Journal of Colloid And Interface Science (v.325, #2)
Complexity of ammonia interactions on activated carbons modified with V2O5
by Camille Petit; Teresa J. Bandosz (pp. 301-308).
A micro/mesoporous wood-based activated carbon was modified with different loadings of vanadium pentoxide via incipient impregnation with ammonium vanadate solution followed by heating in nitrogen at 500 °C. The materials were used as adsorbents for ammonia. Both adsorption and desorption curves were recorded. The initial and exhausted samples were characterized by Fourier transform infrared spectroscopy (FTIR), potentiometric titration, thermal analysis and adsorption of nitrogen. An improvement in ammonia uptake compared to the virgin carbon was observed, and the adsorption capacity was found linearly dependent on the metal content. Water increases ammonia adsorption capacity via dissolution of the gas, but it also competes with ammonia because both of them are preferentially adsorbed on the same vanadium oxide sites (vanadyl oxygens). Even though an increase in the interactions strength between ammonia and the adsorbents' surface has been reached compared to previous studies, some weakly adsorbed ammonia was still released from the surface during air purging.Vanadium pentoxide provides additional Brønsted sites for ammonia retention. Although water favors ammonia dissolution, it has also detrimental effect competing with ammonia for adsorption on the vanadyl oxygen.
Keywords: Ammonia; Activated carbon; Adsorption; Vanadium oxide; Acidity; Porosity
Reduction of protein adsorption to a solid surface by a coating composed of polymeric micelles with a glass-like core
by B. Hofs; A. Brzozowska; A. de Keizer; W. Norde; M.A. Cohen Stuart (pp. 309-315).
Adsorption studies by optical reflectometry show that complex coacervate core micelles (C3Ms) composed of poly([4-(2-amino-ethylthio)-butylene] hydrochloride)49- block-poly(ethylene oxide)212 and poly([4-(2-carboxy-ethylthio)-butylene] sodium salt)47- block-poly(ethylene oxide)212 adsorb in equal amounts to both silica and cross-linked 1,2-polybutadiene (PB). The C3Ms have an almost glass-like core and atomic force microscopy of a dried layer of adsorbed C3Ms shows densely packed flattened spheres on silica, which very probably are adsorbed C3Ms. Experiments were performed with different types of surfaces, solvents, and proteins; bare silica and cross-linked 1,2-PB, NaNO3 and phosphate buffer, and lysozyme, bovine serum albumin, β-lactoglobulin, and fibrinogen. On the hydrophilic surface the coating reduces protein adsorption >90% in 0.1 M phosphate buffer, whereas the reduction on the coated hydrophobic surface is much lower. Reduction is better in phosphate buffer than in NaNO3, except for the positively charged lysozyme, where the effect is reversed.Effect of a coating of complex coacervate core micelles (C3Ms) on solid surfaces on protein (lysozyme, LSZ, beta-lactoglobulin, fibrinogen, and bovine serum albumin) adsorption in different media (NaNO3, phosphate buffer).
Keywords: Protein adsorption; Polymeric micelles; Adsorption of micelles
Regular and irregular deswelling of polyacrylate and hyaluronate gels induced by oppositely charged surfactants
by Peter Nilsson; Per Hansson (pp. 316-323).
The deswelling kinetics of macroscopic polyacrylate (PA) gels in solutions of dodecyltrimethylammonium bromide (C12TAB) and cetyltrimethylammonium bromide (C16TAB), with and without added sodium bromide, as well as hyaluronate (HA) gels in solutions of cetylpyridinium chloride (CPC) are investigated. Additional data are also provided by small-angle X-ray scattering and microgel experiments. The purpose is to study the deswelling behavior of (1) regularly deswelling gels, for which the deswelling is successfully described using a core/shell model earlier employed for microgels, and (2) irregularly deswelling gels, where the gel turns into a balloon-like structure with a dense outer layer surrounding a liquid-filled core. For regularly deswelling gels, the deswelling of PA/C12TAB is found to be controlled by diffusion through both stagnant layer and collapsed surface phase, while for PA/C16TAB it is found to be controlled mainly by the latter. The difference in deswelling rate between the two is found to correspond to the difference in surfactant diffusion coefficient in the surface phase. Factors found to promote irregular deswelling, described as balloon formation, are rapid surfactant binding, high bromide and surfactant concentration, longer surfactant chain length, and macroscopic gel size. Scattering data indicating a cubic structure for HA/CPC complexes are reported.Regular deswelling (upper path), with micelle-free core being gradually converted into dense, micelle-rich surface phase as the gel deswells, and irregular deswelling (lower path), where the core is ruptured and a balloon-like structure enveloping a liquid-filled core, devoid of polymer material, is formed.
Keywords: CTAB; C; 16; TAB; DTAB; C; 12; TAB; CPC; SAXS; Hyaluronic acid; Polyacrylic acid; Deswelling kinetics
Association (micellization) and partitioning of aglycon triterpenoids
by Marjan Rafat; Kit Wah Fong; Arthur Goldsipe; Brian C. Stephenson; Samuel T. Coradetti; T.G. Sambandan; Anthony J. Sinskey; C.K. ChoKyun Rha (pp. 324-330).
Micellization and solution properties of the aglycon triterpenoids asiatic acid (AA) and madecassic acid (MA) were examined experimentally and in computational simulations. AA and MA belong to the large class of bioactive aglycon triterpenoids, for which limited physicochemical data are available. In this study, solubility, partition coefficient, critical micelle concentrations (CMC), and surface tensions of AA and MA were measured. Reverse phase HPLC data, supported by dye probe experiments and drop shape analysis, showed the CMC in phosphate buffered saline (PBS) to be15±2 μM, and86±9 μM for AA and MA, respectively. The surface tensions of AA and MA in PBS were 64.1 and 64.4 mN/m, respectively. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry indicated the aggregation numbers of AA and MA to be 5 to 7. Molecular dynamics simulations confirmed that molecular association could occur between 5 and 7 molecules in solution. The IC50 of AA and MA on human small cell carcinoma and human glioblastoma cell lines was25±5 μM and66±13 μM, respectively. The IC50 is within the range of calculated CMC of AA and MA in bioassay media, suggesting that the micellar aggregates may lead to their cytotoxicity.GROMACS simulations indicate that asiatic acid and madecassic acid form small micelles with aggregate number 5–7. The IC50 coincided with CMC, suggesting that the micellar association may be responsible for cytotoxicity. (Figure: (left) molecular dynamics simulation of asiatic acid (AA) molecules self-assembly, forming a 5–7 molecule aggregate; (right) viability of DMS114 and HTB-14 cells treated with AA.)
Keywords: Surface activity; Partition coefficient; Solubility; Asiatic acid; Madecassic acid; CMC; Triterpenoids; Aggregation number; Molecular dynamics
Structure transition from aragonite to vaterite and calcite by the assistance of SDBS
by Zhaodong Nan; Xiangna Chen; Qianqian Yang; Xiuzhen Wang; Zuoyi Shi; Wanguo Hou (pp. 331-336).
Structure transition from aragonite to vaterite and calcite with the help of anionic surfactant sodium dodecyl benzene sulfonate (SDBS) was investigated, respectively, by a hydrothermal method. When the experimental temperature was controlled at 90 °C, aragonite of crystal calcium carbonate was transformed into vaterite with the assistance of SDBS. Pure vaterite was obtained as the concentration of SDBS reaches to 2.5 mM. When the experimental temperature was controlled at 120 and 150 °C, respectively, aragonite was transformed into calcite, and pure calcite was obtained as the concentrations of SDBS were equal to 1.0 and 2.5 mM, respectively. Possible formation mechanism of different CaCO3 polymorphs was proposed based on the obtained experimental results.Structure transformations from aragonite to vaterite and calcite were found with the assistance of SDBS at different experimental temperatures, respectively. The formation mechanism was proposed.
