Journal of Colloid And Interface Science (v.346, #1)
Cover 1 (OFC).
Gold nanoparticle membranes as large-area surface monolayers by Flavio Ciesa; Anton Plech (1-7).
Transfer of self-assembled nanoparticle array from a liquid–liquid interface yields tunable large-area photonic monolayers.An aqueous suspension of gold nanoparticles of sizes from 20 to 90 nm can be conjugated with mercaptosuccinic acid and exposed to a second phase of toluene containing an electrostatic coupler, tetraoctylammonium bromide, to organize the gold particles at the interface between water and toluene. The particles have an amphiphilic character similarly to Janus beads. The thus formed membrane can be transferred to a solid surface to yield centimeter-sized densely packed particle layers. We show that by changing the coupler concentration, the particle distances can be tailored, which modifies the optical properties.
Keywords: Gold nanoparticles; Phase transfer; Langmuir layer; Plasmon resonance; SERS;
Synthesis and photoluminescence of ZnAl2O4:Eu3+ hollow nanophosphors using carbon nanospheres as hard templates by Xiang Ying Chen; Chao Ma; Shi Ping Bao; Zhao Li (8-11).
ZnAl2O4:Eu3+ hollow nanophosphors have been for the first time prepared by using carbon nanospheres as hard templates.ZnAl2O4:Eu3+ hollow nanophosphors have been for the first time prepared by using carbon nanospheres as hard templates. The ZnAl2O4:Eu3+ hollow nanophosphors were well characterized by means of XRPD, FESEM, TEM, HRTEM, N2 adsorption and desorption and PL techniques. The N2 adsorption and desorption data reveal the porous nature of ZnAl2O4:Eu3+ hollow nanophosphors and high surface area of 195.3 m2 g−1. The PL measurement illustrates red-emitting feature of ZnAl2O4:Eu3+ hollow nanophosphors arising from the characteristic transitions of Eu3+ from 5D0 → 7F j (j = 0, 1, 2, 3, and 4). This simple and efficient synthetic strategy could be extended to prepare other series of aluminates nanophosphors with novel hollow structures.
Keywords: ZnAl2O4; Nanophosphor; Template; Luminescence;
Preparation, characterization and electrical properties of fluorine-doped tin dioxide nanocrystals by Shanshan Wu; Shuai Yuan; Liyi Shi; Yin Zhao; Jianhui Fang (12-16).
The HRTEM image and FFT pattern reveal that the fluorine doped SnO2 nanocrystals are of cassiterite structure.Fluorine-doped tin dioxide (FTO) nanocrystals were prepared with a sol–gel process followed by a hydrothermal treatment using SnCl4 and NH4F as SnO2 and fluorine dopant, respectively. The nanostructure and composition were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), zeta potential analysis, electrochemical measurement technology and X-ray photoelectron spectroscopy (XPS) respectively. The diameter of the fluorine doped SnO2 nanocrystal in rutile-type structure is about 10 nm. Compared to the pure SnO2 nanocrystals, the fluorine doped SnO2 nanocrystals can be dispersed homogeneously in H2O, forming transparent sol with high stability. The powder of fluorine doped SnO2 nanocrystals could be obtained by removing the solvent, and the electrical resistivity properties were measured by a four-point probe measurement. The results show that sheet resistances (Rs) of fluorine doped SnO2 decrease with the increasing NH4F/Sn molar ratio in the range from 0 to 2. However, further increase of NH4F/Sn molar ratio from 2 to 5 leads to higher sheet resistance. The F/Sn molar ratio of fluorine doped SnO2 measured by XPS is about 0.18 when NH4F/Sn molar ratio is equal to 2, and the sheet resistance of fluorine doped SnO2 powder is 110Ω/□.
Keywords: Fluorine doped SnO2; Nanocrystals; Colloids; Resistance;
Placement of alkanethiol-capped Au nanoparticles using organic solvents by Tae-Jin Yim; Hyeunseok Choi; Xiang Zhang (17-22).
Alkanethiol-capped Au nanoparticles were linearly placed by toluene with its physical properties and its wettability in the presence of the nanoparticles.We report that alkanethiol-capped Au nanoparticles can be linearly placed by toluene with its physical properties as well as its wettability in the presence of the nanoparticles. It is visually confirmed that toluene can be pinned with the aid of the nanoparticles to transport the nanoparticles to pinned contacts and to form linear placements. Whether the nanoparticles in various solvents can be linearly placed or not is explained based on the results of evaporating the nanoparticle solutions and the physical properties of each solvent. Further studies on controlled placement of the nanoparticles by manipulating the physical properties of organic solvents or by selecting an organic solvent can lead to applications such as a waveguide and other optoelectronic devices.
Keywords: Au nanoparticle; Nanoparticle placement; Organic solvent; Pinning;
Geometrical determination of the lacunarity of agglomerates with integer fractal dimension by Magín Lapuerta; Francisco J. Martos; Gema Martín-González (23-31).
The prefactor of the power-law relationship, associated with the lacunarity, was determined for different agglomerates. It was shown to vary with the compactness of the initial geometrical arrangement the agglomerate.Different agglomerates composed by a variable number of spherical primary particles corresponding to extreme and intermediate values of fractal dimension (Df = 1, Df = 2 and Df = 3) are analysed in this work. In each case, the moment of inertia, diameter of gyration and prefactor of the power-law relationship are determined as a function of the number of composing primary particles. The obtained results constitute the geometrical data base for the development of a method for the determination of the fractal dimension of individual agglomerates from their planar projections, although it is not the aim of this paper to describe the method itself. As a result of these calculations, the prefactor of the power-law relationship was shown not to be a constant parameter, but to tend asymptotically to a limit value with increasing number of primary particles. This limit value is closely related with the compactness of the initial geometrical arrangement in the agglomerate, this justifying the historical association of this parameter with the lacunarity of the agglomerate. A correlation for the determination of the prefactor as a function of the fractal dimension and the number of elementary structures is proposed and compared with other methods proposed in the literature.
Keywords: Lacunarity; Agglomerates; Fractal dimension; Power-law relationship; Packing density;
A master curve for the onset of shear induced restructuring of fractal colloidal aggregates by Volker Becker; Heiko Briesen (32-36).
The onset of restructuring of colloidal aggregates is investigated by means of DEM simulation. The probability r q for an aggregate to be affected from restructuring can be represented by a master curve. The dependency of the critical particle number on the tangential/torsional resistance shear rates ratios Π 1 , Π 2 reveals a power law relation.Colloidal aggregates exposed to shear flow exhibit a size-dependent qualitative behavior [Becker et al. JCIS, 339, 362–372, 2009]. Under the same flow conditions small aggregates rotate like rigid bodies, whereas larger aggregates change their structure and even bigger aggregates break. In this study the transition from the rotational regime to the restructuring regime is investigated by DEM simulations. We applied a model for tangential interaction, capable of supporting bond-bending moments and torsional torques [Becker, Briesen, Phys. Rev. E, 78, 2008, 061404]. The probability for an aggregate to be affected by restructuring changes with the number of primary particle from zero to one in a small interval. The probability becomes a master curve being independent of the shear flow and the interparticle interactions if it is represented as a function of the relative deviation from the critical particles number, i.e. the number of primary particle where the probability of restructuring is equal to 0.5. Investigating the dependency of the critical particle number on the shear rates reveals power law relations which adequately represents the data. The exponents in the power law relations can particularly obtained from a fractal scaling argument.
