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Journal of Colloid And Interface Science (v.346, #2)

Cover 1 (pp. ofc).

Synthesis and characterization of gallium colloidal nanoparticles by M.F. Meléndrez; G. Cárdenas; J. Arbiol (pp. 279-287).
Top view of the reactor metal atoms at the co-deposition. Reactor after the nucleation process. Collecting flask containing the final Ga colloid obtained after the matrix freezing process. Yellow Ga colloids for all solvents used (acetone, 2-propanol and THF) were obtained.In this work, gallium colloidal nanoparticles (Ga-Nps) were synthesized by chemical liquid deposition (CLD). This method involved the deposition of metallic atoms with organic solvents (THF, acetone and 2-propanol) in a freezing matrix of the solvent at 77K, in order to obtain core–shell Ga-Nps which were characterized by: FT-IR, UV–Vis, TEM, SAED and electrophoretic mobility measurements. TEM images revealed a wide distribution of the apparent size of the particles and apparent average size of 5.65, 8.11 and 13.87nm for Ga-Nps obtained with 2-propanol, THF and acetone, respectively. UV spectra showed absorption bands of metal plasmons, interesting quantum size effects and plasmon absorption bands of particles aggregated to λ280 and λ325. Electrophoretic mobility allowed to evidence that nanoparticles had a negative charge as well as to observe that the zeta potential of the colloidal dispersions decreased over time, showing a significant tendency to the aggregation of Ga-Nps. The importance of the functionalization of metal nanoparticles with high dielectric constant solvents in the stabilization of colloidal systems was also observed. FT-IR spectroscopy revealed that the interaction of Ga surface with the solvent possibly produces a (GaC) bond. Experimental details, structural and thermal stability studies were also analyzed in this work.

Keywords: Gallium nanoparticles; Chemical liquid deposition; Colloid stability; Fractal aggregates

Ligand-functionalised copper(II) hydroxide for quantum dot photoluminescence quenching by Benjamin J. Wylie-van Eerd; Aidan G. Young; Najeh I. Al-Salim; Tim Kemmitt; Nick M. Strickland (pp. 288-295).
The preparation of Cu(OH)2 functionalised with 2,2-bipy or n-octanoic acid, and the subsequent conjugation with hydrophobic CdSeS quantum dots is reported.The preparation of ligand-functionalised copper(II) hydroxide (Cu(OH)2) particles and their conjugation with hydrophobic CdSeS quantum dots (QDs) is reported. The photoluminescence of the QDs is efficiently quenched upon their conjugation with the functionalised Cu(OH)2 particles. Cu(OH)2 was functionalised with 2,2′-dipyridyl (2,2-bipy) and n-octanoic acid (OcA), by adsorption of the desired ligand to Cu(OH)2 suspended in solvent. The resulting functionalised Cu(OH)2 substrates were characterised using infrared, UV–visible diffuse reflectance, and X-ray photoelectron spectroscopic techniques, TEM imaging, and micro- and thermogravimetric analysis. The spectral data indicated that both 2,2-bipy and OcA coordinated to Cu(OH)2 in a bidentate manner. The functionalised Cu(OH)2 substrates were introduced to suspensions of hydrophobic CdSeS QDs, and the resulting QD-functionalised Cu(OH)2 conjugates were also characterised using spectroscopic and electron microscopy techniques. UV–visible diffuse reflectance spectroscopy indicated the extension of the optical absorption of the Cu(OH)2 to longer wavelengths upon conjugate formation.

Keywords: Copper(II) hydroxide; Cupric hydroxide; Quantum dot; CdSeS; Photoluminescence; Quenching

Membrane filtration of fullerene nanoparticle suspensions: Effects of derivatization, pressure, electrolyte species and concentration by David Jassby; So-Ryong Chae; Zachary Hendren; Mark Wiesner (pp. 296-302).
Membrane removal efficiency of aggregated carbon nanomaterials is greatly influenced by whether the material is derivatized (hydroxylated). Also, for hydroxylated materials, electrolyte species, concentrations, and transmembrane pressure have a large effect on removal efficiency.Particle aggregation is induced in derivatized fullerene (fullerol) suspensions by introducing different counter-ion species (Na+ Ca2+ and Mg2+) and concentrations. The suspensions are filtered through 20nm ceramic membranes under different transmembrane pressures, and the removal efficiency is compared. In all cases, the average hydrodynamic radius far exceeded the average pore diameter of the membrane. In the case of mono-valent counter-ions, removal efficiency is influenced by transmembrane pressure, with higher removal efficiencies achieved at lower pressures. In contrast, removal efficiencies of fullerol suspensions destabilized with di-valent ions are insensitive to transmembrane pressure, similar to what was found in the case of non-derivatized fullerene. Scanning Electron Microscope (SEM) images of post-filtration membranes indicate that fullerol aggregates destabilized with Mg2+ ions deform and partially penetrate the membrane, but are ultimately trapped. The proposed mechanism suggests that di-valent ions act as bridges between fullerol aggregates, forming strong bonds that were not broken under the experimental conditions. These strong bonds may allow aggregated fullerol particles to deform under high pressure, and partially penetrate the membrane. Mono-valent ions are incapable of functioning as bridges, and subsequently, when sufficient pressure is applied, fullerol aggregates will break apart and pass through the membrane.