Keywords: Crystal polymorph; Calcite; Aragonite; Vaterite; Sodium dodecyl benzene sulfonate (SDBS)
Protein interaction with a Pluronic-modified poly(lactic acid) Langmuir monolayer
by É. Kiss; K. Dravetzky; K. Hill; E. Kutnyánszky; A. Varga (pp. 337-345).
Interaction of bovine serum albumin (BSA) with poly(lactic acid) (PLA) layers mixed with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers (Pluronic) at air/solution interfaces was studied by the Langmuir balance technique. Wettability of the mixed PLA–Pluronic system was characterized in the form of a transferred one-layer Langmuir–Blodgett film, and considerable hydrophilization was obtained for all of the Pluronics (6400, 6800, 10500, and 12700) applied here. The density of PEO chains in the monolayer and hence the coverage of PLA was controlled by the composition and the compression of the mixed monolayers. Tensiometric investigations revealed that a significant reduction of BSA adsorption/penetration was achieved by applying the Pluronic 6800 and 12700 with long PEO blocks for hydrophilization of PLA. Interaction of BSA with the modified PLA monolayer depended on the density and length of the PEO chains. The surface morphological characteristics of the films determined by atomic force microscopy were in good correlation with the results of BSA interaction. The average roughness of the polymer LB layer was high due to BSA penetration into the PLA film, while smooth surfaces with small roughness were obtained when the PLA layer was modified by Pluronic 6800.
Keywords: Langmuir monolayer; Protein penetration; Hydrophilization; AFM; PLA; Pluronic; BSA; LB film
Interactions between chitosan-modified particles and mucin-coated surfaces
by Olof Svensson; Krister Thuresson; Thomas Arnebrant (pp. 346-350).
Lipid-based particles (Cubosome® particles) were surface-modified by chitosan and the ratio between particles and chitosan was optimized to minimize the free chitosan concentration in the dispersion. The modified particles were characterized by electrophoretic measurements and the pH dependence of the zeta potential could be directly related to the protonation of chitosan. Interaction between the modified particles and mucin-coated silica surfaces were subsequently investigated in situ by ellipsometry to assess the mucoadhesive properties at physiologically relevant conditions. The result showed that a substantial amount of modified particles was adsorbed to mucin-coated silica surfaces at both pH 4 and pH 6, probably due to electrostatic interactions between amino groups in chitosan and negatively charged groups in mucin. Furthermore, the amount of bound particles decreased by less than 15% upon rinsing indicating relatively strong interactions. This investigation demonstrates that ellipsometry is a useful tool to study mucoadhesive properties of particles in the submicrometer range. Moreover, the novel chitosan-modified particles may be of interest for mucosal drug delivery applications.Illustration of the differences in binding of lipid particles and chitosan-modified lipid particles to a mucin-coated silica surface. Adsorbed amount versus time is shown.
Keywords: Mucin; Chitosan; Mucoadhesion; Drug delivery; Particle; Ellipsometry
Syringe pump-assisted synthesis of water-soluble cubic structure Ag2Se nanocrystals by a cation-exchange reaction
by Shang-Bing Wang; Bo Hu; Chang-Chang Liu; Shu-Hong Yu (pp. 351-355).
Water-soluble cubic structure Ag2Se ( α-Ag2Se) nanocrystals smaller than 5 nm can be obtained by cation-exchange reaction at room temperature, using water-dispersed ZnSe nanocrystals as precursors, which is achieved by controlling the injection speed of AgNO3 solutions via a syringe pump in the presence of the stabilizer of trisodium citrate. Meanwhile, the thermal stability of the product Ag2Se nanocrystals is studied. The results show that the mean sizes and shapes of the precursor ZnSe and product Ag2Se nanocrystals are similar, and Se anion sublattices between them are topotaxial. In addition, no phase transition is observed for the product Ag2Se (cubic structure) nanocrystals below 180 °C. The present synthetic method based on cation-exchange reactions can also be applied to the syntheses of PbSe and CuSe nanocrystals.Water-soluble cubic structure Ag2Se nanocrystals can be obtained by cation-exchange reaction at room temperature by using ZnSe as precursors with the aid of a syringe pump.
Keywords: Ag; 2; Se; Cubic structure; Water-soluble; Cation exchange; Thermal stability
Preparation and characterization of the biomineralized zinc oxide particles in spider silk peptides
by Z.B. Zhongbing Huang; D.H. Danhong Yan; Mei Yang; X.M. Xiaoming Liao; Y.Q. Yunqing Kang; G.F. Guangfu Yin; Y.D. Yadong Yao; B.Q. Baoqing Hao (pp. 356-362).
In this work, hierarchical ZnO particles were prepared using a biomineralization strategy at room temperature in the presence of peptides acidified from spider silk proteins. A mechanism of the mineralization of the ZnO particles was that the affinity of original ZnO nanoparticles and zinc ions in the peptide chains played an important role in controlling the biocrystallizing formation of the pore ZnO particles. The intensity of their visible green luminescence was enhanced with increases of the mineralization time due to the porous surface defects. The hierarchical ZnO materials with biomolecules will facilitate their photoluminescence spectra applications as biosensors or optoelectronic nanodevices in the future, when covalently coupled with peptides or other biomolecules to achieve patterned growth over large areas of substrate.Hierarchical ZnO particles were prepared using a biomineralization strategy at room temperature under peptides acidified from spider silk protein. Their visible green luminescence is enhanced with increased mineralization time.
Keywords: ZnO particles; Porous; Peptide; Biomineralization
Comparison between batch and column experiments to determine the surface charge properties of rutile TiO2 powder
by Lenka Svecova; Sebastien Cremel; Catherine Sirguey; Marie-Odile Simonnot; Michel Sardin; Manuel Dossot; Florence Mercier-Bion (pp. 363-370).
This paper reports a comparative study of three methods for determining the surface charge and acid–base behavior of a TiO2 rutile material. Electrophoretic mobility measurements were performed using two different batch protocols: (i) a “static” mode that consisted of immersing the rutile powder in aqueous solutions of given pH's and ionic strengths for 10 h, and (ii) a “dynamic” mode that consisted of using an automatic titrator to continuously adjust the solution pH with a contact time of 15 min. The same apparatus (a Nanosizer from Malvern) was used to measure the zeta potential of the particles in both methods. These batch experiments were next compared to the determination of the surface charge of rutile using nonlinear chromatography in column experiments. In that case, the rutile powder was compacted to enable the formation of a proper column bed. Therefore, Raman scattering and X-ray photoelectron spectra were used, as well as other physical information such as specific surface area and morphology of the particles, to verify that the rutile powder and compacted form were identical. The three approaches were then compared and discussed in relation to the acid–base behavior of the rutile material.Two experimental approaches for measuring surface charge of TiO2 were compared: zetametry in batch conditions, or nonlinear chromatography in column experiments.
Keywords: TiO; 2; Rutile; Electrophoretic mobility; Surface charge; Zeta potential; Nonlinear chromatography
Facile preparation and characterization of highly antimicrobial colloid Ag or Au nanoparticles
by Yongwen Zhang; Huashong Peng; Wei Huang; Yongfeng Zhou; Deyue Yan (pp. 371-376).