Keywords: Colloidal aggregates; Colloid; Discrete element method; Interaction forces; Restructuring;
Size control and characterization of wustite (core)/spinel (shell) nanocubes obtained by decomposition of iron oleate complex by Hoang Tri Hai; Hai Tao Yang; Hiroaki Kura; Daiji Hasegawa; Yasunobu Ogata; Migaku Takahashi; Tomoyuki Ogawa (37-42).
Monodisperse wustite (core)/spinel (shell) nanocubes with controllable size from 9 to 22 nm were synthesized by decomposition of iron oleate complex in organic solvent.Monodisperse wustite (core)/spinel (shell) nanocubes with controllable size from 9 to 22 nm were synthesized by the decomposition of iron oleate complex at high temperature. The composition of the nanocubes was confirmed by X-ray diffraction and magnetic analysis, meanwhile the distributions of wustite and spinel phases within the nanocubes were directly observed by high resolution transmission electron microscopy using the dark-field image technique. The core/shell structure is quite unique, in which spinel phase is distributed not only preferentially on the surface, but also in the interior, while almost all of the wustite phase is located in the core of the nanocubes. The formation of wustite is inherent in the decomposition of the iron oleate complex, as indirectly inferred through the detection of a huge quantity of carbon monoxide generated from the reactor.
Keywords: Wustite–spinel core–shell structure; Nanocubes; Iron oleate decomposition;
Separation of photo-active nano-crystalline anatase from titanate nanotubes by Jeffrey S. Church; Andrea L. Woodhead; Keith Fincher (43-47).
The colloidal anatase (A) prepared by acid refluxing of titanate nanotubes showed greater catalytic efficiency than P25 (B) and anatase obtained by calcining the nanotubes (C).Photo-active colloidal anatase was prepared from sodium titanate nanotubes by refluxing in 0.3 M HCl. The refluxing was carried out in cycles, replacing the acid each time. After the second reflux cycle a suspension of colloidal anatase was formed above the residual solids. After three reflux cycles all of the nanotubes were converted to a residual mixture of anatase, rutile and brookite. More colloidal anatase could be isolated from this mixture through a series of water rinses. The anatase suspension was found to be made up of particles with an average diameter of 40 nm as well as a very fine 10–15 nm diameter material. This latter dimension is in line with the crystallite size determined from the anatase isolated from the suspension. At pH 1 the anatase suspension was found to be significantly more photo-active in bleaching methyl orange than P25 at exposure times up to 1.5 h. The photo-activity after 1.5 h was found to be 29% higher than the best catalyst prepared by calcining the same titanate nanotube starting material. The increased activities can probably be attributed to the increased surface area, decreased crystallite size and decreased sodium content of the anatase suspension.
Keywords: Titanate nanotubes; Anatase; Photo-activity; UV-A; Nano-crystallinity; Methyl orange;
Onion-like microspheres with tricomponent from gelable triblock copolymers by Ke Zhang; Lei Gao; Yongming Chen; Zhenzhong Yang (48-53).
Functional microspheres with three alternate layers were obtained by aerosol-assisted self-assembly of poly(3-(triethoxysilyl)propyl methacrylate)-block-polystyrene-block-poly(2-vinylpyridine) triblock copolymer and then a gelation process in the selected layers.Onion-like functional microspheres with three alternate layers were obtained by aerosol-assisted self-assembly of a functional block copolymer, poly(3-(triethoxysilyl)propyl methacrylate)-block-polystyrene-block-poly(2-vinylpyridine) (PTEPM-b-PS-b-P2VP). Through self-gelation reaction occurred in the PTEPM layers, organic/inorganic hybrid functional spheres with highly ordered concentric curved lamellar structure were prepared. Using these hybrid onion-like microspheres as templates, gold ions were entrapped into the P2VP layers and then gold nanoparticles located in each P2VP layers were formed by a reduction. By dispersing in acidic water, the onion-like polymeric spheres were broken and, as a result, sandwich-like nanoplates with curved morphology were obtained.
Keywords: Aerosols; Block copolymers; Gold nanoclusters; Organic/inorganic hybrids; Self-assembly;
Bifunctionalized organic–inorganic charged nanocomposite membrane for pervaporation dehydration of ethanol by Bijay P. Tripathi; Mahendra Kumar; Arunima Saxena; Vinod K. Shahi (54-60).
Cross-linked N-p-carboxy benzyl chitosan (NCBC)–silica nanocomposite membrane grafted with highly acidic –SO3H groups and –COOH are for pervaporation dehydration of water–ethanol mixture. These membranes were tailored to consist of hydrophobic region, highly charged region and selective region, responsible for selective dehydration.Chitosan was modified into N-p-carboxy benzyl chitosan (NCBC) by introducing an aromatic ring grafted with acidic –COOH group and highly stable and cross-linked nanostructured NCBC–silica composite membranes were prepared for pervaporation dehydration of water–ethanol mixture. These membranes were tailored to comprise three regions namely: hydrophobic region, highly charged region and selective region, in which weak acidic group (–COOH) was grafted at organic segment while strong acidic group (–SO3H) was grafted at inorganic segment to achieve high stability and less swelling in water–ethanol mixture. Cross-linking density and NCBC–silica content in membrane matrix has been systematically optimized to control the nanostructure of the developed polymer matrix for studying the effects of molecular structure on the swelling, and PV performance. Among prepared membranes, nanocomposite membrane with 3 h cross-linking time and 90% (w/w) of NCBC–silica content (PCS-3-3) exhibited 1.66 × 10−4 cm3(STP) cm/cm2 s cmHg water permeability (PW ), while 1.35 × 10−7 cm3(STP) cm/cm2 s cmHg ethanol permeability (PEtOH ) of developed membrane and 1231 PV selectivity factor at 30 °C for separating water from 90% (w/w) ethanol mixture.
Keywords: Organic–inorganic nanocomposite; Modified chitosan; Pervaporation; Separation; Water–ethanol mixture;
Mesoporous organosilicas with ultra-large pores: Mesophase transformation and bioadsorption properties by Wei Na; Qi Wei; Ze-Chang Zou; Qun-Yan Li; Zuo-Ren Nie (61-65).
Ordered mesoporous organosilicas materials with ultra-large pores were synthesized by the modified low temperature route and a mesophase transformation from p6mm to Fm3m with the temperatures decreasing from 20 to 8 °C can be observed.Large pore ordered mesoporous organosilicas (OMOs) with distinct mesophase structure was synthesized under low temperatures by the co-condensation of 1,2bis(triethoxysilyl)ethane (BTESE) and tetraethyl orthosilicate (TEOS) in acidic solution, using triblock copolymer F127 as a template and 1,3,5-trimethylbenzene (TMB) as a swelling agent. With the decrease of temperature, a mesophase transformation from 2D hexagonal structure (p6mm) via mesostructured cellular foam to a highly ordered 3D cubic structure (Fm3m) was evidenced by small angle X-ray diffraction (SAXS), transmission electron microscopy (TEM) and N2 sorption. It reveals that the lower synthesis temperatures may influence the hydrolysis and condensation of silica species and the hydrophilic–hydrophobic property of F127, as well as the swelling capacity of F127 micelles with TMB, which resulting in a formation of large pores ordered mesoporous organosilicas with various mesostructures materials. Finally, the enzyme adsorption properties of the OMOs were investigated and the results showed that the OMOs with a 3D large pore structure and regular morphology is much more qualified for enzyme adsorption.
Keywords: Ordered mesoporous organosilicas; Synthesis temperature; Mesophase transformation; Enzyme adsorption;
Colloidal TiO2 nanocrystals prepared from peroxotitanium complex solutions: Phase evolution from different precursors by Sang Il Seok; Muga Vithal; Jeong Ah Chang (66-71).
