Journal of Colloid And Interface Science (v.297, #1)
Editorial Board (CO1).
The effects of energy sites on adsorption of Lennard–Jones fluids and phase transition in carbon slit pore of finite length a computer simulation study by A. Wongkoblap; D.D. Do (1-9).
A Monte Carlo simulation method is used to study the effects of adsorption strength and topology of sites on adsorption of simple Lennard–Jones fluids in a carbon slit pore of finite length. Argon is used as a model adsorbate, while the adsorbent is modeled as a finite carbon slit pore whose two walls composed of three graphene layers with carbon atoms arranged in a hexagonal pattern. Impurities having well depth of interaction greater than that of carbon atom are assumed to be grafted onto the surface. Different topologies of the impurities; corner, centre, shell and random topologies are studied. Adsorption isotherms of argon at 87.3 K are obtained for pore having widths of 1, 1.5 and 3 nm using a Grand Canonical Monte Carlo simulation (GCMC). These results are compared with isotherms obtained for infinite pores. It is shown that the surface heterogeneity affects significantly the overall adsorption isotherm, particularly the phase transition. Basically it shifts the onset of adsorption to lower pressure and the adsorption isotherms for these four impurity models are generally greater than that for finite pore. The positions of impurities on solid surface also affect the shape of the adsorption isotherm and the phase transition. We have found that the impurities allocated at the centre of pore walls provide the greatest isotherm at low pressures. However when the pressure increases the impurities allocated along the edges of the graphene layers show the most significant effect on the adsorption isotherm. We have investigated the effect of surface heterogeneity on adsorption hysteresis loops of three models of impurity topology, it shows that the adsorption branches of these isotherms are different, while the desorption branches are quite close to each other. This suggests that the desorption branch is either the thermodynamic equilibrium branch or closer to it than the adsorption branch.
Keywords: Adsorption; Argon; Carbon; Chemical impurity; GCMC; Pore topology; Simulation;
Thermodynamics of micellization of tetraethylammonium perfluorooctylsulfonate in water by José L. López-Fontán; Alfredo González-Pérez; Julian Costa; Juan M. Ruso; Gerardo Prieto; Pablo C. Schulz; Félix Sarmiento (10-21).
Conductivity, density, and sound velocity measurements as functions of temperature were made on tetraethylammonium perfluorooctylsulfonate solutions to determine the Krafft point, the dependence on temperature of the critical micelle concentration, the micellar ionization degree, and several thermodynamic properties: Gibbs free energy, enthalpy and entropy of micellization, apparent molar partial volume, thermal expansion coefficient, and the adiabatic compressibility factor of both micellized and unmicellized surfactants. Important changes occur at about 30 °C. Results are interpreted on the basis of dehydration of surfactant on micellization and on temperature increase.
Keywords: Tetraethylammonium perfluorooctylsulfonate; Conductivity; Density; Sound velocity; Thermodynamics of micellization; Krafft point;
Interactions of anionic dyes with silica–aminopropyl by Antonio R. Cestari; Eunice F.S. Vieira; Esdras S. Silva (22-30).
In this work silica–aminopropyl (Sil–NH2) was synthesized and employed to evaluate the quantitative roles of temperature, pH, dye concentration, and Hg(II) or anionic surfactant SDB interferents in the adsorptions of blue and red remazol dyes in aqueous medium using four distinct 24 factorial designs. The results were analyzed statistically using multiple regressions, Student's t-test, analysis of variance, and F-test. Polynomial modelings were used to define the most important factors affecting dye adsorption. The results indicate that the principal effects of dye concentration and pH, as well as most of the interactions of all factors, are statistically very important in relation to the equilibrium adsorption quantities. However, the adsorption Gibbs free energies are influenced, in general, only by pH, dye concentration, and some binary interactions. Temperature changes do not affect the ΔG values significantly.Silica–aminopropyl (Sil–NH2) was employed to evaluate the adsorptions of remazol dyes in aqueous medium by 24 factorial designs. The Δ ads G values are influenced by pH, dye concentration, and some binary interactions.
Keywords: Aminopropyl–silica; Adsorption; Anionic dyes; Factorial designs; Chemometrics;
Thermodynamics of monochlorophenol isomers and pyrite interfacial interactions in the activation state by R. Weerasooriya; M. Makehelwala; M.M. Miedaner; H.J. Tobschall (31-37).
Thermodynamic parameters of the activation state for phenol and three monochlorophenol (MCP) isomer–pyrite complexes, i.e., MCP isomers used were 2-chlorophenol (2-CP), 3-chlorophenol (3-CP), 4-chlorophenol (4-CP), have been derived from the temperature-dependent kinetic data. Both the initial rate and adsorption density values increased in the order phenol < 2-CP < 3-CP < 4-CP. This suggests that the presence of chlorine substituent on the aromatic ring results in enhanced CP adsorption on pyrite. The activation energy ( E a ) , Gibbs free energy ( Δ G # ) , entropy ( Δ S # ) , and enthalpy ( Δ H # ) of the activation stage for MCP adsorption on pyrite were calculated by Arrhenius and Eyring models. Always Δ S # values approximate to zero and − T Δ S # values are positive, which indicates that the activation state of MCP adsorption process is entropy-controlled, and the observed linear dependence of Δ H # on − T Δ S # signals an entropy–enthalpy compensation effect of the MCP adsorption process. The Γ MCP data were quantified well both by 1 − p K diffused double layer ( 1 − p K DLM) and Langmuir models.
Keywords: Pyrite; Monochlorophenol isomers; Phenol; Activation state; Electrical double layer; Langmuir model;
Molecular dynamics simulation of dense carbon dioxide fluid on amorphous silica surfaces by Xiaoning Yang; Zhijun Xu; Cuijuan Zhang (38-44).
Molecular dynamics (MD) simulations of dense carbon dioxide on the amorphous dehydroxylated silica surfaces have been carried out. The adsorption potential surfaces of the silica solids have been obtained in order to evaluate the characteristics of the amorphous surfaces. The atom density profiles, adsorption free energy profiles, surface orientation order parameters, and radial distribution functions for the CO2 molecules have been presented in order to study the effect of the amorphous surfaces on the microscopic interfacial structure properties of the CO2 molecules. The translational diffusion and orientation rotation at silica surfaces have also been investigated. It was observed that there is marked hindrance of the translational diffusion and orientation rotation of CO2 molecules near amorphous silica surfaces.
Keywords: Dense CO2; Molecular dynamics simulation; Amorphous; Silica; Surface;
Removal of pentachlorophenol from aqueous solutions by dolomitic sorbents by Reda Marouf; Noreddine Khelifa; Kheira Marouf-Khelifa; Jacques Schott; Amine Khelifa (45-53).
The partial decomposition of dolomite carried out within the temperature range 600–1000 °C provides new sorbents, called dolomitic sorbents. Their surface properties and identification by X-ray diffraction are discussed. The lowest specific surface area value was found for the raw dolomite, while the highest value was achieved by the D-1000 sample. The adsorption equilibrium of pentachlorophenol from aqueous solutions on the examined sorbents was investigated at 30, 40, and 50 °C via a bath process. Langmuir, Freundlich, Langmuir–Freundlich, and Redlich–Petersen models were fitted to experimental equilibrium data, and their goodnesses of fit are compared. The adjustable parameters of Langmuir–Freundlich and Redlich–Petersen isotherms were estimated by nonlinear least-squares analysis. Langmuir and Freundlich models were found insufficient to explain the adsorption equilibrium, while Langmuir–Freundlich and Redlich–Petersen isotherms provide the best correlation of the pentachlorophenol adsorption onto dolomitic sorbents.
Keywords: Pentachlorophenol removal; Dolomite; Thermal treatment; Adsorption isotherms;
An in situ ATR–FTIR study of polyacrylamide adsorption at the talc surface by Linh T. Chiem; Le Huynh; John Ralston; David A. Beattie (54-61).
