids; Clay gelation
Transitional properties of starch colloid with particle size reduction from micro- to nanometer
by Dagang Liu; Qinglin Wu; Huihuang Chen; Peter R. Chang (pp. 117-124).
High-pressure homogenization was used to reduce starch particles from micro- to nanosize and to disperse them in water. From a state of mixture containing sediment, sol, gel, and suspension, different starch colloids were formed as a result of reduction of the colloid particle size from 3–6μm to 5–20nm.High-pressure homogenization was used to disperse starch particles in water and reduce the size from micro- to nanometer. The resultant starch colloids were characterized by particle morphology, mean size, size distribution, and zeta potential. Starch slurries were transformed from a mixture containing sediment, dispersion, and sol, to gel as a result of reduction of the particle size from 3–6μm to 10–20nm under a pressure of 207MPa. Furthermore, this process led to the transition of fluid properties without affecting the crystal structure and thermal stability of starch granules. Viscosity of the colloids increased with an increased number of homogenization passes, accompanied by a decreased particle size, narrower particle size distribution (PSD), and an increased absolute zeta potential, indicating the formation of a suspension or stable gel composed of nanoparticles. Lognormal and two other mathematical functions were established to describe the PSDs and their relationship to the homogenization passes. Hence, an environmentally friendly means of producing starch-based nanoparticles or nanogels with high yields, and predictable size and viscosity properties was presented.
Keywords: Colloid particle size; Starch; High-pressure homogenization; Zeta potential
The hexagonal close-packed nickel nanocrystals prepared by fast scan voltammetry
by Ramin Mohamed Ali Tehrani; Sulaiman Ab Ghani (pp. 125-132).
The hcp Ni nanocrystals with average particle size 9.7±2.3nm were deposited onto composite graphite electrode using scan rate of 6500mVs−1.The nickel (Ni) nanocrystals (average diameter 9.7±2.3nm) were deposited onto composite graphite electrode from a plating solution of 5.0mM NiCl2⋅6H2O and 1.0M NH4Cl using scan rate of 6500mVs−1. The initial potential −1.5V and final potential −0.5V vs. Ag/AgCl with applied time 120s were used for the whole deposition process. The variations of applied overpotentials and deposition times have affected the characteristics of Ni nanocrystals. It was found that the structural formation of Ni nanocrystals obtained were almost pure hexagonal close-packed (hcp). This study has demonstrated that the tuning of the final size, morphology and structural formation of the Ni nanocrystal were affected by control of nucleation, growth and hydrogen evolution processes in fast scan voltammetry technique used.
Keywords: Hexagonal close-packed; Nanocrystals; Nickel; Electrodeposition; Fast scan voltammetry
Degradation of phenol by mechanical activation of a rutile catalyst
by M.C. Cotto; A. Emiliano; S. Nieto; J. Duconge; R. Roque-Malherbe (pp. 133-139).
Phenol solutions in water were ball-milled with and without a rutile powder catalyst, and the reaction products analyzed. It was established, that when the catalyst was not included in the process, phenol was not affected, but when it was included, phenol was decomposed by theOH radical mechanism.In the present paper a novel mechanochemical process for the elimination of organic pollutants dissolved in water is proposed. In this regard, phenol aqueous solutions (100mgL−1) were ball-milled for 0, 12, 18, 24, 36, 48, and 72h with and without a well-characterized (XRD, SEM, and N2 Adsorption), rutile powder catalyst and the reaction products analyzed with UV and GC/MS. It was found that when the catalyst was not included in the process, phenol was not affected, but when it was included, phenol was decomposed. The catalyst itself did not change and the reaction follows a pseudo-first-order kinetics. Besides, intermediates which are characteristic of theOH radical mechanism were found in the reaction products. Then, a mechanism similar to those accepted for other advanced oxidation processes was proposed. The value measured for the pseudo-first-order reaction constant was very low, indicating that the reported process is inefficient. Nevertheless, this problem could be solved by applying catalysts consisting of particles with smaller diameters.
Keywords: Mechanochemistry; Catalysis; Phenol; Degradation; OH radical mechanism; Rutile
Differential transport and dispersion of colloids relative to solutes in single fractures
by Q. Zheng; S.E. Dickson; Y. Guo (pp. 140-151).