We report the preparation of nanocrystalline anatase and rutile TiO2 from aqueous peroxotitanium complex (PTC) solutions and their characterization by powder X-ray diffraction (XRD), infrared spectroscopy, and Raman spectroscopy. The phase evolution of TiO2 prepared using PTC derived from different precursors, i.e., TiCl4 and titanium tetraisopropoxide (TTIP), is related to the nature of the intermediate steps. Phase-pure nanoanatase was formed in PTC solution derived from TiCl4, while a mixture of minor anatase and dominant rutile were prepared from PTC when TTIP was used as precursor. On the other hand, in the case of calcining PTC powders in air, a pure anatase phase of TiO2 was obtained, regardless of the precursor used. Thus, the formation and attachment of hydrated TiO6 units or TiO2·xH2O under a different environment, especially pH, plays a critical role in determining the phase during the crystallization of TiO2.
Keywords: TiO2 nanocrystals; Peroxotitanium complex; Different precursors; Phase evolution;
Effect of annealing on the phase structure and the properties of the film formed from P(St-co-BA)/P(MMA-co-BA) composite latex by Xianyong Yuan; Dongxia Huo; Qingwen Qian (72-78).
Phase rearrangement had occurred in the composite latex film when the annealing temperature was higher than critical temperature. Micro-pinholes and micro-cracks were detected on the surface of the film.Composite latex of P(St-co-BA)/P(MMA-co-BA) was prepared by two-step semi-continuous emulsion polymerization under starved conditions. Optical properties, water resistance and heat aging process of the film formed by the composite latex were examined. It was revealed that annealing temperature played an important role on the structure of the composite latex film. The surface of the film prepared at room temperature was very rough. Many micro-cracks were observed both on the surface and inside of the film. Increase of annealing temperature assisted film formation. There was a critical temperature at which the film properties, such as water resistance and transparency, were significantly improved. However, it was worth to note that phase rearrangement had occurred when the annealing temperature was higher than critical temperature. Micro-pinholes and micro-cracks were detected on the surface of the film. Meanwhile, the properties of the film, such as transparency and water adsorption, became remarkable deteriorated.
Keywords: Core–shell latex; Film formation; Property; Morphology;
SAXS exploration of the synthesis of ultra monodisperse silica nanoparticles and quantitative nucleation growth modeling by Sarah Fouilloux; Anthony Désert; Olivier Taché; Olivier Spalla; Jean Daillant; Antoine Thill (79-86).
La Mer-like nucleation and growth of monodisperse Silica nanoparticles. SAXS measurements and quantitative modeling.The production of highly monodisperse nanoparticles of precisely controlled size is a very important research field. It has important applications notably for the optical properties of nanoparticles (e.g. quantum dot) or nanoparticle assemblies (e.g. photonic band gap crystals) and for electromagnetic properties (e.g. information storage). Understanding monodisperse nanoparticle synthesis mechanism is based mostly on the Classical Nucleation Theory (CNT). It has been shown in the literature and in this work that CNT is able to predict the nanoparticle concentration and average size correctly. However, until recently only a few models based on CNT were able to predict the size distribution of the synthesized objects. In this work, we show that a CNT based model is not able to predict the size distribution of silica nanoparticles formed in a pure La Mer like nucleation growth process. Reasons for this discrepancy are discussed and should be taken into account to develop more complete models able to predict the size distribution especially if it is desired to use them as tools to optimize monodispersity.
Keywords: Silica; SAXS; TEM; Nucleation; Growth; Kinetic;
Molecular-level interactions of an azopolymer and poly(dodecylmethacrylate) in mixed Langmuir and Langmuir–Blodgett films for optical storage by Lucinéia F. Ceridório; Débora T. Balogh; Luciano Caseli; Marcos R. Cardoso; Tapani Viitala; Cleber R. Mendonça; Osvaldo N. Oliveira (87-95).
Photoinduced birefringence for optical storage was studied for an azopolymer-poly(dodecylmetacrylate) LB film. This mixture was characterized on Langmuir films with surface pressure, surface potential, Brewster Angle Microscopy, and infrared spectroscopy.The applicability of azopolymers in optical storage can be extended through the use of nanostructured films produced with the Langmuir–Blodgett (LB) technique, but the film properties need to be optimized since these polymers generally do not form stable Langmuir films to be transferred onto solid substrates. Here, photoinduced birefringence was investigated for mixed Langmuir–Blodgett films from the homopolymers 4-[N-ethyl-N-(2-methacryloxyethyl)]-4′-nitroazobenzene (HPDR1-MA) and poly(dodecylmethacrylate) (HPDod-MA). The interactions between these polymers were studied in Langmuir and LB films. Surface pressure–area isotherms pointed to molecular-level interactions for proportions of 51 mf%, 41 mf% and 31 mf% of HPDR1-MA. Phase segregation was not apparent in the BAM images, in which the morphology of the blend film was clearly different from that of the Langmuir films of neat homopolymers. Through PM-IRRAS, we noted that the interaction between the azopolymer and HPDod-MA affected the orientation of carbonyl groups. Strong interactions for the mixture with 41 mf% of poly(dodecylmethacrylate) led to stable Langmuir films that were transferred onto solid supports as LB films. The photoinduced birefringence of 101-layer mixed LB films show features that make these films useful for optical storage, with the advantage of short writing times in comparison to other azopolymer films.
Keywords: Azopolymers; Optical storage; ATRP; Langmuir–Blodgett; PM-IRRAS;
Anomalously stable dispersions of graphite in water/acetone mixtures by Yoshimune Nonomura; Yusuke Morita; Shigeru Deguchi; Sada-atsu Mukai (96-99).
Highly stable dispersions of graphite are obtained in water/acetone mixtures, while graphite precipitates promptly in water and in acetone.Highly stable dispersions of graphite are obtained in water/acetone mixtures, while graphite precipitates promptly in water and in acetone. We found that acetone facilitates disintegration of the graphite particles and their aggregates during a sonication process. Fine graphite particles are stabilised by the electrostatic repulsion due to negative charges on the graphite particle surfaces.
Keywords: Graphite; Dispersion; Acetone;
Viscoelastic solutions formed by worm-like micelles of amine oxide surfactant by L. Brinchi; R. Germani; P. Di Profio; L. Marte; G. Savelli; R. Oda; D. Berti (100-106).
pDoAO oxide forms viscoelastic gel-like wormlike micellar solutions in water without additive; the system reverses to fluid when acid is added (pH < 2).Formation and properties of viscoelastic wormlike aqueous micellar solutions of the zwitterionic surfactant p-dodecyloxybenzyldimethylamine oxide (pDoAO) were studied. Semi-dilute aqueous solutions of pDoAO show a sharp increase in viscosity, which exceeds 160 cST for concentrations >50 mM, leading to viscoelastic solutions. Viscoelasticity relates to the surfactant charge type. In fact this viscoelastic system reverses to fluid when acid is added (pH < 2), which changes the system to cationic. Under acidic conditions the system resembles solutions of the similar cationic surfactant p-dodecyloxybenzyltrimethylammonium bromide, (pDoTABr) in terms of viscosity. Properties of aqueous solutions of pDoAO were investigated by dynamic light scattering (DLS), rheology and small angle neutron scattering (SANS). Data support the idea that small micelles grow in length (wormlike or threadlike micelles) as surfactant concentration increases and viscoelastic solutions form as micelles become entangled. The micellar diameter as calculated by different techniques is about 5 nm.