A series of colloid silver or gold nanoparticles (AgNPs or AuNPs) were successfully prepared by in situ reduction and stabilization of hyperbranched poly(amidoamine) with terminal dimethylamine groups (HPAMAM-N(CH3)2) in water, and they all exhibited highly antimicrobial activity. The particle size could be controlled easily by adjusting the molar ratio of N/Ag (or N/Au) in feed. When the molar ratio was 2, some aggregates of the nanoparticles separated from the colloidal solution, which showed some limited antimicrobial activity with the bacterial inhibition ratio of below 15%. As the molar ratio increased from 10 to 30, the average particle diameters decreased (from ca. 7.1 to 1.0 nm for AgNPs and from ca. 7.7 to 3.9 nm for AuNPs, respectively) and they all showed high dispersion stability and excellent antimicrobial efficiency. All the bacterial inhibition ratios reached up to ca. 98% at the low silver content of ca. 2.0 μg/mL or at the low gold content of ca. 2.8 μg/mL. The AgNPs or AuNPs with smaller particle size can provide much more effective contact surface with the bacteria, thus enhancing their antimicrobial efficiency. Besides, the cationic HPAMAM-N(CH3)2 can also do some contribution to the antimicrobial activity through the strong ionic interaction with the bacteria.A series of colloid silver or gold nanoparticles were successfully prepared by in situ reduction and stabilization of hyperbranched poly(amidoamine) with terminal dimethylamine groups in water and they all exhibited highly antimicrobial activity.
Keywords: Silver nanoparticles; Gold nanoparticles; Hyperbranched polymer; Antimicrobial activity
Colloidal dynamics: Influence of diffusion, inertia and colloidal forces on cluster formation
by Nina Kovalchuk; Victor Starov; Paul Langston; Nidal Hilal; Viacheslav Zhdanov (pp. 377-385).
Computer simulations of colloidal suspensions are discussed. The simulations are based on the Langevin equations, pairwise interaction between colloidal particles and take into account Brownian, hydrodynamic and colloidal forces. Comparison of two models, one taking into account inertial term in Langevin equation and another based on diffusional approximation proposed in [D.L. Ermak, J.A. McCammon, J. Chem. Phys. 69 (1978) 1352], has shown that both models enable the prediction of the correct values of the diffusion coefficient and residence time of particle in a doublet and are therefore suitable to study the dynamics of formation and breakage of clusters in colloidal suspensions. It is shown that the appropriate selection of the time step and taking into account inertia of particles provides also the correct value of the average kinetic energy of each particle during the simulations, what allows to use the model based on full Langevin equations as a reference model to verify the validity of the numerical scheme for simulation using diffusion approximation.Time evolution of ensemble of 4 colloidal particles depending on the depth of the potential well of colloidal forces.
Keywords: Colloidal suspensions; Langevin equations; Colloidal forces; Brownian forces; Hydrodynamic interactions; Fluctuation–dissipation theorem; Clusters
Effect of sonication on the particle size of montmorillonite clays
by Alessandra L. Poli; Tatiana Batista; Carla C. Schmitt; Fergus Gessner; Miguel G. Neumann (pp. 386-390).
This paper reports on the effect of sonication on SAz-1 and SWy-1 montmorillonite suspensions. Changes in the size of the particles of these materials and modifications of their properties have been investigated. The variation of the particle size has been analyzed by DLS (dynamic light scattering). In all cases the clay particles show a bimodal distribution. Sonication resulted in a decrease of the larger modal diameter, as well as a reduction of its volume percentage. Simultaneously, the proportion of the smallest particles increases. After 60 min of sonication, SAz-1 presented a very broad particle size distribution with a modal diameter of 283 nm. On the other hand, the SWy-1 sonicated for 60 min presents a bimodal distribution of particles at 140 and 454 nm. Changes in the properties of the clay suspensions due to sonication were evaluated spectroscopically from dye–clay interactions, using Methylene Blue. The acidic sites present in the interlamellar region, which are responsible for dye protonation, disappeared after sonication of the clay. The changes in the size of the scattering particles and the lack of acidic sites after sonication suggest that sonication induces delamination of the clay particles.Sonication induces the deaggregation of clay tactoids.
Keywords: Sonication; Clays; Dyes; Clay–dye interactions
Controllable synthesis of CuS–P(AM- co-MAA) composite microspheres with patterned surface structures
by Ying Zhang; Huijin Liu; Ya Zhao; Yu Fang (pp. 391-397).
Copper sulfide–poly(acrylamide- co-methacrylic acid) (CuS–P(AM- co-MAA)) composite microspheres with patterned surface structures have been synthesized in a controllable manner by means of the polymer microgel template method. The formation of CuS particles can be regulated by controlling the decomposition of thioacetamide (TAA) in acidic solution. Compared with the microgel template, the surface morphologies of the composite microspheres are characterized by compact and creased textures. The surface morphology of the composite microspheres has been found to be mainly influenced by the amount of copper sulfide precipitated and hence by the rate of H2S gas generation. This study might provide a potential route for controlling the synthesis of various metal sulfide–polymer composites with patterned surface structures.CuS–P(AM- co-MAA) composite microspheres with patterned surface structures have been synthesized in a controllable manner by means of the polymer microgel template technique.
Keywords: Polymer microgels; Template method; Metal sulfides; Composites
Adsorption and self-assembly of octyl hydroxamic acid at a fluorite surface as revealed by sum-frequency vibrational spectroscopy
by Xuming Wang; Jin Liu; Jan D. Miller (pp. 398-403).
In the study described here, the surface structure of a self-assembly octyl hydroxamic acid at a calcium fluoride (CaF2) surface is evaluated using sum-frequency vibrational spectroscopy (SFVS). Of particular significance are the results that show octyl hydroxamic acid adsorbs at the fluorite surface from octanol solution and has more ordering and molecular conformation than the octyl hydroxamic acid adsorbed from solution. At the fluorite/0.1 M octyl hydroxamic acid octanol solution interface a bilayer-like structure consisting of an octyl hydroxamic acid layer in contact with fluorite and a tilted alcohol layer was observed by SFVS. The alcohol molecules are oriented with respect to the hydroxamic acid monolayer with the OH groups directed towards the bulk alcohol phase and the terminal CH3 group oriented to face the alkyl chains of the hydroxamic acid monolayer.
Keywords: Surfactant adsorption; Surface structure; Hydroxamic acid; Fluorite; Sum-frequency vibrational spectroscopy
Nucleation and crystal growth in supersaturated solutions of a model drug
by Lennart Lindfors; Sara Forssén; Jan Westergren; Ulf Olsson (pp. 404-413).
The crystallization process in aqueous solutions of the drug bicalutamide and the effect of the polymer polyvinylpyrrolidone (PVP) have been studied. Results showed that PVP decreased the crystallization rate significantly in a system with PVP concentrations as low as 0.01% (w/w), without changing the polymorph formed. The crystal habit was altered already at PVP concentrations as low as 0.001% (w/w). Measurements made with self-diffusion NMR indicated that the decrease in crystallization rate was not because of a reduced supersaturation due to bicalutamide binding to PVP in solution. Furthermore, in experiments designed to specifically study crystal nucleation, the same nucleation rate was found in the absence and presence of PVP. Instead, PVP adsorbs to the crystals formed in solution and by doing so, the crystal growth rate is reduced. This was confirmed in separate experiments using bicalutamide nanocrystals. By combining theories describing classical nucleation and crystal growth, with some modifications, a consistent description of several independent experiments performed in polymer-free systems was obtained. From these experiments a crystal–water interfacial tension of 22.1 mN/m was extracted. We also analyze the interfacial tension of other crystalline organic solids and find that it varies approximately as the logarithm of the solubility. This finding is discussed within the framework of the Bragg–Williams regular solution theory where we also compare with the tension of liquid alkanes.Bicalutamide nanocrystal growth in a supersaturated solution is strongly influenced by the presence of an adsorbing polymer, polyvinylpyrrolidone (PVP).