Keywords: Fullerene; Fullerol; Aggregation; Transmembrane pressure; Stability; Ionic bridging

Evolution of carboxymethyl cellulose layer morphology on hydrophobic mineral surfaces: Variation of polymer concentration and ionic strength by Audrey Beaussart; Agnieszka Mierczynska-Vasilev; David A. Beattie (pp. 303-310).
Caption: Adsorption isotherms for CMC on molybdenite at three different electrolyte concentrations (KCl) at pH 9. Alongside the isotherms are AFM images of a CMC layer adsorbed from 25mgL−1 CMC solution with sequentially increasing KCl concentration.The adsorption of carboxymethyl cellulose (CMC) on the basal planes of talc and molybdenite has been studied using in situ atomic force microscope (AFM) imaging. These experiments were partnered with quantitative adsorption isotherm determinations on particulate samples. The isotherms revealed a clear increase of the CMC adsorbed amount upon increasing the solution ionic strength for adsorption on both minerals. In addition, the shapes of the isotherms changed in response to the change in the electrolyte concentration, with CMC on talc displaying stepped (10−3M KCl), Langmuir (10−2M KCl), then Freundlich isotherm shapes (10−1M KCl), and CMC on molybdenite displaying stepped (10−3M KCl), Freundlich (10−2M KCl), then Langmuir isotherm shapes (10−1M KCl). AFM imaging of the polymer layer on the mineral surfaces with varying solution conditions mirrored and confirmed the conclusions from the isotherms: as the polymer solution concentration increased, coverage on the basal plane increased; as the ionic strength increased, coverage on the basal plane increased and the morphology of the layer changed from isolated well-distributed polymer domains to extensive adsorption and formation of dense, uneven polymer domains/features. In addition, comparison of the talc and molybdenite datasets points toward the presence of different binding mechanisms for CMC adsorption on the talc and molybdenite basal plane surfaces.

Keywords: Polymer adsorption; Talc; Molybdenite; CMC; AFM imaging; Adsorption isotherms

Influence of smectite suspension structure on sheet orientation in dry sediments: XRD and AFM applications by Marek S. Żbik; Ray L. Frost (pp. 311-316).
The structure-building phenomena within clay aggregates are governed by forces acting between clay particles. Measurements of such forces are important to understand in order to manipulate the aggregate structure for applications such as dewatering of mineral processing tailings. A parallel particle orientation is required when conducting XRD investigation on the oriented samples and conduct force measurements acting between basal planes of clay mineral platelets using atomic force microscopy (AFM). To investigate how smectite clay platelets were oriented on silicon wafer substrate when dried from suspension range of methods like SEM, XRD and AFM were employed. From these investigations, we conclude that high clay concentrations and larger particle diameters (up to 5μm) in suspension result in random orientation of platelets in the substrate. The best possible laminar orientation in the clay dry film, represented in the XRD 001/020 intensity ratio of 47 was obtained by drying thin layers from 0.02wt.% clay suspensions of the natural pH.Conducted AFM investigations show that smectite studied in water based electrolytes show very long-range repulsive forces lower in strength than electrostatic forces from double-layer repulsion. It was suggested that these forces may have structural nature. Smectite surface layers rehydrate in water environment forms surface gel with spongy and cellular texture which cushion approaching AFM probe. This structural effect can be measured in distances larger than 1000nm from substrate surface and when probe penetrate this gel layer, structural linkages are forming between substrate and clay covered probe. These linkages prevent subsequently smooth detachments of AFM probe on way back when retrieval. This effect of tearing new formed structure apart involves larger adhesion-like forces measured in retrieval. It is also suggested that these effect may be enhanced by the nano-clay particles interaction.Cryo-SEM micrograph showing the cellular micro-structure in gelled smectite in 2wt% water suspension.

Keywords: Smectite suspension; Nano-colloids; Nano-clays; AFM; Suspension structure

The synthesis of zinc oxide nanoparticles from zinc acetylacetonate hydrate and 1-butanol or isobutanol by Gabriela Ambrožič; Srečo D. Škapin; Majda Žigon; Zorica Crnjak Orel (pp. 317-323).
The mechanism and growth of ZnO nano particles of different morphologies (nanorods and coral-like structures), synthesized by refluxing an oversaturated solution of zinc acetylacetonate hydrate in 1-butanol and/or isobutanol is described.ZnO nanoparticles of different sizes, from 20 to 200nm in length, and morphologies, nanorods and coral-like structures, were synthesized via a simple one-pot synthesis by refluxing an oversaturated solution of zinc acetylacetonate hydrate in 1-butanol and isobutanol.On the basis of1H and13C NMR experiments, the reactions in both alcohols were found to proceed via the alcoholytic C–C cleavage of the acetylacetonate ligand, followed by the hydrolytic formation of the reactive Zn–OH intermediate from the water molecules present in the precursor hydrate species and/or those released during the condensation cycle. The zinc acetylacetonate conversion into ZnO in isobutanol is significantly slower than in the case when 1-butanol was used as both the medium and the reagent.FE-SEM studies showed that in 1-butanol the growth of the rod-shaped particles occurs via the agglomeration of ZnO primary particles that are less than 10nm in size. The morphology of the particles formed in the isobutanol is time dependent, with the final coral-like structures developing from initially formed bundle-like structures.

Keywords: ZnO; Nanostructures; Sol–gel synthesis; Crystal growth

Synthesis of heteroarchitectures of PbS nanostructures well-erected on electrospun TiO2 nanofibers by Chunyan Su; Changlu Shao; Yichun Liu (pp. 324-329).
From panoramic FESEM image of TiO2/PbS heteroarchitectures obtained via hydrothermal treatment, we can see that PbS nanocubes are closely attached to TiO2 nanofibres.In this paper, we have successfully fabricated TiO2/PbS heteroarchitectures with high-quality single-crystalline PbS nanostructures well-erected on electrospun TiO2 nanofibers matrices via hydro(solvo)thermal method usingl-cysteine as the sulfur donor and chelating reagent. The experiment results showed that the morphology and size of secondary PbS nanostructures grown on TiO2 nanofibers can be changed significantly by utilizing two kinds of different reaction solvents (water and acetylacetone, respectively). In case of water serving as solvent, the superb cube-shaped PbS nanocrystals with the edge length ranging from 150 to 300nm were prepared. While acetylacetone acting as solvent, the high-density PbS nanoparticles with 10–30nm in length were obtained. And, it is interesting that PbS nanostructures were not only uniformly monodispersed but also closely attached to TiO2 nanofibers surface. What is more, the further studies suggested that the formation of TiO2/PbS heteroarchitectures might take on chelation-anchoring-nucleation-directional growth strategy.