The adsorption of a low molecular weight unmodified polyacrylamide (Polymer-N) and a hydroxyl-substituted polyacrylamide (Polymer-H) onto talc was studied using in situ particle film ATR–FTIR spectroscopy in the multiple internal reflection mode. Spectra of the adsorbed polymer were collected as a function of increasing concentration and as a function of time. Measurement of the peak intensities of the adsorbed polymer allowed adsorption isotherms and adsorption kinetics to be determined for both polymers. Langmuir adsorption isotherm analysis of in situ data yielded Gibbs free energies of adsorption ( Δ G ads 0 ) for Polymer-N and Polymer-H of −44.5 and −45.7 kJ/mol, respectively, which correlate well with similar values determined from ex situ adsorption isotherms. Kinetic analysis indicated that the adsorption of both polymers was a pseudo-first-order process. The apparent rate constants for Polymer-N and Polymer-H were 0.10 and 0.15 min−1, respectively. Absence of spectral shifts in the spectra of adsorbed polymer is indicative of a hydrophobic interaction between the polyacrylamides and the talc surface.
Keywords: ATR–FTIR; In situ adsorption studies; Polymer adsorption; Talc; Polyacrylamides; Depression;
Sorption of bisphenol A, 17α-ethynylestradiol and estrone to mineral surfaces by Ali Shareef; Michael J. Angove; John D. Wells; Bruce B. Johnson (62-69).
Sorption of the endocrine disrupting chemicals (EDCs) bisphenol A (BPA), 17α-ethynylestradiol (EE2) and estrone (E1) from 3 μM aqueous solutions in 10 mM KNO3 to goethite, kaolinite and montmorillonite was investigated at 25 °C. Uptake of the EDCs by goethite and kaolinite suspensions was <20%, and little affected by pH. Sorption by montmorillonite was greater, ranging from 20 to 60%, and steadily increased from about pH 7. The amount of EDC sorbed to the mineral phases generally increased in the order of decreasing solubility (BPA < EE2 < E1). Sorption to goethite and kaolinite was rapid (<10 min), but much slower for montmorillonite, to which sorption continued for 24–48 h. Although the EDCs desorbed rapidly and completely from goethite and kaolinite, only small amounts desorbed from montmorillonite below pH 7, and no recovery was observed at pH 10. The kinetic and desorption experiments indicate that the EDCs intercalate into the interlayer spaces of montmorillonite, but for goethite and kaolinite sorption probably occurs at external surfaces.
Keywords: Endocrine disrupting chemicals; Mestranol; Goethite; Kaolinite; Montmorillonite;
Sorption of nitroaromatic compounds to synthesized organoclays by R.T. Upson; S.E. Burns (70-76).
This project quantifies the ability of seven engineered organoclays to sorb TNT and two of its reduction products: 2-amino-4,6-dinitrotoluene (2-A-4,6-DNT) and 4-amino-2,6-dinitrotoluene (4-A-2,6-DNT). The organoclays used in the TNT sorption studies were synthesized in the laboratory by combining bentonite with benzyltriethylammonium chloride (BTEA) at 50, 75, and 100% of the bentonite's cation exchange capacity and with hexadecyltrimethylammonium bromide (HDTMA) at 25, 50, 75, and 100% of the bentonite's cation exchange capacity. For sorption of 2-A-4,6-DNT and 4-A-2,6-DNT, two organoclays were tested: BTEA at 50% CEC and HDTMA at 75% CEC. Sorption data with HDTMA organoclay and TNT were fit to linear isotherms and demonstrated that the clay's sorptive capacity increased as the amount of total organic carbon exchanged onto the clay increased. Sorption data with BTEA organoclay and TNT were fit to Langmuir isotherms; however, the clay's sorptive capacity increased as the amount of total organic carbon sorbed to the clay's surface was decreased. Sorption behavior for TNT reduction products 2-A-4,6-DNT and 4-A-2,6-DNT to one HDTMA organoclay and one BTEA organoclay demonstrated that HDTMA organoclay at 10.3% total organic carbon was a more effective sorbent than BTEA organoclay at 5.2% total organic carbon.
Keywords: Organoclay; Remediation; Sorption; TNT;
Porous structure of natural and modified clinoptilolites by Piotr Kowalczyk; Myroslav Sprynskyy; Artur P. Terzyk; Mariya Lebedynets; Jacek Namieśnik; Bogusław Buszewski (77-85).
The evaluation of the pore-size distribution (PSD) of natural and modified mesoporous zeolites, i.e., clinoptilolites is presented. We demonstrate the SEM results showing that the pores of fracture-type from 25–50 nm to 100 nm in size between clinoptilolite grains, as well as pores between crystal aggregates up to 500 nm in size are present in the studied material. The detailed distribution of pore sizes and tortuosity factor of the above-mentioned materials are determined from the adsorption–desorption isotherms of nitrogen measured volumetrically at 77 K. To obtain the reliable pore size distribution (PSD) of the above-mentioned materials both adsorption and desorption branches of the experimental hysteresis loop are described simultaneously by recently developed corrugated pore structure model (CPSM) of Androutsopoulos and Salmas. Evaluated pore size distributions are characterized by well-defined smooth peaks placed in the region of the mesoporosity. Moreover, the mean pore diameter calculated from the classical static measurement of nitrogen adsorption at 77 K correspond very well to the pore diameters from SEM, showing the applicability of the CPSM for characterization of the porosity of natural zeolites. We conclude that classical static adsorption measurements combined with the proper modeling of the capillary condensation/evaporation phenomena are a powerful method which can be applied for pore structure characterization of natural and modified clinoptilolites.
Keywords: Adsorption; Pore size distribution; CPSM model; Clinoptilolites;
Energetics of arsenate sorption on amorphous aluminum hydroxides studied using flow adsorption calorimetry by Nadine J. Kabengi; Samira H. Daroub; R. Dean Rhue (86-94).
Flow adsorption calorimetry was used to investigate the energetics of arsenate sorption on amorphous aluminum hydroxide (AHO) and its effect on surface charge and ion exchange. Arsenate sorption at pH 5.7 was exothermic and the molar heats of adsorption were quite variable, ranging from −3.0 to −66 kJ/mol. Repetitive exposure of the same sample to arsenate in the calorimeter showed that the AHO was able to regenerate a considerable amount of reactive surface over time periods as short as 15 to 20 min. The large variability in heats of arsenate adsorption and the ability to regenerate reactive surface is believed to result from the amorphous nature of the AHO used. Heats of Cl/NO3 exchange were much smaller and more consistent, ranging from about 3.0 to 6.0 kJ/mol. The molar ratio of exchangeable Cl:Al was about 6:1 for the AHO, indicating a highly porous material. At pH 5.7, arsenate sorption neutralized surface positive charge as measured by Cl/NO3 exchange. Only at the two highest loadings (>60,000 mg/kg) did arsenate sorption result in any negative surface charge as measured by Na/K exchange. These results showed that most of the arsenate was adsorbed by a mechanism that involved no increase in surface negative charge. The PZNC of the AHO decreased by about 1 pH unit when exposed to arsenate in the flow calorimeter. Exposure to arsenate in a batch system decreased the PZNC about 4 pH units. This difference in behavior between batch and flow systems was related to differences in the amount of arsenate adsorbed.The complex reaction of arsenate with amorphous aluminum hydroxides.
Keywords: Arsenate; Sorption mechanisms; Oxide–water interface; Amorphous aluminum hydroxides; Molar heats; Surface charge;
Some features associated with organosilane groups grafted by the sol–gel process onto synthetic talc-like phyllosilicate by José A.A. Sales; Giovanni C. Petrucelli; Fernando J.V.E. Oliveira; Claudio Airoldi (95-103).
