Journal of Colloid And Interface Science (v.291, #2)
Editorial Board (CO1).
Adsorption of CTAB onto perlite samples from aqueous solutions by Mahir Alkan; Mecit Karadaş; Mehmet Doğan; Özkan Demirbaş (309-318).
In this study, the adsorption properties of unexpanded and expanded perlite samples in aqueous cetyltrimethylammonium bromide (CTAB) solutions were investigated as a function of ionic strength, pH, and temperature. It was found that the amount of cetyltrimethylammonium bromide adsorbed onto unexpanded perlite was greater than that onto expanded perlite. For both perlite samples, the sorption capacity increased with increasing ionic strength and pH and decreasing temperature. Experimental data were analyzed by Langmuir and Freundlich isotherms and it was found that the experimental data were correlated reasonably well by the Freundlich adsorption isotherm. Furthermore, the isotherm parameters ( K F and n) were also calculated. The adsorption enthalpy was determined from experimental data at different temperatures. Results have shown that the interaction between the perlite surface and CTAB is a physical interaction, and the adsorption process is an exothermic one.
Keywords: Perlite; Zeta potential; Surfactants; Adsorption; Adsorption heat; Adsorption isotherms;
Copper and zinc removal from aqueous solution by mixed mineral systems by D.E. Egirani; A.R. Baker; J.E. Andrews (319-325).
This study investigates the reactivity and removal kinetics of Cu and Zn onto mixed mineral systems from aqueous solution related to acid mine drainage impacted areas. The sorbents used were kaolinite, Al-montmorillonite, goethite, and their mixtures. The effects of surface charge, proton coefficient, and sorption kinetics were studied at room temperature ( 23 ± 2 °C). Using an empirical model, mineral mixing reduced the exchange of protons for sorbing ions and the acidity of the reactive sites, thus impeding Cu and Zn removal by proton exchange. Based on the amount of Cu and Zn sorbed on the mixed mineral suspensions at ionic strength 0.01 to 0.1 M and pH 4, it is suggested that Cu and Zn removal from aqueous solution was by both inner and outer sphere complexation. Mineral mixing reduced the transfer rate of Cu relative to the single mineral suspensions in both slow and fast reaction phases. The behavior of the mixed suspensions in Cu and Zn sorption suggest that different reactive sites were involved at the onset of sorption, becoming similar to those of the single mineral components over time.
Keywords: Zinc; Copper; Clay minerals; (Hydr)oxides; Sorption; Freundlich model; Mixed mineral systems; Reactivity; Removal kinetics;
Copper and zinc removal from aqueous solution by mixed mineral systems by D.E. Egirani; A.R. Baker; J.E. Andrews (326-333).
This study investigates Cu and Zn removal onto binary mixed mineral sorbents from simulated wastewater, relevant to streams impacted by acid mine drainage and effluents. Mixed suspensions of kaolinite/montmorillonite and kaolinite/goethite exhibited different sorption behavior from the single mineral components, reducing Cu and Zn removal (except Cu sorbed on montmorillonite/goethite) over the range of pH investigated. Cu and Zn removal by the electrolyzed systems showed a complex response to increased ionic strength, which increased solid concentration, leading to lower Cu and Zn sorption. Enhanced Cu sorption on the montmorillonite/goethite as age increased may be attributed to increased hydroxylation of the mineral surface resulting in the formation of new reactive sites.
Keywords: Copper; Zinc; Clay minerals; (Hydr)oxides; Sorption; Mixed minerals; pH; Ionic strength; Solid concentration and aging;
New approach to determination of surface heterogeneity of adsorbents and catalysts from the temperature programmed desorption (TPD) technique: One step beyond the condensation approximation (CA) method by Piotr Kowalczyk; Katsumi Kaneko; Artur P. Terzyk; Hideki Tanaka; Hirofumi Kanoh; Piotr A. Gauden (334-344).
Recovery of the desorption activation energy distribution from the experimental temperature programmed desorption (TPD) spectra is among the most difficult problems of adsorption science. Since the heterogeneity effects strongly influence on transport, diffusion, and catalytic reaction time, the estimation of their magnitude is very important for practical purposes. Up to the present, several theories have been used for the interpretation of the TPD results. Almost all advanced theoretical approaches take into account the effect of surface disorder (heterogeneity in desorption activation energy); however, they ignore the numerical difficulties coming from the “ill-posed” character of the linear Fredholm integral equations appearing in the theoretical description of the TPD results. Thus, there is a growing interest in developing novel methods supported by powerful numerical algorithms taking this into account. In the current study we propose a new approach and consider the theoretical aspect as well as numerical problems appearing in the TPD analysis. Our modeling is based on the well-known and generally accepted “absolute rate theory,” which has been used extensively for the interpretation of TPD results. We propose and verify (applying computer simulations) the new advanced numerical hybrid type algorithms taking into account the heterogeneity effects. They seem to be very promising in TPD spectra analysis. The stability of the proposed advanced numerical methods is confirmed by the computer simulation experiments, and the results are compared with those obtained from the condensation approximation (CA) method.
Keywords: Temperature programmed desorption; Adsorption rate theory; Computer simulations;
Adsorption behavior of copper and cyanide ions at TiO2–solution interface by M.A. Barakat (345-352).