Keywords: Lead sulfide; Titanium dioxide; Heteroarchitectures; Electrospun; Nanofibers

CdTe nanocrystal–polymer composite thin film without fluorescence resonance energy transfer by using polymer nanospheres as nanocrystal carriers by Minjie Li; Xiang Xu; Yue Tang; Zhinan Guo; Henan Zhang; Hao Zhang; Bai Yang (pp. 330-336).
Nano-sized polystyrene spheres were used to immobilize CdTe nanocrystals (NCs) by static interaction and prevented them from aggregation in polymer thin film.A series of positively charged polystyrene (PS) nanosphere emulsions were prepared by copolymerization of quaternary ammonium chloride cationic monomer with styrene via emulsifier-free emulsion polymerization. The average diameter of the nanospheres was tuned in the range of 35–100nm by adjusting the recipe. The PS nanospheres were used as carriers of aqueous CdTe nanocrystals (NCs) by adsorbing them on the surface through static interaction. After attached to the nanospheres, NCs’ stability against pH change and UV light irradiation was enhanced. The CdTe–PS composite nanospheres were blended with compatible poly (vinyl alcohol) (PVA) matrix to prepare fluorescent thin film by spin coating. CdTe–PS nanospheres had homogenous distribution in the thin film and their light scattering performance was largely reduced after solvent evaporated, as a result, the composite thin film was highly transparent. In the meantime, the immobilization effect of PS nanospheres prevented NCs from aggregation, thus they preserved original high fluorescence without fluorescence resonance energy transfer. The CdTe–PS/PVA composite solution has potential applications in light emitting devices by inkjet printing.

Keywords: CdTe nanocrystal; Fluorescence; Polymer composite; Fluorescence resonance energy transfer; Thin film

Synthesis and characterization of β-cyclodextrin-conjugated magnetic nanoparticles and their uses as solid-phase artificial chaperones in refolding of carbonic anhydrase bovine by A.Z.M. Badruddoza; K. Hidajat; M.S. Uddin (pp. 337-346).
Schematic diagram of cyclodextrin-coated magnetic nanoparticle-assisted in vitro protein refolding.Surface-functionalized magnetic nanoparticles are widely used in various fields of biotechnology. In this study, β-cyclodextrin-conjugated magnetic nanoparticles (CD-APES-MNPs) are synthesized and the use of CD-APES-MNPs as a solid-phase artificial chaperone to assist protein refolding in vitro is demonstrated using carbonic anhydrase bovine (CA) as model protein. CD-APES-MNPs are fabricated by grafting mono-tosyl-β-cyclodextrin (Ts-β-CD) onto 3-aminopropyltriethoxysilane (APES)-modified magnetic nanoparticles (APES-MNPs). Results obtained from transmission electron microscopy (TEM) and vibrating sample magnetometery (VSM) show that the synthesized magnetic nanoparticles are superparamagnetic with a mean diameter of 11.5nm. The β-CD grafting is confirmed by Fourier transform infrared spectroscopy (FTIR) and elemental analysis. The amount of β-CD grafted on the APES-MNPs is found to be 0.042mmolg−1 from elemental analysis. Our refolding results show that a maximum of 85% CA refolding yield can be achieved using these β-CD-conjugated magnetic nanoparticles which is at the same level as that using liquid-phase artificial chaperone-assisted refolding. In addition, the secondary and tertiary structures of the refolded CA are the same as those of native protein under optimal conditions. These results indicate that CD-APES-MNPs are suitable and efficient stripping agents for solid-phase artificial chaperone-assisted refolding due to easier and faster separation of these nanoparticles from the refolded samples and also due to recycling of the stripping agents.

Keywords: Magnetic nanoparticles; β-Cyclodextrin; Artificial chaperone; Carbonic anhydrase; Protein refolding

The effects of staggered bandgap in the InP/CdSe and CdSe/InP core/shell quantum dots by Sunghoon Kim; Jaehyun Park; Sungwoo Kim; Won Jung; Jaeyoung Sung; Sang-Wook Kim (pp. 347-351).
New type-II structures of CdSe/InP and InP/CdSe core–shell nanocrystals which have staggered bandgap alignment were fabricated. The simply modeled wave function for electrons and holes in InP/CdSe and CdSe/InP core/shell nanocrystals showed the wave function of the electron and hole spread into the shell, respectively. As a result, the structure exhibits increased delocalization of electrons and holes, leading to a red-shift in absorption and emission.New type-II structures of CdSe/InP and InP/CdSe core–shell nanocrystals which have staggered bandgap alignment were fabricated. Using a simple model for the wave function for electrons and holes in InP/CdSe and CdSe/InP core/shell nanocrystals showed the wave function of the electron and hole spread into the shell, respectively. The probability density of the InP/CdSe and CdSe/InP core/shell QDs also showed a similar tendency. As a result, the structure exhibits increased delocalization of electrons and holes, leading to a red-shift in absorption and emission. Quantum yield increased in the InP/CdSe, however decreased in the CdSe/InP. The reason may be due to the surface trap and high activation barrier for de-trapping in the InP shell.

Keywords: Type-II quantum dots; Core–shell; InP; CdSe; Bandgap

Investigation of internal microstructure and thermo-responsive properties of composite PNIPAM/silica microcapsules by Jitka Čejková; Jaroslav Hanuš; František Štěpánek (pp. 352-360).
The dynamic thermo-responsive behavior and drying/re-hydration properties of composite PNIPAM–silica microcapsules have been studied as function of the polymer cross-linking ratio. During shrinking, the particle retains a spherical shape but during swelling, buckling occurs as the rate of water ingress cannot keep up with the rate of shell relaxation.Composite microcapsules consisting of a thermo-responsive hydrogel poly- N-isopropylacrylamide (PNIPAM) and coated by silica (SiO2) nanoparticles have been synthesized by the inverse Pickering emulsion polymerization method. The composite capsules, whose mean diameter is in the 25–86μm range in the expanded state, were characterized by static light scattering, atomic force microscopy (AFM), scanning electron microscopy (SEM), and laser scanning confocal microscopy (LSCM). It is reported that the hydrogel surface is uniformly covered by a monolayer of silica nanoparticles and that depending on the capsule size and degree of polymer cross-linking, either hollow-core or partially-filled hydrogel-core microcapsules can be created. Equilibrium thermo-responsive behavior of the composite microcapsules is investigated and it is found that after heating the particles above the lower critical solution temperature (LCST) of PNIPAM, the shrinkage ratio V/V max varies from 0.8 to 0.4 for a cross-linking ratio from 0.6% to 9% on a mass basis. Dynamic temperature cycling studies reveal no hysteresis in the shrinking and recovery phases, but a small measurable dependence of the asymptotic shrinkage ratio V/V max on the rate of temperature change exists. The composite capsules are stable under long-term storage in both dried and hydrated states and easily re-dispersible in water.

