Journal of Colloid And Interface Science (v.283, #2)
Editorial Board (OFC).
Sorption of divalent metal ions on CrPO4 by S. Mustafa; S. Murtaza; A. Naeem; K. Farina (287-293).
The divalent metal ion sorption (Cu2+, Cd2+, Ni2+, and Pb2+) on chromium phosphate (CrPO4) was studied as a function of pH, temperature, and concentration of metal ions. The sorption of metal ions is observed to increase with the increase in pH, temperature, and concentration of metal ions in solution. The mechanism of sorption is found to be the exchange of the hydrolyzed metal cations with the protons from solid at high temperature. The sorption at low temperature is found to be accompanied by the precipitation of the corresponding metal phosphates such as Pb3(PO4)2.
Keywords: Ion exchange; Sorption; Metal phosphates; CrPO4; Metal ions;
Studies on the adsorption of Brij-35 and CTAB at the coal–water interface by S.K. Mishra; D. Panda (294-299).
The adsorption behavior of polyoxyethylene (23) lauryl ether (Brij-35) and cetyl trimethyl ammonium bromide (CTAB) on coal sample has been studied. The adsorption process is found to be sensitive to pH, temperature, electrolyte concentration, and the amount of surface active agent. An attempt has been made to explain the adsorption behavior of the surfactants using the Langmuir equation. The extent of adsorption of Brij-35 on coal is found to be the highest at pH 2, which decreases with increase in pH and remains constant in the neutral and alkaline pH regions. But, the adsorption of CTAB exhibits the opposite behavior of that of Brij-35. Adsorption of any of the surfactant at the coal/water interface sharply decreases the apparent viscosity of 55 wt% coal–water slurry (CWS) at a shear rate of 100 s−1. Electrostatic adsorption of the surfactants on the coal surface decreases the surface charge and renders the coal surface hydrophobic which is manifested in the form of high apparent viscosity of the coal–water slurry under the test conditions.
Keywords: Adsorption; Brij-35; CTAB; Coal; Rheology; Apparent viscosity;
Metal-modified silica adsorbents for removal of humic substances in water by Takeshi Moriguchi; Kazuyuki Yano; Muneaki Tahara; Kazuhiko Yaguchi (300-310).
As novel adsorbents for humic substances, Fe-, Mg-, and Ca-modified silica gels SiO2 ―Fe, SiO2 ―Mg, and SiO2 ―Ca were prepared, and their adsorbabilities to humic and fulvic acids were evaluated in water at 25 °C for 20 h. Among these adsorbents, SiO2 ―Fe indicated the highest adsorbability, in which removing humic substances in water was accomplished to 80–97%. By calcination at 600 °C and washing with water, adsorbabilities of the silica adsorbents deteriorated except for the case of calcination of SiO2 ―Ca. This is due to changing metal modification structures and losing chlorine, judging from elemental analysis, TG-DTA, and XPS. Especially, the modifier Fe was tightly fixed on the silica surface of SiO2 ―Fe, since the metal content was almost constant even after the calcination and water washing unlike the other adsorbents. Therefore, we found that SiO2 ―Fe is the most useful adsorbent among the silica adsorbents and that its modification structure is composed of Si―O―Fe, Fe―Cl, and Fe―OH. In addition, the adsorption mechanism is explained by an interaction between Fe and humic substance molecule having carboxylate and phenolate groups, accompanied with anion exchange of chloride ion Cl− for the humic substance molecule via the silica pores. SiO2 ―Fe may be applied to an adsorbent alternative for charcoal in water purification plants, and the used SiO2 ―Fe may be further reused as a fertilizer since humic substances have plant-glowing ability and silica strengthens plant parts.
Keywords: Humic substances; Humic acid; Fulvic acid; Silica gel; Metal; Chlorine; Adsorbability; Charcoal; Water purification plant;
Role of copper chloride on the surface of activated carbon in adsorption of methyl mercaptan by Dae Jung Kim; Jae Eui Yie (311-315).
In this paper, adsorption characteristics of methyl mercaptan on virgin activated carbon and copper chloride impregnated activated carbons were studied by using a dynamic adsorption method in a fixed bed. The activated carbons were characterized by nitrogen adsorption, XRD, TGA and solubility tests. The impregnation of copper chloride on the activated carbon significantly enhanced the adsorption capacity of methyl mercaptan, despite a notable decrease in microporosity. It is likely that copper chloride may act as adsorption site for methyl mercaptan. Copper chloride on the activated carbon in a range of 3–20 wt% Cu content was present mostly in the amorphous form of CuCl2, according to the results of the solubility, XRD and TGA tests. Starting at 10 wt% in Cu loading, the adsorption capacity for methyl mercaptan decreases gradually. It is likely that a decrease in the degree of copper chloride dispersion and an accessibility of small pores may lead to the decrease in the adsorption capacity of the activated carbon for methyl mercaptan.
Keywords: Methyl mercaptan; Copper chloride; Activated carbon; Pore structure; Adsorption;
The adsorption of Cu(II) ions on bentonite—a kinetic study by M.H. Al-Qunaibit; W.K. Mekhemer; A.A. Zaghloul (316-321).
The kinetics of sorption of Cu2+ on a Saudi clay mineral (bentonite) was investigated at 20 ± 0.5 ° C using different weights of the clay (0.5, 1.0, 1.5, and 2 g). Each weight represents a certain sample size. The order of the process appeared to be 1 with respect to the Cu2+, and 1 1 2 with respect to the clay surface area. The rate was found to depend on internal diffusion.,which produced a decrease in the specific rate of sorption as a function of time. Sorption characteristics were described using two site Langmuir isotherms. The desorption experiments proved that Cu2+ ions are chemisorbed on the bentonite surface. The maximum adsorption obtained was 909 mg Cu2+/g clay. This value is of great significance, as it is much higher than any reported one.
Keywords: Bentonite; Sorption; Kinetics; Desorption; Cu2+ ions;
Monolayer formation of PBLG–PEO block copolymers at the air–water interface by Youngmi Park; Young-Wook Choi; Sangwook Park; Chong Su Cho; Michael J. Fasolka; Daewon Sohn (322-328).
Physicochemical properties of PBLG (poly(γ-benzyl-l-glutamate))–PEO (poly(ethylene oxide)) diblock copolymers composed of PBLG as the hydrophobic rod component and PEO as the hydrophilic component were investigated at the air–water interface. Surface pressure–area isotherms obtained by the Wilhelmy plate method provide several variables such as molecular size, compressibility of PEO, and the free energy change of the PBLG–PEO block copolymer. GE-1 ( M w of PBLG:PEO = 103,700:12,000 ), with a relatively longer rod, has negative temperature effects and GE-3 ( M w of PBLG:PEO = 8400:12,000 ), with a relatively shorter rod, shows a positive temperature effect because of the large entropy loss. These competitions were based on the block size of PBLG and PEO and were affected by various microstructures of the PBLG–PEO diblock copolymer. Monolayer aggregations transferred onto mica from the air–water interface were analyzed with AFM. AFM images of GE-1 monolayers show cylindrical micelles, but the self-assembled structure has many large domains. The monolayer of GE-2 ( M w of PBLG:PEO = 39,800:12,000 ), which has a medium size rod, forms a spherical structure at the air–water interface. Monolayers of GE-3, with a short rod length, form bilayer structures. These results demonstrate that the microstructures of PBLG–PEO diblock copolymers are related to free energy changes between rod and coil blocks.