Two new lamellar inorganic–organic magnesium silicates have been successfully synthesized by using sol–gel based processes under mild temperature conditions. The talc-organosilicates derived using two silylating agents as the silicon source, (i) 3-chloropropyltrimethoxysilane, and (ii) from the attachment of 5-amino-1,3,4-thiadiazole-2-thiol molecule to this precursor agent, yielded PhMg-Cl and PhMg-Tz phyllosilicates. These organoclays were characterized through elemental analyses, infrared spectroscopy, X-ray diffractometry, surface area, thermogravimetry, and carbon and silicon solid state nuclear magnetic resonance spectroscopy. The results confirmed the presence of organic moieties covalently bonded to the inorganic silicon sheet network of the 2:1 class of phyllosilicates, with a density of organic molecules of 6.6 ± 0.1 and 2.7 ± 0.2 mmol g −1 anchored on the inorganic layer and with interlayer distances of 1158 and 1628 pm, respectively. The nuclear magnetic resonances results in the solid state are in agreement with the sequence of carbons distributed in the pendant chains of the original silylating agents and the silicon bonded to oxygen atoms or carbon atoms of the inorganic sheets, as expected for the organically functionalized phyllosilicates. The enhanced potential of the new compound PhMg-Tz as a multi property material was explored in adsorbing cations from aqueous solution. The basic sulfur and nitrogen centers attached to the pendant chains inside the lamellar cavity can coordinate mercury, by presenting an isotherm saturated at 0.19 mmol g−1 of this heavy metal. The functionality of this organoclay-like material expresses its potential for heavy cation removal from an ecosystem.Synthetic talc-like phyllosilicates obtained from sol–gel process with attached covalently basic centre atoms extract cations from aqueous solution.
Keywords: Phyllosilicate; Organosilane; Sol–gel; Adsorption;
Probing the viscoelastic response of glassy polymer films using atomic force microscopy by Guanwen Yang; Nanxia Rao; Zejie Yin; Da-Ming Zhu (104-111).
The mechanical properties of glassy films and glass surfaces have been studied using an atomic force microscope (AFM) through various imaging modes and measuring methods. In this paper, we discuss the viscoelastic response of a glassy surface probed using an AFM. We analyzed the force–distance curves measured on a glassy film or a glassy surface at temperatures near the glass transition temperature, T g , using a Burgers model. We found that the material's characteristics of reversible anelastic response and viscous creep can be extracted from a force–distance curve. Anelastic response shifts the repulsive force–distance curve while viscous creep strongly affects the slope of the repulsive force–distance curve. When coupled with capillary force, due to the condensation of a thin layer of liquid film at the tip-surface joint, the anelasticity and viscous creep can alter the curve significantly in the attractive region.
Growth mechanism of soap-free polymerization of styrene investigated by AFM by Tetsuya Yamamoto; Masaki Nakayama; Yoichi Kanda; Ko Higashitani (112-121).
To clarify the growth mechanism of polystyrene (PSL) particles in the soap-free polymerization, characteristics of not only particles but also polymeric materials floating in the bulk were investigated on the molecular scale by using atomic force microscope (AFM), where a cationic initiator V-50 is used to make the formed polymeric materials transfer on the mica plate in sampling. Our main attention here is to know the reason why the particle size increases with increasing initiator concentration in the production of PSL particles. The following are found. (1) As far as the initiators and monomers remain in the bulk solution, the polymeric materials are born in the bulk continuously, because of the slow decomposition rate of initiators. (2) The growth of particles at the early stage of t r ⩾ 0.75 h is considered to be attributable mainly to the particle swelling by absorbing monomers from the bulk. The rapid growth at the intermediate stage is due to the deposition of polymeric materials in the bulk on the particle surface and their simultaneous swelling by monomers in the bulk. (3) The reason why the particle size increases with increasing concentration of initiator is that the growth process is controlled by the deposition rate of polymeric materials in the bulk whose amount increases with the initiator concentration. (4) The particle size and the smoothness of particle surface depend on the relative concentration of initiators and monomers remained.The possible processes of the growth of PSL particles in the soap-free polymerization.
Keywords: Polystyrene particle; AFM; Growth mechanism; Nucleation; Soap-free emulsion polymerization;
Preparation of siloxy focal dendron-protected TiO2 nanoparticles and their photocatalysis by Yuko Nakanishi; Toyoko Imae (122-129).
TiO2 nanoparticles were synthesized at ∼0 °C by hydrolyzing [(CH3)2CHO]4Ti in 1-propanol solutions of poly(amido amine) dendrons with a siloxy focal point and long alkyl chain spacers. Transmission electron microscopic photographs showed that TiO2 nanoparticle was 1–5 nm in size and protected by dendrons, when prepared at a mixing ratio 1:10 of Ti ion and dendron. At higher contents of Ti ion, TiO2 nanoparticles aggregated up to a maximum size of 90 nm, depending on the dendron generation (first to third). It was confirmed from X-ray photoelectron spectroscopy that Si―O―Ti covalent bond was formed in dendron-protected TiO2 nanoparticles. The ability of dendron-protected TiO2 nanoparticles as a photocatalyst for the photodegradation of 2,4-dichlorophenoxyacetic acid was higher than that of nonprotected nanoparticle and superior at higher generation. It was suggested that the dendrons protecting TiO2 nanoparticle have enough void volume to conserve guest molecules and behave effectively as a reservoir of guest molecules.
Keywords: TiO2; Nanoparticle; Dendron; Siloxy focal dendron; Long alkyl chain spacer; Poly(amido amine) dendron; Transmission electron microscopy; X-ray photoelectron spectroscopy; Photodegradation; 2,4-Dichlorophenoxyacetic acid; Photocatalysis;
The effect of the size of raw Gd(OH)3 precipitation on the crystal structure and PL properties of Gd2O3:Eu by Haiyong Chen; Jiahua Zhang; Xiaojun Wang; Shiyong Gao; Mingzhe Zhang; Yanmei Ma; Quanqing Dai; Dongmei Li; Shihai Kan; Guangtian Zou (130-133).
Our experiments show that cetyltrimethylammonium bromide (CTAB) has an obvious effect on the particle size of the precipitation of Gd(OH)3. Without CTAB, the particle size of the Gd(OH)3 precipitation is about 50 nm, whereas with CTAB, the particle size is less than 5 nm. We propose a mechanism where CTAB micelles work as a catalyst for the nucleation process and result in the precipitation of 5 nm particles. These small particles, after heat treatment at 1073 K, did not result in small Gd2O3 nanoparticles of the same size, but instead, forming crystals of 30–80 nm size in both cubic and monoclinic phases. When monitoring the photoluminescence (PL) peak at 610 nm, we found that the charge transfer state (CTS) absorption amplitude of Eu–O is reduced in the mixed structures. We speculate that the mixed structures modify the surface properties of the Gd2O3:Eu nanoparticles, leading to the reduction of Eu–O CTS absorption.When CTAB were added in the solution, the size of the Gd(OH)3 deposition decreased from 50 nm to less than 5 nm. After they were heated at 1073 K, Gd2O3 nanoparticles of roughly 40 nm formed. The Gd2O3:Eu sample from Gd(OH)3 deposition with size of about 50 nm shows the characteristic emission of Eu3+ in a pure cubic structure (curve a). However, the sample from Gd(OH)3 of less than 5 nm presents the characteristic emissions of Eu3+ in both cubic and monoclinic structures (curve b).
Synthesis of single-crystal β-Ni(OH)2 nanodisks and α-Fe2O3 nanocrystals in C2H5OH–NaOH–NH3⋅H2O system by Rui Yang; Lian Gao (134-137).
Circular β-Ni(OH)2 nanodisks and rhombohedral and hexagonal α-Fe2O3 nanocrystals were prepared using the C2H5OH–NaOH–NH3⋅H2O system under hydrothermal conditions. The C2H5OH/H2O solvent is an appropriate one for the growth of these two materials with their thermodynamically favored morphologies. The possible formation mechanisms are discussed.Circular β-Ni(OH)2 nanodisks and rhombohedral and hexagonal α-Fe2O3 nanocrystals were prepared using the C2H5OH–NaOH–NH3⋅H2O system under hydrothermal conditions. The C2H5OH/H2O solvent is an appropriate one for the growth of these two materials with their thermodynamically favored morphologies and the possible formation mechanisms are discussed.
Keywords: Ni(OH)2; Fe2O3; Hexagonal; Rhombohedral; Nanodisks; Nanocrystals; C2H5OH/H2O solvent;
Redispersible rutile TiO2 nanocrystals in organic media by surface chemical modification with an inorganic barium hydroxide by Bok Yeop Ahn; Sang Il Seok; Nimai Chand Pramanik; Hoon Kim; Suk-In Hong (138-142).