A new phenomenon for differential transport was observed. There exists a threshold value for the ratio of colloid radius to half of the fracture aperture, below which the ratio of colloid retention time to solute retention time decreases.This work employed numerical experiments simulating colloid and solute transport in single parallel-plate fractures, using the random walk particle tracking method, to demonstrate that (1) there exists an aspect ratio of the colloid radius to half the fracture aperture,δ o, where the average velocities of colloids and solutes are similar. Whenδ> δo, the velocity distribution assumption is satisfied, and the fact that the ratio of the colloid transport velocity to the solute transport velocity,τ p, decreases as δ increases is well documented in the literature. However, when δ<δ o, the velocity distribution assumption is violated, andτ p increases as δ increases and (2) the Taylor dispersion coefficient and its extension by James and Chrysikopoulos [S.C. James, C. V. Chrysikopoulos, J. Colloid Interface Sci. 263 (2003) 288] will overestimate the colloid dispersion coefficient significantly. Additionally, numerical experiments simulating colloid and solute transport in variable-aperture fractures demonstrated thatτ p andD L,coll/D L,solute decrease with increasing CoV, and the anisotropy ratio only plays a minor role compared to the CoV. These observations have important implications towards the interpretation of colloid transport in both porous and fractured media.
Keywords: Colloid transport; Differential transport; Single fracture; Variable-aperture fracture; Velocity distribution assumption; Dispersion
Pervaporation separation of n-heptane/thiophene mixtures by polyethylene glycol membranes: Modeling and experimental
by Ligang Lin; Yuzhong Zhang; Ying Kong (pp. 152-159).
Dynamic sorption curve for thiophene and n-heptane in PEG membrane: the thiophene component has a higher solubility coefficient than n-heptane, which is key in fulfilling the separation of thiophene/hydrocarbon mixtures.Gasoline desulfurization by membrane processes is a newly emerged technology, which has provided an efficient new approach for sulfur removal and gained increasing attention of the membrane and petrochemical field. A deep understanding of the solution/diffusion of gasoline molecules on/in the membrane can provide helpful information in improving or optimizing membrane performance. In this study, a desulfurization mechanism of polyethylene glycol (PEG) membranes has been investigated by the study of sorption and diffusion behavior of typical sulfur and hydrocarbon species through PEG membranes. A solution–diffusion model based on UNIFAC and free volume theory has been established. Pervaporation (PV) and sorption experiments were conducted to compare with the model calculation results and to analyze the mass transport behavior. The dynamic sorption curves for pure components and the sorption experiments for binary mixtures showed that thiophene, which had a higher solubility coefficient than n-heptane, was the preferential sorption component, which is key in the separation of thiophene/hydrocarbon mixtures. In all cases, the model calculation results fit well the experimental data. The UNIFAC model was a sound way to predict the solubility of solvents in membranes. The established model can predict the removal of thiophene species from hydrocarbon compounds by PEG membranes effectively.
Keywords: Pervaporation; Sorption; Gasoline desulfurization; Solution–diffusion model
Expanding mesoporosity of triblock-copolymer-templated silica under weak synthesis acidity
by Jinjun Li; Qin Hu; Hua Tian; Chunyan Ma; Landong Li; Jie Cheng; Zhengping Hao; Shizhang Qiao (pp. 160-167).
The protonation degree of the PEO chains decreases with lowering the synthesis acidities, leading to large hydrophobic volume of the template phases and large pore of the final products.With initial aging at low temperature for enough time, silicas with large mesoporosity were synthesized using triblock copolymer as template agent under weak acidities. SBA-15 with periodic mesostructure and short mesochannels could be synthesized at pH 2.5–3.0 within weak acidity range, and the surface areas, pore diameters and pore volumes reached up to ca. 1000m2/g, 8.8nm and 2.0cm3/g, respectively, which were significantly higher than those of the conventional SBA-15 synthesized under strong acidities. Mesoporous silica with wormhole structure and abundant textural porosity was formed at pH∼3.5. The increased hydrophobic volume of the copolymer micelles at elevated pH values was responsible for the enlargement of mesoporosity in the products. The materials synthesized under weak acidities showed lower hexagonal ordering in comparison to the general SBA-15 synthesized under strong acidities because the decreased hydronium ion concentration induced relatively weaker assembly forces during the synthesis. Nonetheless, the short mesochannels and large pore diameter in the products might be beneficial to some applications in which fast diffusion of molecules is required.