Keywords: PBLG–PEO; Langmuir–Blodgett; Compressibility; Block copolymer; Surface pressure;
Structured water in partially dehydrated yeast cells and at partially hydrophobized fumed silica surface by V.V. Turov; V.M. Gun'ko; V.M. Bogatyrev; V.I. Zarko; S.P. Gorbik; E.M. Pakhlov; R. Leboda; O.V. Shulga; A.A. Chuiko (329-343).
Nonfreezable water structured due to interaction with endocellular objects in yeast cells (endocellular water) or with partially hydrophobic fumed silica (interfacial water) was studied by means of 1H NMR spectroscopy with layer-by-layer freezing-out of bulk water and quantum chemical methods applied to water clusters in the gas and liquid (chloroform and cyclohexene) phases and adsorbed on silylated silica. Variation in cell hydration as well as in amount of water adsorbed on modified fumed silica leads to changes in the ratio between contributions of two water states characterized by NMR chemical shifts at δ H = 1.1 – 1.7 and 4–5 ppm. Lowering of hydration and temperature results in an enhancement of the first signal, and the opposite result is observed for the second signal. These effects may be explained by structured water distribution in the form of relatively large nanodroplets ( δ H = 4 – 5 ppm is close to that for bulk water) and small clusters of the 2D structure, in which the fraction of hydrogen atoms out of the hydrogen bonds ( δ H = 1.1 – 1.7 ppm ) is larger than that in nanodroplets.
Keywords: Yeast Saccharomyces cerevisiae cells; 1H NMR spectroscopy; AFM; SEM; TSDC; Freezing-out of water; Bound nonfreezable water; Modified fumed silica; Structural characteristics;
Physicochemical characterization of chitosan nanoparticles: electrokinetic and stability behavior by T. López-León; E.L.S. Carvalho; B. Seijo; J.L. Ortega-Vinuesa; D. Bastos-González (344-351).
Some physical properties of nanogel particles formed by chitosan ionically cross-linked by tripolyphosphate (TPP) have been studied. Electrokinetic properties and colloidal stability were analyzed as a function of pH and ionic strength of the medium. Chitosan particles showed volume phase transitions (swelling/shrinking processes) when the physicochemical conditions of the medium were changed. Experimental data were mainly obtained by electrophoretic mobility measurements and by photon correlation spectroscopy and static light scattering techniques. Chitosan chains possess glucosamine groups that can be deprotonated if the pH increases. Therefore, modification of pH from acid to basic values caused a deswelling process based on a reduction of the intramolecular electric repulsions inside the particle mesh. Electrophoretic mobility data helped to corroborate the above electrical mechanism as responsible for the size changes. Additionally, at those pH values around the isoelectric point of the chitosan–TPP particles, the system became colloidally unstable. Ionic strength variations also induced important structural changes. In this case, the presence of KCl at low and moderate concentrations provoked swelling, which rapidly turned on particle disintegration due to the weakness of chitosan–TPP ionic interactions. These last results were in good agreement with the predictions of gel swelling theory by salt in partially ionized networks.
Keywords: Electrophoretic mobility; Colloidal stability; Gel phase transitions; Chitosan nanoparticles;
Surface modification of monodisperse magnetite nanoparticles for improved intracellular uptake to breast cancer cells by Yong Zhang; Jing Zhang (352-357).
Nanoparticles have been widely used for a variety of biomedical applications and there is a growing need for highly specific and efficient uptake of the nanoparticles into target cells. Poly(ethylene glycol) (PEG), folic acid (FA), and their conjugate PEG-FA were attached to magnetite nanoparticles to compare their effects on the improvement of intracellular uptake of the nanoparticles to human breast cancer cells, BT-20. AFM and TEM results indicated that the nanoparticles after surface modification were monodisperse, with coatings on individual nanoparticles. The cell culture experiments showed that the PEG-FA coated nanoparticles were internalized into BT-20 cancer cells and exhibited higher efficiency of intracellular uptake than only PEG- or FA-coated nanoparticles. The surface modification protocols can also be used to modify the surfaces of other nanoparticles for targeting intracellular delivery.
Keywords: Magnetite nanoparticles; PEG; Folic acid; PEG-FA; Intracellular uptake;
Fengycin interaction with lipid monolayers at the air–aqueous interface—implications for the effect of fengycin on biological membranes by Magali Deleu; Michel Paquot; Tommy Nylander (358-365).
In this study, we investigated the interaction of fengycin, a lipopeptide produced by Bacillus subtilis, with lipid monolayers using the Langmuir trough technique in combination with Brewster angle microscopy. Thermodynamic analyses were performed to get further information about the mixing behavior and the molecular interactions between the two components. The effect of fengycin on the structural and morphological characteristics of DPPC monolayers, as a simple model of biological membranes, depends on the fengycin molar ratio. With a small proportion of fengycin ( X f ⩽ 0.1 ), the compressibility of the monolayer is modified but the morphological characteristics of the DPPC are not significantly affected. At an intermediate molar ratio ( 0.1 < X f ⩽ 0.5 ), fengycin has a fluidizing effect on the DPPC monolayer by interacting partially with DPPC molecules. At higher molar ratio ( X f = 0.66 ), fengycin totally dissolves the ordered phase of the lipid. These results highlight the capacity of fengycin to perturb the DPPC organization and are discussed in relation to fengycin capacity to affect biological membranes.
Keywords: Lipopeptide; DPPC; Isotherm; Thermodynamic analysis; BAM;
Controlling submicron-particle template morphology: effect of solvent chemistry by Maria M. Cortalezzi; Vicki Colvin; Mark R. Wiesner (366-372).
Porous solids were obtained from self-assembled deposits of silica particles used as templates to form 3-D porous membranes. The effect of the solvent chemistry on the morphology of the deposits was investigated. The parameters of interest are surface tension and ionic strength of the solvent, as they impact electrostatic and capillary interactions. Deposits of particles of different sizes were obtained from a variety of conditions. The deposits were imaged by SEM and showed distinctive structures for each of the solvent chemistries. The phenomenon is qualitatively consistent with DLVO theory and calculations of capillary interaction energy as developed by Kralchevsky and co-workers.
Swelling behavior of organoclays in styrene and exfoliation in nanocomposites by X.A. Fu; S. Qutubuddin (373-379).
Organoclays were prepared by cationic exchange of montmorillonite (MMT) with three commercial surfactants: octadecylamine (ODA), hexadecyltrimethylammonium bromide (HTAB), benzalkonium chloride (BAC), and an in-house synthesized surfactant, vinylbenzylalkyldimethylammonium chloride (VDAC). The swelling behaviors of organoclays in styrene were compared by wettability and rheology measurements. VDAC-MMT had the slowest capillary rise rate in styrene. The Washburn equation was found not suitable for the swellable organoclay powders. All organoclay–styrene and organoclay–toluene mixtures demonstrated yield stress. However, VDAC-MMT–styrene and VDAC-MMT–toluene mixtures showed significant higher yield stresses than the other organoclay mixtures. The wettability and rheology measurements indicate that VDAC-MMT bearing a styryl functional group has the strongest interaction with styrene monomer and toluene. In order to further evaluate the extent of swelling and the microstructure, polystyrene (PS)–clay nanocomposites were prepared by in situ polymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that ODA and HTAB-MMT led to intercalated PS–clay nanocomposites, while VDAC-MMT formed exfoliated PS–clay nanocomposites.