Keywords: Crystal nucleation; Crystal growth; Poorly soluble drugs; Classical nucleation theory
Preparation and characterization of composite polyaniline materials for catalytic purposes
by M.A. Bavio; T. Kessler; A.M. Castro Luna (pp. 414-418).
Composite film electrodes were prepared by open-circuit Pt deposition on polymeric PANI films that were electrosynthesized from aniline acid solutions with suspended carbon particles (CPs). Gold, nickel, and a Ni-based alloy, Nichrome, were used as substrates, and carbon particles, carbon nanotubes (CNT), and Vulcan XC-72R carbon black, suspended in the monomer acid solution, were incorporated into the film. Pt particles were dispersed on films grown on Ni-based substrates by deposition from a Pt(IV) acid solution at open circuit (OC). CNT trapped into the PANI films have a favorable influence on Pt dispersion. The novel composite electrodes showed significant catalytic activity for methanol oxidation.Composite electrodes were developed on Ni and Ni-based alloy substrates by electropolymerization of polyaniline films with the incorporation of carbon particles followed by open-circuit deposition of catalytic material, yielding effective methanol electrocatalysts.
Keywords: Carbon nanoparticles; Polyaniline; Platinum; Nichrome; Carbon monoxide; Methanol
Solution decomposition of the layered double hydroxide of Co with Fe: Phase segregation of normal and inverse spinels
by Sylvia Britto; P. Vishnu Kamath; N. Ravishankar (pp. 419-424).
The nitrate-intercalated layered double hydroxide of Co with Fe decomposes on hydrothermal treatment to yield an oxide residue at a temperature as low as 180 °C. The oxide product is phase segregated into a Co3O4-type normal spinel and a CoFe2O4-type inverse spinel. Phase segregation is facilitated as decomposition in a solution medium takes place by dissolution of the precursor hydroxide followed by reprecipitation of the oxide phases. In contrast, thermal decomposition takes place at 400 °C. This temperature is inadequate to induce diffusion in the solid state whereby phase segregation into the thermodynamically stable individual spinels is suppressed. The result is a single-phase metastable mixed spinel oxide. This is rather uncommon in that a hydrothermal treatment yields thermodynamically stable products where as thermal decomposition yields a metastable product.PXRD pattern of phase segregated normal and inverse spinels.
Keywords: Layered double hydroxides; Solution decomposition; Inverse spinel
Urea-based hydrothermal growth, optical and photocatalytic properties of single-crystalline In(OH)3 nanocubes
by Tingjiang Yan; Xuxu Wang; Jinlin Long; Ping Liu; Xianliang Fu; Guoying Zhang; Xianzhi Fu (pp. 425-431).
Nearly monodisperse single-crystalline In(OH)3 nanocubes were successfully synthesized using In(NO3)3⋅4.5H2O as indium source in the presence of urea and cetyltrimethyl ammonium bromide (CTAB) by a two-step hydrothermal process: the stock solution was heated at 70 °C for 24 h and then at 120 °C for 12 h. The structure and morphology of the resultant In(OH)3 samples were determined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results revealed that most of as-synthesized In(OH)3 nanocubes were uniform in size, with the average edge length of ∼700 nm. The influences of the reaction temperature, the reaction time, the mineralizer, and the surfactant on the morphology of the obtained products were discussed in detail. Room-temperature photoluminescence (PL) spectrum of the In(OH)3 nanocubes showed a peculiar strong emission peak centered at 480 nm. Furthermore, the photocatalytic properties of the In(OH)3 nanocubes were tested. It was found that In(OH)3 exhibited not only higher activity for benzene removal, but also better H2 evolution from water than the commercial Degussa P25 TiO2.Single-crystalline In(OH)3 nanocubes with an average edge length of 700 nm have been successfully synthesized through a mild urea-based hydrothermal process in the presence of CTAB.
Keywords: Urea; Hydrothermal synthesis; Benzene; Photocatalyst; In(OH); 3
Behavior of two different constituents of natural organic matter in the removal of sodium dodecylbenzenesulfonate by O3 and O3-based advanced oxidation processes
by J. Rivera-Utrilla; M. Sánchez-Polo; J.D. Méndez-Díaz; M.A. Ferro-García; M.I. Bautista-Toledo (pp. 432-439).
The objective of this study was to analyze the role played by two components of natural organic matter (NOM), gallic acid (GAL) and humic acid (HUM), in the removal of the surfactant sodium dodecylbenzenesulfonate (SDBS) from waters by O3-based oxidation processes, i.e., O3/H2O2, O3/granular activated carbon (GAC), and O3/powdered activated carbon (PAC). It was found that the presence of low concentrations of these compounds (1 mg/L) during SDBS ozonation increases both the ozone decomposition rate and the rate of SDBS removal from the medium. Because of the low reactivity of SDBS with ozone, these effects are mainly due to an increase in the transformation rate of ozone into HO• radicals. Results obtained demonstrate that the presence of GAL and HUM during SDBS ozonation increases the concentration of O−•2 radicals in the medium, confirming that GAL and HUM act as initiating agents of ozone transformation into HO•. It was also found that this effect was smaller with a larger molecular size of the acid. Presence of GAL and HUM during SDBS removal by O3/H2O2, O3/GAC, and O3/PAC systems also increases the SDBS degradation rate, confirming the role of these compounds as initiators of ozone transformation into HO• radicals.The presence of gallic acid (GAL) or humic acid (HUM) during SDBS ozonation increases the oxidation of the surfactant and the transformation rate of ozone into HO• radicals. This increase in the SDBS degradation rate is lower with larger molecular size of the acid considered.
Keywords: Ozone; SDBS; Activated carbon; Advanced oxidation processes; NOM
Sessile droplet spread into porous substrates—Determination of capillary pressure using a continuum approach
by Homayun K. Navaz; Bojan Markicevic; Ali R. Zand; Yuri Sikorski; Ewen Chan; Matthew Sanders; Terrence G. D'Onofrio (pp. 440-446).
The problem of primary and secondary spread of sessile droplets into a porous substrate was formulated and solved numerically. A continuum approach for liquid- and gas-phases was utilized. The governing equations were discretized by finite difference method and solutions for both phases are obtained by marching in time using the fourth-order Runge–Kutta integration algorithm. This type of spread is a purely momentum-driven process that is caused by gradients both in capillary pressure and in saturation. A methodology was developed for finding the capillary pressure function for sessile droplets, which has not been described before. This approach was based on experimental data for a liquid/porous medium pair, and using universal, non-dimensional curves. Similar solutions were generated by the continuum approach and validated using experimental results. The model shows qualitative and quantitative agreement with experimental data. Although the focus of this work was to understand the interaction of chemical warfare agents with porous media, the approaches are universal and can be applied to determining the spread of any liquid into a porous material.The spread of sessile droplet(s) into porous medium is solved as a multiphase flow problem and the method how to determine the capillary pressure from the experimental spread time is developed.