The present paper describes the synthesis of the redispersible rutile TiO2 nanocrystals in organic media by surface chemical modification reaction in an aqueous barium hydroxide solution. In our facile surface modification reactions, the surfaces of the TiO2 nanocrystals are coated by bimetallic Ti―O―Ba spices and saturated with Ba―OH terminal groups. The inherent characteristics such as morphology, size, crystallinity, and color of the nanocrystals remained almost unchanged after surface-treatment, but their dispersibility in organic media such as methanol and DMF were remarkably enhanced. It is ascribed that Ba―OH groups in the surface of the TiO2 nanocrystals prevented the formation of covalently bound agglomerates through Ti―O―Ti condensation reaction among the nanocrystals during the purification and water-elimination procedures.The present paper describes the synthesis of the redispersible rutile TiO2 nanocrystals in organic media by surface chemical modification reaction in an aqueous barium hydroxide solution.
Keywords: Dispersion in organic medium; Surface modification; Nanocrystals; Rutile TiO2;
Chemical preparation of Pd nanoparticles in room temperature ethylene glycol system and its application to electroless copper deposition by Li-Jung Chen; Chi-Chao Wan; Yung-Yun Wang (143-150).
Room-temperature synthesis of Pd nanoparticles protected by polyvinylpyrrolidone (PVP) has been successfully achieved by merely adding sodium hydroxide (NaOH) acting as accelerator for the reduction of Pd(II) in ethylene glycol (EG) without any externally added reducing agent. The Pd particle sizes were controlled in the range from 8.6 to 2.4 nm by changing the concentration of NaOH from 0 to 3.2 × 10 −1 M . The particle formation was monitored by UV–vis spectroscopy and the microstructure of Pd nanoparticles was analyzed by TEM and XRD. The product of adding NaOH in EG was characterized by FTIR and a ―CHO group which possesses reductive ability was identified. In addition, the prepared Pd nanoparticle could serve as an effective activator for electroless copper deposition (ECD) on epoxy substrate, which is an essential process in the printed circuit board (PCB) industry. In contrast to existing commercial activators, the new activator shows superior stability and excellent performance for ECD.Room-temperature synthesis of Pd nanoparticles protected by polyvinylpyrrolidone (PVP) has been successfully achieved by merely adding sodium hydroxide (NaOH) acting as accelerator for the reduction of Pd(II) in ethylene glycol (EG) without any externally added reducing agent. The Pd particle sizes and shapes of spherical and nonspherical are controlled by NaOH concentration and this Pd nanoparticle used as activator are well absorbed on the epoxy substrate facilitates the application of electroless copper deposition in the printed circuit board (PCB) industry.
Keywords: Pd nanoparticles; Pd colloids; Catalyst; Activator; Electroless copper;
Study on interaction between poly(amidoamine) dendrimer and CdSe nanocrystal in chloroform by Bifeng Pan; Feng Gao; Rong He; Daxiang Cui; Yafei Zhang (151-156).
The binding of different categories of molecules to quantum dot has been studied for many years through different spectroscopic techniques to elucidate details of binding mechanism. In this work we present the results of the study of the interactions between CdSe and poly(amidoamine) dendrimer monitored by photoluminescence spectroscopy of CdSe in chloroform. Dendrimers with different terminal groups and different generations were used to bind with CdSe nanocrystal of different size. Significant differences in the values of binding constant K b ( n ) and K SV were found in these experiments. The binding constant for poly(amidoamine) dendrimer of generation 4.0 is higher as compared to generation 3.5. The interaction of CdSe with poly(amidoamine) dendrimer shows an increase of binding constants with increasing dendrimer generation from 2.0 to 4.0, as well as with decreasing CdSe diameter. From HRTEM and FTIR analysis, we suggest that dendrimer/CdSe interactions are primarily hydrogen-bonding.
Keywords: CdSe; Poly(amidoamine) (PAMAM) dendrimer; Photoluminescence; Quenching;
Synthesis of silica hollow spheres assisted by ultrasound by Wugang Fan; Lian Gao (157-160).
A simple and effective method for synthesizing silica hollow spheres is presented. The synthesis utilizes vesicles from oppositely charged surfactants sodium dodecyl sulfate (SDS) and tetrapropylammonium bromide (TPAB) aqueous solution as template for the silica growth. Tetraethyl orthosilicate (TEOS) is added to the vesicular template as a precursor for the silica formation. Ultrasound was employed to accelerate the formation of vesicles template. The morphology of the silica spheres is uniform and well-defined (diameter: 200 nm–5 μm, wall thickness: 50 nm). The product was also characterized by FTIR, TG-DTA, N2 adsorption. TEM images reveal that the spheres have structure stability after calcinations at 550 °C.A simple and effective method for synthesizing silica hollow spheres is presented. The synthesis utilizes vesicles from oppositely charged surfactants sodium dodecyl sulfate and tetrapropylammonium bromide aqueous solution as template for the silica growth. Ultrasound was employed to accelerate the formation of vesicles template.
Keywords: Silica hollow spheres; Ultrasound; Vesicle template;
The effects of added nanoparticles on aqueous kaolinite suspensions by J.C. Baird; J.Y. Walz (161-169).
The results of an experimental study focused on the effect of added silica nanospheres on the structure of an aqueous suspension of disc-shaped kaolinite particles are presented. In the absence of any additives, kaolinite particles rapidly aggregate and settle. When only nanoparticles were added to a 14% vol. kaolinite suspension, some stabilization was observed, although a thick, fluid-like sediment still formed. Adding both nanoparticles and salt (NaCl or KCl), however, caused the entire suspension to transition into a solid material that was strong enough to actually be sliced. A phase diagram was constructed showing the concentration of salt and nanoparticles needed to produce this transition. With smaller nanoparticles, the transition occurred at much lower nanoparticle volume fractions. Scanning electron micrographs of both the sediment and solid-like material, obtained by cryogenic drying, showed that the latter consisted of a porous, ‘sponge-like’ structure. The characteristic size of the pores decreased as the number density of the added nanoparticles increased. Although the nanoparticles were not visible in the SEM images, it is believed that they had separated into the pores of the solid-like material. While a similar type of transition could be produced in suspensions containing only the silica nanospheres, the structure and flow behavior of this material were markedly different from that obtained with the added clay.
Keywords: Clay suspensions; Liquid–solid phase transition; Nanoparticle/colloid mixtures; Clay gels;
Electrokinetic behavior and colloidal stability of polystyrene latex coated with ionic surfactants by A.B. Jódar-Reyes; J.L. Ortega-Vinuesa; A. Martín-Rodríguez (170-181).
This work is focused on analyzing the electrokinetic behavior and colloidal stability of latex dispersions having different amounts of adsorbed ionic surfactants. The effects of the surface charge sign and value, and the type of ionic surfactant were examined. The analysis of the electrophoretic mobility ( μ e ) versus the electrolyte concentration up to really high amounts of salt, much higher than in usual studies, supports the colloidal stability results. In addition, useful information to understand the adsorption isotherms was obtained by studying μ e versus the amount of the adsorbed surfactant. Aggregation studies were carried out using a low-angle light scattering technique. The critical coagulation concentrations (ccc) of the particles were obtained for different surfactant coverage. For latex particles covered by ionic surfactants, the electrostatic repulsion was, in general, the main contribution to the colloidal stability of the system; however, steric effects played an important role in some cases. For latices with not very high colloidal stability, the adsorption of ionic surfactants always improved the colloidal stability of the dispersion above certain coverage, independently of the sign of both, latex and surfactant charge. This was in agreement with higher mobility values. Several theoretical models have been applied to the electrophoretic mobility data in order to obtain different interfacial properties of the complexes (i.e., zeta potential and density charge of the surface charged layer).
Keywords: Interfaces and colloids; Polystyrene latex; Ionic surfactant; Electrophoretic mobility; Colloidal stability; Diffuse potential; Zeta potential; Electrolyte concentration;
Preparation and characterization of a new layered double hydroxide, Co–Zr–Si by Osama Saber (182-189).