Keywords: Organoclays; Swelling behavior; Surfactants; Dispersion; Polymer nanocomposites;
Preparation of ZnO colloids by aggregation of the nanocrystal subunits by L. Dong; Y.C. Liu; Y.H. Tong; Z.Y. Xiao; J.Y. Zhang; Y.M. Lu; D.Z. Shen; X.W. Fan (380-384).
Colloidal ZnO particles with narrow size distribution were prepared via a sol–gel process by base-catalyzed hydrolysis of zinc acetate. The morphology of ordered arrays of the particles was recorded by SEM. SEM also reveals that these uniform particles were composed of tiny ZnO subunits (singlets) sized of several nanometers. The size of the singlets, which is confirmed by X-ray diffraction and UV–vis absorption spectra, increases as the aging time is prolonged. The size-selective formation of colloids by aggregation of nanosized subunits is proposed to consist of two-stage growth by nucleation of nanosized crystalline primary particles and their subsequent aggregation into polycrystalline secondary colloids. The aggregates are all spherical because the internal rearrangement processes are fast enough. The ZnO colloids, i.e., the aggregates, tend to self-assemble into well-ordered hexagonal close-packed structures. Room-temperature photoluminescence was characterized for green and aged ZnO.
Keywords: Sol–gel processing; Colloidal ZnO particles; X-ray diffraction; UV–vis absorption spectrum; Scanning electron microscopy; Photoluminescence; Self-assembly;
Interfacial-chemistry mediated behavior of colloidal talc dispersions by Kristen E. Bremmell; Jonas Addai-Mensah (385-391).
Interfacial chemistry and rheological behavior of talc suspensions as a function of pH, talc solid content, and type and concentration of ions have been investigated using electrokinetic measurements, rheology, settling behavior, and solution analysis. Zeta potential measurements show a strong dependence on the pH history of the talc suspension that only occurs when the surface area (solid content) of the talc is high. Particle interactions measured through dispersion yield stress measurements show a similar dependence. Talc is a magnesium silicate mineral and the dependence seen in the electrokinetic properties in this study has been attributed to Mg(II) dissolution at low pH, and has been confirmed by solution analysis. At high solid content ( > 20 wt% ), pronounced Mg(II) ion dissolution occurs at low pH values. Formation and adsorption of electropositive Mg(II) hydrolysis products occurs at high pH (>9), and these lead to zeta potential reduction and, at high solid contents, charge reversal. Particle interactions reflect the surface chemistry behavior. Consequently, for a freshly prepared suspension at high pH, the yield stress is lower compared to after the pH has been taken to 5 and subsequently increased.
Keywords: Clay; Talc; Interfacial chemistry; Rheology; Metal ions; Dewatering;
Silica coating of silver nanoparticles using a modified Stöber method by Yoshio Kobayashi; Hironori Katakami; Eiichi Mine; Daisuke Nagao; Mikio Konno; Luis M. Liz-Marzán (392-396).
Silver nanoparticles prepared through a borohydride-reduction method were directly coated with silica by means of a seeded polymerization technique based on the Stöber method. Various amine catalysts were used for initialization of a sol–gel reaction of TEOS with no need for a prior surface modification. Use of dimethylamine (DMA) as a catalyst was found to be necessary to obtain a proper coating. The silica shell thickness was varied from 28 to 76 nm for TEOS concentrations of 1–15 mM at 11.1 M water and 0.8 M DMA. The optical spectra of the core–shell silver–silica composite particles show a qualitative agreement with predictions by Mie theory.
Keywords: Silver; Nanoparticle; Silica; Sol–gel; Coating; Stöber method; Seeded polymerization; Core–shell; Surface plasmon resonance; Mie theory;
Revised state diagram of LAPONITE® dispersions by Philippe Mongondry; Jean François Tassin; Taco Nicolai (397-405).
We propose a state diagram of charged disk-like mineral particle (LAPONITE®) dispersions as a function of the LAPONITE® concentration (C) and the concentration of added salt ( C s ), based on simple observation and light-scattering measurements. At low C or high C s the dispersions separate into two domains due to sedimentation of LAPONITE® aggregates, while at high C and low C s they form homogeneous gels that do not flow upon tube reversal. The aggregation rate and the structure factor of the LAPONITE® dispersions is determined with light scattering as a function of C and C s . We discuss in detail the controversy on the origin of gelation of LAPONITE® dispersions in the absence of added salt. We argue that aggregation rather than glass formation causes gelation.
Keywords: LAPONITE®; Aggregation; Gelation; Disk-like colloid;
Cationic-modified cyclodextrin nanosphere/anionic polymer as flocculation/sorption systems by Huining Xiao; Norlito Cezar (406-413).
Simultaneous removal of dissolved and colloidal substances has been a challenging task. The cationic-modified β-cyclodextrin nanospheres synthesized in this work, in conjunction with a water-soluble polyacrylamide-based anionic polymer, potentially provide a novel approach to address the problem. The cyclodextrin was rendered cationic using (2,3-epoxypropyl)trimethylammonium chloride as a reagent. The cationicity of the modified cyclodextrin and the reaction between cyclodextrin and the reagent were characterized by electrophoresis measurement, polyelectrolyte titration, and NMR. As a dual-component flocculation system, the cationic cyclodextrin/anionic polymer significantly induced clay flocculation, lowering the relative turbidity of the clay suspension over a wide pH range. Meanwhile, as a nanospherical absorbent, the modified cyclodextrins exhibited strong affinity toward aromatic compounds via inclusion complex formation in the hydrophobic cavities, which was monitored by UV spectroscopy. These systems facilitated the simultaneous removal of dissolved and colloidal substances, which was unachievable previously. In addition, the interaction between anionic polymers and the clay particles pretreated with cationic cyclodextrin was investigated in order to reveal the flocculation mechanism.
Keywords: Cationic cyclodextrin; Clay flocculation; Anionic polymer; Inclusion complex formation; Sorption;
The feasibility of inert colloidal processing of silicon nanoparticles by Michele L. Ostraat; Harry A. Atwater; Richard C. Flagan (414-421).
Silicon nanoparticles have important applications, including nonvolatile floating-gate memory devices. To prevent device performance variations, particle size and oxide thicknesses need to be controlled with a high degree of precision. Additionally, producing well-ordered, two-dimensional arrays of nanoparticles may require the exploitation of self-assembly techniques and colloidal forces, which in turn requires that silicon nanoparticles first come into contact with liquids. Until recently, aerosol silicon nanoparticle collection into liquid was assumed to be an inert process. Once formed, the silicon nanoparticle colloid was assumed to be inert. In fact, silicon nanoparticles produced in the aerosol phase by dilute silane pyrolysis and size classified with a differential mobility analyzer undergo a size reduction upon collection in ethylene glycol, water, and ethanol. Unclassified polydisperse silicon aerosol nanoparticles with an average diameter of 11 nm become monodisperse when collected in a colloid and have a final particle diameter of 2–5 nm. Further evidence suggests that silicon nanoparticles collected in ethanol react with the ethanol to produce tetraalkylorthosilicate-like species. Collections of aerosol silicon nanoparticles in degassed water do not show measurable differences between the aerosol and colloidal size distributions. This reduced reactivity to the solvent indicates that the presence of dissolved oxygen in the solvent may be responsible for the reactivity between the silicon nanoparticles and the solvent.
