Journal of Colloid And Interface Science (v.344, #2)
Cover 1 (OFC).
Self-assembling systems: Mining a rich vein by Fredric M. Menger; Lei Shi; Syed A.A. Rizvi (241-246).
The graphic shows a vesicle self-assembly adhering to a cell via a steroid/mannose-phosphonate conjugate.This paper summarizes a few of the self-assembling systems investigated in the authors’ laboratory over the years. These include systems that mimic an enzyme, solubilize drugs, release encapsulated guests, assemble via hydrophobic surfaces, exhibit hysteresis in films, link cancer cells to vesicles, and destroy toxic compounds. Although the amphiphilic molecules are all rather different, one overriding theme predominates: just as the properties of molecules are not simple extrapolations from atoms, properties of self-assemblies are not simple extrapolations from molecules. Groups of molecules, properly assembled, can accomplish much more than an equal number of molecules functioning separately.
Keywords: Surfactant; Amphiphile; Gemini; Enzymes; Self-assembly; Solubilization; Vesicles; Films; Cells;
Low temperature synthesis of visible light-driven vanadium doped titania photocatalyst by Hong Li; Gaoling Zhao; Zhijun Chen; Gaorong Han; Bin Song (247-250).
To enhance the photocatalytic activity of TiO2 nanoparticles under visible light and extend the application field of TiO2, vanadium ions doped TiO2 nanocrystalline is prepared at low temperature.A simple method based on sol–gel method was developed to prepare vanadium ions doped TiO2 nanocrystalline at low temperature. Thus-obtained vanadium doped TiO2 was proved to be V x Ti1− x O2 solid solution. Doping vanadium could enhance the formation of stable phase. Its optical absorption spectrum shows a red shift to 445 nm. Photodegradation experiments suggest that thus-prepared vanadium doped TiO2 nanocrystalline can be excited by visible light and is a good photocatalyst under daylight. These properties are the same as the vanadium doped TiO2 prepared under high temperature conditions (⩾350 °C). However, in the present work, the vanadium doped TiO2 crystal particle is very uniform and fine, about 5 nm. It is much smaller than the production prepared under high temperature.
Keywords: Photocatalyst; Low temperature; TiO2; Sol–gel;
Fabrication of one-dimensional ZnO/4-Mpy/Ag assemblies and their spectroscopic studies by Hailong Hu; Wei Song; Weidong Ruan; Yanfei Wang; Xu Wang; Weiqing Xu; Bing Zhao; Yukihiro Ozaki (251-255).
This research provides a direct spectroscopic evidence for the formation of mixed 1D ZnO/4-Mpy/Ag assemblies using Raman and X-ray photoelectron spectroscopy techniques.One-dimensional (1D) ZnO/4-mercaptopyridine (4-Mpy)/Ag assemblies have been prepared by immersing ZnO rod arrays modified by 4-MPy into Ag nanoparticles colloid. Scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) have been employed to investigate the formation process of ZnO/4-Mpy/Ag assemblies. It shows that 4-Mpy molecules are adsorbing on the surface of the ZnO rod arrays, then 4-Mpy molecules are partially dissociated from ZnO rod arrays by desorption and connect with Ag nanoparticles via the S atom. The analysis of XPS confirms the result obtained from Raman spectra of ZnO/4-Mpy/Ag assemblies. This research provides a direct spectroscopic evidence for the formation of mixed 1D ZnO/4-Mpy/Ag assemblies.
Keywords: ZnO nanorod; Ag nanoparticles; Surface-enhanced Raman scattering; X-ray photoelectron spectroscopy;
Simulations of color development in tinted paints by A. Stuiver; G.T. Barkema (256-260).
Monte Carlo simulations have been used to investigate how several thermodynamic and kinetic factors affect the distribution of pigments, when a water-based pigment dispersion is added to a solvent-borne paint.Monte Carlo simulations have been used to investigate how several thermodynamic and kinetic factors affect the distribution of pigments, when a water-based pigment dispersion is added to a solvent-borne paint. Our model contains three types of lattice particles: water, pigment and organic solvent, with short-ranged interactions. These particles move through biased diffusion, with a species-dependent mobility. Moreover, to mimic the crosslinking of the resin, the mobility of the solvent particles decreases in time. Also, the water of the pigment dispersion evaporates slowly. First, we study which conditions yield the desired equilibrium phase behavior, with homogeneously distributed pigment. Next, we study how kinetics can prevent the system to reach equilibrium. We present examples in which these kinetic processes prevent dispersion in spite of favorable equilibrium conditions, as well as examples in which a homogeneous distribution is reached against unfavorable equilibrium conditions.
Keywords: Color development; Tinted paint; Monte Carlo simulation; Phase behavior; Kinetics;
Aggregation of zinc oxide nanoparticles: From non-aqueous dispersions to composites used as photoactive layers in hybrid solar cells by R. Rhodes; M. Horie; H. Chen; Z. Wang; M.L. Turner; B.R. Saunders (261-271).
Aggregation of ZnO nanoparticles within non-aqueous dispersions and composites used for photoactive layers within hybrid solar cells is shown to be related to the pKa of the co-solvent present.Hybrid solar cells are third-generation solar cells that are colloidal in nature. The composites used as photoactive layers within hybrid solar cells comprise conjugated polymers and inorganic semiconductor nanoparticles (e.g., nanocrystals and nanorods). The composites are usually prepared by spin casting non-aqueous dispersions consisting of polymer, nanoparticles and a co-solvent blend. The factors governing colloidal stability of the dispersions used for composite preparation have not been reported in detail. Here, the factors governing the stability of non-aqueous ZnO nanocrystal and nanorod dispersions as well as the relationship between dispersion stability and the extents of nanoparticle aggregation within model composites are studied. The polymers used are poly[[(2-methyl-4-methoxyphenyl)imino]-9,9-di-(2′-ethylhexyl)-fluorene-2,7-diyl] (PTAA) and poly[2,6-(4,4-bis-(2-ethyhexyl)-4H-cyclopenta [2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzo thiadiazole)] (PCPDTBT). FTIR in conjunction with thermogravimetric analysis data showed that up to 30% of the surfaces for the as-prepared ZnO nanocrystals and nanorods were occupied by acetate ligands. 1-Propylamine was found to form covalent coordinate bonds with ZnO and this contributes the ability of this co-solvent to promote enhanced ZnO dispersion stability. The morphologies of the composites were investigated using optical microscopy, AFM and TEM. A strong link was found between colloidal stability of the parent ZnO dispersions, extent of nanoparticle aggregation within the composites and pKa for the conjugate acid of the co-solvent. Electrostatic interactions did not control ZnO dispersion stability or composite morphology. Extensive nanometer-scale nanoparticle aggregation was evident within the composites. This was attributed to incompatibility between the polymer and (ligand covered) ZnO nanoparticles. Strategies for reducing uncontrolled nanoparticle aggregation are suggested.
Keywords: Composites; ZnO; Nanoparticles; Non-aqueous dispersion stability; Hybrid solar cells;
Bioinspired assembly of surface-roughened nanoplatelets by Tzung-Hua Lin; Wei-Han Huang; In-Kook Jun; Peng Jiang (272-278).
Transparent polymer nanocomposites with enhanced tensile strength and toughness can be obtained by electrodepositing surface-roughened gibbsite nanoplatelets into layered structures that mimic the nacreous layers of mollusk shells.Here we report a novel electrophoretic deposition technology for assembling surface-roughened inorganic nanoplatelets into ordered multilayers that mimic the brick-and-mortar nanostructure found in the nacreous layer of mollusk shells. A thin layer of sol–gel silica is coated on smooth gibbsite nanoplatelets in order to increase the surface roughness to mimic the asperity of aragonite platelets found in nacres. To avoid the severe cracking caused by the shrinkage of sol–gel silica during drying, polyelectrolyte polyethyleneimine is used to reverse the surface charge of silica-coated-gibbsite nanoplatelets and increase the adherence and strength of the electrodeposited films. Polymer nanocomposites can then be made by infiltrating the interstitials of the aligned nanoplatelet multilayers with photocurable monomer followed by photopolymerization. The resulting self-standing films are highly transparent and exhibit nearly three times higher tensile strength and one-order-of-magnitude higher toughness than those of pure polymer. The measured tensile strength agrees with that predicted by a simple shear lag model.
Keywords: Nanocomposites; Electrophoresis; Self-assembly; Nonspherical colloids; Biomimetics;
A versatile method for the preparation of water-soluble amphiphilic oligomer-coated semiconductor quantum dots with high fluorescence and stability by Changhua Zhou; Huaibin Shen; Yi Guo; Li Xu; Jinzhong Niu; Zhijun Zhang; Zuliang Du; Jianmin Chen; Lin Song Li (279-285).