The layered double hydroxides (LDHs) are nano-ordered layered compounds and well known for their ability to intercalate anionic compounds. Most LDH is prepared conventionally only with divalent and trivalent cations. In this study, Co–Zr–Si LDH, consisting of divalent, tetravalent, and tetravalent cations, was prepared and reacted with monocarboxylic acids at room temperature. The Co–Zr–Si LDH and intercalated compounds have been characterized by energy-dispersive X-ray spectrometry, X-ray powder diffraction, IR spectra, thermal analysis, and scanning electron microscopy (SEM). The insertion of cyanate and carbonate anions into LDH was confirmed by IR spectra. XRD patterns of the prepared Co–Zr–Si LDH showed that the interlayer spacing of the LDH is 0.78 nm. The spacing is similar to that of usual LDH in which chloride, carbonate, or bromide anion is the guest. SEM images showed that Co–Zr–Si LDH can exist as plate-like or fibrous structures.Co–Zr–Si layered double hydroxides consisting of divalent and two tetravalent cations have been prepared for the first time. SEM images indicate that we can control the morphology of LDH by intercalation reactions.
Keywords: Preparation; Intercalation; Layered double hydroxide; Characterizations;
Interpretation of the ultrasonic effect on induction time during BaSO4 homogeneous nucleation by a cluster coagulation model by Z. Guo; A.G. Jones; N. Li (190-198).
The effects of power ultrasound on the induction time of BaSO4 are studied experimentally and theoretically. In the experiments, barium sulfate is precipitated by mixing aqueous BaCl2 solution and Na2SO4 solution. The induction time is identified and measured by recording the change of turbidity in solution. Various energy inputs are used to investigate the effect of energy on nucleation. The results show that the induction time decreases with increasing supersaturation and increasing energy input. Employing the classical nucleation theory, the interfacial tension is estimated. In addition, the ultrasonic effects on nucleation order (n) and the nucleation coefficient ( k N ) are also investigated. A cluster coagulation model, which brings together the current nucleation models and the theories describing the behavior of colloidal suspensions, was applied to estimate the induction time under various energy inputs. A comparison between the results of model and the results of experiments shows that the number of monomers in dominating clusters ( g ¯ ) in the solution remains constant with increasing of energy input.The paper summarizes the ultrasonic effect on cluster coagulation and diffusion coefficient during BaSO4 homogeneous nucleation.
Keywords: Ultrasound; Induction time; Homogeneous nucleation; Crystallization; Coagulation; Cluster;
pH dependence of friction forces between silica surfaces in solutions by Elena Taran; Bogdan C. Donose; Ivan U. Vakarelski; Ko Higashitani (199-203).
The pH dependence of the friction between a silica particle and a silica wafer was investigated using lateral force microscopy. Measurements were done in the range of 3.6 ≦ pH ≦ 10.6 and the effect of high loading force was also examined. It is found that the friction is independent of the pH of solutions and increases linearly with the applied load, when the pH is between 3.6 and 8.6. On the other hand, once the pH is above 9.0, the friction becomes extremely small and the dependence on the applied load becomes nonlinear. It is postulated that this transition is due to the development of a gel layer composed of polymer-like segments of silicilic acid anchored on the surface; at the lower applied load, this layer acts as a boundary lubricant between the surfaces, but, at the higher applied load, the entanglements of these segments and more direct contact between two solid surfaces leads to the increase of the friction. The effects found here are expected to play an important role in elucidating the basic mechanism of the planarization process of silica wafers.Independence of the friction force between silica surfaces in solutions within pH 3.6 and 8.6, but the dramatic decrease at pH > 8.6.
Keywords: Friction; Gel layer; Silica surface; CMP;
Monte Carlo simulation of the electrical differential capacitance of a double electrical layer formed at the heterogeneous metal oxide/electrolyte interface by Piotr Zarzycki (204-214).
A semiempirical simulation study of differential capacitance c d is presented for the case in which the formula for the macroscopic surface potential is known. Both the differential capacity and the surface potential are treated as unique functions of the potential determining ions (H+ ions). The effects of surface heterogeneity on the surface charge density curves σ 0 = f ( pH ) , and capacity curves c d = f ( pH ) , as well as on the position of maximum capacitance are discussed. The “model” effects (influence of the model parameter on the results) are presented.
Keywords: Differential capacitance; Monte Carlo simulation; Surface heterogeneity; Metal oxide/electrolyte interface;
The effect of inorganic particles on slot die coating of poly(vinyl alcohol) solutions by Wen-Bing Chu; Jia-Wei Yang; Yu-Chin Wang; Ta-Jo Liu; Carlos Tiu; Jian Guo (215-225).
Among various coating processes, slot die coating belongs to a class of pre-metered coating, in which the coating film thickness can be predetermined. In the past, most research works on slot die coating have focused mainly on polymer solutions; very little information is available using suspensions as coating fluids. In this study, the effect of adding TiO2 and SiO2 in aqueous polyvinyl alcohol (PVA) solutions on slot die coating is investigated. It was found that the stable coating window was enlarged with the addition of particles, and its size increased with solids concentration. This is due to the strong interaction between polymer and particles, resulting in a higher viscosity and surface tension. As a result, the upstream coating bead is more stable and the maximum coating speed is extended to a high value, hence the coating window becomes larger. Although both viscosity and surface tension appear to contribute to the stability of coating flow, the effect of surface tension is more dominant. The surface tension of a suspension with porous particles was higher than one with hard solid particles. Consequently, the coating window obtained with the former was significantly larger than the latter. Flow visualization revealed that under the same operating conditions, the upstream dynamic contact angle for the suspension was smaller than for the aqueous polymer solution. This observation could be related to the stability of the upstream coating bead, and hence the coating window. The experimental flow fields were verified numerically with the aid of a numerical simulation package (Flow-3D).Coating windows of polyvinyl alcohol solution at different concentrations of SiO2 suspensions. (■) 2.5% PVA, (○) 3.5% C803 in 2.5% PVA, (▵) 7% C803 in 2.5% PVA. V is the coating speed and q is the volumetric flow rate/coating width. Coating window is expanded if particles are added.
Keywords: Slot die coating; Coating window; Inorganic particles; Viscosity; Surface tension; Flow visualization;
Modification of active and porous sublayers of aged polyamide/polysulfone composite membranes due to HNO3 treatment: Effect of treatment time by J. Benavente; M.I. Vázquez; R. de Lara (226-234).
Changes in electrical and transport parameters for aged composite polyamide/polysulfone membrane samples (PAC) and their porous support layers (PSU) as a result of chemical treatment (immersion in 1 M HNO3 solution) at four different times ( 12 h ⩽ t ⩽ 72 h ) have been obtained. Salt permeability, ion transport number, and membrane electrical resistance for the treated samples were determined from salt diffusion, membrane potential, and impedance spectroscopy measurements, which were carried out with the membranes in contact with NaCl solutions at different concentrations and compared with those determined for fresh and aged nontreated samples. Results show the strong effect of aging on membrane parameters, particularly the decrease in salt permeability ( P s ) and the increase in membrane electrical resistance ( R m ), while ion transport number is hardly affected by aging, chemical treatment, or treatment time. Results show how the compaction of the porous structure causes by aging (dried membrane matrix structure) can be partially reduced by HNO3 treatment, and they also allow the estimation of 24-h treatment as the optimum time (higher salt permeability and lower membrane electrical resistance), mainly for the polysulfone support layer. The use of equivalent circuits in the analysis of impedance spectroscopy data allows separate estimation of the electrical resistance associated with each sublayer of the composite PAC membrane samples. On the other hand, chemical changes in the active top layer of the PAC membrane (polyamide active layer) were obtained from XPS analysis, which show some modifications in the atomic concentration percentages of the polyamide characteristic elements as a result of acidic treatment time, which are more significant after 72-h acidic immersion.Changes in electrical and transport parameters for aged composite polyamide/polysulfone membrane samples (PAC) and its porous support layer (PSU) as a result of chemical treatment (immersion in 1 M HNO3 solution) at four different times ( 12 h ⩽ t ⩽ 72 h ) have been obtained. Results show the strong effect of aging on some membrane parameters; particularly a decrease in salt permeability ( P s ) and an increase in membrane electrical resistance ( R m ) were obtained, while ion transport number is hardly affected by aging or chemical treatment as well as by the treatment time, since they represent relative fluxes. The use of impedance spectroscopy (IS) allows the separate estimation of active and porous layers contribution to the composite membrane electrical resistance, and estimation of the stronger effect of age on the support polysulfone sublayer than on the active polyamide layer. This study also shows that 24-h immersion in 1 M HNO3 solution strongly reduces the effect of age increasing permeability and decreasing electrical resistance of the PSU sample, while for PAC membrane both parameters present similar values after 12–48-h treatment.