Keywords: Surfactants; Worm-like micelles; Amine oxide; Viscoelasticity; Rheology;
Thermodynamic investigation of the systems poly(ethylene glycol) + sodium pentane-1-sulfonate + water and poly(vinyl pyrrolidone) + sodium pentane-1-sulfonate + water by Rahmat Sadeghi; Mehdi Ziaii (107-117).
Variation of activity of H2O (○) and C5SO3Na (●) against surfactant molality.Thermodynamic properties for aqueous solutions containing sodium pentane-1-sulfonate (C5SO3Na) in the absence and presence of poly(ethyleneglycol) (PEG) or poly(vinylpyrrolidone) (PVP) determined as a function of surfactant concentration from the density, sound velocity, viscosity, conductivity and vapor–liquid equilibria data, are reported here. Densities and sound velocities, allowing for the determination of apparent molar volumes and compressibilities, were measured at 288.15–313.15 K. Changes in the apparent molar properties upon micellization were derived using a pseudo-phase-transition approach and the infinite dilution apparent molar volumes and compressibilities of the monomer and micellar state of C5SO3Na in the investigated solutions were determined. The values of the infinite dilution apparent molar properties of micellar states of C5SO3Na in aqueous polymer solutions are larger than those in pure water. Vapor–liquid equilibrium data such as water activity, vapor pressure, osmotic coefficient, activity coefficient and Gibbs free energies were obtained through isopiestic method at 298.15 K. The variations of the critical micelle concentration (CMC) of C5SO3Na in water and in aqueous PEG and PVP solutions with temperature were obtained and a comparison between the CMC of C5SO3Na obtained from different thermodynamic properties was also made.
Keywords: Sodium pentane-1-sulfonate; Poly(ethylene glycol); Poly(vinyl pyrrolidone); Volumetric; Compressibility; Vapor–liquid equilibria; Micellization;
The rheology of concentrated suspensions of arbitrarily-shaped particles by I. Santamarı´a-Holek; Carlos I. Mendoza (118-126).
Left panel: relative viscosity η ( ϕ ) / η 0 as predicted by our model for isotropic rods with different aspect ratios and intrinsic viscosities as given by Table . Silica rods (solid line), schizophylian (dashed line), xanthan (dotted line), and PMMA fibre (dash-dotted line). Right panel: the same as left panel but assuming orientational order and using ϕ max ≃ 0.9069 . The fitted values of [ η ] were 90 for silica rods (solid line), 50 for schizophylian (dashed line), 40 for xanthan (dotted line), and 13 for PMMA fibre (dash-dotted line). The data sets were taken from Ref. .We propose an improved effective-medium theory to obtain the concentration dependence of the viscosity of particle suspensions at arbitrary volume fractions. Our methodology can be applied, in principle, to any particle shape as long as the intrinsic viscosity is known in the dilute limit and the particles are not too elongated. The procedure allows to construct a continuum-medium model in which correlations between the particles are introduced through an effective volume fraction. We have tested the procedure using spheres, ellipsoids, cylinders, dumbells, and other complex shapes. In the case of hard spherical particles, our expression improves considerably previous models like the widely used Krieger–Dougherty relation. The final expressions obtained for the viscosity scale with the effective volume fraction and show remarkable agreement with experiments and numerical simulations at a large variety of situations.
Keywords: Suspensions; Viscosity–concentration relation; Effective medium theory;
Effect of α-helical peptides on liposome structure: A comparative study of melittin and alamethicin by Per Wessman; Malin Morin; Karin Reijmar; Katarina Edwards (127-135).
The amphiphilic peptides alamethicin, melittin and magainin 2 show high affinity for positively curved lipid surfaces as shown by a competitive binding assay and cryo-transmission electron microscopy.Cryo-transmission electron microscopy was used in combination with turbidity and leakage measurements to explore and compare the membrane perturbing effects of melittin and alamethicin on POPC-based liposomes of varying composition. The results show that the two peptides, despite their differences in physico-chemical properties and proposed mode of action, induce similar structural effects on the liposomes. Importantly, whereas low peptide concentrations leave pure POPC liposomes intact and seemingly unperturbed, POPC liposomes supplemented with 40 mol.% cholesterol change their shape, rupture and fuse in response to the addition of both melittin and alamethicin. In the case of alamethicin, but not melittin, fusion is effectively prevented by inclusion of 10 mol.% POPG in the liposome membranes. By means of a competitive binding assay we furthermore show that alamethicin, in line with earlier findings for melittin, possess high affinity for positively curved lipid surfaces. Moreover, results from the present study show that magainin 2 has a similar preference for curved surfaces.
Keywords: Melittin; Alamethicin; Magainin; Liposomes; Affinity; Cryo-transmission electron microscopy;
Highly concentrated emulsions: 1. Average drop size determination by analysis of incoherent polarized steady light transport by Emilio Paruta-Tuarez; Hala Fersadou; Véronique Sadtler; Philippe Marchal; Lionel Choplin; Christophe Baravian; Christophe Castel (136-142).
A geometric relationship is proposed to determine the average drop size (R) of highly concentrated emulsions from the film thickness measurements (Rpol ) obtained via analysis of incoherent polarized steady light transport (AIPSLT).The analysis of incoherent polarized steady light transport is reported as a convenient technique for the drop size determination in highly concentrated oil-in-water emulsions. The studied system consists in heptane-in-water emulsions stabilized with a copolymeric surfactant (Synperonic PE®/L64). Hundred grams of parent emulsions, at two volume fractions of dispersed phase (φ = 0.958 and 0.937) were prepared using a semi-batch process. Then, they were diluted with the aqueous phase to obtain volume fractions ranging from 0.886 to 0.958. The use of a copolymeric surfactant allows the dilution of the highly concentrated emulsions without any change in the particle size distribution as confirmed by laser diffraction measurements. We found that the polarization technique allows the determination of the film thickness between water drops rather than their sizes. Consequently, we propose a geometrical relationship to determine an average drop size from the film thickness. The sensitivity of this alternative technique to detect changes in average drop size was studied by changing some process and formulation parameters. Drop size determination in highly concentrated emulsions via this method is useful since the measurement protocol neither involves dilution nor induces structural changes in the emulsion.
Keywords: Highly concentrated emulsions; Incoherent polarized steady light transport; Film thickness; Average drop size; Geometrical relationship;
Adsorption and emulsification properties of amphiphilic poly(styrene-co-octadecyl maleamic acid salt) with comb-like architecture by R. Vijay; S. Angayarkanny; B.S.R. Reddy; A.B. Mandal; Geetha Baskar (143-152).
Adsorption of Triton X-100 on hollow spheres of amphiphilic poly(styrene) with comb-like architecture has a profound effect on the emulsification properties.Amphiphilic poly(styrene-co-octadecyl maleamic acid salt) (PS-co-ODMAS) with a comb-like architecture was synthesized employing a heterophase aqueous polymerization reaction. The side-chain comonomer from octadecyl maleamic acid salt exhibited hydrogelation characteristics and provided conditions for a controlled polymerization reaction. PS-co-ODMAS polymers consisting of 5 and 10 mol% side-chain monomer showed a high molecular weight on the order of 106 and narrow polydispersity index at 1.33 + 0.02. The polymer consisting of 10 mol% side-chain monomer was shown to exhibit properties that are significantly different from those with 5 mol%, and the control poly(styrene) synthesized using sodium dodecyl sulfate surfactant. The polymer consisting of 10 mol% side-chain monomer formed hollow spherical spheres of 30 nm size. It also showed close-packed structures of the side-chain monomer on the polymer surface. Detailed adsorption studies at the liquid/liquid interface were carried out to evaluate and understand the scope for modification in surface energy characteristics of polymers in the presence of additives drawn from simple surfactants. Triton X-100 was shown to undergo effective adsorption on the polymer consisting of 10 mol% side-chain monomer and thus could generate stable emulsions with different volume fractions of heptadecane. The results from electron microscopy studies and viscosity of emulsions are discussed.