Hydrophobic CdSe/ZnS QDs can be well transferred into water by using amphiphilic oligomer and the oligomer-functionalized QDs were excellent fluorescence labels for detecting the human hepatoma cells.High quality water-soluble semiconductor CdSe quantum dots (QDs) were prepared by a phase transfer method, in which amphiphilic oligomers (polymaleic acid aliphatic alcohol ester) was used as surface coating agents. The as-prepared aqueous QDs were high fluorescent and extremely stable. Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy all indicated that the surfaces of the QDs were coated with amphiphilic oligomers. Alkyl chain length of the amphiphilic oligomers could dramatically affect the phase transfer efficiency. It was found that the use of polymaleic acid n-hexadecanol ester had the best result. A biocompatible test has been carried out and such prepared water-soluble QDs were used to target tumor cells and found that the oligomer-functionalized QDs were excellent fluorescence labels for detecting the human hepatoma cells.
Keywords: CdSe/ZnS QDs; Amphiphilic oligomer; Fluorescence labeling;
Convenient synthesis of silver nanowires with adjustable diameters via a solvothermal method by Dapeng Chen; Xueliang Qiao; Xiaolin Qiu; Jianguo Chen; Renzhi Jiang (286-291).
This simple strategy is propitious to the formation of silver nanowires in high-yield, and the diameters of these nanowires can be controlled by adjusting the concentration of sodium sulfide (Na2S).Silver nanowires have been successfully synthesized via a simple solvothermal method by adding sodium sulfide (Na2S) into the solution. The Ag2S colloids produced in the initial stage help reduce the concentration of free Ag+ ions in the initial formation of silver seeds and subsequently release Ag+ ions to the solution. Otherwise, there is no oxidative etching owing to the absence of oxygen. In these cases, silver nanowires are grown preferentially. Furthermore, silver nanowires with adjustable diameters can be obtained by adjusting the concentration of Na2S. Electron microscopy, X-ray diffraction, and absorption spectra have been used to investigate the products, and a mechanism is proposed to interpret the controlled synthesis of silver nanowires. Finally, our results indicate that this approach provides a versatile route to prepare silver nanowires with controllable diameters.
Keywords: Silver nanowires; Na2S; Solvothermal method;
Evolution of size distribution in pressure drop induced decomposition synthesis of cobalt nanoparticles by Maija Huuppola; Nguyet Doan; Kyösti Kontturi; Christoffer Johans (292-297).
Significant narrowing of the size distribution coincident with particle growth is observed in a synthesis of cobalt nanoparticles from Co2(CO)8.Cobalt nanoparticles with average diameters of 8.8 nm and a standard deviation of 8% were obtained in a pressure drop induced decomposition synthesis in an autoclave. Samples were taken during the experiment and characterized with TEM. A significant narrowing of the size distribution coincident with particle growth was observed. The standard deviation decreased from 31% to 8% while the average size increased from 5.5 nm to 8.8 nm. In order to explain the experimentally observed narrowing of the size distribution, a model that accounts for the influence of the capping layer on the growth rate was developed. The transfer of the reacting monomer into the capping layer was considered to be similar to an adsorption process. A rate constant of 4 × 10−5 cm4 mol−1 s−1 was obtained for the growth reaction, and it was thus concluded that the growth reaction proceeds under kinetic control rather than under diffusion control.
Keywords: Cobalt nanoparticles; Size distribution evolution; Capping layer; Growth model;
Charge stabilized crystalline colloidal arrays as templates for fabrication of non-close-packed inverted photonic crystals by Justin J. Bohn; Matti Ben-Moshe; Alexander Tikhonov; Dan Qu; Daniel N. Lamont; Sanford A. Asher (298-307).
Highly ordered non-close-packed inverted opals are fabricated directly by silica infiltration of non-close-packed polymerized crystalline colloidal arrays allowing for lattice constant tuning and healing of lattice stresses from particle size/charge polydispersity.We developed a straightforward method to form non-close-packed highly ordered fcc direct and inverse opal silica photonic crystals. We utilize an electrostatically self assembled crystalline colloidal array (CCA) template formed by monodisperse, highly charged polystyrene particles. We then polymerize a hydrogel around the CCA (PCCA) and condense silica to form a highly ordered silica impregnated (siPCCA) photonic crystal. Heating at 450 °C removes the organic polymer leaving a silica inverse opal structure. By altering the colloidal particle concentration we independently control the particle spacing and the wall thickness of the inverse opal photonic crystals. This allows us to control the optical dielectric constant modulation in order to optimize the diffraction; the dielectric constant modulation is controlled independently of the photonic crystal periodicity. These fcc photonic crystals are better ordered than typical close-packed photonic crystals because their self assembly utilizes soft electrostatic repulsive potentials. We show that colloidal particle size and charge polydispersity has modest impact on ordering, in contrast to that for close-packed crystals.
Keywords: CCA; PCCA; siPCCA; Inverted; Photonic crystal; Non-close-packed; Electrostatic stabilization;
The effect of adsorption kinetics on film formation of silica/PVA suspension by Sunhyung Kim; Jun Hee Sung; Kangheon Hur; Kyung Hyun Ahn; Seung Jong Lee (308-314).
The porous film microstructure of silica/PVA suspension at short mixing time became close-packed with longer mixing time because of increasing polymer adsorption.Particle/binder/solvent systems are widely used in many applications and have long been studied. Understanding and controlling polymer adsorption in these complex material systems are important to achieve successful final performance. In this study, the effect of polymer adsorption on film formation and the relation between the microstructures of the suspension and film have been investigated by measuring the amount of polymer adsorption and the stress development during drying. In terms of mixing (or dispersion) time (tm ), the adsorption amount (Γ PVA), characteristic stress (σch ) and dried film density (ρ) showed a similar behavior in the form of 1 - e t m / τ with a single characteristic time τ = 45 h, which implies that the drying process is determined by this single time constant. The porous and non-uniform microstructure of the dried film at short tm became close-packed and uniform with longer tm . The polymer adsorption was found to play a key role in film formation as it introduces steric repulsion in suspension and suppresses the flocculation during solvent evaporation. It was also pointed out that enough mixing time for the saturated polymer adsorption is critical to acquire the consolidated and uniform film microstructure.
Keywords: Adsorption kinetics; Suspension stability; Film formation; Stress development;
Restricted meniscus convective self-assembly by Kai Chen; Stefan V. Stoianov; Justin Bangerter; Hans D. Robinson (315-320).
A variant of convective self-assembly for thin colloidal crystal is introduced, with growth speeds twice those of the conventional technique. The scaling of growth speed with humidity is also investigated.Convective (or evaporation-induced) self-assembly is a standard technique for depositing uniform, poly-crystalline coatings of nanospheres across multiple square centimeters on the timescale of minutes. In this paper, we present a variation of this technique, where the drying meniscus is restricted by a straight-edge located approximately 100 μm above the substrate adjacent to the drying zone. Surprisingly, we find this technique to yield films at roughly twice the growth rate compared to the standard technique. We attribute this to differing rates of diffusion of vapor from the drying crystal in the two cases. We also investigate the crystal growth rate dependence on ambient relative humidity and find, contrary to some previous reports, that the growth rate depends strongly on the humidity. We introduce a model which indicates that while the length of the drying zone may increase with humidity, this alone cannot compensate for the simultaneous reduction in evaporation rate, so a lower humidity must always lead to a higher growth speed. Comparing the model to our experimental results, we find that the length of the drying zone is constant and mostly independent of parameters such as humidity and surface tension.
Keywords: Colloidal crystal; Self-assembly; Wetting film; Nanospheres; Evaporation; Humidity;
Preparation of SrAl2O4:Eu2+, Dy3+ fibers by electrospinning combined with sol–gel process by Yongliang Cheng; Yu Zhao; Yanfei Zhang; Xueqiang Cao (321-326).
SrAl2O4:Eu2+, Dy3+ fibers have been fabricated by electrospinning process. The fibers show green emission.One-dimensional SrAl2O4:Eu2+, Dy3+ fibers were fabricated by a simple electrospinning combined with sol–gel process. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence were used to characterize the fibers. The results show that the phase structure of SrAl2O4:Eu2+, Dy3+ belongs to a monoclinic one, the composite fibers and fibers calcined at high temperature remain the original one-dimensional texture, and the SrAl2O4:Eu2+, Dy3+ was a green emission.
Keywords: Electrospinning; Fibers; Alkaline earth aluminates; Luminescence;
Zirconium-doped and silicon-doped TiO2 photocatalysts synthesis from ionic-liquid-like precursors by Marc Estruga; Concepción Domingo; Xavier Domènech; José A. Ayllón (327-333).
Highly photoactive mesoporous nanocrystalline anatase doped with either Zr or Si was synthesized (85 °C, 24 h) via destabilization of ionic-liquid-like precursors, containing TiF 6 2 - anions and +NH3CH2COOH cations.Nanocrystalline titania powders doped with either zirconium or silicon were synthesized at low temperature via destabilization of ionic-liquid-like precursors. Titania materials prepared at low temperature (85 °C) consisted of anatase nanocrystals of about 25 nm, according to powder X-ray diffraction and transmission electron microscopy. Dopant incorporation was evaluated using inductively coupled plasma-optical emission spectrometry, and it was found that dopant/titanium ratios in the powder (0.011 for Zr and 0.026 for Si) were lower than those in the precursor (0.11 for both). Low-temperature nitrogen adsorption–desorption isotherms displayed the characteristic hysteresis loop of mesoporous materials. Specific surface areas reached values of 130 and 155 m2 g−1 for Zr-doped and Si-doped TiO2, respectively. The photocatalytic activity of the synthesized nanopowders was tested using methyl orange and 4-chlorophenol as target pollutants.