Keywords: Composite and porous membranes; Chemical treatment; Diffusion; Impedance spectroscopy; Transport numbers; XPS;
A novel organoclay with antibacterial activity prepared from montmorillonite and Chlorhexidini Acetas by Hongping He; Dan Yang; Peng Yuan; Wei Shen; Ray L. Frost (235-243).
A series of novel organoclays with antibacterial activity were synthesized using Ca-montmorillonite and Chlorhexidini Acetas (CA) by ion-exchange. The resultant organoclays were characterized using X-ray diffraction (XRD), high-resolution thermogravimetric analysis (HRTG) and Fourier transform infrared spectroscopy (FTIR). Their antibacterial activity was assayed by so-called halo method. In the organoclays prepared at low CA concentration, CA ions within the clay interlayer adopt a lateral monolayer while a ‘kink’ state or a special state with partial overlapping of the intercalated CA in the organoclays prepared at 1.0–4.0 CEC. HRTG analysis demonstrates that CA located outside the clay interlayer exists in all synthesized organoclays, resulting from the complex molecular configuration of CA. The dramatic decrease of the surface adsorbed water and interlayer water is caused by the surface property transformation and the replacement of hydrated cations by cationic surfactant. These observations are supported by the results of FTIR. Antibacterial activity test against E. coli demonstrates that the antibacterial activity of the resultant organoclays strongly depends on the content of CA. Meanwhile, the resultant organoclay shows a long-term antibacterial activity that can last for at least one year. These novel organoclays are of potential use in synthesis of organoclay-based materials with antibacterial activity.A series of novel organoclays with antibacterial activity were synthesized using Ca-montmorillonite and Chlorhexidini Acetas (CA) by ion-exchange. The resultant organoclays were characterized using XRD, HRTG and FTIR. Their antibacterial activity was assayed by so-called halo method. In the organoclays prepared at low CA concentration, CA ions within the clay interlayer adopt a lateral monolayer while a ‘kink’ state or a special state with partial overlapping of the intercalated CA in the organoclays prepared at 1.0–4.0 CEC. HRTG analysis demonstrates that CA located outside the clay interlayer exists in all synthesized organoclays. Antibacterial activity test against E. coli demonstrates that the antibacterial activity of the resultant organoclays strongly depends on the content of CA. Meanwhile, the resultant organoclay shows a long-term antibacterial activity that can last for at least one year.
Keywords: Organoclay; Chlorhexidini Acetas; Antibacterial materials; Antibacterial activity; Halo method; Nanocomposite;
Structure and property studies of hybrid xerogels containing bridged positively charged 1,4-diazoniabicycle[2.2.2]octane dichloride by Leliz T. Arenas; Sílvio L.P. Dias; Celso C. Moro; Tania M.H. Costa; Edilson V. Benvenutti; Alzira M.S. Lucho; Yoshitaka Gushikem (244-250).
The compound di-3-n-propyltrimethoxysilane (1,4-diazoniabicycle[2.2.2]octane) dichloride, [(MeO)3Si(CH2)3N+(CH2CH2)3N+(CH2)3Si(OME)3]Cl2 was obtained and was used as a precursor reagent to obtain hybrid xerogels where the organic molecule was bonded to a silica framework by reacting the ends of both sides of the precursor reagent. That is, both ―Si(OME)3 groups react with tetraethylorthosilicate (TEOS) by hydrolysis–condensation reactions. The resulting hybrid xerogels with variable C/Si mole ratios were prepared and analyzed and their textural characteristics determined. The samples prepared presented micropores with diameter 1.5 nm, the chain length of which matched with the estimated length of the organic bridging group. The charged organic bridging groups allow the immobilization of hexacyanoferrate ions by an ion exchange process. The electron transfer process of the hexacyanoferrate anionic complex confined in the pores of the matrices was studied by cyclovoltammetry.
Keywords: Dabco; Silica-based polymers; Sol–gel; Electrochemical measurements;
Bubble vortex at surfaces of evaporating liquids by V.V. Yaminsky (251-260).
Air bubble in volatile liquid on exiting to the surface spins a vortex maintaining integrity of the film over an indefinite period of time. The shear stress associated with the surface tension increase in the adiabatic evaporation cooling drags the warmer liquid inwards into the film counteracting its capillary drainage out under gravity. The chaotic patterns, visualized with the aid of light interferometry, depend on liquid volatility, degree of vapor saturation, and air convection. The circulation intensifies and the frequency of hydrodynamic instabilities in the multiphase flow increases on the transition to strong turbulent regimes with increasing evaporation rate. Self-consistency of the physical mechanisms of solute and evaporation inhibition of bubble coalescence is verified through dimensional parametric analysis.
Keywords: Bubble coalescence; Surface elasticity; Interfacial slip; Film drainage; Multiphase flow; Marangoni effect;
Measurement and calculation of surface tension of molten Sn–Bi alloy by Jing Li; Zhangfu Yuan; Zhiyu Qiao; Jianfeng Fan; Yankun Xu; Jiajun Ke (261-265).
The surface tension of molten Sn–Bi (mole fraction X Bi = 0.455 ) alloy has been determined by the sessile drop method at oxygen partial pressure ( P O 2 ) of 1.0 × 10 −6 MPa and different temperatures. The experimental results have been analyzed and discussed, and the positive temperature coefficient of surface tension of molten Sn–Bi alloy has been elucidated. The surface tension of this molten alloy has also been obtained by calculation using STCBE based on Butler's equation and thermodynamic data. The experimental results agree well with the calculation values.The surface tensions of molten Sn–Bi alloy have been measured by sessile drop method, and the data acquirement comes from our self-developed software. The surface tension calculation is based on Butler's equation.
Keywords: Surface tension; Molten Sn–Bi alloy; STCBE; Sessile drop method; Temperature coefficient;
Interfacial tension of ethylene and aqueous solution of sodium dodecyl sulfate (SDS) in or near hydrate formation region by Hu Luo; Chang-Yu Sun; Qiang Huang; Bao-Zi Peng; Guang-Jin Chen (266-270).
The interfacial tensions between ethylene and an aqueous solution of SDS were measured using the pendant-drop method at 274.2 and 278.2 K and in the pressure range from 0.1 to 3.1 MPa, including hydrate formation points. The concentrations of sodium dodecyl sulfate (SDS) aqueous solution were 0, 100, 300, 500, 600, 700, 800, 900, and 1000 ppm. The effects of pressure on the critical micelle concentration (CMC) and the surface excess concentration were studied. It was demonstrated that both the CMC and the saturated surface excess concentration decreased with the increase of pressure.The critical micelle concentration and the surface excess concentration were dependent on pressure and SDS concentration. The coexistence of high-pressure ethylene changed the structure of bulk SDS solution and the interfacial properties.
Keywords: Critical micelle concentration; Ethylene; Interfacial tension; Sodium dodecyl sulfate; Surface excess concentration;
Understanding the role of surfactants on the preparation of ZnS nanocrystals by Milan Kanti Naskar; Amitava Patra; Minati Chatterjee (271-275).