Keywords: Chemical warfare agents; Depth penetration; Permeation; Non-dimensional curves
Synthesis of Pd particle-deposited microporous silica membranes via a vacuum-impregnation method and their gas permeation behavior
by Dong-Wook Lee; Chang-Yeol Yu; Kew-Ho Lee (pp. 447-452).
Pd particle-deposited microporous silica membranes were synthesized to improve hydrogen permselectivity of the microporous silica membrane and to overcome high cost of palladium and crack formation through hydrogen embrittlement. Pd particles below 400 nm in diameter were readily deposited on the microporous silica membrane via a vacuum-impregnation method by using a Pd(C3H5)(C5H5) precursor. After deposition of Pd particles on the microporous silica membrane, hydrogen permselectivity over nitrogen considerably increased from 11–28 to 30–115 in a permeation temperature range of 25–350 °C due to plugging membrane defects and hydrogen adsorption diffusion through the interface between the Pd and silica layer. The activation energy of the Pd-deposited silica membrane (6.32 kJ mol−1) was higher than that of the microporous silica membrane (4.22 kJ mol−1). In addition, the Pd-particle deposition led to an increase in the permselectivity of He and CO2 with little chemical affinity for the Pd particles, which indicates that Pd-particle deposition gives the effect of plugging defects such as pinholes or cracks, which could be formed during the membrane preparation. Therefore it is demonstrated that Pd-particle deposition on the silica membrane is effective for induction of the hydrogen adsorption diffusion and plugging membrane defects.Pd particle-deposited microporous silica membranes were synthesized to improve hydrogen permselectivity of the microporous silica membrane and to overcome high cost of palladium and crack formation through hydrogen embrittlement.
Keywords: Palladium; Silica; Membrane
Formation of porous epoxy monolith via concentrated emulsion polymerization
by Jianli Wang; Chen Zhang; Zhongjie Du; Aiming Xiang; Hangquan Li (pp. 453-458).
Step polymerization was introduced into the concentrated emulsion templating method and was illustrated with the preparation of porous epoxy monolith. A solution of diglycidyl ether of bisphenol-A (DGEBA), its curing agent low molecular weight polyamide resin, and surfactant nonyl phenol polyoxyethylene ether in 4-methyl-2-pentanon as a solvent was used as the continuous phase, an aqueous suspension of colloidal silica as the dispersed phase of the concentrated emulsion. After the continuous phase polymerized and the dispersed phase removed, a porous material is obtained. The key point in this work is to find a compromise between the rates of curing and phase separating and thus achieve a kinetic stability of the concentrated emulsion. The effects of loading of colloidal silica, the pre-curing of the epoxy precursors, and the volume fraction of the dispersed phase were systematically investigated.Step polymerization was introduced into the concentrated emulsion templating method for the first time and was illustrated with the preparation of porous epoxy monolith.
Keywords: Porous; Epoxy; Monolith; Concentrated emulsion; Colloidal silica
In situ forced hydrolysis-assisted fabrication and photo-induced electrical property in sensor of ZnO nanoarrays
by Xiulan Hu; Yoshitake Masuda; Tatsuki Ohji; Kazumi Kato (pp. 459-463).
ZnO nanowhiskers are successfully fabricated on an anhydrous zinc acetate coated substrate by its in situ forced hydrolysis at the initial stage without pre-existing ZnO seeds or catalyst. HR-TEM clarified the formation mechanism that in situ forced hydrolysis of an anhydrous zinc acetate layer to ZnO nanocrystals at the initial stage promoted growth of ZnO nanowhiskers by heterogeneous nucleation and growth. ZnO nanowhiskers films show high transmittance over 80% in the visible range and bandgap energy of 3.29 eV. Porous semiconductor ZnO films show good photo-induced electrical properties after various concentrations of DNA molecules labeled with photoactive dye molecules were adsorbed. In situ forced hydrolysis-assisted technique at low temperature can be useful for the fabrication of optoelectronic devices with low cost and without using expensive catalyst.In situ forced hydrolysis of an anhydrous zinc acetate layer to ZnO at the initial stage promoted epitaxial growth of ZnO nanowhiskers by heterogeneous nucleation and growth.
Keywords: ZnO; Nanoarrays; Aqueous solution deposition; Anhydrous zinc acetate; Forced hydrolysis; Heterogeneous nucleation and growth; Photo-induced electrical property
Study of the collapse mechanism of selected fluorinated surfactants
by Marcin Broniatowski; Nuria Vila Romeu; Patrycja Dynarowicz-Łątka (pp. 464-471).
Two semifluorinated alkanes (SFAs), differing in their fluorinated segment lengths (F6H18 and F10H19), were compared with typical surfactants (F8H10OH and C18OH) as regards their collapse mechanism. It has been found that analysis of theπ–A isotherms under different experimental conditions is insufficient for a reliable description of the collapse phenomenon, and the importance of the relaxation experiments complemented with Brewster angle microscopy observation has been emphasized in this respect. The applied nucleation–growth–collision model points out differences between typical (alcohols) and nontypical (SFAs) surfactants as regards the collapse mechanism. Our results indicate that for the collapse process the presence of the polar head group in the molecule is more important than the structure of the hydrophobic chain.Nucleation and growth of 3D domains in the collapsed monolayer of F6H18 at 20 °C.
Keywords: Fluorinated surfactants; Semifluorinated alkanes; Langmuir monolayers; Monolayer collapse; Nucleation–growth–collision model
Theoretical model for the wetting of a rough surface
by K.M. Hay; M.I. Dragila; J. Liburdy (pp. 472-477).
Many applications would benefit from an understanding of the physical mechanism behind fluid movement on rough surfaces, including the movement of water or contaminants within an unsaturated rock fracture. Presented is a theoretical investigation of the effect of surface roughness on fluid spreading. It is known that surface roughness enhances the effects of hydrophobic or hydrophilic behavior, as well as allowing for faster spreading of a hydrophilic fluid. A model is presented based on the classification of the regimes of spreading that occur when fluid encounters a rough surface: microscopic precursor film, mesoscopic invasion of roughness and macroscopic reaction to external forces. A theoretical relationship is developed for the physical mechanisms that drive mesoscopic invasion, which is used to guide a discussion of the implications of the theory on spreading conditions. Development of the analytical equation is based on a balance between capillary forces and frictional resistive forces. Chemical heterogeneity is ignored. The effect of various methods for estimating viscous dissipation is compared to available data from fluid rise on roughness experiments. Methods that account more accurately for roughness shape better explain the data as they account for more surface friction; the best fit was found for a hydraulic diameter approximation. The analytical solution implies the existence of a critical contact angle that is a function of roughness geometry, below which fluid will spread and above which fluid will resist spreading. The resulting equation predicts movement of a liquid invasion front with a square root of time dependence, mathematically resembling a diffusive process.By what mechanism is water propelled along rough surfaces? A theoretical relationship describing the wetting of a rough surface is derived based on capillary and frictional forces.
Keywords: Roughness; Wetting; Capillarity
The association of Na,K-ATPase subunits studied by circular dichroism, surface tension and dilatational elasticity
by Carolina Fortes Rigos; Thatyane Morimoto Nobre; Maria Elisabete Darbello Zaniquelli; Richard John Ward; Pietro Ciancaglini (pp. 478-484).