Keywords: Zr-doped TiO2; Si-doped TiO2; Low temperature; Photocatalysis; Mineralization; Ionic liquids;
Photochemical formation of electrically conductive silver nanowires on polymer scaffolds by Subrata Kundu; David Huitink; Ke Wang; Hong Liang (334-342).
Electrically conductive micron long silver (Ag) nanowires having diameter of 135 ± 20 nm were synthesized in PVA within 8 min of UV-photoirradiation.A photochemical method has been exploited for the synthesis of electrically conductive silver (Ag) nanowires in a polymer solution in the presence of negatively charged Au seed particles. The synthesis was completed within 8 min of UV-photoirradiation in ambient conditions. The nanowires were fabricated on a PVA template having an average diameter of 135 ± 20 nm and a length of 10–20 μm. The current–voltage (I–V) characterization showed that the PVA–Ag nanowires were continuous, having Ohmic behavior with low contact resistance. Results indicate that the PVA acted as a reducing agent, stabilizing agent, and a template for the nucleation and growth of Ag nanowires. The Ag deposition was highly selective and on the PVA only. Our research indicated that the PVA–Ag nanowires might be useful as interconnects in nanoscale integrated circuitry, functional nanodevices, and in optoelectronics.
Keywords: UV-photoirradiation; Silver; Nanowires; PVA; Polymer;
Direct observation on the Brownian coagulation of PSL particles through optical microscope in the regime near critical coagulation concentration (CCC) by Tomonori Fukasawa; Yasuhisa Adachi (343-347).
Coagulation near CCC resulted in the formation of flocs with compact structure. Constant rate of coagulation in the later stage contrasts to that of rapid coagulation.Microscopic monitoring of floc structure, floc size distribution and the rate of coagulation was carried out for Brownian coagulation of PSL particles. Experiments were designed for the condition of salt concentration that is slightly below critical coagulation concentration (CCC). The density of the solvent was controlled by using deuterium oxide ( D 2 O ) to avoid sedimentation. Results are summarized as follows: (i) Near CCC, floc restructuring from the beginning stage of coagulation was evidenced, i.e., the ratio of linear triplet is found to be remarkably reduced as compared with the result obtained for the case of rapid coagulation which was implemented under sufficiently high salt concentration. (ii) The increase of fractal dimension from 1.8 in the case of rapid coagulation to 2.2 was confirmed by the analysis of mass balance using size distribution of flocs. This increment resulted in the decrease of effective excluded volume of flocs. (iii) The rate of coagulation was constant until later stage. This result contrasts to the result of rapid coagulation [T. Fukasawa, Y. Adachi, J. Colloid Interface Sci. 304 (2006) 115].
Keywords: Brownian coagulation; Floc structure; Restructuring; Critical coagulation concentration; Coagulation rate; Polystyrene latex;
Hybrid photosynthetic materials derived from microalgae Cyanidium caldarium encapsulated within silica gel by Joanna Claire Rooke; Alexandre Léonard; Christophe F. Meunier; Hugo Sarmento; Jean-Pierre Descy; Bao-Lian Su (348-352).
A study of the interaction of silica gel and micro-organisms resulting from the encapsulation of photosynthetic cells in silica matrices in the investigation of novel photobioreactors. Cyanidium caldarium (Tilden) Geitler SAG 16.91 has been encapsulated within a porous silica host structure to target novel photosynthetic hybrid materials suitable for use in solar cells or CO2 fixation. C. caldarium cells are both thermophilic and acidophilic; on account of these tolerances the hybrid materials could be employed in more extreme heat conditions. TEM highlights that the external cell membrane can remain intact after encapsulation. The images reveal an alignment of silica gel around the external membrane of the cell, providing evidence that the cell wall acts as both a nucleation and polymerisation site for silica species and that the silica scaffold formed by the aggregation of colloidal particles, generates a porosity that can facilitate the transport of nutrients towards the cell. Epifluorescence microscopy and UV–visible spectroscopy have revealed the preservation of photosynthetic apparatus post-immobilisation. Productivity studies showed how the presence of silica nanoparticles within the matrix can adversely interact with the exterior cellular structures preventing the production of oxygen through photosynthesis.
Keywords: Cyanidium caldarium; Photosynthesis; Silica; Encapsulation; Cellular interaction; Biomineralization;
Three-dimensional off-lattice Monte Carlo simulations on a direct relation between experimental process parameters and fractal dimension of colloidal aggregates by Songkil Kim; Kwang-Sung Lee; Michael R. Zachariah; Donggeun Lee (353-361).
Different microstructure evolution of aggregates at various pHs.It has been a big challenge to explore a direct relation of experimental parameters such as pH, electrolyte concentration, particle size, and temperature with the final structures of aggregates, because Monte Carlo simulations have been performed on the basis of arbitrarily chosen sticking probability. We attempted to incorporate colloidal theory to Monte Carlo simulations for two model systems of CuO– and SiO2–water systems, so as to resolve this difficulty. Conducting three-dimensional off-lattice MC simulations at various pHs for both systems, we investigated effects of pH on fractal structures of aggregates, encompassing the whole aggregation regime from diffusion-limited cluster–cluster aggregation to reaction-limited cluster–cluster aggregation. Moreover, developing a functional analysis, we found an explicit correlation between experimental parameters, sticking probability, and the fractal dimension of aggregates for both systems.
Keywords: Monte Carlo simulation; Aggregation; Fractal structure; Suspension stability;
Surface force measurements at the basal planes of ordered kaolinite particles by Vishal Gupta; Jan D. Miller (362-371).
We demonstrate via surface force measurements that both the silica tetrahedral face (iep < pH 4) and the alumina octahedral face (iep between pH 6 and 8) of kaolinite show a distinct pH dependence and a significant difference in the calculated surface potential.An experimental procedure is presented to order kaolinite particles on substrates for interrogation of the two basal plane surfaces by atomic force microscopy. Surface force measurements were performed between a silicon nitride tip and each of the two faces (silica tetrahedral face and alumina octahedral face) of kaolinite in 1 mM KCl solution at pH 4, 5, 6, 8 and 10, using atomic force microscopy. The colloidal force measurements reveal that the silica tetrahedral face of kaolinite is negatively charged at pH > 4, whereas the alumina octahedral face of kaolinite is positively charged at pH < 6, and negatively charged at pH > 8. Such measurements have not been reported previously and the results suggest that the iso-electric point of the silica tetrahedral face is at pH < 4, and that the iso-electric point of the alumina octahedral face lies between pH 6 and 8. These results contradict the generally accepted view that basal plane surfaces of kaolinite carry a permanent negative charge due to minor substitution of Al3+ for Si4+ in the silica tetrahedral layer, and suggest some surface charge dependency of the two faces with respect to solution pH. With this new information it may be possible to further explain the electrokinetic behavior of kaolinite particles, and their interactions in aqueous suspensions.
Keywords: Kaolinite; AFM; Iso-electric point; Surface forces; Basal plane surfaces; Silica tetrahedral face; Alumina octahedral face;
Surface adsorption alters the susceptibility of whey proteins to pepsin-digestion by Amir Malaki Nik; Amanda J. Wright; Milena Corredig (372-381).
Whey protein-stabilized emulsions were treated with pepsin and the physico-chemical properties and the hydrolysis behaviour were tested. While adsorption at the interface increased the susceptibility of β-lactoglobulin to hydrolysis, it significantly decreased the susceptibility of α-lactalbumin. This behaviour was also affected by the amount of unadsorbed protein present in the emulsion.An in vitro digestion model mimicking the gastric phase of the human gastrointestinal tract coupled with SDS–PAGE and MALDI-TOF mass spectroscopy was employed to study the hydrolysis profiles of whey proteins in solution and adsorbed at the oil–water interface. The objective of this work was to understand the differences in hydrolysis behaviour of whey protein isolates once adsorbed at the interface, and comparisons were carried out with pure β-lactoglobulin and α-lactalbumin fractions. In solution, while β-lactoglobulin appeared to be resistant to enzymatic treatment, α-lactalbumin was fully degraded. Adsorption of both proteins at the oil–water interface affected their conformational structure and susceptibility to peptic hydrolysis. Adsorbed β-lactoglobulin was hydrolyzed into small polypeptides and in contrast, the resistance of α-lactalbumin to pepsin increased upon adsorption at the interface. In addition, changes in the particle size distribution of the droplets during pepsin hydrolysis mainly depended on the original protein concentration. The results suggested that exchanges occur at the interface between adsorbed and non-adsorbed protein, that is to say that either some protein desorb from the interface and does not fully recover its structure in solution, or that hydrolysis of the protein at the interface induces further adsorption and hydrolysis of the protein in solution. These mechanisms have important implications in the digestibility of the proteins.