Keywords: Aerosol; Nanoparticle; Colloid; Silicon; Passivation; TEOS; Colloid stability; Nanoparticle reactivity;
Phase transfer of oleic acid capped NicoreAgshell nanoparticles assisted by the flexibility of oleic acid on the surface of silver by Tanushree Bala; Anita Swami; B.L.V. Prasad; Murali Sastry (422-431).
The phase transfer protocols in vogue for the oleic acid capped silver nanoparticles, viz., salt-induced precipitation and redispersion or phosphoric acid-induced method, are examined and compared thoroughly. A comprehensive evaluation with respect to the mechanistic aspects involved is made and the merits and demerits of the different procedures are delineated. It is found that the salt-induced precipitation and redispersion is more versatile in that the precipitate can actually be redispersed in both aqueous and organic media. However, in terms of mechanism both the routes seem to be very similar wherein the orientational change of oleic acid on the silver surface in the two different environments—organic and aqueous—plays a crucial role in the adaptability of the system to the different environments. Subsequently, this change of orientation of oleic acid on silver surface in aqueous and organic media has been utilized to phase transfer Ni-based nanoparticulate systems. The nascent oleic acid-capped Ni nanoparticles, which were synthesized by a foam-based protocol, were dispersible in water but not in nonpolar organic media such as cyclohexane or toluene. Then, just by coating a thin shell of silver on them we could achieve complete phase transfer of the NicoreAgshell from aqueous to organic media following similar procedures used for oleic acid-capped silver nanoparticles. Here, the phase transfer seems to be facilitated by the orientational flexibility of oleic acid on the silver surface as opposed to other metal surfaces as evidenced from the infrared and thermogravimetric analyses of oleic acid-capped Ni and NicoreAgshell nanoparticles. This orientation-assisted phase transfer method could be generalized and can be adapted to other systems where, if the nascent nanoparticles cannot be phase transferred as is, they can be coated by a silver shell and oleic acid making them suitable for dispersion in both aqueous and organic media.
Keywords: Phase transfer; Transmetalation; Core–shell nanoparticles; FTIR; 1H NMR; UV–vis;
Effects of vinyl series polymers on the formation of hematite particles in a forced hydrolysis reaction by Kazuhiko Kandori; Yukihiro Yamoto; Tatsuo Ishikawa (432-439).
The influence of polymers on the formation of hematite particles from forced hydrolysis of acidic FeCl3 solution was investigated using vinyl series polymers with different functional groups. The disk-like hematite particles were produced from forced hydrolysis of acidic FeCl3 solution in the presence of polyvinyl alcohol (PVA: 0–1 wt%). On the other hand, spherical particles were produced by addition of very small amounts of polyacrylamide (PAAm: 0–0.004 wt%). The size of spherical particles was slightly decreased with increase in the concentration of PAAm. The ellipsoidal particles were precipitated by addition of a very low concentration of polyacrylic acid (PAAc: 0–0.004 wt%). The effect of polymers on the hematite particle formation was expressed in the order of PVA < PAAm < PAAc that is in the reverse order from their average molecular weight. Therefore it was concluded that the effects of polymer molecules strongly depend on the functional groups of polymers. The secondary reduction steps of the concentration of Fe3+ ions ([Fe]) were observed during aging. This secondary step of [Fe] corresponded to the time of the complete phase transformation from β-FeOOH to hematite. Thus one was forced to conclude that the dissolution of β-FeOOH particles is a rate-determining step in the reaction sequence for the systems with polymers. A rotational particle preparation procedure suggested that the morphology of hematite particle is governed by the mode and strength of polymer adsorption onto β-FeOOH and polynuclear primary particles.
Keywords: Hematite; Disk-like particle; Ellipsoidal particle; Aggregate; Effects of polymers; Forced hydrolysis reaction; Polyvinyl alcohol; Polyacrylamide; Polyacrylic acid; Micropores; Mesopores;
Influence of configuration of carboxylic acid capping ligands on the salt-induced aggregation of gold clusters by Di Li; Yunjie Huang; Jinghong Li (440-445).
Oxalic acid (Ox) and 1,2,3,4-cyclobutanetetracarboxylic acid (CBTCA) were employed as capping ligands in the preparation of gold colloids. FTIR indicated that Ox adopted a linear configuration through one oxygen atom and one gold atom, while CBTCA adopted a bridge configuration through two oxygen atoms and two gold atoms. Ox–gold colloids exhibited aggregation upon addition of NaClO4, while they remained as isolated particles upon NaCl. For CBTCA–gold colloids, not NaClO4 but NaCl resulted in aggregation. The reversed results were considered to have been influenced by the different configurations of Ox and CBTCA, which were combined results of the Lewis basicity and steric hindrance of the added ions.
Keywords: Gold colloid; Carboxylic acid; Configuration; Salt-induced aggregation;
Preparation and adsorption properties of monodisperse chitosan-bound Fe3O4 magnetic nanoparticles for removal of Cu(II) ions by Yang-Chuang Chang; Dong-Hwang Chen (446-451).
Monodisperse chitosan-bound Fe3O4 nanoparticles were developed as a novel magnetic nano-adsorbent for the removal of heavy metal ions. Chitosan was first carboxymethylated and then covalently bound on the surface of Fe3O4 nanoparticles via carbodiimide activation. Transmission electron microscopy micrographs showed that the chitosan-bound Fe3O4 nanoparticles were monodisperse and had a mean diameter of 13.5 nm. X-ray diffraction patterns indicated that the magnetic nanoparticles were pure Fe3O4 with a spinel structure, and the binding of chitosan did not result in a phase change. The binding of chitosan was also demonstrated by the measurement of zeta potential, and the weight percentage of chitosan bound to Fe3O4 nanoparticles was estimated to be about 4.92 wt%. The chitosan-bound Fe3O4 nanoparticles were shown to be quite efficient for the removal of Cu(II) ions at pH > 2 . In particular, the adsorption rate was so fast that the equilibrium was achieved within 1 min due to the absence of internal diffusion resistance. The adsorption data obeyed the Langmuir equation with a maximum adsorption capacity of 21.5 mg g−1 and a Langmuir adsorption equilibrium constant of 0.0165 L mg−1. The pH and temperature effects revealed that the adsorption capacity increased significantly with increasing pH at pH 2–5, and the adsorption process was exothermic in nature with an enthalpy change of − 6.14 kJ mol −1 at 300–330 K.
Keywords: Chitosan; Magnetic; Nanoparticles; Adsorbent; Cu(II);
Raman spectroscopic study on the structure of water in aqueous solution of α , ω -amino acids by Hiromi Kitano; Kohei Takaha; Makoto Gemmei-Ide (452-458).