Keywords: Microencapsulation; Hydrogel; Stimuli-responsive polymer; Pickering emulsion; Drying

Monodisperse microspheres with poly( N-isopropylacrylamide) core and poly(2-hydroxyethyl methacrylate) shell by Ya-Lan Yu; Rui Xie; Mao-Jie Zhang; Peng-Fei Li; Lihua Yang; Xiao-Jie Ju; Liang-Yin Chu (pp. 361-369).
Monodisperse microspheres are fabricated with poly( N-isopropylacrylamide) core possessing thermo-responsive swelling/shrinking function and biocompatible poly(2-hydroxyethyl methacrylate) shell exhibiting “open/close” switching function.Monodisperse core–shell microspheres, composed of poly( N-isopropylacrylamide) (PNIPAM) core with thermo-responsive swelling/shrinking function and biocompatible poly(2-hydroxyethyl methacrylate) (PHEMA) shell with “open/close” switching function, have been successfully prepared by microfluidic emulsification, free-radical polymerization and atom transfer radical polymerization (ATRP). The effects of grafting time for the ATRP and polyvinyl alcohol (PVA) concentration inside the core on the thermo-responsive behavior of core–shell microspheres are investigated. For the core–shell microspheres prepared with PVA concentration of 2% (w/v) and grafting time of 2h, the PNIPAM core is in the shrunken state and the solid PHEMA shell protect the whole PNIPAM core at temperatures above the volume phase transition temperature (VPTT); as environmental temperature decreases below the VPTT, the PNIPAM core swells dramatically and the PHEMA shell ruptures a large area. The thermo-responsive function of the core–shell microspheres is reversible and the appearance/recovery of PHEMA shell crack exhibits an “open/close” switching function. Such core–shell microspheres are highly attractive for developing drug delivery systems with both biocompatible and thermo-responsive characteristics.

Keywords: Core–shell microspheres; Biocompatible polymer; Thermo-responsive microgels; Poly(; N; -isopropylacrylamide); Poly(2-hydroxyethyl methacrylate)

Effect of particle and surfactant acid–base properties on charging of colloids in apolar media by Saran Poovarodom; John C. Berg (pp. 370-377).
Surface charging in apolar media by reverse micelles via acid–base interaction. Here proton transfers from acidic surfaces to basic, neutrally charged micelles producing negative surfaces and positive counter-charges.The present work examines role of particle and surfactant acid–base properties using model spherical silica particles, one type with acidic functionality and the other with basic functionality, dispersed in an apolar solvent containing either a basic or an acidic surfactant. The electrical properties of each of the four systems types are quantified by measuring the particle electrophoretic mobility using phase angle light scattering (PALS). Since the magnitude of the mobility in each case also depends strongly on the concentration of the surfactant, this dependence was investigated concurrently. It was found that at sufficiently high surfactant concentration, i.e., where micelles begin to form in the bulk, the particle surfaces could be electrically charged. Both the polarity and magnitude of the surface charge are found to depend strongly on the acid–base properties of the surface and the surfactant. The basic surfactant produces negatively-charged particles, and the magnitude of the mobility increases with the particle surface acidity. The acidic surfactant, on the other hand, charges the particle positively and produces the highest mobility when used with basic particles. This finding is consistent with the acid–base charging mechanism initially proposed by Fowkes and coworkers. It is also found that further increases in micelle concentration can have the effect of lowering the particle mobility. The decline in electrophoretic mobility (or zeta potential) at high surfactant concentration is caused by the increasing concentration of electrically charged micelles, which may partially neutralize the surface charge or compress the electrical double layer.

Keywords: Colloids; Apolar liquids; Acid–base; Surface charging; Zeta potential; Reverse micelles

Size and density dependent sedimentation analysis of advanced nanoparticle systems by V. Mittal; M.D. Lechner (pp. 378-383).
Sedimentation coefficient distributions of the polystyrene–silica nanoparticles as a function of duration of polymerization. I: pure silica particles, II: intermediate hybrid particles and III: final hybrid particles.Various functional colloidal systems like polymer grafted inorganic particles, complex multi-component mixtures, organic–inorganic hybrid particles, inorganic–inorganic core–shell particles and swellable particles were characterized by sedimentation coefficient analysis in analytical ultracentrifuge owing to the accurate correlation of the sedimentation coefficient with variations in size and density of the materials. The sedimentation coefficient is absolute in nature and does not require any property information beforehand. By following the changes in the sedimentation coefficient and its distribution, it could be established if the polymer grafting on the surface of the inorganic particles took place or if the organic–inorganic or inorganic–inorganic hybrid was formed or if the particles were strongly crosslinked or swellable. The complex particle mixtures were also quantified for the number of components contained in them and their exact amounts by following the sedimentation coefficient distributions.

Keywords: Sedimentation coefficient; Analytical ultracentrifugation; Density; Colloidal dispersions; Core–shell morphology; Swelling; Hybrid; Silica

Grafting aluminum(III) 8-hydroxyquinoline derivatives on MCM-41 mesoporous silica for tuning of the light emitting color by Yousef Fazaeli; Mostafa M. Amini; Ezeddin Mohajerani; Masoomeh Sharbatdaran; Naime Torabi (pp. 384-390).
Aluminum(III) 8-hydroxyquinoline complexes, (Q)3− n(2-BuO) nAl, were grafted on MCM-41 mesoporous silica and their photoluminescence properties were investigated.Fluorescent materials ( Q)3− n(2-BuO) nAl ( Q=8-hydroxyquinoline, 2-methyl-8-hydroxyquinoline and 5-chloro-8-hydroxyquinoline, n=1 or n=2) were prepared in toluene by reacting aluminum 2-butoxide with 8-hydroxyquinoline and its derivatives. The compounds were characterized by1H,13C and27Al NMR in solution, and the coordination status of the aluminum atom in the complexes were determined by27Al NMR chemical shifts. The compounds were grafted on mesoporous silica (MCM-41) at room temperature without isolation of the complexes. The prepared materials were characterized by elemental analysis, FT-IR spectroscopy, low-angle X-ray diffraction (XRD), thermal analysis (TGA/DSC) and N2 adsorption and desorption measurements. The results showed that the characteristic mesoporous structure of MCM-41 after grafting aluminum complexes remains intact. The photoluminescence (PL) properties of (Q)3− n(2-BuO) n−1@Al–MCM-41 were investigated. The results revealed that the maximum wavelength is modulated by the MCM-41 guest.