Keywords: α-Lactalbumin; β-Lactoglobulin; Whey proteins; Pepsinolysis; SDS–PAGE; MALDI-TOF;
Thermally stable SiO2-doped mesoporous anatase TiO2 with large surface area and excellent photocatalytic activity by Chenxu He; Baozhu Tian; Jinlong Zhang (382-389).
Mesoporous SiO2-doped TiO2 with large surface area was prepared, which exhibited much higher photocatalytic activity than P25 in a large range of calcination temperatures, even at 900 °C.A thermally stable SiO2-doped mesoporous TiO2 with high crystallinity was prepared by a templating method. The content of SiO2 dopant was varied from 3% to 20%. The gels were characterized by TG-DTA analysis. And the resultant catalysts were investigated by various physicochemical techniques, such as WAXRD, Raman spectroscopy, N2 adsorption–desorption, TEM, FT-IR, and XPS. The WAXRD, TEM, and Raman measurements suggest that the SiO2 dopant can enhance the thermal stability of the anatase phase remarkably. Rutile phase did not present at all even at 1000 °C when the SiO2 content was up to 15%. N2 adsorption–desorption results show that the SiO2-doped samples have uniform pore diameters and large specific surface area, which is beneficial for photocatalytic reaction. The photocatalytic activities of the samples were evaluated by degradation of Rhodamin-6G solution under UV irradiation. The results show that the SiO2-doped mesoporous TiO2 have better activity than commercial P25. Especially, the 15% SiO2-doped mesoporous TiO2 exhibited much higher photocatalytic activity than P25 in a large range of calcination temperatures, even at 900 °C. The excellent photocatalytic activity of the samples can be attributed to the high anatase crystallinity, large specific surface area, preserved surface hydroxyl groups and mesoporous channels.
Keywords: Mesoporous; TiO2; SiO2-doped; Thermally stable anatase; Photocatalyst;
Fabrication of tantalum oxide/carbon nanotubes thin film composite on titanium substrate by C. Arnould; T.I. Korányi; J. Delhalle; Z. Mekhalif (390-394).
SEM pictures of (a) Ta2O5 sol–gel deposition on titanium plate, (b) after peeling test, (c) Ta2O5 sol–gel deposition with oxidized MWCNT’s incorporation.The development of new biomaterials is one of the most challenging tasks in material science. Metals and particularly titanium and its alloys are widely used because of their good corrosion resistance, mechanical properties and biocompatibility. However, the toxicity of alloys, long term degradation in body fluids and risks of loosening are still problematic. To increase the corrosion resistance of the material and reduce ion release, our interest focused on tantalum, another metal well known for its excellent biocompatibility and resistance to bio-corrosion. These very good properties make tantalum a metal of interest for biomaterials but its high cost and high density disqualify it for use as bulk material.In this paper, we propose to combine the good bulk properties of titanium with the excellent surface properties of tantalum by using sol–gel deposition of a tantalum oxide layer on bare titanium. Furthermore, as orthopedics implants are part of our long term goals, we report on the formation of a composite layer of tantalum oxide and multiwalled carbon nanotubes (MWCNTs). MWCNTs have been shown to have promising properties in contact with bone and bone cells and could strengthen the implant. Characterizations are performed using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).
Keywords: Biomaterials; Tantalum oxide; Carbon nanotubes; Sol–gel deposition;
Electrical and optical percolations of polystyrene latex–multiwalled carbon nanotube composites by Selim Kara; Ertan Arda; Fahrettin Dolastir; Önder Pekcan (395-401).
Comparison of electrical and optical percolation processes for PS–MWCNT composite films.Electrical conductivity and optical transmittance properties of polystyrene (PS)–multiwalled carbon nanotube (MWCNT) composite films were investigated. Composite films were prepared by mixing of various mass fractions of MWCNT in PS–water dispersions. After water evaporates, powder composite films were annealed at 175 °C above the glass transition of PS for 20 min. Photon transmission and two point probe resistivity techniques were employed to determine the variations of the optical and the electrical properties of composites. Transmitted light intensity, Itr and surface resistivity, Rs were monitored as a function of MWCNT mass fraction (M). It was observed that, both the surface resistivity and the optical transparency were decreased by increasing the amount of MWCNT added to the polymeric system. Conductivity and optical results were interpreted according to the classical and site percolation theory, respectively. The electrical (σ) and the optical (op) percolation threshold values and critical exponents were calculated as Mσ = 1.8 wt.%, Mop = 0–0.13 wt.% and βσ = 2.25, βop = 0.32, respectively.
Keywords: PS–MWCNT composite; Percolation threshold; Electrical conductivity;
Competitive interactions between components in surfactant–cosurfactant–additive systems by Radhouane Chaghi; Louis-Charles de Ménorval; Clarence Charnay; Jerzy Zajac (402-409).
Interactions operating in surfactant–cosurfactant–additive systems may be competitive, and also be a function of system composition, leading to an irregular trend in the enthalpy of micellization.Complex interactions of phenol (PhOH), heptanol (HeOH) and heptanoic acid (HeOIC) with micellar aggregates of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions at surfactant concentrations close to the CMC, HeOH or HeOIC content of 0.5 mmol kg−1, and phenol molality of 1, 5, or 10 mmol kg−1 have been investigated at 303 K by means of 1H NMR spectroscopy, titration calorimetry and solution conductimetry. The analysis of the composition-dependence of the 1H chemical shifts assigned to selected protons in the surfactant and additive units revealed the location of PhOH both within the hydrophobic micelle core and in the vicinity of the quaternary ammonium groups, the phenol penetration being somewhat deeper in the presence of HeOIC. The phenomenon was globally more exothermic with increasing extent of PhOH solubilization and it was accompanied by a gradual decrease in the positive entropy of micellization. The solubilization was competitive for high phenol contents in the aqueous phase, with some HeOH and HeOIC units being displaced progressively towards the aqueous phase.
Keywords: Micellar solubilization; Competitive interactions; Hexadecyltrimethylammonium bromide; Phenol; 1-heptanol; n-heptanoic acid; 1H NMR spectroscopy; Titration calorimetry; Conductimetry;
Polyelectrolyte-assisted synthesis of polystyrene microspheres by dispersion polymerization and the subsequent formation of silica shell by Jinho Hong; Jeongwoo Lee; Young-Mok Rhym; Doo-Hyun Kim; Sang Eun Shim (410-416).
Polystyrene microspheres were synthesized via dispersion polymerization using a cationic polyelectrolyte, polyethyleneimine as a steric stabilizer, and the as-prepared microspheres were used for the formation of a silica shell.Polystyrene (PS) microspheres were synthesized via dispersion polymerization in alcoholic media. A cationic polyelectrolyte, polyethyleneimine (PEI) was successfully used as a steric stabilizer. The concentration of initiator, monomer, and the solubility parameter of medium showed typical phenomena observed in dispersion polymerization. However, the sensitivity to the change in the particles size was almost twofold greater than conventional stabilizers. Spherical PS particles were synthesized with the PEI concentrations ranging from 5 to 20 wt.% to styrene, but conversion over 95% was achieved over 10 wt.% PEI. As-prepared PEI-stabilized PS microspheres were used as the template for the subsequent formation of a silica shell. As a result, a robust silica layer was fabricated on PS microspheres due to the increased interaction between PEI and tetraethyl orthosilicate (TEOS).
Keywords: Dispersion polymerization; Polystyrene; Steric stabilizer; Polyelectrolyte; Core/shell; Silica;
Nano-emulsions prepared by the phase inversion composition method: Preparation variables and scale up by Isabel Solè; Carmen M. Pey; Alicia Maestro; Carmen González; Montserrat Porras; Conxita Solans; José M. Gutiérrez (417-423).
Nano-emulsion droplet sizes obtained at the two scales tested converge in a unique response surface if droplet size is plotted vs. total addition time, tt, and lineal mixing rate, vC .The aim of this work is to study, through experimental design, the effect of vessel geometry and scale-up in the properties of nano-emulsions prepared through the phase inversion composition method (PIC). Results show that a proper mixing is crucial for small droplet-sized nano-emulsions, especially when remaining free oil is found together with the key liquid crystal phase formed during the emulsification process. In these cases, mixing must be near the perfect mixed model. Proper geometries must be selected to promote a good mixture. Small addition rates Vad and high mixing rates ω promote the necessary mixing level. However, results indicate that, if free oil remains together with liquid crystal formed during emulsification, a too high ω could promote coalescence of oil droplets. When a cubic liquid crystal phase Pm3n is formed instead during emulsification, without free oil, coalescence is not promoted, probably due to the extremely high viscosity. For the system where Pm3n is formed during emulsification, scale-up cannot be done, as it would be expected, maintaining adimensional variables – Reynolds, Re, and adimensional time. A perfect correspondence between scales is observed when the total addition time and the lineal mixing rate are maintained between scales instead. Re, i.e. the ratio between inertial and viscous forces, does not seem adequate to describe the system, as inertial forces are worthless due to the extremely high viscosity.