We have synthesized surface modified ZnS nanoparticles of size 2–3 nm using non-ionic surfactant-stabilized reverse emulsions. The non-ionic surfactants in the Span series, i.e. sorbitan monolaurate (Span 20) and sorbitan monooleate (Span 80) of hydrophilic–lipophilic balance (HLB) values of 8.6 and 4.3, respectively, have been used for the stabilization of emulsions. The role of these surfactants in controlling the size and properties of the ZnS nanoparticles has been discussed. The triethylamine (TEA) has been proved to be the effective surface modifying (capping) agent for the preparation of free-standing ZnS nanoparticles. The Span 20 with the higher HLB value of 8.6 has been found to be highly suitable in synthesizing TEA-capped ZnS nanoparticles of smaller size and higher photophysical characteristics compared to that of the Span 80 of lower HLB value of 4.3. A mechanism for the formation of TEA-capped ZnS nanoparticles from the surfactant-stabilized reverse emulsions has been proposed.Photoluminescence spectra of ZnS nanoparticles using (a) Span 80 and (b) Span 20.
Keywords: Nanoparticles; ZnS; Emulsion; Span-80; Photoluminescence;
Structure modifications of AOT reverse micelles due to protein incorporation by Hadas Gochman-Hecht; Havazelet Bianco-Peled (276-283).
Structural modifications of AOT/water/isooctane reverse micelles due to incorporation of proteins were studied at various water contents and protein concentrations, using small-angle X-ray scattering (SAXS) experiments under static conditions, rheometry analysis, and SR-SAXS experiments under induced shear flow. Two proteins, lysozyme (pI 11.1, M w 14,300 Da) and BSA (pI 4.3, M w 66,700 Da), were chosen as models. SAXS analysis of protein-containing reverse micelles at low water content detected minima in the average micelle size versus protein concentration curve, for both proteins, below and above their isoelectric point. This minimum was attributed to changes in the size distribution of the reverse micelles. SAXS measurements of reverse micelles at high water content have shown them to have a cylindrical form. Incorporation of lysozyme at pH 7 into the cylindrical micelles induced a shape transition to spherical micelles, which was associated with a decreased viscosity. SR-SAXS measurements under induced shear flow and dynamic conditions revealed alignment of the cylindrical micelles in the flow direction. The anisotropy parameter, a measure of the degree of the spatial order, was found to increase with increasing shear rate and to decrease with increasing lysozyme concentration.
Keywords: AOT reversed micelles; Small-angle X-ray scattering; Lysozyme; BSA; Shear-induced alignment;
Characterization of mixed micelles of cationic twin tail surfactants with phospholipids using fluorescence spectroscopy by Mandeep Singh Bakshi; Kulbir Singh; Jasmeet Singh (284-291).
The pyrene fluorescence measurements have been carried out for various binary mixtures of micelle forming (L-α-diheptanoylphosphatidycholine, DHPC) and vesicle forming (L-α-dimyristoylphosphatidycholine, DMPC) phospholipids with different twin tail alkylammonium surfactants. The mixed micelle formation in all binary mixtures has been evaluated and it has been observed that the mixed micelle formation between the unlike components of phospholipid and cationic surfactants takes place due to the synergistic interactions. The influence of hydrophobicity of series of twin tail cationic surfactants has been studied on the degree of synergism.The pyrene fluorescence measurements have been carried out for various binary mixtures of micelle forming (L-α-diheptanoylphosphatidycholine, DHPC) and vesicle forming (L-α-dimyristoylphosphatidycholine, DMPC) phospholipids with different twin tail alkylammonium surfactants with and without spacer. It has been found that increase in the hydrophobicity of both twin hydrocarbon tails as well as that of spacer, generates stronger synergism with DHPC. In contrast, synergism decreases with an increase in the hydrophobicity of both hydrocarbon twin tails and spacer length in the mixed micelles of DMPC. The origin of synergism of both phospholipids with present cationic surfactants can only be attributed to an identical mechanism that is the reduction in polar head group repulsions.
Keywords: Mixed micelles; Phospholipids; Twin tail cationic surfactant; Synergism; Fluorescence measurements;
pH at the micellar interface: Synthesis of pH probes derived from salicylic acid, acid–base dissociation in sodium dodecyl sulfate micelles, and Poisson–Boltzmann simulation by T.P. Souza; D. Zanette; A.E. Kawanami; L. de Rezende; H.M. Ishiki; A.T. do Amaral; H. Chaimovich; A. Agostinho-Neto; I.M. Cuccovia (292-302).
The study of the H+ concentration at the micellar interface is a convenient system for modeling the distribution of H+ at interfaces. We have synthesized salicylic acid derivatives to analyze the proton dissociation of both the carboxylic and phenol groups of the probes, determining spectrophotometrically the apparent p K a 's (p K ap ) in sodium dodecyl sulfate, SDS, micelles with and without added salt. The synthesized probes were 2-hydroxy-5-(2-trimethylammoniumacetyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumacetyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumhexanoyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumundecanoyl)benzoate; 2-hydroxy-5-acetylbenzoic acid; and 2-hydroxy-5-dodecanoylbenzoic acid. Upon incorporation into SDS micelles the p K ap 's of both carboxylic and phenol groups increased by ca. 3 pH units and NaCl addition caused a decrease in the probe-incorporated p K ap . The experimental results were fitted with a cell model Poisson–Boltzmann (P–B) equation taking in consideration the effect of salt on the aggregation number of SDS and using the distance of the dissociating group as a parameter. The conformations of the probes were analyzed theoretically using two dielectric constants, e.g., 2 and 78. Both the P–B analysis and conformation calculations can be interpreted by assuming that the acid groups dissociate very close to, or at, the interface. Our results are consistent with the assumption that the intrinsic p K a 's of both carboxylic and phenol groups of the salicylic acid probes used here can be taken as those in water. Using this assumption the micellar and salt effects on the p K ap 's of the (trialkylammonium)benzoate probes were described accurately using a cell model P–B analysis.
Keywords: pH at the interface; pH probes; Surface pH in micelles; Synthesis of pH probes; Poisson–Botzmann analysus of surface pH;
Quantitative characterization of food products by two-dimensional D– T 2 and T 1 – T 2 distribution functions in a static gradient by Martin D. Hürlimann; Lauren Burcaw; Yi-Qiao Song (303-311).
We present new NMR techniques to characterize food products that are based on the measurement of two-dimensional diffusion– T 2 relaxation and T 1 – T 2 relaxation distribution functions. These measurements can be performed in magnets of modest strength and low homogeneity and do not require pulsed gradients. As an illustration, we present measurements on a range of dairy products that include milks, yogurt, cream, and cheeses. The two-dimensional distribution functions generally exhibit two distinct components that correspond to the aqueous phase and the liquid fat content. The aqueous phase exhibits a relatively sharp peak, characterized by a large T 1 / T 2 ratio of around 4. The diffusion coefficient and relaxation times are reduced from the values for bulk water by an amount that is sample specific. The fat signal has a similar signature in all samples. It is characterized by a wide T 2 distribution and a diffusion coefficient of 10 −11 m 2 / s for a diffusion time of 40 ms, determined by bounded diffusion in the fat globules of 3 μm diameter.
Keywords: Food product; Diffusion; Relaxation; Globule size;
Dynamics of shear-thinning suspensions of core–shell structured latex particles by Hiroshi Nakamura; Kazuyuki Tachi (312-316).
The rheological behavior and microstructure of shear-thinning suspensions of core–shell structured carboxylated latex particles were examined. The steady shear viscosity of the suspension increased with increasing dissociation of the carboxyl groups or increasing particle concentration, however the critical shear stress σ c and inter-particle distance ξ of the microstructure did not change. With increasing particle diameter, σ c increased and ξ decreased. These results were consistent with a Brownian hard sphere model, in which competition exists between the bulk mass transfer due to the applied field and diffusion of the particles. We confirmed that σ c depends on ξ, as expressed by σ c = 3 k T / 4 π ξ 3 . This relationship is consistent with the dynamics of a Brownian hard sphere model with particle diameter ξ. Thus the dynamics of shear-thinning suspensions of core–shell particles can be explained by a Brownian thermodynamic model.
Keywords: Suspension rheology; Core–shell particle; Carboxylated latex; Critical shear stress; Inter-particle distance; Brownian dynamics;
Effect of polyethyleneimine ion on the sorption of a reactive dye onto Leacril fabric: Electrokinetic properties and surface free energy of the system by M.M. Ramos-Tejada; A. Ontiveros-Ortega; E. Giménez-Martín; M. Espinosa-Jiménez; A. Molina Díaz (317-321).