Keywords: MCM-41; Aluminum; 8-Hydroxyquinoline complex; Photoluminescence

Measuring properties of interfacial and bulk water regions in a reverse micelle with IR spectroscopy: A volumetric analysis of the inhomogeneously broadened OH band by Timothy D. Sechler; Edward M. DelSole; John C. Deák (pp. 391-397).
The water IR spectrum of a reverse micelle is separated into spectra of the individual interfacial and bulk water regions inside the water droplet.The water OH stretching band (3000–3600cm−1) was analyzed for absorption contributions from the respective bulk and interfacial water regions of a reverse micelle. This analysis was performed by correlating volume changes of these regions to changes in the OH band absorption as the micelle radius grows. The volumetric analysis is based on the well established expanding core–shell model for AOT reverse micelles and yields the dimensions of the water regions and their individual spectral responses in the OH band. The interfacial shell thickness was determined to be 0.45nm for AOT reverse micelles in i-octane. It was found that each water region absorbs at most frequencies in the OH band; however, absorption on the red side of the OH band is dominated by bulk water, while absorption on the blue side is dominated by interfacial water. The bulk spectral response was found to be more similar to pure water, while the interfacial spectrum is strongly blue-shifted reflecting the weaker hydrogen bonding in this region. AOT reverse micelles with radii in the range 2–4nm conformed well to the volumetric model. However, it was found that determination of the bulk water spectral response is particularly sensitive to uncertainty in the micelle radius.

Keywords: Reverse micelle; FTIR; AOT; Water; Interface

Interactions of different counterions with cationic and anionic surfactants by Anna Jakubowska (pp. 398-404).
Linear correlations are obtained between the parameters determined for micelles in the aqueous phase and the affinity of counterions to surfactant free monomers in the gas phase.Specific counterion effects on the formation and electrolytic dissociation of micelles have been studied for sodium dodecyl sulfate and hexadecyl-N,N,N-trimethyl ammonium bromide in the presence of different electrolytes. Mass spectrometry has been used to investigate the affinity of counterions to surfactant free monomers in the gas phase. Linear correlations have been found between the parameters determined for micelles in the aqueous phase and the fraction of counterions preferably bound to surfactant free monomers in the gas phase. The work presents a new insight into specific ion effects.

Keywords: Interfaces; Ion binding; Micelles; Specific ion effect; Surfactants; Mass spectrometry

Solution behavior of mixed systems based on novel amphiphilic cyclophanes and Triton X100: Aggregation, cloud point phenomenon and cloud point extraction of lanthanide ions by Asiya Mustafina; Lucia Zakharova; Julia Elistratova; Juliana Kudryashova; Svetlana Soloveva; Alexander Garusov; Igor Antipin; Alexander Konovalov (pp. 405-413).
The cyclophanic structure of novel non-ionic surfactants is the key reason of the formation of large lamellar-like aggregates with TX100, exhibiting the unusual CP behavior and CPE efficiency.Aggregation and cloud point (CP) behavior, as well as CP extraction of lanthanide ions have been studied for novel non-ionic cyclophanic surfactants with the varied length of polyoxyethylene and hydrophobic moieties (CnEm) based on calix[4]arene platform in their mixtures with Triton X100 (TX100). The dynamic light scattering data reveal the contribution of the large size lamellar or stack like mixed aggregates in CnEm–TX100 solutions. Aggregation and CP behavior of TX100–CnEm mixed solutions are quite different from those of conventional non-ionic surfactants. The effect of the hydrophobic substituents and polyoxyethylene chains length of CnEm on the CP extraction of La(III), Gd(III) and Lu(III) in the mixed TX100–CnEm micellar solutions is discussed in the correlation with their aggregation and cloud point behavior. The obtained data elucidate the cyclophanic structure of CnEm as the key reason of the formation of large lamellar-like aggregates with TX100, exhibiting the unusual CP behavior and CPE efficiency.

Keywords: Non-ionic surfactants; Mixed aggregates; Cloud point behavior; Extraction; Lanthanides; Calix[4]arene

Foaming properties of mixtures of a non-ionic (C12DMPO) and an ionic surfactant (C12TAB) by Enda Carey; Cosima Stubenrauch (pp. 414-423).
A study of the foaming properties of non-ionic dodecyldimethyl phosphineoxide (C12DMPO) and cationic dodecyltrimethyl-ammonium bromide (C12TAB) mixtures. Shown is the variation of foam volume Vfoam as a function of time for foams generated at 2.0cmc with a gas flow rate of 20mlmin−1 using the commercial available FoamScan method. The foaming process starts att =0 and ends once a foam volume of 60ml is generated.An extensive study of the foaming properties of a surfactant mixture consisting of the non-ionic dodecyldimethyl phosphineoxide (C12DMPO) and the cationic dodecyltrimethyl ammonium bromide (C12TAB) with mixing ratios of C12DMPO:C12TAB=1:0, 50:1, 1:1, 1:50, 0:1 is performed both above and below the critical micelle concentration. Foamability and foam stability were examined using the commercially available FoamScan (sparging), the standardised Ross-Miles (pouring) and a home-built winding (shaking) technique. The focus, however, was on FoamScan measurements as they allowed for the evaluation of the foam’s liquid content. The foamability and foam stability of C12TAB was found to be larger than that of C12DMPO. The foamability continually increased with increasing C12TAB content in the surfactant mixture, which reflects the reduction of the diffusion relaxation time (i.e. faster adsorption). Where possible correlations are drawn between the foam properties on the one hand and adsorption and foam film properties on the other hand, which were studied previously. Interestingly, the 1:1 mixture shows weak/negligible surfactant interactions but – counterintuitively – an increased foam stability compared to the single surfactant systems. However, at this ratio charge neutralization occurs, which leads to the formation of a Newton Black Film thus suggesting that the foam film type plays an important role in the foam stability.