The structure and hydrogen bonding of water in an aqueous solution of various α , ω -amino acids were analyzed using the contours of the O―H stretching in the polarized Raman spectra. From the relative intensity of the collective band (C value) corresponding to a long-range coupling of the O―H stretching in the aqueous amino acid solutions, the number of hydrogen bonds disrupted due to the presence of one amino acid molecule ( N corr value) was evaluated. The N corr value for glycine was slightly positive, whereas with an increase in the number of methylene groups between ammonium and carboxylate groups, the N corr value gradually increased. These results suggest that the species with proximal anionic and cationic groups do not disturb the hydrogen-bonded network structure of water significantly, probably due to the counteraction of the electrostatic hydration effect attributable to the anionic and cationic groups.
Keywords: Amino acid; Collective band; Hydrogen-bonded network; Raman spectroscopy; Structure of water; Zwitterionic molecule;
SERS of C60/C70 on gold-coated filter paper or filter film influenced by the gold thickness by Zhixun Luo; Yan Fang (459-463).
SERS of C60/C70 adsorbed on gold nanoparticles coated on filter paper or filter film was studied. As a new SERS substrate, dried gold-coated filter paper or filter film has a high SERS activity, whose enhancement factor can be up to about 105, because it avoided the influence of solvents in C60/C70 solution and water in gold hydrosols. The influence of the gold thickness coated on filter paper or filter film to SERS of C60/C70 adsorbed on gold nanoparticles was mainly discussed. It is indicated that the SERS effect of C60/C70 was very sensitive to the distribution and aggregated characteristics of gold nanoparticles, and the SERS intensity of each mode increased at its own proportion, but it integrally tended to saturation when the thickness of colloidal gold coatings increased.
Keywords: SERS; C60/C70; Gold nanoparticles;
Morphological and structural characteristics of diazo dyes at the air–water interface: in situ Brewster angle microscopy and polarized UV/vis analysis by Sahori B. Yamaki; Acácio A. Andrade; Cléber R. Mendonça; Osvaldo N. Oliveira; Teresa D.Z. Atvars (464-471).
A morphological analysis is presented for Langmuir films of the diazo dyes Sudan 4 (S4), Sudan 3 (S3), and Sudan red (SR), using Brewster angle microscopy. Stable nonmonomolecular structures are formed at the air–water interface denoted as a plateau in the pressure–area isotherms. Monolayer domains are evident by the contrastless image even before the pressure onset, which grow in size until it reached a condensed monolayer. This behavior resembles that of Langmuir films from simple aromatic fatty acids. Films from all the azo dyes display similar features, according to the surface potential isotherms and in situ polarized UV/vis spectroscopy except for the larger area per molecule occupied by S4 and SR. This is attributed to the presence of CH3 groups that cause steric hindrance modifying the organization of diazo dye molecules at the air–water interface. UV/vis polarized absorption spectroscopy showed preferential orientation of S4 and S3 on the water surface, while SR molecules lie isotropically. For these three diazo dyes, film absorption was negligible at very large areas per molecule, becoming nonzero only at a critical area coinciding with the onset of surface potential. The critical area is ascribed to the formation of a H-bonded network between water molecules and diazo dye headgroups.
Keywords: BAM; Diazo dyes; Polarized UV/vis; Langmuir monolayers;
Effects of the molar ratio of hydroxide and fluoride to Al(III) on fluoride removal by coagulation and electrocoagulation by C.Y. Hu; S.L. Lo; W.H. Kuan (472-476).
The effect of the molar ratio of hydroxide and fluoride ions to Al(III) ions ( γ OH and γ F ) on coagulation and electrocoagulation (EC) was studied to solve the problem of the over addition of acid or base. The efficiency of defluoridation was approximately 100% when the sum of γ OH and γ F ( γ OH + F ) was close to 3. This finding reveals that the fluoride ions and the hydroxide ions can co-precipitate with Al(III) ions and the formula of the precipitate is Al n F m (OH)3n−m . However, when γ OH was less than 2.4, the defluoridation efficiency, given that γ OH + F = 3 , dropped as γ OH fell, because the amount of aluminum polymer formed dropped. The efficiency of defluoridation of EC exceeded that of coagulation for equal γ OH and γ OH + F , when γ OH + F > 3 , proving the existence of an electrocondensation effect.
Keywords: Aluminum; Coagulation; Electrocoagulation; Defluoridation; Fluoride; Molar ratio;
Influence of electrostatic interaction on fibrinogen adsorption on gold studied by imaging ellipsometry combined with electrochemical methods by Yong Yu; Gang Jin (477-481).
Imaging ellipsometry was combined with electrochemical methods for studying electrostatic interactions of protein and solid surfaces. The potential of zero charge for gold-coated silicon wafer/solution interfaces wad determined by AC impedance method. The potential of the gold-coated silicon wafer was controlled at the potential of zero charge, and the adsorption of fibrinogen on the potential-controlled and non-controlled surfaces was measured in real time at the same time by imaging ellipsometry. The effect of electrostatic interaction was studied by comparing the difference between the potential of controlled adsorption and the potential of noncontrolled adsorption. It was shown that the rate of fibrinogen adsorption on the potentiostatic surface was faster than that on the nonpotentiostatic surface. The electrostatic influence on fibrinogen adsorption on the gold-coated silicon wafer was weak, so the hydrophobic interaction should be the major affinity.
Keywords: Electrostatic interaction; Protein adsorption; Imaging ellipsometry; Electrochemistry;
Enhanced efficiency of dye-sensitized TiO2 solar cells (DSSC) by doping of metal ions by Kyung Hyun Ko; Young Cheol Lee; Young Jin Jung (482-487).
Doped TiO2 semiconductor powders were synthesized using Al and W as photovoltaic property-enhancing impurities. Al-doped TiO2 electrodes increased open-circuit voltage ( V oc ), but reduced short-circuit current ( I sc ). In contrast, W-doped TiO2 had an opposite effect. However, dye-sensitized solar cell efficiency fabricated with doped TiO2 was remarkably better than that of undoped TiO2. It seems that these phenomena were related to electrical surface-state modifications induced by metal-ion dopants. These modifications led to significant changes in powder aggregation, charge transfer kinetics, and dye adsorption characteristics. The highest efficiency was found by using (Al + W)-doped TiO2 nanopowders.
Keywords: Photovoltaic; Dye-sensitized solar cell; TiO2; Al; W; Dopants;
Synthesis and properties of supramolecular systems based on silica by Lyudmila A. Belyakova; Konstantin A. Kazdobin; Vladimir N. Belyakov; Sergiy V. Ryabov; Angela F. Danil de Namor (488-494).
The synthesis of mono-tosyl-β-cyclodextrin (Ts-β-CD) and its attachment to the surface of aminopropylsilica are reported. The resulting material was characterized by IR spectroscopy, elemental analysis, and quantitative evaluation of the surface compounds. The maximum amount of β-cyclodextrin (β-CD) grafted on the surface of silica was 60% of the computer-calculated value. The uptake of Cu(II), Cd(II), and Pb(II) ions by this modified material as a function of the pH and salt concentration in the aqueous phase was investigated. It is shown that the silica modified with β-CD has a much greater capacity to uptake these ions than the starting materials. The formation of grafted inclusion compounds of β-cyclodextrin molecules with polymeric hydroxo complexes of metal cations is demonstrated.