Keywords: SBA-15; Weak acidity; Large pore volume; Short mesochannel; Mesoporous silica; Wormhole structure; Textural porosity
Quantification of the velocity acceleration factor for colloidal transport in porous media using NMR
by Sarah A. Creber; Thomas R.R. Pintelon; Michael L. Johns (pp. 168-174).
The velocity acceleration of colloids in porous media is quantified using oil-in-water emulsions studied with NMR and confirmed with lattice Boltzmann simulations.Nuclear magnetic resonance (NMR) techniques were used to quantify the transport of colloids through porous media. This was achieved via the application of chemically-resolved pulsed field gradient (PFG) methods, hence probing the displacement (probability distribution) propagators of both the colloidal and continuous liquid phase. A dilute decane-in-water emulsion was used with flow through a random glass sphere packing being considered. The acquired propagators allowed for quantification of both colloidal entrapment and the velocities of both the continuous phase and the flowing colloids. The flowing colloids were found to experience a velocity acceleration factor (VAF) increase of 1.08 relative to the continuous phase. This was found to be independent of displacement observation time or flowrate. It was speculated to be a consequence of radial exclusion due to the finite size of the colloids. Simulations of the colloidal transport were also performed using a lattice Boltzmann platform and a Lagrangian particle-tracking algorithm which incorporated colloidal radial exclusion. Reasonable agreement was observed between the simulation and the experimental data.
Keywords: NMR; Displacement propagator; Colloid; Velocity acceleration factor (VAF); Porous media; Lattice Boltzmann
Nano-structured calcium silicate hydrate functionalised with iodine
by Thomas Borrmann; James H. Johnston; Andrew J. McFarlane; Michael J. Richardson; Sean J. O’Connor (pp. 175-182).
In this article chemisorption and physisorption processes involving iodine and nano-structured calcium silicate hydrate are outlined. At elevated temperatures iodine reacts with nano-structured calcium silicate hydrate to form a charge transfer complex.Nano-structured calcium silicate hydrate can physisorb or chemisorb iodine, making it interesting for medical or materials science applications, where a slow, controlled release of iodine is desired. It was found that iodine can be sorbed and released by applying the elemental halogen in solution, either as a gas or as a solid. At ambient temperatures the sorption and desorption process is quantitative and physical, meaning that the same amount of iodine is taken up and released. At temperatures above 32.5°C (305.7K) iodine reacts with the calcium silicate hydrate forming a complex, which is stable above the sublimation temperature of iodine. The formation energy for the iodine calcium silicate hydrate complex was established to be 41.8±0.8kJmol−1 by calorimetry and the nature of the complex was investigated using X-ray photoelectron spectroscopy.
Keywords: Nano-structured calcium silicate hydrate; Iodine; Iodine sorption; Iodine release; Calorimetry
Nanoparticle films as a conducting layer for anodic aluminum oxide template-assisted nanorod synthesis
by Sang-Hoon Yoo; Lichun Liu; Sungho Park (pp. 183-186).
A synthetic route for fabricating conductive film substrates by mechanical packing nanoparticles on one side of anodic aluminum oxide (AAO) templates is described.A simple, inexpensive, and robust methodology was developed to fabricate conductive film substrates by mechanically packing nanoparticles (NPs) on one side of anodic aluminum oxide (AAO). Gold, silver NPs, and carbon nanotubes were used as building blocks in the synthesis of conductive film substrates, upon which perpendicular nanorod arrays and colloidal free-standing nanorods were easily constructed. Characterizations by field emission scanning electron microscopy (FE-SEM) and optical dark-field microscopy confirmed the validity of the conductive NP film substrates on the AAO template. This contribution could provide a convenient and low-cost means for the fabrication of various conductive substrates on AAO.
Keywords: Metal nanorods; AAO; Nanoparticle aggregate; Electrochemical deposition; Conducting polymer; CNT
Static and dynamic contact angles of water droplet on a solid surface using molecular dynamics simulation
by Seung Do Hong; Man Yeong Ha; S. Balachandar (pp. 187-195).
In order to observe the dynamic contact angle, we applied a body force in the positive x direction to a water droplet in equilibrium with the solid surface.The present study investigates the variation of static contact angle of a water droplet in equilibrium with a solid surface in the absence of a body force and the dynamic contact angles of water droplet moving on a solid surface for different characteristic energies using the molecular dynamics simulation. With increasing characteristic energy, the static contact angle in equilibrium with a solid surface in the absence of a body force decreases because the hydrophobic surface changes its characteristics to the hydrophilic surface. In order to consider the effect of moving water droplet on the dynamic contact angles, we apply the constant acceleration to an individual oxygen and hydrogen atom. In the presence of a body force, the water droplet changes its shape with larger advancing contact angle than the receding angle. The dynamic contact angles are compared with the static contact angle in order to see the effect of the presence of a body force.