Keywords: Nano-emulsions; Scale-up; Low-energy emulsification; Experimental design; Liquid crystal;
Antibacterial activity of poly(vinyl alcohol)-b-poly(acrylonitrile) based micelles loaded with silver nanoparticles by Rayna Bryaskova; Daniela Pencheva; Mariya Kyulavska; Dimitriya Bozukova; Antoine Debuigne; Christophe Detrembleur (424-428).
The formation of silver nanoparticles in the micelles is confirmed by UV–vis spectroscopy by detection of a band at a wavelength of 400 nm characteristics for silver.A new amphiphilic poly(vinyl alcohol)-b-poly(acrylonitrile) (PVOH-b-PAN) copolymer obtained by selective hydrolysis of well-defined poly(vinyl acetate)-b-poly(acrylonitrile) copolymer synthesized by cobalt mediated radical polymerization was used for the preparation of PVOH-b-PAN based micelles with embedded silver nanoparticles. The successful formation of silver loaded micelles has been confirmed by UV–vis, DLS and TEM analysis and their antibacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa) and spore solution of Bacillus subtilis (B. subtilis) has been studied. PVOH-b-PAN based micelles with embedded silver nanoparticles showed a strong bactericidal effect against E. coli, S. aureus and P. aeruginosa and the minimum bactericidal concentration for each system (MBC) has been determined.
Keywords: Block copolymers; Micelles; Silver; Nanoparticles; Antibacterial activity; Minimum bactericidal concentration;
In situ atomic force microscopy of modified dextrin adsorption on hydrophobic and hydrophilic layered silicate minerals by Agnieszka Mierczynska-Vasilev; David A. Beattie (429-437).
The characteristics of the adsorbed layer (and properties of the polymer material) influenced the surface forces experienced between hydrophobic surfaces and those between hydrophilic surfaces.We have used in situ atomic force microscopy (AFM), captive bubble contact angle measurements, and colloid-probe AFM to investigate the adsorption of two modified dextrins (a phenyl succinate substituted dextrin, PS Dextrin, and a styrene oxide substituted dextrin, SO Dextrin) on the basal plane surfaces of talc and clinochlore. The experiments have probed the effect that the polymers have on the mineral hydrophobicity and on the expected particle–particle interactions in single mineral aggregation. Distinct correlations were seen between the adsorbed polymer layer morphology (coverage, thickness) and the ability of the polymers to reduce the contact angle of the talc basal plane surfaces (SO Dextrin > PS Dextrin). Both polymers were seen to lower the contact angle of clinochlore to an apparent limiting value of approximately 25°. The effect of the polymers on the forces between hydrophobic surfaces (talc basal plane and a hydrophobised titania sphere) and between hydrophilic surfaces (clinochlore cleaved surface and a silica sphere) was seen to be a complicated relationship between the adsorbed layer morphology and bulk polymer properties, with polymers exhibiting a clear tendency to bridge between hydrophobic surfaces. Neither of the dextrins was found to encourage attraction between hydrophilic surfaces, in spite of adsorbing to a significant extent on the clinochlore cleaved surface.
Keywords: Polymer adsorption; Morphology; Layered silicate minerals; Dextrin; AFM; Colloid probe;
Solubilisation of model adjuvants by Pluronic block copolymers by Melissa A. Sharp; Clive Washington; Terence Cosgrove (438-446).
Small-angle scattering curves as increasing concentrations of benzyl alcohol are solubilised by Pluronic P85.The effect of two model adjuvants (benzyl benzoate and benzyl alcohol) on the structure and dynamics of three Pluronic triblock copolymers (P85, P105 and F127) was studied using small-angle neutron scattering and pulsed-field gradient NMR. The two adjuvants studied have different aqueous solubilities. It was found that both adjuvants promoted the micellisation of the Pluronic block copolymers. In addition they lead to a swelling of the micelles, as shown by small-angle neutron scattering. From the pulsed-field gradient NMR results it was possible to determine the amount of adjuvant bound to the micelles.
Keywords: Pluronic; P85; P105; F127; Micelle; Adjuvant; SANS; PFG-NMR; Benzyl benzoate; Benzyl alcohol;
Bidisperse colloids: Nanoparticles and microemulsions in coexistence by Rico F. Tabor; Julian Eastoe; Peter J. Dowding; Isabelle Grillo; Sarah E. Rogers (447-450).
Schematic and neutron contrast conditions showing microemulsion droplets in coexistence with large (∼80 nm) silica nanoparticles stabilised by a layer of anionic surfactant in toluene.Mixed ‘hard–soft’ colloidal systems have been generated in which the ‘hard’ components (80 nm diameter silica nanoparticles) coexist with a population of ‘soft’ microemulsion droplets, both structures stabilised by the anionic surfactant sodium bis(ethylhexyl)sulfosuccinate (AOT) with toluene as solvent. The addition of water to swell the inverse micelles to form microemulsion droplets appears to increase attractive interactions between the silica particles (determined by DLS), possibly due to adsorption of some water at the silica–toluene interface; however, long-term stability of the dispersions is maintained. Small-angle neutron scattering was used to examine the structures present in these new colloidal systems.
Keywords: Bidisperse; Colloids; Silica nanoparticles; Water-in-oil; Microemulsions; w/o;
A comparison between physically and chemically driven etching in the oxidation of graphite surfaces by P. Solís-Fernández; J.I. Paredes; A. Cosío; A. Martínez-Alonso; J.M.D. Tascón (451-459).
Scanning tunneling microscopy imaging of selective and non-selective etching processes in the oxidation of graphite surfaces.The etching of graphite surfaces by two different types of oxidative treatments, namely dielectric barrier discharge (DBD) air plasma and ultraviolet-generated ozone (UVO), has been investigated and compared by means of scanning tunneling microscopy (STM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Although the attack is initiated in both cases with the formation of individual, isolated atomic-scale defects (in particular, atomic vacancies), its subsequent evolution indicated that different mechanisms drive the surface modification in the two types of treatment, which greatly differ in etching selectivity. Thus, physical processes (i.e., ion bombardment) dominate the attack by DBD air plasma, which are not present in the case of UVO oxidation. The effects of the different etching mechanisms on the graphite surface structure, as visualized by STM down to the atomic scale, are discussed and found to be consistent with the Raman spectroscopy and XPS data. This type of information can be relevant when selecting the most appropriate type of surface modification of carbon materials for specific purposes.
Keywords: Graphite; Oxidation; Plasma; Etching; Scanning tunneling microscopy;
Water sorption on coals by Delphine Charrière; Philippe Behra (460-467).
Adsorption process of water in open coal micropores is dependent on the relative water pressure.Water vapor adsorption/desorption isotherm studies were performed on high volatile bituminous B coal and lignite to investigate the behavior of water on coal. The characterization of water sorption was studied by kinetic and equilibrium data, at a temperature of 298 K and a relative vapor pressure up to 0.95. Water sorption isotherms have a standard type II sigmoid shape obeying the BET model in the relative pressure range 0.05–0.35. A modified BET model was used to estimate the water adsorbed on primary and secondary sites, respectively. The specific surface areas estimated with water and CO2 were similar and about 95 and 52 m2 g−1 for high volatile bituminous B coal and lignite, respectively. The adsorption capacity of water and CO2 was related to the oxygen content of coal and the proportion of inorganic matter. The water adsorption and desorption isotherms produce a different hysteresis loop for the two coals. On the other hand, the diffusion coefficient of water adsorption was estimated at about 10−16 m2 s−1, by the unipore model. From the diffusion coefficient of water, which varied with increase in relative pressure, it is shown that water adsorbs first on primary sites, before formation of water clusters and their micropore filling which was a slow process.
Keywords: Water sorption; BET; Hysteresis; Diffusion; Coal;
Studies on the conformational change of adsorbed BSA onto a moderately hydrophobic surface at different denaturant concentrations and surface coverages by Huan Gao; Xin-Peng Geng; Bao-Huai Wang; Ye Zhou (468-474).
The schematic diagram of BSA adsorbed onto PEG-600 packings showed that the surface occupied by β-sheet of per adsorbed BSA molecule increased with GuHCl concentration increment.This paper is aimed at investigating the conformational change of denatured bovine serum albumin (BSA) in combination with thermodynamic functions and their fractions, adsorption isotherms, Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). Microcalorimetric measurements of displacement adsorption enthalpies ΔH of denatured BSA (by guanidine hydrochloride (GuHCl)) adsorbed onto a moderately hydrophobic surface (PEG-600) from solutions were carried out. The contents of secondary structure elements of BSA in solutions and in the adsorbed state were determined by FTIR and the thermal stability of adsorbed BSA was measured by DSC. The adsorption thermodynamic functions ΔH, ΔS, ΔG, and their fractions were calculated based on the thermodynamics of the stoichiometric displacement theory for adsorption (SDT-A) and adsorption isotherms. The results showed that the surface can provide energy to denatured BSA and make it gain a more ordered conformation with GuHCl concentration increment. At a given GuHCl concentration, although the ordered secondary structure of adsorbed BSA molecules decreased, their tertiary structure may be more perfect with surface coverage increment. The thermodynamic analysis of four subprocesses associated with adsorption also confirmed the increment of conformational gain.