Different stoichiometries are observed between α and β subunits of Na,K-ATPase that depend on the method employed to solubilize and purify the enzyme. It is not known whether this variability is due to loss of protein–protein association, or is a result of the replacement of essential phospholipids by detergent molecules. With the aim of understanding the effect of enzyme/surfactant ratio on both the catalytic activity and the enzyme structure, we have investigated the bulk and surface properties of the enzyme. The circular dichroism (CD) spectra, surface tension and dilatational surface elasticity results were compared with the residual ATPase activity of the Na,K-ATPase in different surfactant and protein concentrations. Na,K-ATPase in the ( αβ)2 form dissociated to the αβ form on dilution, and associated to the ( αβ)4 form when concentrated. These different stoichiometries have similar ATPase activities and are in equilibrium at C12E8 concentrations below the CMC (0.053 mg mL−1). At detergent concentrations above the CMC the ATPase activity of all forms was abolished, which is concomitant with the dissociation of the α and β subunits.A direct dependence of the detergent/protein concentration ratio on the Na,K-ATPase structure is described. Subunit dissociation results in the loss of ATPase activity and changes in the CD spectra.
Keywords: Na,K-ATPase subunits; Circular dichroism; Surface tension; Dilatational elasticity; ATPase activity; Detergent; CMC; C12E8; Subunits dissociation; Protein aggregation
Dynamic and structural aspects of PEGylated liposomes monitored by NMR
by Cecília Leal; Sibylla Rögnvaldsson; Sigrid Fossheim; Esben A. Nilssen; Daniel Topgaard (pp. 485-493).
Proton-detected NMR diffusion and31P NMR chemical shifts/bandwidths measurements were used to investigate a series of liposomal formulations where size and PEGylation extent need to be controlled for ultrasound mediated drug release. The width of the31P line is sensitive to aggregate size and shape and self-diffusion1H NMR conveys information about diffusional motion, size, and PEGylation extent. Measurements were performed on the formulations at their original pH, osmolality, and lipid concentration. These contained variable amounts of PEGylated phospholipid (herein referred to as PEG-lipid) and cholesterol. At high levels of PEG-lipid (11.5 and 15 mol%) the self-diffusion1H NMR revealed the coexistence of two entities with distinct diffusion coefficients: micelles (1.3 to3×10−11m2/s) and liposomes (≈5×10−12m2/s). The31P spectra showed a broad liposome signal and two distinct narrow lines that were unaffected by temperature. The narrow lines arise from mixed micelles comprising both PEG-lipids and phospholipids. The echo decay in the diffusion experiments could be described as a sum of exponentials revealing that the exchange of PEG-lipid between liposomes and micellar aggregates is slower than the experimental observation time. For low amounts of PEG-lipid (1 and 4.5 mol%) the31P spectra consisted of a broad signal typically obtained for liposomes and the diffusion data were best described by a single exponential decay attributed solely to liposomes. For intermediate amounts of PEG-lipid (8 mol%), micellization started to occur and the diffusion data could no longer be fitted to a single or bi-exponential decay. Instead, the data were best described by a log-normal distribution of diffusion coefficients. The most efficient PEG-lipid incorporation in liposomes (about 8 mol%) was achieved for lower molecular weight PEG (2000 Da vs 5000 Da) and when the PEG-lipid acyl chain length matched the acyl chain length of the liposomal core phospholipid. Simultaneously to the PEGylation extent, self-diffusion1H NMR provides information about the size of micelles and liposomes. The size of the micellar aggregates decreased as the PEG-lipid content was increased while the liposome size remained invariant.Formulations prepared with high amounts of PEG-lipid comprise both micelles and liposomes resulting in a coexistence of sharp and broad31P NMR lines, respectively. A coexistence of fast (micelles) and slow (liposomes)1H diffusion coefficients is also observed. The micelles contain both PC-lipid and PEG-lipid molecules. When the amount of PEG-lipid is kept low only liposomes are formed.
Keywords: PEGylated liposomes; PEG-lipid micelles; Self-diffusion; 1; H NMR; 31; P NMR; Drug delivery; Ultrasound
Mechanism of nitromethane liquid membrane oscillator containing sodium oleate
by Maria Szpakowska; Aneta Magnuszewska; Ottó B. Nagy (pp. 494-499).
The oscillatory behavior of a liquid membrane oscillator with anionic surfactant was investigated in order to understand the oscillation mechanism at the molecular level. As a theoretical framework, an approach based on chemical kinetics laws has been used. The chosen system involved nitromethane with2,2′-bipyridine as liquid membrane. The aqueous donor phase contained sodium oleate and butanol, while sodium chloride was added to the aqueous acceptor phase. It was established that the oscillations take place exclusively at the aqueous acceptor phase/membrane interface. Therefore, liquid membrane oscillators with anionic surfactants behave the same way as oscillators with cationic surfactants as to the location of oscillations. An oscillation mechanism involving three stages is proposed and confirmed by numerical simulations. The oscillations of electrical potential differences between the two aqueous phases are produced by sudden adsorption and desorption of anionic surfactant in solvated form and butanol at the acceptor/membrane interface. The whole process is controlled by the slow diffusion of these species across the liquid membrane. The chaotic character of the oscillations was demonstrated by Lyapunov exponents obtained from the strange attractor of the system.Oscillation curve of electric potential difference between aqueous phases of liquid membrane oscillator with sodium oleate, I, II, III—three stages of oscillation mechanism.
Keywords: Liquid membrane oscillator; Oscillation mechanism; Chaotic oscillations; Lyapunov exponents; Anionic surfactant
Dielectric behavior of double emulsions with “core–shell droplet” morphology
by Rajinder Pal (pp. 500-507).
The dielectric behavior of double emulsions with “core–shell droplet” morphology is investigated over a broad range of frequency. A new modified Pauly–Schwan model is proposed for the complex permittivity of double emulsions. The proposed model takes into consideration the morphology and packing limit of droplets. The dielectric behaviors of oil-in-water-in-oil (O/W/O) and water-in-oil-in-water (W/O/W) types of double emulsions, as predicted by the proposed model, are discussed.The dielectric behavior of double emulsions with “core–shell droplet” morphology is investigated. This figure shows the effect of shell-to-core radii ratio δ on the dielectric behavior of O/W/O double emulsion.
Keywords: Double emulsion; Dielectric behavior; Complex permittivity; Core–shell droplets; Dielectric relaxation
Solubilisation of triolein by microemulsions containing C12E4/hexadecane/water: Equilibrium and dynamics
by Peter R. Garrett; Denise Carr; Dennis Giles; Gina Pierre-Louis; Edward Staples; Clarence A. Miller; Bing-Hung Chen (pp. 508-515).
Increasing triolein content of oil-in-water microemulsions in the pure C12E4/water/ n-hexadecane/triolein system while maintaining a fixed surfactant concentration and volume fraction of drops raises the temperature of the solubilisation boundary, where excess oil separates, but has only a slight effect on the (higher) cloud point temperature, where excess water appears. Thus, the temperature range of the single-phase microemulsion shrinks and ultimately disappears. When such microemulsions are in equilibrium with excess oil, the hexadecane/triolein ratio is greater in the microemulsion, probably because the larger triolein molecules are unable to penetrate the hydrocarbon chain region of the surfactant films of the microemulsion droplets. Indeed, monolayer studies and calculations based on microemulsion and excess oil compositions indicate that the films have minimal triolein and similar ratios of hexadecane to surfactant. Triolein drops brought into contact with hexadecane-in-water microemulsions first swell as they incorporate hexadecane, then shrink owing to solubilisation. Interfacial tension decreases during this process until it becomes almost constant near 0.01 mN m−1, suggesting that the drops in the final stages of solubilisation have high hexadecane contents. A microemulsion containing 10 wt% C12E4 and 15 wt% hexadecane was able to remove over 50% of triolein from polyester fabric at 25 °C, more than twice that removed by an oil-free solution with the same surfactant concentration in similar experiments.Triolein drops initially swell when contacted with an o/w microemulsion containing C12E4, n-hexadecane and water. Later they shrink as both triolein and hexadecane are solubilised by the microemulsion.