Keywords: Silica surface; Aminopropylsilica; Mono-tosyl-β-cyclodextrin; Immobilization; IR spectroscopy; Adsorption; Uptake; Toxic metal cations;
Encapsulation and retention of decanoic acid in sol–gel-made silicas by Susanne R. Veith; Matthias Perren; Sotiris E. Pratsinis (495-502).
Porous sol–gel-made silica particles are investigated as encapsulation matrices for controlled release of substances in food and pharmaceutical applications. Here the retention performance of an entrapped model flavor, decanoic acid, inside silica matrices made by hydrolysis of tetraethyl orthosilicate (TEOS) is studied. The retention of decanoic acid is measured by gas chromatography and thermogravimetric analysis. The morphology, specific surface area, porosity, and pore size distribution of the particle matrix is controlled by the sol–gel preparation method. During drying, the weakly cross-linked polymers in a slowly hydrolyzing silica gel deform and wrap around flavor molecules, creating a denser gel structure. There the flavor molecules are entrapped more efficiently than in fast-hydrolyzing matrices that result in more porous particles. Kinetic annealing studies show that flavor molecules are entrapped quite efficiently even at high temperatures.
Keywords: Sol–gel encapsulation; Particle morphology; Silica; Flavor retention; Decanoic acid;
Ozonation of activated carbons: Effect on the adsorption of selected phenolic compounds from aqueous solutions by P.M. Álvarez; J.F. García-Araya; F.J. Beltrán; F.J. Masa; F. Medina (503-512).
The impact of ozonation on textural and chemical surface characteristics of two granular activated carbons (GAC), namely F400 and AQ40, and their ability to adsorb phenol (P), p-nitrophenol (PNP), and p-chlorophenol (PCP) from aqueous solutions have been studied. The porous structure of the ozone-treated carbons remained practically unchanged with regard to the virgin GAC. However, important modifications of the chemical surface and hydrophobicity were observed from FTIR spectroscopy, pH titrations, and determination of pHPZC. As a rule, the ozone treatment at either room temperature (i.e., about 25 °C) or 100 °C gave rise to acidic surface oxygen groups (SOG). At 25 °C primarily carboxylic acids were formed while a more homogeneous distribution of carboxylic, lactonic, hydroxyl, and carbonyl groups was obtained at 100 °C. The experimental isotherms for phenolic compounds on both GAC were analyzed using the Langmuir model. Dispersive interactions between π electrons of the ring of the aromatics and those of the carbon basal planes were thought to be the primary forces responsible for the physical adsorption whereas oxidative coupling of phenolic compounds catalyzed by basic SOG was a major cause of irreversible adsorption. The exposure of both GAC to ozone at room temperature decreased their ability to adsorb P, PNP, and PCP. However, when ozone was applied at 100 °C adsorption was not prevented but in some cases (P and PNP on F400) the adsorption process was even enhanced.
Keywords: Activated carbon; Phenol; p-Chlorophenol; p-Nitrophenol; Ozone; Adsorption; Surface chemistry;
Effects of thermal annealing on the structural and optical properties of Mg x Zn1−x O nanocrystals by J.H. Li; Y.C. Liu; C.L. Shao; X.T. Zhang; D.Z. Shen; Y.M. Lu; J.Y. Zhang; X.W. Fan (513-517).
Mg x Zn1−x O ternary alloy nanocrystals with hexagonal wurtzite structures were fabricated by using the sol–gel method. X-ray diffraction patterns, UV–vis absorption spectra, and photoluminescence spectra were used to characterize the structural and optical properties of the nanocrystals. For as-prepared nanocrystals, the band gap increases with increasing Mg content. Weak excitonic emission with strong deep-level emission related to oxygen vacancy and interface defects is observed in the photoluminescence spectra at room temperature. Thermal annealing in oxygen was used to decrease the number of defects and to improve the quality of the nanocrystals. In terms of XRD results, the grain sizes of nanocrystals increase with increasing annealing temperature and the lattice constants of alloy are smaller than those of pure ZnO. The band gap becomes narrower with increasing annealing temperature. For Mg x Zn1−x O nanocrystals ( x = 0.03 – 0.15 ) annealed at temperatures ranging from 500 to 1000 °C, intense near-band-edge (NBE) emissions and weak deep-level (DL) emissions are observed. Consequently, the quality of Mg x Zn1−x O nanocrystals can be improved by thermal annealing.
Keywords: Sol–gel method; Mg x Zn1−x O alloy nanocrystals; Thermal annealing;
Discrete model of random-pore aging by wall relief softening by Freddy Romm (518-521).
A new (discrete) model for random-pore aging in isochoric system with wall relief softening is proposed. The main criterion of the evolution of such system is the reduction of solid–gas interface area with time. The model allows simulations of the evolution of aging porous system with time, and estimations of free energy of the system. Equations of the model are used for simulations of the evolution of porous system with time. It is shown that the proposed model is effective for theoretical studies of processes of pore transformations by aging.
Keywords: Pores; Pore aging; Models of pores; Discrete models of solids;
Weakly nonlinear study of Marangoni instabilities in an evaporating liquid layer by M. Dondlinger; J. Margerit; P.C. Dauby (522-532).
We propose a theoretical study of Marangoni driven convection in an evaporating liquid layer surmounted by an inert gas–vapor mixture. After reduction of the full two-layer problem to a one-sided model we use a Galerkin–Eckhaus method leading to a finite set of amplitude equations for the weakly nonlinear analysis of the problem. We analyze the stability of the roll, square, and hexagonal patterns emerging above the linear stability threshold for a water–air and for an ethanol–air system.
Keywords: Marangoni convection; Evaporation; Pattern formation; Amplitude equations;
Surface properties and structures of diblock copolymer and homopolymer with perfluoroalkyl side chains by Takashi Nishino; Yoshimasa Urushihara; Masashi Meguro; Katsuhiko Nakamae (533-538).
The surface free energy of diblock copolymer, composed of methyl methacrylate and 2-perfluorooctylethyl methacrylate (PMMA-b-PFEMA), was compared with that of PFEMA homopolymer (P-PFEMA) in correlation with their structures in the solid state and in the solution using dynamic contact angle, X-ray photoelectron spectroscopy, X-ray diffraction, and dynamic light scattering. The PMMA-b-PFEMA film cast from chloroform solution was found to possess very low surface free energy (7.8 mJ/m2) compared with the surface free energies of the P-PFEMA (8.5 mJ/m2) and the PMMA-b-PFEMA (9.8 mJ/m2) films cast from CF3CF2CHCl2 solutions. These differences in the surface free energy were brought about by the variations in their surface structures. The very low surface free energy was considered to have originated from the surface segregation of the PFEMA segments highly self-assembled by the presence of chloroform.
Keywords: Surface free energy; Diblock copolymer; Perfluoroalkyl side chain; CF3 group; Hexagonal packing; Cast solvent; Collapse;
Kinetics of N-glutaryl-L-phenylalanine p-nitroanilide hydrolysis catalyzed by α-chymotrypsin in aqueous solutions of dodecyltrimethylammonium bromide by Elsa Abuin; Eduardo Lissi; Roxanna Duarte (539-543).