Keywords: Water droplet; Contact angle; Hydrophobic; Hydrophilic; Molecular dynamics simulation
Calculation of contact angles from surfactant adsorption isotherms
by Stephen Chwastiak (pp. 196-201).
Thermodynamic Model For Contact Angle.Wetting in the system hematite–water–diisobutyl ketone was studied in the presence of an anionic surfactant, hexadecyl sulfonic acid. Adsorption isotherms of surfactant on hematite powder were measured separately at the interfaces between hematite–water and hematite–ketone, and the interfacial tension of the water–ketone interface was determined as a function of surfactant concentration. The Gibbs and Young’s equations were used to calculate contact angles from the adsorption data. For comparison, contact angles were measured as a function of surfactant concentration on the face of a hematite crystal selected from the same supply of specular hematite used for preparing the hematite powder. Overall, contact angles calculated from the equations correlate closely with measured contact angles.
Keywords: Adsorption isotherms; Surfactants; Contact angle; Wetting; Surface chemistry
Wettability of nanoengineered dual-roughness surfaces fabricated by UV-assisted capillary force lithography
by Hoon Eui Jeong; Moon Kyu Kwak; Chan Ick Park; Kahp Yang Suh (pp. 202-207).
Our experimental and theoretical studies have demonstrated that there can be two distinct wetting states (Cm–Wn and Cm–Cn states) for a hydrophobic dual-roughness surface.Micro- and nanoscale combined hierarchical polymer structures were fabricated by UV-assisted capillary force lithography. The method is based on the sequential application of engraved polymer molds with a UV-curable resin of polyurethane acrylate (PUA) followed by surface treatment with a trichloro(1H,1H,2H,2H-perfluorooctyl) silane in vapor phase. Two distinct wetting states were observed on these dual-roughness structures. One is “Cassie–Wenzel state” where a water droplet forms heterogeneous contact with microstructures and homogeneous contact with nanostructures. The other is “Cassie–Cassie state” where a droplet makes heterogeneous contact both with micro- and nanostructures. A simple thermodynamic model was developed to explain static contact angle, hysteresis, and wetting transition on dual-roughness structures.
Keywords: Wettability; Lithography; Dual roughness; Hierarchical structure
A modified Cassie–Baxter relationship to explain contact angle hysteresis and anisotropy on non-wetting textured surfaces
by Wonjae Choi; Anish Tuteja; Joseph M. Mabry; Robert E. Cohen; Gareth H. McKinley (pp. 208-216).
We propose a modified Cassie–Baxter relation to correlate the details of the local surface texture with contact angle hysteresis, and validate our hypothesis both through experiments and numerical simulations.The Cassie–Baxter model is widely used to predict the apparent contact angles obtained on composite (solid–liquid–air) superhydrophobic interfaces. However, the validity of this model has been repeatedly challenged by various research groups because of its inherent inability to predict contact angle hysteresis. In our recent work, we have developed robust omniphobic surfaces which repel a wide range of liquids. An interesting corollary of constructing such surfaces is that it becomes possible to directly image the solid–liquid–air triple-phase contact line on a composite interface, using an electron microscope with non-volatile organic liquids or curable polymers. Here, we fabricate a range of model superoleophobic surfaces with controlled surface topography in order to correlate the details of the local texture with the experimentally observed apparent contact angles. Based on these experiments, in conjunction with numerical simulations, we modify the classical Cassie–Baxter relation to include a local differential texture parameter which enables us to quantitatively predict the apparent advancing and receding contact angles, as well as contact angle hysteresis. This quantitative prediction also allows us to provide an a priori estimation of roll-off angles for a given textured substrate. Using this understanding we design model substrates that display extremely small or extremely large roll-off angles, as well as surfaces that demonstrate direction-dependent wettability, through a systematic control of surface topography and connectivity.
Keywords: Abbreviations; CB; Cassie–Baxter; CAH; contact angle hysteresis; TCL; triple-phase contact lineCassie–Baxter relation; Contact angle hysteresis; Anisotropic wettability; Roll-off angle; Triple-phase contact line
Nanopattern transfer and wettability modification of regularly structured metallic and polymeric surfaces with replication
by Mee Rahn Kim; Soo Yeon Heo; Du-Jeon Jang (pp. 217-221).