Keywords: Foaming Properties; FoamScan; Non-ionic dodecyldimethyl phosphineoxide (C; 12; DMPO); Cationic dodecyl trimethylammonium bromide (C; 12; TAB); Surfactant mixtures

A two-step model for surfactant adsorption at solid surfaces by Rico F. Tabor; Julian Eastoe; Peter J. Dowding (pp. 424-428).
In some cases, surfactant adsorption at solid surfaces appears to show a two-stage kinetic profile, suggesting two distinct processes may occur.A theoretical model is presented which accounts for two stages of surfactant adsorption onto a solid surface. The model incorporates both mass transfer (diffusion) and attachment terms, making it applicable to systems where mass transport and adsorption may occur on similar timescales. The model is tested against example systems which appear to show two-step adsorption processes, consisting of cationic ammonium bromide surfactants adsorbing onto silica from water and organic solvents. Kinetic parameters suggest that adsorption may occur in a broadly similar fashion from both water and low-dielectric solvents, and that the fast adsorption step appears to be transport-limited for organic solvents but may experience an adsorption barrier in aqueous systems.

Keywords: Surfactant; Adsorption; Silica; Non-polar solvents; Kinetics; Modeling; Toluene

Synthesis of large-pore phenyl-bridged mesoporous organosilica with thick walls by evaporation-induced self-assembly for efficient benzene adsorption by Na Hao; Yunxia Yang; Huanting Wang; Paul A. Webley; Dongyuan Zhao (pp. 429-435).
Phenyl-bridged PMOs with ordered hexagonal mesostructures were synthesized via the EISA approach by using Pluronic F127 as a template. The materials exhibit an adsorption capacity of benzene up to 2.06mmolg−1.Large-pore phenyl-bridged periodic mesoporous organosilicas (PMOs) were facilely synthesized by evaporation-induced self-assembly of 1,4-bis(triethoxysily)benzene and triblock copolymer Pluronic F127 as a template under acid conditions combined with a mixed-solvothermal treatment. The ordered PMOs exhibit large uniform mesopores of ∼9.9nm in diameter after calcination at 350°C in a nitrogen atmosphere. The mesoporous phenyl-bridged organosilica products have an ordered hexagonal mesostructure with space group p6mm. N2 adsorption/desorption isotherms reveal imperfect mesopore channels with high surface areas (up to 1150m2/g) and thick pore walls (up to 7.7nm). The mesopores can be expanded with the decrease of acidity, as well as the increase of Pluronic F127 content. A mixed-solvothermal treatment in N, N-dimethylformamide (DMF) and water at 100°C was first used to improve the periodicity of the mesopore walls, as well as increase the wall thickness. The composites exhibit efficient adsorption capacities (2.06mmolg−1) for benzene, suggesting a potential adsorbent for removal of volatile organic compounds. The EISA approach combined with the mixed-solvothermal treatment provides important insights into the development of large-pore PMOs by using long-chain organosilanes, and further demonstrates the ability to fabricate materials with thick walls.

Keywords: Mesoporous materials; Synthesis; Periodic mesoporous organosilica; Evaporation-induced self-assembly; Adsorption

Interaction of annexin A6 with cholesterol rich membranes is pH-dependent and mediated by the sterol OH by Magdalena M. Domon; Gladys Matar; Agnieszka Strzelecka-Kiliszek; Joanna Bandorowicz-Pikula; Slawomir Pikula; Françoise Besson (pp. 436-441).
Influence of pH on the interaction of annexin A6-1 with preformed cholesterol monolayer.Annexin A6 (AnxA6), a calcium- and membrane-binding protein, is well-known to play a role in calcium homeostasis, membrane traffic and membrane organization. It had been suggested that, despite calcium-dependent interaction with anionic phospholipids, AnxA6 displays calcium-independent cholesterol binding properties. In this study, the following questions were addressed: does AnxA6 bind preferentially to cholesterol-containing biomimetic membranes? If so, what is the molecular mechanism of the binding? To answer these questions, human recombinant AnxA6-1 isoform was prepared and used with Langmuir monolayers containing various lipids. The interactions between AnxA6 and the lipid monolayers were examined by kinetic measurements of the interfacial adsorption and Brewster angle microscopy. We focused on the pH effect on the AnxA6 binding to monolayers containing cholesterol. At acidic pH, AnxA6-1 exhibits the highest affinity to monolayers containing the highest amount of cholesterol. Replacing cholesterol by cholesteryl acetate provided evidence that the hydroxyl group of cholesterol plays a role in AnxA6-lipid interactions. In addition, the affinity of recombinant AnxA6-1 tryptophan mutant (W343F) to the air/water interface and to lipid monolayers was tested. Substitution of Trp343 modified the interfacial properties of the protein and its interactions with sterol monolayers. Our results suggest that the linker region containing Trp343 is important for the interactions between AnxA6-1 and cholesterol.