Keywords: Conformational change; Thermodynamics; Displacement adsorption enthalpy; Adsorption subprocess; Bovine serum albumin;
A study on the potential application of natural phosphate in photocatalytic processes by Jesús Hidalgo-Carrillo; Jalila Sebti; María A. Aramendía; Alberto Marinas; José M. Marinas; Said Sebti; Francisco J. Urbano (475-481).
The valorisation of Moroccan natural phosphate through its use in selective photooxidations would fulfill some of the principles of Green Chemistry.In an attempt at increasing surface area of the resulting solids, different titanium-based systems were synthesized on natural phosphate through the sol–gel process using diverse ageing conditions (reflux, magnetic stirring, sonication or microwaves) and tested for gas-phase selective photooxidation of propan-2-ol. The best results were obtained for the system aged under ultrasounds which was ascribed to its lower band-gap energy. Moreover, the synthesis of TiO2 on natural phosphate seemed to produce retardation in crystallization as well as a change in titanium and phosphorus electronic environments (as determined by XPS) which in the case of the sonicated system resulted in an improved catalytic behavior as compared to pure titania. All in all, the present piece of research shows that provided that its surface area can be increased natural phosphate can be used as support for a photocatalytic active phase thus widening the scope of its application.
Keywords: Titania; Natural phosphate; Selective photooxidation: propan-2-ol;
Ion specificity of the zeta potential of α-alumina, and of the adsorption of p-hydroxybenzoate at the α-alumina–water interface by Manash R. Das; Jayanta M. Borah; Werner Kunz; Barry W. Ninham; Sekh Mahiuddin (482-491).
The effect of anions on the zeta potential of α-alumina is highly ion specific. The same ion specificity occurs with the adsorption density of p-hydroxybenzoate onto α-alumina surfaces.The influence of inorganic anions ( NO 3 - , I−, Br−, Cl−, SO 4 2 - , and S 2 O 3 2 - ) and of divalent cations (Ca2+ and Mg2+) on the zeta potential and on the isoelectric point of α-alumina in aqueous medium has been studied. The effect of the anions is highly ion specific even at salt concentrations as low as 5 × 10−4 M. This unexpected finding is in line with a recent report [Böstrom et al., J. Chem. Phys. 128 (2008) 135104]. It is also in agreement with an earlier theoretical prediction [B.W. Ninham, V.V. Yaminsky, Langmuir 13 (1997) 2097]. The results are consistent with the classical Hofmeister series, except for the case of NO 3 - . Divalent anions ( SO 4 2 - and S 2 O 3 2 - ) decrease the magnitude of the zeta potential of α-alumina in aqueous medium, more precisely; S 2 O 3 2 - produced large negative zeta potential (∼−12 to −47 mV) within the pH range of the study without the isoelectric point (IEP) of α-alumina. However, the SO 4 2 - decreased the zeta potential of α-alumina of different magnitudes (maximum ∼25 mV at both ends of the experimental acidic and basic pH scale) with a minor shift of the IEP (∼0.5 unit) toward lower pH. Ca2+ and Mg2+ produce zeta potentials of α-alumina roughly equal to that of neat α-alumina but slightly higher than that of Na+ at both sides of the IEP. We have shown further that the same ion specificity or equivalently competitive ion effects occur with the adsorption density of p-hydroxybenzoate onto α-alumina surfaces. The sequence of anions (with common cation) for the adsorption density of p-hydroxybenzoate on the α-alumina surfaces follows the Hofmeister series sequence: S 2 O 3 2 - < SO 4 2 - < Cl− > Br− > I− > NO 3 - . The divalent cations (Ca2+ and Mg2+) exhibit a roughly equivalent effect on the adsorption of p-hydroxybenzoate onto α-alumina surfaces. Using the frequency shifts of ν as(–COO−) and ν s(–COO−) in the DRIFT spectra of p-hydroxybenzoate after adsorption and other characteristic peaks, we have demonstrated that p-hydroxybenzoate forms outer-sphere complexes onto α-alumina surfaces at pH 5 and 6 and inner-sphere complexes at pH 7, 8, and 9 in the presence of 5 × 10−4 M NaCl(aq).
Keywords: Adsorption; Alumina; DRIFT; Hofmeister effect; Ion specificity; p-Hydroxybenzoate; Surface complexation; Zeta potential;
A modified microbial adhesion to hydrocarbons assay to account for the presence of hydrocarbon droplets by Caroline Warne Zoueki; Nathalie Tufenkji; Subhasis Ghoshal (492-496).
Hydrocarbon droplets confound spectrophotometric assessments of concentrations of non-adhered cells in the microbial adhesion to hydrocarbons assay. Use of a Helber cell counting chamber allows reliable measurements of the number of non-adhered cells.The microbial adhesion to hydrocarbons (MATH) assay has been used widely to characterize microbial cell hydrophobicity and/or the extent of cell adhesion to hydrophobic liquids. The classical MATH assay involves spectrophotometric absorbance measurements of the initial and final cell concentrations in an aqueous cell suspension that has been contacted with a hydrocarbon liquid. In this study, microscopic examination of the aqueous cell suspension after contact with hexadecane or a hexadecane/toluene mixture revealed the presence of hydrocarbon droplets. The hydrocarbon droplets contributed to the absorbance values during spectrophotometric measurements and caused erroneous estimates of cell concentrations and extents of microbial adhesion. A modified MATH assay that avoids such artefacts is proposed here. In this modified assay, microscopic examination of the aqueous suspension and direct cell counts provides cell concentrations that are free of interference from hydrocarbon droplets. The presence of hydrocarbon droplets was noted in MATH assays performed with three bacterial strains, and two different hydrocarbons, at ionic strengths of 0.2 mM and 20 mM and pH 6. In these experiments, the formation of quasi-stable hydrocarbon droplets cannot be attributed to the presence of biosurfactants, or stabilization by biocolloids. The presence of surface potential at the hydrocarbon–water interface that was characterized by electrophoretic mobility of up to −1 and −2 μm cm/Vs, likely caused the formation of the quasi-stable hydrocarbon droplets that provided erroneous results using the classical MATH assay.
Keywords: Microbial adhesion; Cell hydrophobicity; Surface potential; Emulsion stability; Hexadecane; Toluene;
Removal and recovery of Chrysoidine Y from aqueous solutions by waste materials by Alok Mittal; Jyoti Mittal; Arti Malviya; V.K. Gupta (497-507).
Effect of pH on adsorption of Chrysoidine Y by bottom ash and de-oiled soya.This article describes the use of bottom ash [a power plant waste] and de-oiled soya [an agricultural waste] as effective adsorbents for the removal of a hazardous azo dye [Chrysoidine Y] from its aqueous solutions. This paper presents an experimental study and discussion of the adsorption characteristics of this dye on the two adsorbents. The adsorbents have been characterized, and also the effects of time, temperature, concentration, pH, and sieve size on the extent of adsorption have been evaluated. Batch adsorption measurements, kinetic studies, and column operations have been performed to elucidate the dye uptake capacity of the adsorbents. The monolayer adsorption capacities at 30 °C have been found from Langmuir analysis to be 7.27 × 10−5 mol g−1 and 3.35 × 10−5 mol g−1 for bottom ash and de-oiled soya, respectively. Adsorption kinetics experimental data are indicative of pseudo-second order kinetics during these processes. Column experiments indicate practical utility of the adsorbents for eradicating hazardous dyes from effluents. The recovery of the adsorbed dye from bottom ash and de-oiled soya, have been found to be 85% and 99%, respectively.
Keywords: Chrysoidine Y; Bottom ash; De-oiled soya; Langmuir isotherm; Kinetics; Column;
Interlayer structure of iodide intercalated layered double hydroxides (LDHs) by S.V. Prasanna; P. Vishnu Kamath; C. Shivakumara (508-512).
Strongly hydrogen bonding OH− ions effectively displace positionally disordered I− ions from the interlayer. This renders the mineralization of iodine by the LDH host inefficient.The iodide-containing layered double hydroxides (LDHs) of Mg and Zn with Al crystallize by the inclusion of extensive positional disorder of I− ions in the interlayer region. I− ion given its poor charge to size ratio can neither screen effectively the positive charge nor participate in H-bonding with the metal hydroxide layers. Thereby the I− ions are not stabilized in sites close to the seat of positive charge of the metal hydroxide layers (6c), nor in sites that facilitate H-bonding (3b or 18h). On the other hand, OH− from water can do both and effectively displaces I− from the interlayer.
Keywords: Layered double hydroxides; Iodide; Positional disorder;
Steady viscoelastic fluid flow between parallel plates under electro-osmotic forces: Phan-Thien–Tanner model by S. Dhinakaran; A.M. Afonso; M.A. Alves; F.T. Pinho (513-520).