Data are presented on the kinetics, electrokinetics, and surface free energy in the process of adsorption of polyethyleneimine (PEI) as a pretreatment of Leacril, later dyed with the reactive dye Remazol Brilliant Blue R (RBBR). The electrokinetic potential of Leacril is negative, due probably to the presence of sulfonate and sulfate end-group onto Leacril fibers. The zeta potential of Leacril decreases in absolute value as a function of NaCl concentration in solution, probably because of compression of the electrical double layer. The zeta potential of Leacril as a function of the concentration of PEI in solution increases because of the adsorption of PEI ions through chemical reaction between the sulfonate end-groups of Leacril and the amine groups of PEI. The adsorption kinetics shows that an increase in the concentration of PEI, brings about an increase in the amount of RBBR adsorbed onto the fiber. This may be an indication of the chemical reaction between the reactive groups of the polyelectrolyte and dye molecules. The behavior of the surface free energy of the systems involved confirms these conclusions.
Keywords: Textile fabrics; Dyeing; Polyelectrolytes; Zeta potential; Surface free energy;
Compression of dispersions to high stress under electric fields: Effects of concentration and dispersing oil by Rachel Lynch; Y. Meng; F.E. Filisko (322-328).
Dispersions of various concentrations (15–35%) were prepared in silicone oils of vastly different viscosities (40, 1000, 10,000, and 30,000 mPa s) and compressed to high values of stress while under an electric field of 2 kV/mm. A purpose of this study was to observe the effect of compression and E field simultaneously on these dispersions and assess predictions of most common and relevant theories. As shown, static stresses of over 1000 kPa could readily be obtained although the data presented here were held below 300 kPa to protect the load cell and equipment. The results are compared to and discussed in terms of a power law fit for stress vs gap since most theories predict such a dependence. The PL exponents fall around 3 ranges: (−2), (−3), and much less than (−3). The PL coefficients however reflect in systematic way the viscosities of the dispersing oils. The compressive stress vs strain behavior is studied with regard to particle concentration and dispersing oil viscosity.
Keywords: Squeeze flow; Electrorheological fluids; Suspension rheology; Complex fluids;
The effect of membrane potential on the development of chemical osmotic pressure in compacted clay by S. Bader; K. Heister (329-340).
When clay soils are subjected to salt concentration gradients, various interrelated processes come into play. It is known that chemical osmosis induces a water flow and that a membrane potential difference develops that counteracts diffusive flow of solutes and osmotic flow of water. In this paper, we present the results of experiments on the influence of membrane potential on chemical osmotic flow and diffusion of solutes and we show how we are able to derive the membrane potential value from theory. Moreover, the simultaneous development of water pressure, salt concentration and membrane potential difference are simulated using a model for combined chemico-electroosmosis in clays. A new method for short-circuiting the clay sample is employed to assess the influence of electrical effects on flow of water and transport of solutes.
Keywords: Chemical osmosis; Membrane potential; Modeling; Clay membranes; Electroosmosis;
Coupling between electroosmotically driven flow and bipolar faradaic depolarization processes in electron-conducting microchannels by Shizhi Qian; Jérôme F.L. Duval (341-352).
A quantitative theory is proposed for the analysis of steady electroosmotically driven flows within conducting cylindrical microchannels. Beyond a threshold value of the electric field applied in the electrolyte solution and parallel to the conducting surface, electrochemical oxidation and reduction reactions take place at the two extremities of the substrate. The spatial distribution of the corresponding local faradaic currents along the bipolar electrode is intrinsically coupled to that of the electric field in solution. The nonuniform distribution of the electric field alters the double layer composition, and in particular the zeta-potential value, along the conducting surface via the occurrence of concomitant electronic and ionic double layer charging processes. The combined spatial dependencies of the lateral electric field and electrokinetic potential considerably affects the distribution of the electroosmotic velocity field in the directions parallel and perpendicular to the surface depolarized by faradaic processes. In this paper, the coupling between bipolar electrodic behavior and electroosmosis is explicitly investigated for the case of irreversible—that is, kinetically controlled—electron transfer reactions. Typical simulation results are presented and illustrate the possibility of controlling and optimizing electroosmotic flows in conducting channels by electrochemical means.A mathematical model which accounts for the effects of the faradaic depolarization processes on the lateral electric field in solution, the interfacial zeta-potential and the electroosmotic flow within an electron-conducting cylindrical microchannel is proposed for the first time within the framework of kinetically controlled electron transfer reactions. The promising possibility of manipulating electroosmotic flows in metallic channels by electrochemical means is shown for the first time.
Keywords: Electroosmosis; Bipolar faradaic processes; Microfluidics; Lab-on-a-chip;
Electrokinetic phenomena in saturated compact clays by M. Rosanne; M. Paszkuta; P.M. Adler (353-364).
The membrane potential, the pressure difference, and the concentration difference induced by an applied concentration gradient through samples of compact clay were measured as functions of sodium chloride concentration and of porosity. The results of some previous numerical predictions are recalled to be functions of a characteristic length scale which can be derived from conductivity and permeability. Generally, the experimental data were in agreement with these numerical predictions. Therefore, nondiagonal coupling coefficients can be derived with acceptable precision from the diagonal coefficients.The membrane potential (see figure), the pressure difference, and the concentration difference induced by an applied concentration gradient can be estimated from conductivity and permeability.
Keywords: Porous media; Coupled transports; Clay; Experimental;
A novel preparation route for platinum–polystyrene heterogeneous nanocomposite particles using alcohol-reduction method by Dae-Wook Kim; Jong-Min Lee; Chul Oh; Deok-Soo Kim; Seong-Geun Oh (365-369).
Platinum nanoparticles are homogeneously immobilized onto the polystyrene surface using alcohol-reduction method for the first time. Sulfonate groups were employed as a chemical protocol to make a binding between platinum nanoparticle and polystyrene surface. A large number of quasi-spherical platinum nanoparticles with a size of ∼5 nm in diameter are formed and strongly attached to the polystyrene surface modified with sulfonate groups. The formation mechanism of composite materials was discussed briefly. The most distinguished features of this novel preparation route include simple operation, and absence of the toxic reducing agent. In addition, this novel preparation route can be extended to the preparation of other noble metal–polymer heterogeneous nanocomposites such as silver, gold, palladium, iridium and ruthenium.
Keywords: Nanocomposite; Alcohol reduction; Polyol process; Polystyrene; Platinum;
Computer simulations of surfactant monolayers at solid walls by Hector Dominguez; Armando Gama Goicochea; Noé Mendoza; José Alejandre (370-373).
A series of molecular dynamics simulations to study the structure of a surfactant monolayer near real surfaces was carried out. A comparison of two different surfaces, TiO2 and SiO2, with the same monolayer was performed. Moreover, each surface was modeled by two different approaches, the first model considers the complete structure of a TiO2 (or SiO2) wall, whereas the second model is a continuous solid wall with an effective potential. Both wall models give essentially the same monolayer configuration suggesting that the explicit form of the wall does not play a relevant role to study the structure of surfactant monolayers close to planar surfaces.The structure of a surfactant monolayer close to a continuous or a corrugated wall does not show much difference at each solid surface.
Keywords: Liquid–solid interface; Surfactant monolayers; Computer simulations; Monolayer structure;
Calculation of interparticle spacing in colloidal systems by Tian Hao; Richard E. Riman (374-377).
Interparticle spacing (IPS) is a very important parameter for estimation of the viscosity of a suspension. A new equation for calculating IPS was derived on the assumption that each particle is surrounded by a virtual cell, which is the free volume that each particle can occupy. This idea was originated by Kuwabara and widely used for calculating electrophoretic mobility in concentrated suspensions. Our new IPS equation was evaluated and compared with a pre-existing IPS equation proposed by Dinger and Funk using experimental data from three commercial sources of titania. Our equation was found to give reasonable values, including cases where the equation of Dinger and Funk gave anomalous values.
by Arthur Hubbard (378).