Keywords: Amphiphiles; Dispersions; Gels; Surfactants; Emulsion polymerization; Pickering emulsifier;
Semifluorinated thiols in Langmuir monolayers by Marcin Broniatowski; Patrycja Dynarowicz-Łątka; Luis Camacho; Maria T. Martin Romero; Eulogia Muñoz (153-162).
Semifluorinated thiol (F6H10) in a Langmuir monolayer. π–A isotherm together with a representative BAM image and PM-IRRAS spectra.A series of semifluorinated thiols of the general formula CF3(CF2) m −1(CH2) n SH (abbreviated to FmHnSH) have been synthesized and the Langmuir monolayers thoroughly characterized using surface pressure (π) and electric surface potential (ΔV) measurements. These data have been complemented with Brewster angle microscopy (BAM) visualization of the monolayers structure and IR spectroscopy (PM-IRRAS) analysis of the alkyl chain conformation. The investigated thiols (namely F4H10SH, F8H6SH, F6H10SH, F10H6SH, F6H11SH, F8H10SH and F10H10SH) differ in the length of the hydrophobic chain as well as in the degree of fluorination. Although the –SH group cannot form strong hydrogen bonds with the water subphase, thereby causing only weak anchoring, it has been found that all the investigated thiols, except for F4H10SH, are capable of stable Langmuir monolayer formation. The investigated thiols can be divided into two categories – thiols with longer alkyl chain (F10H10SH, F10H6SH, F8H10SH) and compounds with shorter hydrophobic part (F6H10SH, F6H11SH, F8H6SH). The monolayers of the latter thiols have their equilibrium surface pressure (ESP) comparable with the collapse pressure (π C) of their monolayers; thus these films are stable within the whole range of compression. On the contrary, thiols with longer perfluorinated fragments have considerably lower ESP than the π C of their monolayers; therefore, both stable and metastable regions can be distinguished in their π–A isotherms. Interestingly, for F8H6SH, a smectic ordering of molecules can be observed in monolayers as visualized with BAM. By comparing film-forming properties of the studied semifluorinated thiols with previously studied semifluorinated alkanes it has been found that the presence of –SH group facilitates spreading at the free water surface. Semifluorinated thiols have been found to maintain their monomolecular ordering in the presence of heavy metal cations in the aqueous subphase, contrary to their hydrogenated analogues, which have been reported to crystallize under the same conditions.
Keywords: Semifluorinated thiols; Langmuir monolayers; Brewster angle microscopy; Monolayer relaxation; Equilibrium surface pressure;
Turbidity diagrams of polyanion/polycation complexes in solution as a potential tool to predict the occurrence of polyelectrolyte multilayer deposition by Hajare Mjahed; Jean-Claude Voegel; Armelle Chassepot; Bernard Senger; Pierre Schaaf; Fouzia Boulmedais; Vincent Ball (163-171).
A strong correlation between the occurrence of interpolyelectrolyte complexation (turbidity) and the deposition of PEM films is shown for six different polycation – polyanion combinations.Surface functionalization with polyelectrolyte multilayer films (PEM films) has become very popular owing to its simplicity and versatility. However, even if some research is already available, this field of surface chemistry lacks a systematic knowledge of how the polyelectrolyte structure and solution conditions influence the growth of PEM films. In this investigation, we focus on the possible relationship between turbidity of polycation and polyanion mixtures in solution, and the buildup of PEM films made from the same polyelectrolytes in the same physicochemical conditions, namely pH, temperature and ionic strength. It comes out that for six different polycation/polyanion combinations there is a clear correlation between the turbidity evolution of polycation/polyanion complexes with the salt concentration and the evolution of the film deposition with the same parameter. In this investigation, the complexes in solution were prepared in conditions where the ratio between the number of cationic to anionic groups was close to unity. Even if there is a correlation between turbidity in solution and PEM film deposition, we found some exceptions in the low salt concentration regime.This work is an extension of the preliminary works of Cohen Stuart (D. Kovačević et al. Langmuir 18 (2002) 5607–5612) and Sukishvili et al. (S.A. Sukhishvili, E. Kharlampieva and V. Izumrudov, Macromolecules 39 (2006) 8873–8881).
Keywords: Polyelectrolyte multilayer films; Polyelectrolyte complexes;
Visible-light hydrogen generation using as photocatalysts layered titanates incorporating in the intergallery space ruthenium tris(bipyridyl) and methyl viologen by Francesc Sastre; Younes Bouizi; Vicente Fornés; Hermenegildo Garcia (172-177).
A ruthenium complex as light harvester inside the intergallery space of a layered titanate is a promising photocatalyst for the generation of hydrogen with visible light.A series of layered titanates containing in the interlayer space tris(2,2′-bipyridyl)ruthenium(II) [ Ru ( bpy ) 3 2 + ] or methyl viologen (MV2+) or both has been prepared and characterized by elemental analyses, XRD, and optical and vibrational spectroscopy. Incorporation of Ru ( bpy ) 3 2 + and MV2+ is confirmed by the increase of the distance between the titanate layers. The presence of Ru ( bpy ) 3 2 + in the material is also revealed in optical spectroscopy where the ligand to metal charge transfer band appearing at λ max 460 nm is observed. Also incorporation of MV2+ leads to the observation of the charge transfer complex band with the titanate host from 350 to 650 nm. These solids are active for the photocatalytic hydrogen generation from water when colloidal platinum as catalyst and EDTA as sacrificial electron donor are present in the solution. The maximum efficiency was obtained for a solid consisting of layered titanate containing a 10.2 wt.% loading of Ru ( bpy ) 3 2 + incorporated in the titanate layers and MV2+ and Pt nanoparticles in the aqueous solution. This heterogeneous system produced about one-half the hydrogen generated for the conventional homogeneous system where all the components [ Ru ( bpy ) 3 2 + , MV2+, Pt, and EDTA] are in solution, with the advantage that it can be used as film or recovered by filtration from the aqueous medium.
Keywords: Renewable energy resources; Hydrogen as fuel; Photocatalysis; Layered materials;
Adsorption of arsenic ions on Brazilian sepiolite: Effect of contact time, pH, concentration, and calorimetric investigation by Denis L. Guerra; Adriano C. Batista; Paulo C. Corrêa da costa; Rúbia R. Viana; Claudio Airoldi (178-187).
This investigation reports the use of original and modified sepiolite as alternative absorbents. The compound 2-aminomethylpyridine was anchored onto Amazon sepiolite surface by heterogeneous route.The original sepiolite clay mineral has been collected from Amazon region, Brazil. The compound 2-aminomethylpyridine (AMP) was anchored onto Amazon sepiolite surface by heterogeneous route. The natural (SPT) and modified (SPTAMP) sepiolite samples were characterized by elemental analysis, SEM, N2 adsorption, and nuclear magnetic nuclei of 29Si and 13C. The well-defined peaks obtained in the 13C NMR spectrum in the 0–160 ppm region confirmed the attachment of organic functional groups as pendant chains bonded into the porous clay. The ability of these materials to remove As(V) from aqueous solution was followed by a series of adsorption isotherms at room temperature and pH 4.0. The maximum number of moles adsorbed was determined to be 7.26 × 10−2 and 11.70 × 10−2 mmol g−1 for SPT and SPTAMP, respectively. In order to evaluate the clay samples as adsorbents in dynamic system, a glass column was fulfilled with clay samples (1.0 g) and it was fed with 2.0 × 10−2 mmol dm−3 As(V) at pH 4.0. The energetic effects caused by metal cations adsorption were determined through calorimetric titrations. Thermodynamics indicated the existence of favorable conditions for such As(V)–nitrogen interactions.