Effect of PTT parameter, ε, on transverse velocity profiles for flow of viscoelastic fluids in microchannels under electro-kinetic forces at De κ = 3 and ξ = 0.01.The electro-osmotic flow of a viscoelastic fluid between parallel plates is investigated analytically. The rheology of the fluid is described by the Phan-Thien–Tanner model. This model uses the Gordon–Schowalter convected derivative, which leads to a non-zero second normal stress difference in pure shear flow. A nonlinear Poisson–Boltzmann equation governing the electrical double-layer field and a body force generated by the applied electrical potential field are included in the analysis. Results are presented for the velocity and stress component profiles in the microchannel for different parametric values that characterize this flow. Equations for the critical shear rates and maximum electrical potential that can be applied to maintain a steady fully developed flow are derived and discussed.
Keywords: Electro-osmotic flow; Parallel plates; PTT model; Viscoelastic fluid; Analytical study; Constitutive flow instability;
Polymer–lipid microbubbles for biosensing and the formation of porous structures by Kanaka Hettiarachchi; Abraham P. Lee (521-527).
Long-lasting polymer–lipid microbubbles are suitable for biosensing and the production of three-dimensional porous structures and surfaces. Droplet microfluidics technology is used for control of particle composition, size, and polydispersity.Polymer–lipid microbubbles (PLBs) are generated by microfluidic flow-focusing devices to form a new class of long-lasting hybrid particles. The specific PLB construct developed is an elastic gas-filled microsphere with a polydimethylsiloxane (PDMS) shell containing phospholipids conjugated to functionalized polyethyleneglycol (PEG). Digital “droplet-based” microfluidics technology enables control of particle composition, size, and polydispersity (σ < 10%). Use of PDMS as a shell component improves the functionality and stability (lifetime > 6 months) of the hybrid particles due to the thermally maneuverable solidification process. With a gas core, they serve as a template material for creating three-dimensional porous structures and surfaces, requiring no cumbersome post-processing removal steps. By adding biotinylated PEG–lipid derivatives that offer targeting capabilities, we demonstrate the immobilization of fluorescent IgG antibodies on stationary PDMS–lipid microbubbles through biotin–avidin interactions and on-chip trapping for immunoassays. A PDMS–lipid composition offers several advantages such as biocompatibility and biodegradability for future in vivo use as porous engineered scaffolds, packing materials, or delivery (e.g. therapeutic) agents with cell targeting capability.
Keywords: Hybrid materials; Microbubble; Microfluidics; Polydimethylsiloxane; Polymer microspheres;
Size controlled synthesis of sub-100 nm monodisperse poly(methylmethacrylate) nanoparticles using surfactant-free emulsion polymerization by Sevket Tolga Camli; Fatih Buyukserin; Oguz Balci; Gurer Guven Budak (528-532).
We demonstrate a single step synthetic approach that yields poly(methylmethacrylate) (PMMA) nanoparticles with controlled sub-100 nm size and relatively high resultant solid content. Acetone was used as a cosolvent in order to obtain monodisperse sub-100 nm diameter particles. Stable dispersions were obtained for all formulations where the persulfate initiator causes the negative charges on the particle surface.Surfactant-free emulsion polymerization (SFEP) is a well-known technique for the production of polymeric nanoparticles that does not require post-synthetic cleaning steps. Obtaining hydrophobic particles at sub-100 nm scale, however, is quite challenging with this polymerization method. Here, we demonstrate a single step synthetic approach that yields poly(methylmethacrylate) (PMMA) nanoparticles with controlled sub-100 nm size and relatively high resultant solid content. Dynamic light scattering (DLS) was used for the particle characterization. Spherical and uniformly sized nanoparticles were confirmed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Acetone was used as a cosolvent in order to obtain monodisperse sub-100 nm diameter particles. Stable PMMA nanoparticle dispersions were obtained for all formulations where the persulfate initiator causes the negative charges on the particle surface. The effects of acetone, monomer and initiator concentration were studied to optimize average particle hydrodynamic diameter and polydispersity index of the final particles. Non-crosslinked monodisperse PMMA nanoparticles (polydispersity index less than 0.05) with diameters from 32 nm to 72 nm were synthesized by using this method.
Keywords: Poly(methylmethacrylate); Nanoparticles; Surfactant-free emulsion polymerization; Monodisperse; Dynamic light scattering;
Adhesion mechanics of ivy nanoparticles by Yu Wu; Xiaopeng Zhao; Mingjun Zhang (533-540).
An AFM image of nanoparticles secreted from the adhering discs of ivy which allow the plant to affix to a surface.Adhesion mechanism of ivy has been of major research interest for its potential applications in high-strength materials. Recent experimental studies demonstrated that nanoparticles secreted from ivy tendrils play an important role in adhesion. In this work, we investigate how various factors such as van der Waals interaction, capillarity, and molecular cross-linking influence the adhesion mechanics of ivy nanoparticles. This paper provides guidelines in choosing different adhesive contact models. Understanding the mechanics of ivy adhesion could potentially inspire the design and fabrication of novel nano-bio-materials.
Keywords: Adhesion; Contact mechanics; Biological materials; Nanostructured materials;
Biomimetic polyimide nanotube arrays with slippery or sticky superhydrophobicity by Shoujun Zhu; Yunfeng Li; Junhu Zhang; Changli Lü; Xin Dai; Fei Jia; Hainan Gao; Bai Yang (541-546).
Three kinds of superhydrophobic polyimide (PI) nanotube arrays with controllable sliding angles were prepared by controlling the solvent evaporation and drying process.In this paper, we report the fabrication of superhydrophobic polyimide (PI) nanotube arrays with different topographies, which possess slippery or “sticky” superhydrophobicity. The PI nanotube arrays were fabricated by the porous alumina membrane molding method. We regulated three kinds of solvent evaporation and drying processes, which controlled different congregated and noncongregated topographies of PI nanotube arrays. Large scale comb-like congregated topography possesses a small sliding angle (SA < 5°) , small scale comb-like congregated topography possesses a medium sliding angle (SA is about 30°), noncongregated topography possesses a large sliding angle (strong adhesive force to water droplet). Moreover, the as-prepared superhydrophobic PI nanotube arrays have remarkable resistivity to acid, weak base, high temperature (up to 350 °C) and various organic solvents. Our work provides a facile and promising strategy to fabricate superhydrophobic surfaces with controlled sliding angles by utilizing self-organization effect, and such high performance superhydrophobic PI nanotube arrays can be used as coating materials in various harsh conditions.
Keywords: Superhydrophobic; Polyimide; Adhesion; Nanotube;
Polyelectrolyte–surfactant complexes on solid surface by Sarathi Kundu (547-555).
DNA–DTAB complexes form lamellar like multilayered structure but carboxymethyl cellulose-DTAB complexes form coil-like structure on hydrophilic silicon substrate.Polyelectrolyte–surfactant complexes have been deposited on hydrophilic silicon substrates by using a horizontal deposition technique. DNA and carboxymethyl cellulose (carboxyMC) were used as short and long polyelectrolyte and dodecyltrimethylammonium bromide (DTAB) was used as water-soluble surfactant. Varying the surfactant concentration, the structural and morphological information have been obtained for these polyelectrolyte–surfactant complexes. Morphology and out-of-plane structures have been obtained by atomic force microscopy and X-ray reflectivity studies. Electron density profiles obtained from the reflectivity study show that DNA–DTAB complexes form lamellar like multilayered structure but carboxyMC–DTAB complexes form coil-like structure. At lower DTAB concentration, these DNA–DTAB and carboxyMC–DTAB complexes form Gibbs layer, whereas at higher surfactant concentration, DTAB molecules themselves form lamellar like multilayered structure that coexists with the structure formed by the complexes.
Keywords: Polyelectrolytes; DNA; Carboxymethyl cellulose; Cationic surfactants; DTAB; Polyelectrolyte–surfactant complexes; Horizontal deposition; X-ray reflectivity; AFM; Surface pressure;
Evaporation influences on the crystallization of an aqueous dihydrate cupric chloride solution with additives by Nicolaas Busscher; Johannes Kahl; Paul Doesburg; Gaby Mergardt; Angelika Ploeger (556-562).
Crystallization of dihydrate cupric chloride in the presence of PVP as an additive in a petri dish (diameter 10 cm).The overall structure of the crystallization results of dihydrate cupric chloride with additives in a petri dish is affected by the duration between the beginning of the evaporation and the start of the crystallization. Experiments done with polyvinylpyrrolidone and freeze-dried carrot as additive are compared with those of the additive free case. The dependency of dewetting on the dihydrate cupric chloride amount is discussed in terms of depletion of the solution and the surface tension properties of the system. The possible influence of the depletion is depending on the moment the crystallization starts. This is defined by the size of the evaporated area on the dish.
Keywords: Dihydrate cupric chloride; Surface-tension; Wetting; Crystallization; Additive;
PDMS spreading morphological patterns on substrates of different hydrophilicity in air vacuum and water by Marek S. Żbik; Ray L. Frost (563-574).