The rate of hydrolysis of N-glutaryl-L-phenylalanine p-nitroanilide (GPNA) catalyzed by α-chymotrypsin (α-CT) has been measured in aqueous solutions of dodecyltrimethylammonium bromide (DTAB) at concentrations below and above the critical micelle concentration, as well as in the absence of surfactant. Under all the conditions employed, the reaction follows a Michaelis–Menten mechanism. The presence of the surfactant leads to superactivity below and above the critical micelle concentration (CMC), with a maximum reaction rate taking place near the CMC when the results are treated in terms of the analytical concentration of the substrate. A similar behavior was observed by working with the enzyme partially deactivated in the presence of 4 M urea. After correction to take into account the partitioning of the substrate between the micelles and the external media, the activity of the enzyme tends to remain almost constant above the corresponding CMCs. This results from a compensation of a decrease in the catalytic constant ( k cat ) and a decrease in the Michaelis constant ( K M ). The behavior of α-CT in the hydrolysis of GPNA in DTAB solutions is at variance with that previously reported for the hydrolysis of 2-naphthyl acetate in solutions of the same surfactant (E. Abuin, E. Lissi, R. Duarte, Langmuir 19 (2003) 5374). An explanation of the different effects of the surfactant on the behavior of the enzyme with both substrates is advanced, taking into account the complexity of the mechanism of the α-CT-mediated reaction, more specifically, in terms of different rate-limiting steps for the formation of the measured products.
Keywords: Enzyme kinetics; α-Chymotrypsin; Dodecyltrimethylammonium bromide; N-Glutaryl-L-phenylalanine p-nitroanilide;
Association properties of diblock copolymer of ethylene oxide and 1,2-butylene oxide: E17B12 in aqueous solution by Chiraphon Chaibundit; Panita Sumanatrakool; Supaporn Chinchew; Proespichaya Kanatharana; Carin E. Tattershall; Colin Booth; Xue-Feng Yuan (544-554).
Copolymer E17B12 (E denotes OCH2CH2, B denotes OCH2CH(C2H5), and the subscripts denote number-average chain lengths) was prepared by sequential oxyanionic polymerization and characterized by GPC (for distribution width) and NMR spectroscopy (for absolute composition and chain length). Dynamic and static light scattering and rheometry were used to characterize micelles in dilute solution and demonstrate the formation of compact micelles at low temperatures and of elongated micelles at higher temperatures, the latter being accompanied by turbidity of the solution. Rheological methods applied across a range of concentrations and temperatures served to demonstrate the formation of worm-like micelles. Gels based on entangled worm-like micelles (some of them turbid) and on packed compact micelles were identified and their properties were explored.
Keywords: Diblock copolymer; Oxyethylene; Oxybutylene; Aqueous solution; Micelles; Gels;
Aggregation behaviors of gemini nucleotide at the air–water interface and in solutions induced by adenine–uracil interaction by Yujie Wang; Bernard Desbat; Sabine Manet; Carole Aimé; Thomas Labrot; Reiko Oda (555-564).
Cationic gemini surfactants having nucleotides as counterions (called nucleo-gemini hereafter) were synthesized and their aggregation behavior at air–water surfaces as well as in bulk solutions were studied. Fluid solutions of these nucleo-gemini surfactants show transitions to hydrogels upon addition of complementary nucleoside bases or other nucleo-gemini surfactants having complementary bases as counterions. The FTIR-ATR measurements show that the carboxylate groups of uridine form hydrogen bonds with the amine groups of adenosine. The aggregation behavior was also confirmed at the air–water interface by Brewster angle microscopy as well as surface pressure measurements; the monolayer of a gemini nucleotide was observed to undergo a transition to multilayers when nucleosides with complementary bases were added into the subphase. Isotherm curves of surface pressure monitored in parallel show a decrease in molecular area upon addition of such nucleosides.
Keywords: Hydrogels; Molecular recognition at air–water interface; Gemini surfactants;
Physicochemical investigations of microemulsification of eucalyptus oil and water using mixed surfactants (AOT + Brij-35) and butanol by Rajib K. Mitra; Bidyut K. Paul (565-577).
Microemulsification of a vegetable oil (eucalyptus) with single and mixed surfactants (AOT and Brij-35), cosurfactant of different lipophilicities (isomers of butanol), and water were studied at different surfactant and cosurfactant mixing ratios. The phase diagrams of the quaternary systems were constructed using unfolded and folded tetrahedron, wherein the phase characteristics of different ternary systems can be underlined. The microemulsion zone was found to be dependent upon the mixing ratios of surfactant and cosurfactant; the largest microemulsion zone was formed with 1:1 (w/w) S:CS. The effects of temperature and additives (NaCl, urea, glucose, and bile salts of different concentrations) on the phase behavior were examined. The mixed microemulsion system showed temperature insensitivity, whereas the Brij-35 (single) stabilized system exhibited a smaller microemulsion zone at elevated temperature. NaCl and glucose increased the microemulsion zone up to a certain concentration, beyond which the microemulsion zones were decreased. These additives decreased the microemulsion zones as temperature was increased. The effect of urea on microemulsion zone was found to be insignificant even at the concentration 3.0 mol dm−3. Little effect on microemulsion zone was shown by NaC (sodium cholate) at 0.25 and 0.5 mol dm−3 at different temperatures. The conductance of the single (AOT) and mixed microemulsion system (AOT + Brij-35) depends upon the water content and mixing ratios of the surfactants, and a steep rise in conductance was observed at equal weight percentages of oil and water. Viscosities for both single (AOT) and mixed (AOT + Brij-35) surfactant systems passed through maxima at equal oil and water regions showing structural transition. The viscosities for microemulsion systems increased with increasing Brij-35 content in the AOT + Brij-35 blend. Conductances and viscosities of different monophasic compositions in the absence and presence of additives (NaCl and NaC) were measured at different temperatures. The activation energy of conduction ( Δ E cond ∗ ) and the activation enthalpy for viscous flow ( Δ H vis ∗ ) were evaluated. It was found that both Δ E cond ∗ and Δ H vis ∗ were a function of the nature of the dispersion medium. Considering the phase separation point of maximum solubility, the free energy of dissolution of water or oil ( Δ G s 0 ) at the microdispersed state in amphiphile medium was estimated and found to be a function of surfactant composition.
Keywords: Eucalyptus oil; AOT; Brij-35; Microemulsion; Phase behavior; Additives; Viscosity; Conductivity; Thermodynamics;
The influence of sodium dodecyl sulfate/benzyl alcohol/H2O system on the photoisomerization of trans-stilbene by Xia Guo; Ling Lin; Rong Guo (578-584).
Photoisomerization of trans-stilbene (TS) was investigated in sodium dodecyl sulfate (SDS)/benzyl alcohol (BA)/H2O systems in order to establish the relationship between the reaction yields and the compositions and structures of molecular organized assemblies. The results show that, in SDS/BA/H2O systems with the structures of oil in water microemulsions, bicontinuous microemulsions, and hexagonal liquid crystals, the reaction yields are much larger than those in benzyl alcohol, both with and without the photosensitizer 9,10-anthracenedicarbonitrile. However, SDS/BA/H2O water in oil microemulsion and lamellar liquid crystal can obviously catalyze the photoisomerization of TS only when the photosensitizer is not present. The yield is increased with the increase in H2O content or with the decrease in BA content.