Keywords: Solubilisation; Microemulsions; with triolein/hexadecane mixtures; Triolein, solubilisation of; Detergency; Triolein removal
Electrophoresis of a charge-regulated sphere at an arbitrary position in a charged spherical cavity
by J.P. Hsu; C.Y. Chen; Duu-Jong Lee; Shiojenn Tseng; Ay Su (pp. 516-525).
The electrophoresis of a charge-regulated spherical particle at an arbitrary position in a charged spherical cavity is modeled under conditions of low surface potential (<25 mV) and weak applied electric field (<25kV/m). The charged cavity allows us to simulate the effect of electroosmotic flow, and the charge-regulated nature of the particle permits us to model various types of surface. The problem studied previously is reanalyzed based on a more rigorous electric force formula. In particular, the influences of various types of charged conditions on the electrophoretic behavior of a particle and the roles of all the relevant forces acting on the particle are examined in detail. Several new results are found. For instance, the mobility of a particle has a local minimum as the thickness of a double layer varies, which is not seen in the cases where the surface of a particle is maintained at a constant potential and at a constant charge density.Electrophoresis of a charge-regulated sphere in a charged cavity.
Keywords: Electrophoresis; Boundary effect; Charge-regulated sphere; Charged spherical cavity; Electroosmotic flow
Electrokinetics in nanochannels
by Fabio Baldessari (pp. 526-538).
In this paper a new model is described for calculating the electric potential field in a long, thin nanochannel with overlapped electric double layers. Electrolyte concentration in the nanochannel is predicted self-consistently via equilibrium between ionic solution in the wells and within the nanochannel. Differently than published models that require detailed iterative numerical solutions of coupled differential equations, the framework presented here is self-consistent and predictions are obtained solving a simple one-dimensional integral. The derivation clearly shows that the electric potential field depends on three new parameters: the ratio of ion density in the channel to ion density in the wells; the ratio of free-charge density to bulk ion density within the channel; and a modified Debye–Hückel thickness, which is the relevant scale for shielding of surface net charge. For completeness, three wall–surface boundary conditions are analyzed: specified zeta-potential; specified surface net charge density; and charge regulation. Predictions of experimentally observable quantities based on the model proposed here, such as depth-averaged electroosmotic flow and net ionic current, are significantly different than results from previous overlapped electric double layer models. In this first paper of a series of two, predictions are presented where channel depth is varied at constant well concentration. Results show that under conditions of electric double layer overlap, electroosmosis contributes only a small fraction of the net ionic current, and that most of the measurable current is due to ionic conduction in conditions of increased counterion density in the nanochannel. In the second of this two-paper series, predictions are presented where well-concentration is varied and the channel depth is held constant, and the model described here is employed to study the dependence of ion mobility on ionic strength, and compare predictions to measurements of ionic current as a function of channel depth and ion density.
Keywords: Nanoscale electrokinetics; Electric double-layer overlap; Fundamental electrokinetics
Electrokinetics in nanochannels
by Fabio Baldessari (pp. 539-546).
In the first of this two-paper series, a new model was developed for calculating the electric potential field in a long, thin nanochannel with overlapped electric double layers. The model takes into account the dependence of ion mobility on local ion densities and pH. This model is used here to study and demonstrate the effect of ion density and pH on ionic current measurements. A comparison is shown of predictions based on each of three boundary conditions, as studied in Part I. The model developed in Part I is validated by comparing simulations with measurements of ionic current as a function of sodium borate concentration. Results show that predictions based on extended Debye–Hückel theory for ion mobility significantly improve the accuracy of simulations, but that these do not predict exact scaling behavior. A simple bulk conductivity measurement used as input parameter for the simulations, in place of the predicted bulk conductivity (K0), guarantees agreement with data in the thin EDL region. Results also indicate that the charge regulation boundary condition, complemented with an adequate bulk electrolyte model, provides better agreement with experimental trends than the specified zeta potential or specified surface net charge boundary conditions. Further, it is shown that currents due to advection (by electroosmotic flow) are in all cases studied less than 25% of the total current in the system.This study demonstrates the effect of ion density and pH on ionic current measurements in nanochannels. Measurements are compared to predictions based on a new model that includes channel-to-well equilibrium, and dependence of ion mobility on ionic strength.
Keywords: Nanoscale electrokinetics; Electric double-layer overlap; Fundamental electrokinetics
Synthesis and morphological studies of nanocrystalline MOR type zeolite material
by Pankaj Sharma; P. Rajaram; Radha Tomar (pp. 547-557).
A number of nanosize mordenite (MOR) analogues with particle size ranging from 5 to 50 nm were synthesized by the hydrothermal method. The effect of various growth parameters like: alkalinity of the medium, type of silica source, etc. on crystal morphology and the crystal size of MOR type of zeolites was investigated. Specific surface and micropore volume were investigated by the Brunauer–Emmett–Teller (BET) method. XRD, SEM, TEM studies indicate nanosize growth of the MOR type crystals. Electron diffraction patterns confirm the crystalline nature of the nanoparticles and the results of their indexing prove that the material is MOR. These synthesized materials show microporous as well mesoporous character. In the case of MOR material synthesized using sodium silicate, it was found that an increase in the alkalinity of the medium led to changes in the morphology and crystal size of the material. For low concentrations of NaOH, the crystallites were spherical in shape whereas at high concentrations, they were in the shape of nanorods of diameter 25 to 50 nm. The morphology of the MOR material synthesized using tetraethyl orthosilicate (TEOS), on the other hand, did not change when the NaOH concentration was increased beyond 2.0 molar.
Keywords: Mordenite; Crystallinity; Zeolite; Morphology; Nanocrystals
Luminescent nanocrystals in phospholipid micelles for bioconjugation: An optical and structural investigation
by Nicoletta Depalo; Antonia Mallardi; Roberto Comparelli; Marinella Striccoli; Angela Agostiano; Maria Lucia Curri (pp. 558-566).
Organic capped luminescent CdSe@ZnS nanocrystals (NCs) have been incorporated in block copolymer micelles, formed by polyethylene glycol modified phospholipids (PEG lipids). The obtained water soluble NC including PEG lipid micelles have been conjugated with bovine serum albumine (BSA). The entire process has been investigated by using optical, structural and electrophoretic complementary techniques. Such an integrated approach has allowed to elucidate critical issues, such as the time and temperature effects on the phase behavior of the PEG lipid/NC aggregate structures, the emitting properties of the NCs before and after micelle formation and bio-conjugation and the effect of conjugation on the biological moiety. The overall results provide relevant insight on the fabrication of the bio-conjugates, on their stability and on preparative procedure reproducibility, in view of the use of the resulting protein decorated NCs as multifunctional hybrid building blocks for the fabrication of a variety of supramolecular assemblies to exploit in biological sensing and diagnostic applications.Organic capped CdSe@ZnS NCs incorporated in PEG modified phospholipids micelles and bioconjugated with bovine serum albumine, as a convenient model for protein–NC conjugates. Micelle composition, time and temperature stability investigated as key factors for the material characteristics.