Optical micrographs of a silicone drop spreading on a silicon wafer in air.In paper has been to investigate the morphological patterns and kinetics of PDMS spreading on silicon wafer using combination of techniques like ellipsometry, atomic force microscope (AFM), scanning electron microscope (SEM) and optical microscopy. A macroscopic silicone oil drops as well as PDMS water based emulsions were studied after deposition on a flat surface of silicon wafer in air, water and vacuum. Our own measurements using an imaging ellipsometer, which also clearly shows the presence of a precursor film. The diffusion constant of this film, measured with a 60,000 cS PDMS sample spreading on a hydrophilic silicon wafer is Df = 1.4 × 10−11 m2/s. Regardless of their size, density and method of deposition, droplets on both types of wafer (hydrophilic and hydrophobic) flatten out over a period of many hours, up to 3 days. During this process neighbouring droplets may coalesce, but there is strong evidence that some of the PDMS from the droplets migrates into a thin, continuous film that covers the surface in between droplets.The thin film appears to be ubiquitous if there has been any deposition of PDMS. However, this statement needs further verification. One question is whether the film forms immediately after forced drying, or whether in some or all cases it only forms by spreading from isolated droplets as they slowly flatten out.
Keywords: PDMS; Silicone oil; Spreading;
Thermodynamic analysis of the wetting behavior of dual scale patterned hydrophobic surfaces by Seyed Hosein Sajadinia; Farhad Sharif (575-583).
A thermodynamic analysis to describe superhydrophobicity due to the synergy between micro and nanoscale roughness in dual scale rough surfaces.Nature-made superhydrophobic surfaces, such as lotus leaves, have a dual scale roughness (in micro and nanoscales) which is the main reason for their unique wettability. While there are a lot of experimental studies on wettability of hierarchical roughness, there is a lack of a thorough analysis of the contribution of micro and nanoscale roughness on wettability behavior despite interesting features these surfaces have. In this paper, a thermodynamic approach has been used to predict the wetting behavior of water droplet on a dual scale roughness. The predictions made by the model are compared with experimental results reported in the literature. The thermodynamic analysis has also been used to provide an insight into the origin of the special hydrophobicity of surfaces with dual scale roughness. It was found that there is an interaction between micro and nanoscale roughness on wettability of each other which results in a synergy among the components of roughness in enhancing hydrophobicity. All possible wetting states of a surface with dual scale roughness were presented in a wetting map. The contact angle for each state was also calculated to determine the maximum water repellency condition.
Keywords: Wettability; Superhydrophobicity; Dual roughness; Hierarchical structure; Thermodynamic analysis;
Superhydrophobic PLA fabrics prepared by UV photo-grafting of hydrophobic silica particles possessing vinyl groups by Geun Yeol Bae; Jinho Jang; Young Gyu Jeong; Won Seok Lyoo; Byung Gil Min (584-587).
Optical micrograph of water droplet onto PLA fabrics: fabric treated with hydrophobic silica particles, UV irradiation, and washing (a); pristine fabric (b).Superhydrophobic poly(lactic acid) (PLA) fabrics are prepared by UV photo-grafting of hydrophobic silica particles possessing vinyl functional groups on the surfaces, which is a novel one-step process to provide surface with roughness as well as hydrophobicity simultaneously. For this purpose, hydrophobic silica particles with vinyl groups and average diameter of 1.51 ± 0.05 μm are synthesized via a sol–gel process. The silica particles possessing vinyl groups are found to be effectively immobilized on PLA fabrics via UV photo-grafting reaction. The water contact angle of the treated PLA fabric is measured to be ∼150°, which is high enough to exhibit the Lotus effect as a result of the superhydrophobicity.
Keywords: Superhydrophobicity; Poly(lactic acid) (PLA); UV photo-grafting; Silica particle; Sol–gel process;
Preparation of highly hydrophobic and lipophobic cellulose fibers by a straightforward gas–solid reaction by Ana Gisela Cunha; Carmen Freire; Armando Silvestre; Carlos Pascoal Neto; Alessandro Gandini; M. Naceur Belgacem; Didier Chaussy; Davide Beneventi (588-595).
The gas–solid reaction of trichloromethylsilane with the surface of cellulose fibers is a simple and green method for generating highly hydrophobic and lipophobic features around them.This work describes a very simple, rapid, and efficient approach to the hydrophobization and lipophobization of cellulose fibers through their reaction with gaseous trichloromethylsilane (TCMS). The characterization of the modified surface involved FTIR-ATR and solid-state 29Si NMR spectroscopy, scanning electron microscopy (SEM), and contact angle measurements with different liquids. The modification generated an inorganic coating around the fibers, associated with the construction of a three-dimensional network of Si–O–Si bridges partly bound to the polysaccharide macromolecules. This coating conferred both a high hydrophobicity and a lipophobicity to the samples even when the treatments applied modest TCMS quantities and reaction times as short as 30 s. The green connotation of this novel process constitutes an additional positive feature.
Keywords: Cellulose fibers; Trichloromethylsilane; Gas–solid reaction; Hydrophobicity; Lipophobicity; Green process;
Investigations on the photoinduced interaction of water soluble thioglycolic acid (TGA) capped CdTe quantum dots with certain porphyrins by M. Asha Jhonsi; R. Renganathan (596-602).
Scheme indicates the interaction between porphyrins and CdTe QDs. Positively charged porphyrin interact with QDs through charge transfer mechanism and negatively charged porphyrins interacted through energy transfer mechanism.The photoinduced interaction of TGA capped CdTe quantum dots (QDs) with porphyrins such as meso-tetrakis(4-sulfonatophenyl)porphyrin [TSPP], meso-tetrakis(4-carboxyphenyl)porphyrin [TCPP], meso-tetrakis (4-N-methylpyridyl)porphyrin [TMPyP] and meso-tetraphenylporphyrin [TPP] has been studied by using absorption, steady state and time resolved fluorescence spectroscopy. The QD surface was negatively charged due to thiol capping agent containing carboxylic group. Positively charged TMPyP interacts with QDs through charge transfer mechanism, negatively charged porphyrins (TCPP and TSPP) interacted through energy transfer mechanism and the neutral one (TPP) does not have any interaction. The Stern–Volmer constant, quenching rate constant, association constants, rate of electron transfer and energy transfer parameters were calculated from the fluorescence data. Effect of molecular structure has also been studied.
Keywords: CdTe QDs; Porphyrins; Fluorescence quenching;
Physicochemical characterization of silylated functionalized materials by Tiago Borrego; Marta Andrade; Moisés L. Pinto; Ana Rosa Silva; Ana P. Carvalho; João Rocha; Cristina Freire; João Pires (603-610).
Materials with different pore structures – internal versus external porosity – were successfully functionalized with amino (APTES and TESA) and mercapto (MPTS) organosilanes.Silylation of several materials where the surface area arises from the internal pores (MCM-41 and FSM-16) or is essentially external (silica gel, and clays) was performed using three organosilanes: (3-aminopropyl)triethoxysilane (APTES), 4-(triethoxysilyl)aniline (TESA) and (3-mercaptopropyl)trimethoxysilane (MPTS). The materials were characterized by nitrogen adsorption–desorption at −196 °C, powder XRD, XPS, bulk chemical analysis, FTIR and 29Si and 13C MAS NMR.For MCM-41 and FSM-16 the highest amounts of organosilane are obtained for APTES, while for the remaining materials the highest amounts are for MPTS; TESA always anchored with the lowest percentage. In terms of surface chemical analysis, TESA anchored with the highest contents irrespectively of the material, and the opposite is registered for MPTS. Comparison of bulk vs surface contents indicate that TESA is mainly anchored at the material external surface. Moreover, with N or S (surface and bulk) contents expressed per unit of surface area, MCM-41 and FSM-16 (internal porosity) show the lowest amounts of silane; the highest amounts of silane per unit of surface area are obtained for the clays.Grafting of the organosilanes to the surface hydroxyl groups was corroborated by FTIR and 29Si and 13C MAS NMR. Furthermore, NMR data suggested that TESA and APTES grafted mostly through a bidentate approach, whereas MPTS grafted by a monodentate mechanism.
Keywords: Silylation; Mesoporous silicas; Clays; Grafting; Organosilanes;
X-ray absorption spectroscopy study of Cu2+ geochemical partitioning in a vineyard soil by Stéphanie Sayen; Emmanuel Guillon (611-615).
EXAFS spectra and their corresponding Fourier transform at Cu K-edge of a soil sample spiked with Cu2+ as a function of aging time.Associations with soil components are of great importance for bioavailability, toxicity, and mobility of trace metals in soils and waters. The copper(II) geochemical partitioning during the aging process within a soil sample was studied through column experiments combined with extended X-ray absorption fine structure (EXAFS) spectroscopy to characterize the copper(II) molecular environment.
Keywords: Soil; Column; Aging; EXAFS; Geochemical partitioning;
by Arthur Hubbard (616).