Keywords: Sepiolite; Arsenic; Adsorption; Calorimetry;
Direct electrochemistry and electrocatalysis of myoglobin immobilized on Fe2O3 nanoparticle–sodium alginate–ionic liquid composite-modified electrode by Tianrong Zhan; Mengying Xi; Yan Wang; Wei Sun; Wanguo Hou (188-193).
A pair of well-defined redox peaks appeared on the cyclic voltammogram of SA–Mb–IL–Fe2O3/CILE (d) in pH 7.0 phosphate buffer solution at a scan rate of 100 mV s−1.A biocomposite material composed of sodium alginate (SA), Fe2O3 nanoparticles, and ionic liquid 1-decyl-3-methylimidazolium bromide ([DMIM]Br) was fabricated and used for the immobilization of myoglobin (Mb) on the surface of a carbon ionic liquid electrode (CILE). The CILE was fabricated by mixing graphite powder with ionic liquid N-butylpyridinium hexafluorophosphate (BPPF6) together. UV–Vis absorption and FTIR spectroscopic results indicated that Mb retained its native structure in the composite material. A pair of well-defined redox peaks appeared on the cyclic voltammogram in pH 7.0 phosphate buffer solution (PBS) with the formal peak potential (E 0′) at −0.256 V (versus SCE), which was the typical electrochemical behavior of Mb heme Fe(III)/Fe(II) redox couples. The Mb-modified electrode showed good electrocatalytic activity to the reduction of trichloroacetic acid (TCA) and NaNO2 with wide linear range, good sensitivity, and reproducibility. The calibration range for TCA detection was between 0.6 and 12.0 mmol L−1 with the linear regression equation as Iss (μA) = 42.44C (mmol L−1) + 50.57 and a detection limit of 0.4 mmol L−1 (3σ). The Mb-modified electrode also applied to NaNO2 determination in the concentration range from 4.0 to 100.0 mmol L−1 with a detection limit of 1.3 mmol L−1 (3σ). So the proposed electrode has potential applications as third-generation biosensors.
Keywords: Direct electrochemistry; Myoglobin; Ionic liquids; Sodium alginate; Fe2O3 nanoparticles;
A study on hydrogen-storage behaviors of nickel-loaded mesoporous MCM-41 by Soo-Jin Park; Seul-Yi Lee (194-198).
The hydrogen-storage capacities of the Ni/MCM-41 as a function of Ni content are described.The objective of the present work was to investigate the possibility of improving the hydrogen-storage capacity of mesoporous MCM-41 containing nickel (Ni) oxides (Ni/MCM-41). The MCM-41 and Ni/MCM-41 were prepared using a hydrothermal process as a function of Ni content (2, 5, and 10 wt.% in the MCM-41). The surface functional groups of the Ni/MCM-41 were identified by Fourier transform infrared spectroscopy (FTIR). The structure and morphology of the Ni/MCM-41 were characterized by X-ray diffraction (XRD) and field emission transmission electron microscopy (FE-TEM). XRD results showed a well-ordered hexagonal pore structure; FE-TEM also revealed, as a complementary technique, the structure and pore size. The textural properties of the Ni/MCM-41 were analyzed using N2 adsorption isotherms at 77 K. The hydrogen-storage capacity of the Ni/MCM-41 was evaluated at 298 K/100 bar. It was found that the presence of Ni on mesoporous MCM-41 created hydrogen-favorable sites that enhanced the hydrogen-storage capacity by a spillover effect. Furthermore, it was concluded that the hydrogen-storage capacity was greatly influenced by the amount of nickel oxide, resulting in a chemical reaction between Ni/MCM-41 and hydrogen molecules.
Keywords: Hydrogen storage; MCM-41; Nickel; Spillover effect;
Synthesis and characterization of composite molecular sieves M1-MFI/M2-MCM-41(M1, M2 = Ni, Co) with high heteroatom content and their catalytic properties for hydrocracking of residual oil by Baoshan Li; Xiao Li; Junqing Xu; Xinmei Pang; Xiaohui Gao; Zhiyuan Zhou (199-207).
The formation process of composite molecular sieves M1-MFI/M2-MCM-41 by using ionic complex [ ( C 4 H 9 ) 4 N ] 2 + [M1(EDTA)]2− and [ C 16 H 33 ( CH 3 ) 3 N ] 2 + [M2(EDTA)]2− as template.The novel rich heteroatom-containing (15 wt.%) composite molecular sieves M1-MFI/M2-MCM-41 have been prepared from the ionic complex [ ( C 4 H 9 ) 4 N ] 2 + [M1(EDTA)]2− and [ C 16 H 33 ( CH 3 ) 3 N ] 2 + [M2(EDTA)]2− as the organic templates, which could effectively introduce a large amount of heteroatoms into the framework of molecular sieves. The products were characterized by XRD, XRF, SEM, HRTEM, N2 adsorption–desorption, H2-TPR, FT-IR, TG and DSC techniques. The catalytic performances of the composite materials were investigated by means of residual oil hydrocracking. Characterization results showed that the composite materials simultaneously possessed a typical orthogonal MFI phase and a hexagonal MCM-41 phase and the two phases were composite rather than the physical mixture. H2-TPR data indicated all of the heteroatoms were incorporated by isomorphous substitution of silicon in framework. N2 adsorption–desorption analysis exhibited that these samples possessed regular and stable structure with high specific surface area and large pore diameters of 550–620 m2 g−1, 3.5 nm and 5.5 nm, respectively. M1-MFI/M2-MCM-41 presented excellent activities in hydrocracking of residual oil, which were superior to the pure materials of MFI/MCM-41.
Keywords: Ionic complex; High heteroatom content; M1-MFI/M2-MCM-41; Composite molecular sieve;
Determination of a setup correction function to obtain adsorption kinetic data at stagnation point flow conditions by Maria F. Mora; M. Reza Nejadnik; Javier L. Baylon-Cardiel; Carla E. Giacomelli; Carlos D. Garcia (208-215).
This paper describes a methodology to characterize flow cells designed to study adsorption kinetics and to correct experimental data for errors associated with the size of the measured spot.This paper is the first report on the characterization of the hydrodynamic conditions in a flow cell designed to study adsorption processes by spectroscopic ellipsometry. The resulting cell enables combining the advantages of in situ spectroscopic ellipsometry with stagnation point flow conditions. An additional advantage is that the proposed cell features a fixed position of the “inlet tube” with respect to the substrate, thus facilitating the alignment of multiple substrates. Theoretical calculations were performed by computational fluid dynamics and compared with experimental data (adsorption kinetics) obtained for the adsorption of polyethylene glycol to silica under a variety of experimental conditions. Additionally, a simple methodology to correct experimental data for errors associated with the size of the measured spot and for variations of mass transfer in the vicinity of the stagnation point is herein introduced. The proposed correction method would allow researchers to reasonably estimate the adsorption kinetics at the stagnation point and quantitatively compare their results, even when using different experimental setups. The applicability of the proposed correction function was verified by evaluating the kinetics of protein adsorption under different experimental conditions.