Keywords: Annexin A6; Cholesterol; Brewster angle microscopy; Langmuir monolayer; pH-sensitivity; Lipid rafts

Chemical modification of a nanocrystalline TiO2 film for efficient electric connection of glucose oxidase by Camila P. Sousa; André S. Polo; Roberto M. Torresi; Susana I. Córdoba de Torresi; Wendel A. Alves (pp. 442-447).
This study demonstrated the physico-chemical adsorption of the viologen mediator to the surface of nanocrystalline TiO2 film. In this approach, the organic compound acts as a molecular wire to link the enzyme and the oxide surface.A novel biosensor for glucose was prepared by adsorption of 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridinium di-bromide compound (H2BpybcBr2) onto the surface of a nanocrystalline TiO2 film deposited onto FTO glasses, which was used as a platform to assemble the enzyme glucose oxidase to the electrode surface. The H2BpybcBr2/TiO2/FTO modified electrode was characterized by scanning electron microscopy, X-ray fluorescence image, cyclic voltammograms and spectroelectrochemical measurements. The immobilization of GOD on functionalized TiO2 film led to stable amperometric biosensing for glucose with a linear range from 153μmolL−1 to 1.30mmolL−1 and a detection limit of 51μmolL−1. The apparent Michaelis–Menten constant (K m) was estimated to be 3.76mmolL−1, which suggested a high enzyme-substrate affinity. The maximum electrode sensitivity was 1.25μAmmolL−1. The study proved that the combination of viologen mediators with TiO2 film retains the electrocatalytic activity of the enzyme, and also enhances the electron transfer process, and hence regenerating the enzyme in the reaction with glucose.

Keywords: Glucose oxidase; Electrical wiring of enzyme; Titanium dioxide; Nanostructured electrode; Viologen; Biosensor

DC dielectrophoretic particle–particle interactions and their relative motions by Ye Ai; Shizhi Qian (pp. 448-454).
Particle chaining and alignment to the imposed external electric field arise from the dielectrophoretic particle–particle interaction.When particles in an electrolyte subjected to an external electric field get close to each other, the presence of particles could alter the local electric field and consequently induce mutual dielectrophoretic (DEP) forces on each other. In this paper, a transient, two-dimensional (2D) multiphysics model taking into account the particle–fluid–electric field interactions under a thin electrical double layer (EDL) assumption is performed to investigate the effects of the imposed electric field, the initial particle’s orientation and distance on the DEP particle–particle interaction between a pair of micro-sized particles and their relative motions. Prior to the study of the DEP particle–particle interaction, the magnitude comparison between the DEP particle–particle interaction and the Brownian motion is analyzed. When the DEP particle–particle interaction dominates the random Brownian motion, it is expected to observe the particle chaining along the direction of the imposed electric field, independent of the initial particle orientation. The numerical predictions are in qualitative agreement with the experimental observations available from the literature. During the attraction motion of particles, their velocities tend to dramatically decrease due to the rapid increase in the repulsive hydrodynamic pressure force when the particle distance decreases to a certain value. One exclusive exception of the particle chaining occurs when the initial connecting line of the particles is perpendicular to the imposed electric field, which is extremely unstable owing to the inevitable Brownian motion.

Keywords: Arbitrary Lagrangian–Eulerian (ALE); Dielectrophoresis; Microfluidics; Particle interactions; Particle chaining

Effect of branching on the interfacial properties of nonionic hydrocarbon surfactants at the air–water and carbon dioxide–water interfaces by Stephanie S. Adkins; Xi Chen; Quoc P. Nguyen; Aaron W. Sanders; Keith P. Johnston (pp. 455-463).
High pressure captive drop apparatus for measurement of effect of surfactant on interfacial tension of water–CO2 interface.The interfacial tensions, surface pressures, and adsorption of nonionic hydrocarbon surfactants at the air–water (A–W) and carbon dioxide–water (C–W) interfaces were investigated systematically as a function of the ethylene oxide (EO) unit length and tail structure. Major differences in the properties are explained in terms of the driving force for surfactant adsorption, tail solvation, area per surfactant molecule, and surfactant packing. As the surfactant architecture is varied, the changes in tail–tail interactions, steric effects, areas occupied by the surfactant at the interface, and tail hydrophobicity are shown to strongly influence the interfacial properties, including the surfactant efficiency (the concentration to produce 20mN/m interfacial tension reduction). For linear surfactants at the A–W interface, high efficiencies result from dense monolayers produced by the high interfacial tension driving force for adsorption and strong tail–tail interactions. At the C–W interface, where a low interfacial tension leads to a much lower surfactant adsorption, the contact between the phases is much greater. Branching or increasing the number of tail chains increase the hydrophobicity, tail solvation, and adsorption of the surfactant. Furthermore, the area occupied by the surfactant increases with branching, number of tails, and number of EO monomers in the head group, to reduce contact of the phases. These factors produce greater efficiencies for branched and double tail surfactants at the C–W interface, as well as surfactants with longer EO head groups.

Keywords: Interfacial properties; Carbon dioxide; Air–water interface; Branched surfactant

An experimental study of the stability of liquid bridges subject to shear-induced closed-flow by A. Kerem Uguz; N.J. Alvarez; R. Narayanan (pp. 464-469).
A series of pictures from an experiment. (a) The bridge is bulging from the bottom. (b) The wall is moved to induce shear. The interface is symmetric. (c) Wall is moved faster. The bulge flips direction.This paper shows via experiments, the effect of closed-flows on the stability of a liquid bridge. Experiments were conducted with a 3M™ HFE-7500 liquid as the liquid bridge and a mixture of sodium polytungstate solution and glycerine as the outer liquid, which is encapsulated in a cylindrical cavity. Depending on the glycerine content, the Bond number ranged from 0.04 to 0.25. It was shown that a closed-flow in both the encapsulating liquid and the bridge would increase the stability of a non-cylindrical bridge depending on the direction of shear, the Bond number and the bridge volume. It was also shown that, for a given bridge volume and Bond number, there is a capillary number that gives the maximum percentage stabilization. Any further increase in the capillary number flips the direction of the bulge from top to bottom or vice versa thereby decreasing the stabilization and at some capillary number even destabilizing the bridge. The scaling of the problem was analyzed through experimental data.