Keywords: Colloidal nanocrystals; Luminescence; Phospholipids micelles; Dynamic light scattering; Bio-conjugation; Bovin serum albumine (BSA); Nanocrystal functionalization
Polystyrene@TiO2 core–shell microsphere colloidal crystals and nonspherical macro-porous materials
by Yunfeng Li; Zhiqiang Sun; Junhu Zhang; Kai Zhang; Yanfang Wang; Zhanhua Wang; Xiaolu Chen; Shoujun Zhu; Bai Yang (pp. 567-572).
High-quality and stable PS@TiO2 core–shell microsphere colloidal crystals were prepared by electrostatic colloid stabilization combined with two-substrate vertical deposition method. The polyelectrolyte stabilized colloids self-assembled into face-centered cubic arrays with the (111) face perpendicular to the substrate. These colloidal crystals are gifted with high mechanical stability toward the flow of solution. Structure-property correlations were made using scanning electron microscopy and UV–vis–NIR spectroscopy. Optical spectra showed the presence of an L-stopband peak in the photonic band structure. Besides, these PS@TiO2 colloidal crystals can be used as templates to fabricate the nonspherical macro-porous materials, and complete band gaps can be more easily obtained from such structure than from their spherical counterparts due to their lower symmetries. This work will hold the promise of enhanced photonic band gap materials.PS@TiO2 microsphere colloidal crystals prepared by electrostatic colloid stabilization combined with two-substrate vertical deposition method, and nonspherical macro-porous materials.
Keywords: Core–shell microspheres; Colloidal crystals; Photonic crystals; Nonspherical macro-porous materials
Adhesion forces in liquid media: Effect of surface topography and wettability
by A.P. Serro; R. Colaço; B. Saramago (pp. 573-579).
This work was motivated by the unexpected values of adhesion forces measured between an atomic force microscopy tip and the hydrophobic surface of ultra-high-molecular-weight polyethylene. Two types of samples with different roughness but similar wettability were tested. Adhesion forces of similar magnitude were obtained in air and in polar liquids (water and Hank's Balanced Salt Solution, a saline solution) with the rougher sample. In contrast, the adhesion forces measured on the smoother sample in air were much higher than those measured in water or in the aqueous solution. Those experimental results suggested the presence of nanobubbles at the interface between the rough sample and the polar liquids. The existence of the nanobubbles was further confirmed by the images of the interface obtained in noncontact tapping mode. The adhesion forces measured in a nonpolar liquid (hexadecane) were small and of the same order of magnitude for both samples and their values were in good agreement with the predictions of the London–Hamaker approach for the van der Waals interactions. Finally, we correlate the appearance of nanobubbles with surface topography. The conclusion of this work is that adhesion forces measured in aqueous media may be strongly affected by the presence of nanobubbles if the surface presents topographical accidents.
Keywords: Adhesion forces; Nanobubbles; Liquid/solid interface; Ultra-high-molecular-weight polyethylene; Atomic force microscopy
Effect of rubbing load on nanoscale charging characteristics of human hair characterized by AFM based Kelvin probe
by Indira P. Seshadri; Bharat Bhushan (pp. 580-587).
The manageability and feel of human hair is significantly affected by its surface charge. Understanding and developing ways to control charge build up is hence highly beneficial. Previous studies have looked at static charging characteristics of hair on a macroscale. In this study, static charging characteristics of hair are studied on the nanoscale with an AFM. Hair is charged by rubbing a control area on its surface with an AFM tip, to which a small voltage bias is applied. The resulting charge distribution is characterized by measuring the surface potential of the control area in situ with AFM based Kelvin probe microscopy. The rubbing load is progressively increased, and the effect of this increase on the charge build up is assessed. Virgin, damaged and conditioner treated hair samples are studied for a better understanding of charge build up and dissipation. Relevant mechanisms are discussed.Understanding ways to control charge build up is highly beneficial. Previous studies have looked at static charging characteristics on a macroscale. Static charging characteristics are studied here on a nanoscale.
Keywords: Kelvin probe microscopy; Human hair; Conditioner; Surface potential
Preparation and physical properties of superhydrophobic papers
by Hongta Yang; Yulin Deng (pp. 588-593).
In this study, we developed a facile method for preparing a superhydrophobic paper surface using a multi-layer deposition of polydiallyldimethylammonium chloride (polyDADMAC) and silica particles, followed by a fluorination surface treatment with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS, CF3(CF2)5CH2CH2Si(OC2H5)3). The superhydrophobic wood fiber products prepared in this study have contact angles of water greater than 150° and sliding angles less than 5°. Besides their high water repelling property, the superhydrophobic paper products kept a high tensile strength at high relative humidity condition. The superhydrophobic paper products also showed high resistance to bacterial contamination.Both the surface roughness and hydrophobicity of wood fiber can be modified. The combination of nano-scale roughness and hydrophobicity could convert wood fibers from hydrophobic to superhydrophobic with a water contact angle >150°.
Keywords: Superhydrophobic; Wood fiber; Silica; Muliti-layer; Humidity
Direct AFM measurements of adhesion forces between calcium oxalate monohydrate and kidney epithelial cells in the presence of Ca2+ and Mg2+ ions
by Yakov I. Rabinovich; Saijit Daosukho; Karen J. Byer; Hassan E. El-Shall; Saeed R. Khan (pp. 594-601).
Adhesion forces between the calcium oxalate monohydrate (COM, whewellite) crystal and the layer of the epithelial kidney cells have been directly measured under buffer solutions by using atomic force microscope (AFM). Two renal epithelial lines, MDCK (a collecting duct line) and LLC-PK1 (a proximal tubular line), were used. All experiments were conducted in buffer solutions containing additional Ca2+ and Mg2+ ions in the various concentrations. For MDCK-cells, the obtained values of the adhesion force were in the range 0.12–0.51 nN and 0.12–0.20 nN for Ca2+ and Mg2+, respectively. No adhesion force (larger than 0.05 nN) has been found for LLC-PK1 cells. The “critical” concentrations of ions, near which the adhesion force (for MDCK-cells) was maximal, were found to be 100 mM. The “critical” concentration of ions and the tendency of the adhesion forces with the changing ions concentration, confirm earlier results of Lieske et al. [J.C. Lieske, G. Farell, S. Deganello, Urol. Res. 32 (2004) 117–123], in which the affinity (rather than the adhesion force) between the COM micro-crystals and the layer of the MDCK-cells were measured, calculating the radioactive signal of radioactive14C COM-crystals stuck to the cells. We believe that the aggregation of the COM crystals does not occur in the bulk urine due to short travel time through the nephron. If so, the kidney stone formation is determined by COM-seeding on the tubules walls. The further growth of the stone on the seed can take practically unlimited time because the COM crystal is practically is not soluble in water or urine solutions. The value of the adhesion force can be useful for evaluation of the adhesion energy or probability of the COM-aggregates to stick to the kidney epithelium under the urine flow. This probability is calculated taking into account the adhesion force,Fad, and hydrodynamic driving force of the flow. This probability reflects the opportunity of the small aggregates to grow and form the kidney stones.Dependence of adhesion force between COM-crystal and MDCK cells vs Ca2+ (curve 1) and Mg2+ (curve 2) ions concentrations. Curves 3 and 4 are results of [J.C. Lieske, G. Farell, S. Deganello, Urol. Res. 32 (2004) 117–123] in counts per minutes which are proportional to the crystal/cell affinity for Ca2+ and Mg2+, respectively.
Keywords: AFM; Calcium oxalate monohydrate; Kidney stone; Kidney epithelial cells; Adhesion force; Ca; 2+; and Mg; 2+; ions; Crystal retention