Keywords: Photoisomerization; trans-Stilbene; Molecular organized assembly; Microemulsion; Liquid crystal; 9,10-Anthracenedicarbonitrile;
Effect of silica colloids on the rheology of viscoelastic gels formed by the surfactant cetyl trimethylammonium tosylate by Ranjini Bandyopadhyay; A.K. Sood (585-591).
The effects of the addition of submicrometer-sized colloidal silica spheres on the linear and nonlinear rheology of semidilute solutions of a viscoelastic gel are studied. For a 1.4 wt% solution of the surfactant CTAT, a peak in the zero-shear rate viscosity η 0 is observed at approximately equal weight percents of silica and CTAT. This peak shifts to lower silica concentrations on increasing either the CTAT concentration or the surface charge on silica and disappears when the CTAT concentration is increased to 2.6 wt%. The increases in η 0 and the high frequency plateau modulus G 0 on the introduction of SiO2 are explained by considering the increasingly entangled wormlike micelles that are formed due to the enhanced screening of the electrostatic interactions. The observed decrease in the values of G 0 and η 0 at higher concentrations of silica particles is explained in terms of the formation of surfactant bilayers due to the adsorption of the positively charged cetyl trimethylammonium to the negatively charged silica.
Boundary effect on electrophoresis: finite cylinder in a cylindrical pore by Jyh-Ping Hsu; Ming-Hong Ku (592-600).
The boundary effect on electrophoresis is investigated by considering a finite cylindrical particle moving along the axis of a long cylindrical pore under conditions of low surface potential and weak applied electric field. The influence of the thickness of the double layer, the aspect ratio of a particle, the ratio particle radius/pore radius, and the charged conditions of the surfaces of the particle and pore on the electrophoretic behavior of a particle are investigated. We show that the effect of the aspect ratio of a particle on its electrophoretic behavior for the case where the particle is charged and the pore is uncharged is larger than that for the case where the particle is uncharged and the pore is charged. Also, depending on the parameters chosen, increasing the aspect ratio of a particle can either promote or hinder its movement, which is not reported in previous studies, and can play a role in electrophoresis measurements. Because both the electric and the flow fields in the gap between the particle and the pore are mediated by those near the top and the end of the particle, the end effect is large when the double layer is thick.
Keywords: Electrophoresis; Boundary effect; Cylinder in cylindrical pore; Constant surface potential;
Deposition of gold nanoparticles on silica spheres by electroless metal plating technique by Yoshio Kobayashi; Yohei Tadaki; Daisuke Nagao; Mikio Konno (601-604).
A previously proposed method for metal deposition with silver [Kobayashi et al., Chem. Mater. 13 (2001) 1630] was extended to uniform deposition of gold nanoparticles on submicrometer-sized silica spheres. The present method consisted of three steps: (1) the adsorption of Sn2+ ions took place on surface of silica particles, (2) Ag+ ions added were reduced and simultaneously adsorbed to the surface, while Sn2+ was oxidized to Sn4+, and (3) Au+ ions added were reduced and deposited on the Ag surface. TEM observation, X-ray diffractometry, and UV–vis absorption spectroscopy revealed that gold metal nanoparticles with an average particle size of 13 nm and a crystal size of 5.1 nm were formed on the silica spheres with a size of 273 nm at an Au concentration of 0.77 M.
Keywords: Nanoparticles; Gold; Electroless metal plating; Surface plasmon resonance; Silica; Deposition;
Sample container temperature gradient influence on the BET specific surface area by Alexander Badalyan; Phillip Pendleton (605-608).
Differences between BET specific surface area (BET SSA) values exist due to data collected in stainless steel and less thermally conductive sample holders. Not accounting for the temperature gradient along stainless steel sample holders during manometric gas adsorption measurements at cryogenic temperatures leads to errors of up to 3.2% in the BET SSA values with a relative combined standard uncertainty (RCSU) of 0.63%. A unidimensional heat flow model accurately accounts for the temperature gradient, leading to an agreement of 0.16% between the BET SSA values for both sample holder units.
Structure of synthetic calcium hydroxyapatite particles modified with pyrophosphoric acid by Hidekazu Tanaka; Masakazu Futaoka; Ryozi Hino; Kazuhiko Kandori; Tatsuo Ishikawa (609-612).
Synthetic colloidal calcium hydroxyapatite (Ca10(PO4)6(OH)2: CaHap) was treated with pyrophosphoric acid (H4P2O7: PP) in acetone and the materials were characterized by XRD, TEM, FTIR, and N2 and H2O adsorption measurements. XRD patterns and morphology of CaHap particles were essentially not changed by the modification. The additional amount of PO4 of CaHap was increased with an increase of PP concentration and the Ca/P molar ratio of the particles decreased from 1.62 to 0.81. IR results indicated that the isolated surface P―OH band developed with increasing the PP concentration up to 6.0 mmol dm −3 by the reaction of isolated surface P―OH groups of CaHap and pyrophosphoric acids. Above 10.2 mmol dm −3 , a hydrogen-bonding surface P―OH band appeared at 2913 cm −1 and enlarged with increasing the PP concentration, while the isolated surface P―OH band was weakened. The results of N2 and H2O adsorption measurements revealed that the modified particles aggregated compared to the unmodified ones, which would be due to the formation of hydrogen-bonding surface P―OH groups among the particles.
Keywords: Calcium hydroxyapatite; Pyrophosphoric acid; Surface modification; IR spectrum; Surface P―OH group;
Near-infrared spectroscopic method for the sensitive and direct determination of aggregations of surfactants in various media by Chieu D. Tran; Shaofang Yu (613-618).
A new cmc determination method based on a NIR spectroscopic technique has been developed. Comparing to other cmc determination methods, this NIR method is universal, sensitive, nonintrusive and nonadditive; namely, it can be used for the direct measurements of cmc of normal micelles as well as reversed micelles, without adding any dye or fluorescent probe. cmc values of various surfactants including CTAB, SDS, Triton X-100, Brij-35, Brij-700, Tween-20, SB-12, SB3-10 determined by this method agree very well with those determined by other methods. Additionally, the method can be used for the sensitive and direct determination of cmc values of various nonionic surfactants in room-temperature ionic liquids including [BMIm]+[PF6]− and [EMIm]+[Tf2N]−. The preliminary results presented here clearly demonstrate that it is possible to use the NIR technique not only to characterize aggregation of surfactants in RTILs but also to determine kinetics and to identify products of reactions in RTILs as well as in microreactors provided by micelles in the RTILs.
Keywords: Surfactant; Micelle; Critical micelle concentration; Near-infrared; Room-temperature ionic liquid;
by Arthur Hubbard (619).
Corrigendum to “Experimental and modeling study of the uranium (VI) sorption on goethite” [J. Colloid Interface Sci. 260 (2003) 291–301] by Tiziana Missana; Miguel García-Gutiérrez; Cesar Maffiotte (620).
Author Index for Volume 283 (621-622).