Keywords: Spectroscopic ellipsometry; Stagnation point; Adsorption kinetics; Polyethylene glycol; Protein adsorption;
Improved photodegradation properties and kinetic models of a solar-light-responsive photocatalyst when incorporated into electrospun hydrogel fibers by Ji Sun Im; Byong Chol Bai; Se Jin In; Young-Seak Lee (216-221).
The rapid removal of dyes occurred due to the excellent swelling behavior of the hydrogel. Then, absorbed dye ions were decolorized by TiO2 effectively due to the high light transparency of the hydrogel.The capacity of a photocatalyst system to degrade water pollutants was optimized using solar-light-sensitive TiO2 and the swelling behavior of a hydrogel. TiO2 synthesized via a sol–gel process was modified by multielement doping to change its solar-light-responsive properties. A hydrogel was used for the rapid absorption of both anionic and cationic water pollutants. TiO2 particles were immobilized in/on hydrogel fibers by an electrospinning method for the easy recovery of TiO2, and the ability of the hydrogel/TiO2 composite to degrade dye molecules was studied. The TiO2 particles were observed to have maintained their original anatase-type crystallinity in/on the electrospun hydrogel fibers. The dye degradation capacity of the hydrogel/TiO2 composite was investigated using both anionic and cationic dyes under sunlight. Two mechanisms were suggested by which the hydrogel/TiO2 composite can remove dye particles from the water: (1) the absorption of dyes by the hydrogel and (2) the degradation of the dye by the TiO2 in the hydrogel. Both of these mechanisms were investigated in this study. We found that the dye was effectively absorbed by the hydrogel fibers as demonstrated by the swelling behavior of the hydrogel and the nano-size effects. The dye was then introduced to the TiO2 particles for degradation.
Keywords: Photodegradation; TiO2; Hydrogel; Electrospinning; Nano-fiber;
Charging of silver bromide aqueous interface: Evaluation of interfacial equilibrium constants from surface potential data by Tajana Preočanin; Filip Šupljika; Nikola Kallay (222-225).
A single crystal silver bromide electrode (SCr–AgBr) was used to measure the inner surface potential (Ψ 0) at the silver bromide aqueous electrolyte interface.A single crystal silver bromide electrode (SCr–AgBr) was used to measure the inner surface potential (Ψ 0) at the silver bromide aqueous electrolyte interface as a function of the activities of Br- and Ag+. Absolute values of the surface potential were calculated from electrode potentials of SCr–AgBr using the value of point of zero charge (pBrpzc = 6.9 [H.A. Hoyen, R.M. Cole, J. Colloid Interface Sci. 41 (1972) 93.]) as the value of point of zero potential. Measurements were performed in potassium nitrate aqueous solutions. The Ψ 0(pBr) function was linear and slightly dependent on the ionic strength. The reduction values of the slope with respect to the Nernst equation, expressed by the α coefficient, were 0.880, 0.935, and 0.950 at ionic strengths of 10−4, 10−3, and 10−2 mol dm−3, respectively. The results were successfully interpreted by employing the surface complexation model, developed originally for metal oxides and adapted for silver halides. The thermodynamic (“intrinsic”) equilibrium constants for binding of bromide ( K n ∘ ) and silver ( K p ∘ ) ions on the corresponding sites at the silver bromide surface were evaluated as lg K n ∘ = 3.98 ; lg K p ∘ = 2.48 . Symmetrical counterion surface association was assumed and equilibrium constants were obtained as lg K NO 3 - ∘ = lg K K + ∘ = 4.30 .
Keywords: Silver bromide; Surface potential; Surface charge; Surface equilibrium constants; Surface complexation model; Single crystal electrode;
Growth modification of seeded calcite using carboxylic acids: Atomistic simulations by Ulrich Aschauer; Dino Spagnoli; Paul Bowen; Stephen C. Parker (226-231).
Molecular dynamics simulations predict differences in calcite growth modification by polyacrylic acid and polyaspartic acid to be a combination of complexing ions in solution, adsorption free energies and adsorption conformations.Molecular dynamics simulations were used to investigate possible explanations for experimentally observed differences in the growth modification of calcite particles by two organic additives, polyacrylic acid (PAA) and polyaspartic acid (p-ASP). The more rigid backbone of p-ASP was found to inhibit the formation of stable complexes with counter-ions in solution, resulting in a higher availability of p-ASP compared to PAA for surface adsorption. Furthermore the presence of nitrogen on the p-ASP backbone yields favorable electrostatic interactions with the surface, resulting in negative adsorption energies, in an upright (brush conformation). This leads to a more rapid binding and longer residence times at calcite surfaces compared to PAA, which adsorbed in a flat (pancake) configuration with positive adsorption energies. The PAA adsorption occurring despite this positive energy difference can be attributed to the disruption of the ordered water layer seen in the simulations and hence a significant entropic contribution to the adsorption free energy. These findings help explain the stronger inhibiting effect on calcite growth observed by p-ASP compared to PAA and can be used as guidelines in the design of additives leading to even more marked growth modifying effects.
Keywords: Calcium carbonate; Calcite; Polycarboxylic acids; Atomistic simulation; Adsorption;
The effect of many-body interactions on the electrostatic force in an array of spherical particles by Ghassan F. Hassan; Adel O. Sharif; Ugur Tuzun; Andy Tate (232-235).
Comparison of the dimensionless electrostatic force as a function of the reduced separation distance, between two similarly charged spheres in different configurations, for conditions of reduced surface potential and reduced sphere radius of unity.The effect of many-body interactions on the electrostatic force between spheres in an array of charged spherical particles has been quantified by solving the non-linear Poisson–Boltzmann equation (PBE) using a finite element method (FEM) model. The equation is solved for conditions of constant surface potential. The effect of the dimensionless Debye length scaled radius of the spheres on the electrostatic force between them has been determined and a significant reduction of the force is observed as the dimensionless Debye radius is decreased. Calculations based on the dimensionless separation distance between a pair of charged spheres in isolation confirm an exponential decay of the repulsive electrostatic force as the surface to surface separation distance is increased. In contrast, calculations based on an array of interacting spheres in certain critical packing conditions reveal considerable reduction in the magnitude of the repulsive electrostatic force at separation distances less than half the sphere radius. The latter results are explained by considering the directional cancellation effects of the electrical double layer between adjacent spheres placed in certain orientations within the array. This is believed to be a surprising many-body effect which has been overlooked in previous studies and whose validity can be used to explain the stability and strength of charged sphere arrays under certain critical geometric configurations.
Keywords: Colloidal particle; Electrostatic force; Multi-body interactions; Non-linear Poisson–Boltzmann equation; Finite element analysis;
Effect of hydrophilicity of polyaniline particles on their electrorheology: Steady flow and dynamic behaviour by Martin Stěnička; Vladimír Pavlínek; Petr Sáha; Natalia V. Blinova; Jaroslav Stejskal; Otakar Quadrat (236-240).