The hexagonally arranged close-packed concave nanotexture of the master surface has been transferred to various materials well with the topological degradation and the wettability modification.The hexagonally arranged close-packed concave nanotexture of the master surface of nanoporous alumina has been imprinted several times on aluminum films and gold films by thermal evaporation and on polystyrene films by spin coating. The degradation of the nanotextures with replica pattern transfer has been monitored by measuring the topology and the wettability of duplicated films. The trough-to-crest height of the topography decreases while the wettability of the nanotexture increases significantly as replication goes on. Air fractions calculated with measured water contact angles decrease substantially with replication although they also depend strongly on the materials and the shapes of duplicating nanotextures.
Keywords: Contact angle; Gold; Nanoporous alumina; Nanotexture; Polystyrene
Phase behavior of bile acid/lipid/water systems containing model dietary lipids
by Yoshimune Nonomura; Keisuke Nakayama; Yuki Aoki; Atsuhiro Fujimori (pp. 222-229).
An increase in the intake of model plant lipid or model animal lipid causes the formation of multi-lamellar vesicles/lamellar liquid crystals or the extraction of fatty acid crystals.Dietary lipids are solubilized in bile acid micelles in the small intestine. In the present study, we investigate the phase behavior of bile acid/model rapeseed oil (or model beef tallow)/water systems to predict interfacial phenomena during consumption of a variety of foods. The structures of molecular assemblies are identified based on polarizing microscope images, wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). The results of in vitro tests suggest that an increase in the intake of model rapeseed oil causes the formation of multi-lamellar vesicles and lamellar liquid crystals. The molecules in the lamellar liquid crystal are formed highly ordered layer structure with the spacing of 8.8nm along the c-axis, while monoclinic packed structure is constructed as two-dimensional structure in ab-plane due to bulky molecular structures of bile acid and unsaturated fatty acid. When the model beef tallow composition in the model system is more than several wt.%, stearic acid crystals are extracted. Moreover, bicarbonate ions are important ingredients to solubilize >10wt.% of the model lipids. These phase transitions might be induced by the addition of dietary lipids in vivo during the consumption of oil or meat. Our findings are significant for understanding the lipid absorption process in the small intestine, and for developing medical and healthcare products.
Keywords: Bile acid; Fatty acid; Micelle; Liquid crystal
Surface properties and aggregate morphology of partially fluorinated carboxylate-type anionic gemini surfactants
by Tomokazu Yoshimura; Miri Bong; Keisuke Matsuoka; Chikako Honda; Kazutoyo Endo (pp. 230-235).
TEM images of 2CnF edda ( n=4, 6, and 8) aggregates.Three anionic homologues of a novel partially fluorinated carboxylate-type anionic gemini surfactant, N,N′-di(3-perfluoroalkyl-2-hydroxypropyl)- N,N′-diacetic acid ethylenediamine (2CnF edda, where n represents the number of carbon atoms in the fluorocarbon chain (4, 6, and 8)) were synthesized. In these present gemini surfactants, the relatively small carboxylic acid moieties form hydrophilic head groups. The surface properties or structures of the aggregates of these surfactants are strongly influenced by the nonflexible fluorocarbons and small head groups; this is because these surfactants have a closely packed molecular structure. The equilibrium surface tension properties of these surfactants were measured at 298.2K for various fluorocarbon chain lengths. The plot of the logarithm of the critical micelle concentration (cmc) against the fluorocarbon chain lengths for 2CnF edda ( n=4, 6, and 8) showed a minimum for n=6. Furthermore, the lowest surface tension of 2C6F edda at the cmc was 16.4mNm−1. Such unique behavior has not been observed even in the other fluorinated surfactants. Changes in the shapes and sizes of these surfactant aggregate with concentration were investigated by dynamic light scattering and transmission electron microscopy (TEM). The TEM micrographs showed that in an aqueous alkali solution, 2CnF edda mainly formed aggregates with stringlike ( n=4), cagelike ( n=6), and distorted bilayer structures ( n=8). The morphological changes in the aggregates were affected by the molecular structure composed of nonflexible fluorocarbon chains and flexible hydrocarbon chains.