Keywords: Liquid bridge; Closed-flow; Experiment; Stability

Determination of the wettability of powders by the Washburn capillary rise method with bed preparation by a centrifugal packing technique by Laurence Galet; Severine Patry; John Dodds (pp. 470-475).
A centrifugal packing technique has been used for preparing reproducible beds of powder with a range of porosities for Washburn wettability measurements. The geometrical constantC w is developed in terms of bed porosity and permeability and shows good agreement with experiments.The Washburn capillary rise method is a standard technique for determining the wettability of powders expressed as a contact angle. The method requires the preparation of two identical beds of powder. One of these beds is used to follow the capillary rise with a perfectly wetting liquid (contact angle=0) giving access to a bed structure parameter. The other bed is used with the liquid of interest (contact angle≠0) and the capillary rise data is analysed using the previously determined structure parameter to obtain the contact angle. In the experiments reported here we have used a centrifugal packing technique to prepare beds of powder. This gives reproducible packings and also allows a certain degree of control of the bed porosity. In addition the air permeability of the beds is also determined prior to the capillary rise experiments. The results show that the value of the contact angle of a powder determined by the Washburn method depends on the porosity of the powder bed, and that the structure parameter can be determined from the air permeability using the Kozeny–Carman expression.

Keywords: Washburn method; Capillary rise; Contact angle; Permeability; Porosity

Self-modulating polymer resist patterns in pressure-assisted capillary force lithography by Hyunsik Yoon; Moon Kee Choi; Kahp Y. Suh; Kookheon Char (pp. 476-482).
The mold’s ceiling is collapsed initially during the contact (roof collapse) and recovers from continuous mass supply from the neighboring regions, which can suppress dewetting of a filled polymer film.We present pressure-assisted capillary force lithography (CFL) to generate self-modulating polymer resist patterns without residual layers and film instability. The method utilizes roof collapse of a patterned, deformable poly(dimethyl siloxane) (PDMS) mold that is placed on a thermoplastic polymer film with a constant external pressure (∼4 bars) and the resulting shape-variable capillary filling of a polymer melt into the reduced void space. A constraint on the coated polymer layer thickness was derived in order to ensure that there is no residual layer left after patterning and at the same time that film stability is guaranteed without film dewetting within the cavity. In addition, the height of a polymer pattern at the center of the filled void was estimated as a function of initial polymer layer thickness based on the assumption of the hemispherical shape of a meniscus and full capillary rise, which agrees well with the experimental data.

Keywords: Dewetting; Polymer; PDMS; Capillary force lithography

Thermodynamic derivation of the Young–Dupré form equations for the case of two immiscible liquid drops resting on a solid substrate by Ahmed H. Ayyad (pp. 483-485).
Young–Dupré form equations have been derived for the case of a drop of a liquid(1) completely encapsulated by another drop of liquid(2) and both are resting on a solid substrate.In this study a form of Young–Dupré equation has been derived for the case of a drop of a liquid(1) completely encapsulated by another drop of liquid(2) and both are resting on a solid substrate. The two liquids considered here are immiscible homogeneous phases. The derivation is mainly based on the powerful thermodynamics formalism with the help of geometrical considerations. The derivation yields two equations describing the equilibrium conditions of the two drops considered. In addition the equilibrium conditions for the four-phase merging along a single contact line is derived. The results show the advantages of thermodynamic formalism over mechanical considerations.

Keywords: Two immiscible liquid drops; Young–Dupré equation; Thermodynamics

Synthesis of spherical-like Pt–MCM-41 meso-materials with high catalytic performance for hydrogenation of nitrobenzene by Huiping Liu; Guanzhong Lu; Yun Guo; Yanqin Wang; Yanglong Guo (pp. 486-493).
Pt–MCM-41 synthesized in the presence of H2SO4 (or HCl) at 0°C has spherical-like morphology. TEM image of as-synthesized Pt–MCM-41 indicates that it is composed of spherical-like particles with different nano-sizes.Spherical-like Pt–MCM-41 meso-materials, including Pt–MCM-41, Pt–Al–MCM-41, and Pt–La–MCM-41, as well as MCM-41, were synthesized by a “one-step” approach with orthosilicate (TEOS) as silica source and cetyltrimethylammonium bromide (CTAB) as a template in the presence of suitable H2SO4 (or HCl) at 0°C. The samples were characterized by XRD, N2 sorption, FTIR, SEM, TEM, ICP-AES, and XPS techniques. The results show that the metallic cations (such as Al3+ and La3+) were hard to be incorporated into the synthesized samples under strong acidic conditions. However, H2PtCl6 can be introduced almost 100% in the as-synthesized Pt-containing meso-materials, and H2PtCl6 in the samples can be decomposed mostly into metallic Pt accompanied by part Pt2Si and few Pt oxides during the calcination at 550°C to remove the template. In the catalytic hydrogenation of nitrobenzene, the calcined Pt–MCM-41 meso-materials, like the corresponding reduced samples, exhibit high catalytic activities with an excellent selectivity to aniline, which are much better than those of the reduced Pt/MCM-41 prepared by the incipient wetness method.

Keywords: Spherical-like meso-materials; Pt–MCM-41; One-step synthesis; Nitrobenzene; Catalytic hydrogenation

Evaluation of removal efficiency of fluoride from aqueous solution using new charcoals that contain calcium compounds by E. Tchomgui-Kamga; E. Ngameni; A. Darchen (pp. 494-499).
Dispersion of CaCl2 into wood, followed by carbonization leads to an efficient material for fluoride removal.Charcoals that contain calcium compounds have been synthesized by impregnating wood with calcium chloride followed by carbonization at 500°C, 650°C or 900°C. The charcoals were characterized by SEM, EDAX, XRD and chemical titrations. These adsorbents were porous with the wood microstructure. XRD revealed the presence of crystallized CaCO3 and CaO. Despite this content, all the charcoals showed acidic surface properties and pH of point of zero charge (pHPZC) values were around 7.4–7.7. Their performance for fluoride removal from aqueous solution was evaluated by batch experiments. Fluoride adsorption kinetic followed a pseudo-second order model. Charcoal prepared at 650°C exhibited the best efficiency with a fluoride sorption capacity of 19.05mgg−1 calculated from the Langmuir model. A fluoride residual concentration of 0.67mgL−1 was achieved within 24h from a 10mgL−1 solution at neutral pH. The fluoride removal was not modified by the presence ofNO3-,SO42- andPO43- in the fluoride solution, whileHCO3- and Cl slightly affected the defluoridation capacity. The charcoals were chemically stable in solution and the amount of dissolved Ca was found to be 3.23mgL−1 at neutral pH.

Keywords: Defluoridation; Wood; Calcium; Carbonization; Adsorption

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