Rheological behaviour of polyaniline particles protonated with different acids, resulting in various contact angles (36°, 61°, 88° and 102°), suspended in silicone oil was investigated at several electric field strengths.Electrorheological properties of suspensions are considerably affected by hydrophilicity of suspension particles. As a model material, polyaniline base powder protonated with sulfamic, tartaric, or perfluorooctanesulfonic acids provided particles of various hydrophilicity. The experiments revealed that, in the absence of electric field, due to a good compatibility of hydrophobic polyaniline particles with silicone-oil medium, their interactions were limited and the viscosity of suspension was low. When the electric field was applied, the rigidity of the polarized chain structure of the particles increased and, consequently, viscosity increased as well. In the contrast, the field-off suspension viscosity of highly interacting hydrophilic particles, which are incompatible with the oil, and where particle aggregation may set in, was high especially at low shear rates, and the material had a pseudoplastic character. Then, a relative increase in viscosity due to the polarization of the particles or their clusters in the electric field was much lower than in the former case. Due to a different primary structure of suspension, depending on the particle compatibility with the oil the field-off storage modulus of suspensions of hydrophobic particles was lower than the loss modulus, while in suspensions of hydrophilic particles the former modulus dominated. In both cases, an increase in elasticity with increasing electric field strength was higher than that in viscosity.
Keywords: Polyaniline; Electrorheology; Steady shear; Oscillatory shear; Hydrophilicity; Hydrophobicity;
Reversible conversion of water-droplet mobility from rollable to pinned on a superhydrophobic functionalized carbon nanotube film by Jin Yang; Zhaozhu Zhang; Xuehu Men; Xianghui Xu; Xiaotao Zhu (241-247).
Superhydrophobic poly(acrylic acid)-block-polystyrene functionalized carbon nanotube films were fabricated, and reversible switching of water-droplet mobility from rollable to pinned on the same surface was realized.Poly(acrylic acid)-block-polystyrene (PAA-b-PS) functionalized multiwall carbon nanotubes (MWNTs) were prepared by nitroxide-mediated “living” free-radical polymerization. The product functionalized MWNTs (MWNT-PAA-b-PS) contained 20% by weight PAA-b-PS based on the infrared spectroscopy analysis and thermal gravimetric analysis. Such MWNT-PAA-b-PS nanoparticles can be used in spray coating method to fabricate superhydrophobic MWNT films, and water-droplet mobility on the superhydrophobic film can be reversibly converted from rollable to pinned through adjusting the appearance of PAA chains on the topmost surface of the film. Switching mechanism has been discussed in detail. We also directly observed the air–solid–liquid interface from the above of a water droplet by a microscope to confirm the superhydrophobic states, and proved that the transition between the wettability states appeared on the same surface with reversible conversion of water-droplet mobility.
Keywords: Carbon nanotubes; Poly(acrylic acid)-block-polystyrene; Superhydrophobic; Reversible; Water-droplet mobility;
The seismoelectric effect: A nonisochoric streaming current by A.S. Dukhin; V.N. Shilov (248-253).
Propagation of ultrasound through a porous body saturated with liquid generates an electric response, which is called “seismoelectric current.” It can be described as “streaming current” under nonisochoric conditions when compressibility becomes important. Seismoelectric currents can be measured with electroacoustic devices originally designed for characterizing liquid dispersions. This effect can be used for characterizing ζ-potential, porosity, and pore size of porous bodies.Propagation of ultrasound waves through a porous body saturated with liquid generates an electric response. This electroacoustic effect is called the “seismoelectric current”; the reverse phenomenon, where an electric field is the driving force, is known as the “electroseismic current”. The seismoelectric current can be measured with existing electroacoustic devices that were originally designed to characterize liquid dispersions. The versatility of electroacoustic devices allows them to be calibrated using dispersions and then applied to the characterization of porous bodies. Here, we present the theory of the seismoelectric effect, which we derived by following the path suggested 65 years ago by Frenkel. To verify this theory, we measured the seismoelectric current generated by sediments of micrometer-sized silica particles. We demonstrated that the measurement allowed the determination of porosity of the sediment and the calculation of the ζ-potential. The ζ-potential value, calculated using the suggested theory, closely agreed with the value independently measured for moderately concentrated dispersions using a well-known electroacoustic theory for dispersions. Measurements of the seismoelectric effect with existing electroacoustic probes open up new ways for characterizing the porosity and ζ-potential of porous bodies, including ones with low permeability.
Keywords: Streaming current; Siesmoelectric effect; Electroacoustics; Porous body; Porosity; Pore size; ζ-Potential;
Performance of PDMS membranes in pervaporation: Effect of silicalite fillers and comparison with SBS membranes by A. Dobrak; A. Figoli; S. Chovau; F. Galiano; S. Simone; I.F.J. Vankelecom; E. Drioli; B. Van der Bruggen (254-264).
Incorporation of silicalites into PDMS network improved selectivity due to reduction of swelling. Performance of novel dense SBS membranes was found to be promising in alcohol/water separations.Laboratory-made silicalite filled PDMS membranes were tested by means of concentration and temperature influence on the membrane performance in removal of ethanol from ethanol/water mixtures. This allowed studying the applicability of solution-diffusion model in the transport mechanism description. Experiments were performed by varying the ethanol concentration in the feed and temperature. Two types of fillers were incorporated into the PDMS network: commercial zeolite silicalite (CBV 3002) and laboratory-made colloidal silicalite-1. Obtained results were then compared with data gathered for unfilled PDMS membranes to examine the effect of fillers incorporation. Moreover, the comparison with novel block co-polymer based porous and dense SBS membranes was done. It was found that the solution-diffusion model was a good representation of ethanol transport through both filled and unfilled PDMS membranes, whereas the water flux did not obey this model due to the swelling effects. Incorporation of the fillers increased membrane stability and improved the selectivity. Performance of the SBS membranes characterized by a dense structure was found to be similar to the performance of filled PDMS membranes.
Keywords: PDMS membranes; Pervaporation; Solution-diffusion model; Temperature effect; Membrane performance;
A facile methodology for the design of functionalized hollow silica spheres by Ambrose Melvin; R. Vijay; Vijay R. Chaudhari; Bhavana Gupta; Rajiv Prakash; Santosh Haram; Geetha Baskar; Deepa Khushalani (265-269).
A versatile synthesis of hollow silica spheres using LET is detailed. The silica spheres were further used as a template for directing the synthesis of silica–silver and silica–polyanthranilic composite spheres.A new amino acid derived amphiphile, lauryl ester of tyrosine (LET) is shown to provide a facile methodology for the preparation of hollow silica spheres. In a previous study on the interface adsorption, it was shown that phenolic OH group in LET plays a key role in the formation and stabilization of close packed structures, typically at the oil/water interface. Drawing an analogy between the air/water and the oil/water interface, we detail here a procedure where air droplets are capped with LET aggregated structures, and in turn they are utilized as viable templates in the production of hollow silica spheres. We demonstrate that hollow silica spheres are formed at pH 4.0 specifically under conditions of vortexing within a short period of time (ca. 15 min). The dimensions of the structures are 0.43 ± 0.15 μm in diameter and they have then subsequently been used as templates for directing the synthesis of silica–silver and silica–polyanthranilic composite hollow spheres.
Keywords: Sol–gel; Composites; Surfactants;
Deformation of a long elastic particle undergoing electrophoresis by T.N. Swaminathan; Tong Gao; Howard H. Hu (270-276).
In electrophoresis a long elastic particle tends to curl up at its ends and arches in the middle, due to the viscous stress acting on its surface.The motion and deformation of a long elastic particle undergoing electrophoresis has been studied numerically and analytically. The particle is elliptical in shape and is initially aligned with its major axis perpendicular to the direction of a uniformly applied electric field. The particle tends to curl up at its ends and arches in the middle as it moves. The deformation of the particle is due to the viscous stress acting on the particle surface. The results from the simulation are explained by evaluating the surface force distribution on a long thin object under similar conditions. The pressure due to the inertia of the flow has a negligible effect on this deformation.
Keywords: Electrophoresis; Coiling; Curl up; Deformable particle;
by Arthur Hubbard (277).