Keywords: Fluorinated surfactant; Micellization; Gemini surfactant; Fluorocarbon; Aggregation; Surface tension
Steady and dynamic rheological behaviors of sodium carboxymethyl cellulose entangled semi-dilute solution with opposite charged surfactant dodecyl-trimethylammonium bromide
by Qiang Wu; Yonggang Shangguan; Miao Du; Jianping Zhou; Yihu Song; Qiang Zheng (pp. 236-242).
Structure evolution of NaCMC–C12TAB complex with adding C12TAB concentration into NaCMC entangled semi-dilute solution.The steady and dynamic rheological behaviors of sodium carboxymethyl cellulose (NaCMC) entangled semi-dilute solution filled with different concentrations of dodecyl-trimethylammonium bromide (C12TAB) were investigated. The results reveal that the zero shear rate viscosity ( η0) and dynamic modules ( G′and G″) increase with C12TAB concentration (C s), and there exist three scaling regions divided by two critical C12TAB concentrations ( C1, C2 andC1′,C2′, respectively, from steady and dynamic tests). The increase of viscosity and modules withC s is ascribed to formation of network due to C12TAB micelles bridging NaCMC chains. The two critical C12TAB concentrations implies that the structure evolution of NaCMC–C12TAB complex is exposed to three states with increasingC s, i.e., no network formation, network extent progressive formation and perfect network formation, respectively. Moreover,C1′,C2′ are a little lower than C1, C2, indicating that the dynamic test is more sensitive to detect the structure change of the complex as compared with steady test. Furthermore, it is found that as NaCMC concentration increases,C1(C1′),C2(C2′),C1(C1′)-CAC andC2(C2′)-CAC increase.
Keywords: Polyelectrolyte; Surfactant; Rheological behavior; Entangled semi-dilute solution
Lysozyme as diffusion tracer for measuring aqueous solution viscosity
by Avanish S. Parmar; Martin Muschol (pp. 243-248).
The small enzyme lysozyme (right) provides a stable tracer particle for dynamic-light-scattering based measurements of saline solution viscosity (left). Lysozyme structure 2lyz (RCSB Protein Data Bank).Measuring tracer diffusion provides a convenient approach for monitoring local changes in solution viscosity or for determining viscosity changes in response to multiple solution parameters including pH, temperature, salt concentrations or salt types. One common limitation of tracer diffusion in biologically relevant saline solutions is the loss of colloidal stability and aggregation of the tracer particles with increasing ionic strength. Using dynamic light scattering to measure tracer diffusion, we compared the performance of two different types of tracer particles, polystyrene nanobeads vs. the small protein lysozyme, for viscosity measurements of saline solutions. Polystyrene beads provide reliable values for water viscosity, but begin flocculating at ionic strengths exceeding about 100mM. Using lysozyme, in contrast, we could map out viscosity changes of saline solutions for a variety of different salts, for salt concentrations up to 1M, over a wide range of pH values, and over the temperature range most relevant for biological systems (5–40°C). Due to its inherently high structural and colloidal stability, lysozyme provides a convenient and reliable tracer particle for all these measurements, and its use can be readily extended to other optical approaches towards localized measurements of tracer diffusion such as fluorescence correlation spectroscopy.
Keywords: Viscosity; Tracer diffusion; Polystyrene; Colloidal stability; Saline solution
Low-temperature polymer-assisted synthesis of shape-tunable zinc oxide nanostructures dispersible in both aqueous and non-aqueous media
by Md. Harunar Rashid; Manoj Raula; Rama Ranjan Bhattacharjee; Tarun K. Mandal (pp. 249-258).
Low-temperature polymer-assisted synthesis of shape-controlled and solvent-adoptable zinc oxide nanostructures of various morphologies including dumbbell, lance and triangle were described.We report the shape-controlled synthesis of zinc oxide (ZnO) nanostructures by a poly(vinyl methyl ether) (PVME)-assisted alkaline hydrolysis of zinc acetate at low temperature (20°C). In this method, ZnO nanostructures of various morphologies including dumbbells, lances and triangles have been successfully prepared via a simple variation of different reaction parameters such as polymer concentration, pH of the reaction mixture and precursor concentration. However, without PVME, ZnO of such structurally uniform morphologies were not formed; rather ZnO of a mixture of defined and undefined morphologies were obtained indicating PVME-assisted the growth of such regular shaped ZnO nanostructures. HRTEM analysis of lance- and triangle-shaped samples as well as SAED patterns of all kinds of samples (dumbbell, lance and triangle) revealed that the ZnO nanostrcutures are single crystalline in nature and might form through oriented growth. XRD analysis also revealed the formation of well crystalline ZnO with a hexagonal structure. FTIR spectroscopy and TGA analysis confirmed the adsorption of PVME on the surface of ZnO nanostructures. Being a solvent adaptable polymer, the adsorbed PVME makes these shaped ZnO nanostructures highly dispersible in both polar and non-polar organic solvents including water. The extent of dispersibility in different solvents was studied by spectroscopic and microscopic techniques. Such solvent adoptability of PVME-coated ZnO nanostructures increases its ease of applications in device fabrication as well as in biological systems.
Keywords: Zinc oxide; Nanostructures; Poly(vinyl methyl ether); Solvent-adoptable; Shape-tunable; Polymer; Mechanism
Gels from a semifluorinated n-alkane in fluorinated solvents as a probe for intermolecular interactions
by Lorenzo Tattini; Pierandrea Lo Nostro /; Luca Scalise; Barry W. Ninham; Piero Baglioni (pp. 259-265).
Thermally reversible gel from a semifluorinated alkane (F8H16) in a fluorocarbon (perfluorooctane). The semifluorinated alkane forms elongated anisotropic aggregates, and the solvent remains entrapped in the tridimensional network.Diblock semifluorinated n-alkanes can form aggregates and gels in fluorinated solvents. We have investigated the thermal behavior of binary mixtures comprising F(CF2)8(CH2)16H and fluorinated solvents. The solvents were perfluorohexane, perfluoroheptane, perfluorooctane, perfluorooctyl bromide, perfluorodecalin, and perfluorotributylamine. The phase diagrams were used to calculate the activity coefficients of the two components and the main excess thermodynamic functions. The solubility and self-assembly behavior of F8H16 in the fluorinated solvents are related to the different solute–solvent dispersion interactions that depend on the polarizabilities and ionization potentials of the interacting species, and on the structural properties of the solvent.
Keywords: Fluorocarbon(s); Fluorinated solvent(s); Semifluorinated alkane(s); Perfluoroalkyl-alkane(s); Interaction(s); Self-assembly
Ratiometric pH-nanosensors based on rhodamine-doped silica nanoparticles functionalized with a naphthalimide derivative
by Tristan Doussineau; Sabine Trupp; Gerhard J. Mohr (pp. 266-270).
A naphthalimide derivative has been successfully immobilized on the outer surface of rhodamine-doped silica nanoparticles yielding pH-nanosensors able to monitor proton concentration in the biologically relevant pH-range.This paper describes the preparation of two-dye-doped silica nanoparticles for ratiometric pH measurements in the biologically relevant pH-range. While a rhodamine derivative is embedded in a silica core and used as the reference, a pH-sensitive naphthalimide dye is immobilized on the previously amino-functionalized core through two different approaches. Either the naphthalimide’s carboxylic group is activated to a succinimidyl-ester to form an amide bond or the system can be built up via solid-phase organic synthesis in only two steps. Both types of nanosensors are characterized in terms of morphology (dynamic light scattering, transmission electron microscopy) and optical properties (steady-state fluorescence spectroscopy). In terms of application, e.g. reproducibility and handling of the synthesis, the first approach gave very good results with respect to size and size distribution and a p Ka value of 6.55 was found that is comparable to the free indicator dye in solution. The solid-phase organic synthesis method proves the possibility of covalent immobilization of naphthalimides to amino-functionalized surfaces, showing the stability of the polymeric substrate and achieving comparable results for pH sensing.
Keywords: pH sensor; Silica nanoparticles; Naphthalimide dyes; Ratiometric measurements; Surface immobilization
Sub-micrometer precision of optical imaging to locate the free surface of a micrometer fluid shape
by J.M. Montanero; E.J. Vega; C. Ferrera (pp. 271-274).
We evaluate the precision of optical imaging for measuring the free surface position of a micrometre fluid shape. The deviations with respect to the expected shapewere smaller than 30nm.In this note, we explore the precision of the optical imaging method for measuring the free surface position of a micrometer fluid shape. For this purpose, images of a liquid film deposited on a rod were acquired and processed. The resulting contour was compared with the corresponding solution to the Young-Laplace equation. The average deviation was about 30nm, 25 times smaller than the pixel size, reflecting the validity of optical imaging for most applications in microfluidics.
Keywords: Free surface; Image analysis; Optical imaging; Liquid film