Adsorption of both copper and cyanide ions in the absence and in the presence of their complexes at TiO2–solution interfaces was investigated. The objective of this study was to demonstrate the possibility of removing heavy metal ions, exemplified by Cu(II), from aqueous solution in the presence of a ligand, e.g., CN−. Several parameters such as pH and Cu(II) and CH− ion concentration that may affect the magnitude of copper and cyanide adsorption were studied. The equilibrium of Cu–CN speciation distribution in solution and stability constant calculations have been investigated to determine the adsorption behavior of Cu(II). Results revealed that free Cu(II) ions (in the absence of CN−) were completely separated at pH ⩾ 8 , while the adsorption of free cyanide ions, in the absence of Cu(II), reached a maximum value of 48% at pH 7. For Cu–CN complexes, the presence of CN− in excessive amount with respect to Cu(II) retarded the adsorption of Cu(II). This is attributed to the formation of multivalent anionic cyano–copper complexes such as Cu(CN)2− 3 and Cu(CN)3− 4.
Keywords: Adsorption; Removal; Cu(II); CN− ions; TiO2;
Physisorbed water layer formation on fully hydroxylated mesoporous silicas by Kenneth E. Collins; Vanessa R. de Camargo; Alessandra B. Dimiras; Deborah T.C. Menezes; Priscila A. da Silva; Carol H. Collins (353-360).
Kinetic adsorption isotherms were obtained by gravimetric determination of water adsorption into fully hydroxylated mesoporous silicas using samples exposed to controlled humidity air at 22 ± 2 °C . Twenty kinetic isotherms at several relative humidities (11, 33, 43, 51, 75, and 85%) were obtained with 11 different batches of silica using this simple procedure to obtain quantitative information on the formation of H2O adsorbates. The H2O surface concentrations obtained from the plateau data of individual kinetic adsorption isotherms at 43 and 51% RH, typically precise to about ±1%, show that a complete monolayer is formed with negligible second-layer adsorption at these relative humidities. This monolayer has a surface concentration of 7.68 ± 0.30 μmol H2O/m2, which is lower than the quasi-equilibrium concentration at these relative humidities obtained by the conventional equilibrium-isotherm procedure. Comparison with the Kiselev–Zhuravlev concentration of silanol groups on fully hydroxylated silicas ( 7.6 ± 0.8 μmol SiOH/m2) confirms 1:1 H2O:SiOH stoichiometry of this monolayer. The presence of partial-layer structures at 2.85 ± 0.1 and 5.7 ± 0.1 μmol H2O/m2 is suggested by isotherms at 11 and 33% RH, respectively, while a bilayer at ∼ 14 ± 1 μmol H2O/m2 is suggested by kinetic isotherms at 75 and 85% RH.
Keywords: Silica; Adsorption; Water; Monolayer; Kinetic isotherms;
Friction force measurements relevant to de-inking by means of atomic force microscope by Katarina Theander; Robert J. Pugh; Mark W. Rutland (361-368).
In the pulping step of the de-inking process, the ink detaches from the fibers due to shear and physical chemical interaction. In order to get a better understanding of the forces involved between cellulose and ink, the atomic force microscope and the colloidal probe technique have been used in the presence of a model chemical dispersant (hexa-ethyleneglycol mono n-dodecyl ether, C12E6). A cellulose bead was used as the colloidal probe and three different lower surfaces have been used, an alkyd resin, mica and a cellulose sphere. The normal and lateral forces have been measured at a range of nonionic concentrations. It was found that the lateral sliding friction forces deceased with increasing surfactant concentration for both the alkyd resin and mica while no differences were observed for the cellulose surface. In addition, only a very small change in normal force could be detected for the alkyd surface as the concentration changed.
Keywords: De-inking; Atomic force microscopy (AFM); Colloidal probe; Sliding friction; Nonionic surfactant; C12E6;
Kinetics and equilibrium adsorption of Cu(II), Cd(II), and Ni(II) ions by chitosan functionalized with 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol by Karin Cristiane Justi; Valfredo T. Fávere; Mauro C.M. Laranjeira; Ademir Neves; Rosely A. Peralta (369-374).
Chitosan biopolymer chemically modified with the complexation agent 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol (BPMAMF) was employed to study the kinetics and the equilibrium adsorption of Cu(II), Cd(II), and Ni(II) metal ions as functions of the pH solution. The maximum adsorption of Cu(II) was found at pH 6.0, while the Cd(II) and Ni(II) maximum adsorption occurred in acidic media, at pH 2.0 and 3.0, respectively. The kinetics was evaluated utilizing the pseudo-first-order and pseudo-second-order equation models and the equilibrium data were analyzed by Langmuir and Freundlich isotherms models. The adsorption kinetics follows the mechanism of the pseudo-second-order equation for all studied systems and this mechanism suggests that the adsorption rate of metal ions by CHS–BPMAMF depends on the number of ions on the adsorbent surface, as well as on their number at equilibrium. The best interpretation for the equilibrium data was given by the Langmuir isotherm and the maximum adsorption capacities were 109 mg g−1 for Cu(II), 38.5 mg g−1 for Cd(II), and 9.6 mg g−1 for Ni(II). The obtained results show that chitosan modified with BPMAMF ligand presented higher adsorption capacity for Cu(II) in all studied pH ranges. Chitosan biopolymer, chemically modified with the complexation agent 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol (BPMAMFF), was employed to study the kinetics and the equilibrium adsorption of metal ions.Display Omitted
Keywords: Cu(II); Cd(II); Ni(II); Chitosan; Biopolymer; Kinetics; Adsorption;
Cluster aggregation and fragmentation kinetics model for gelation by Rujun Li; Benjamin J. McCoy; R. Bertrum Diemer (375-387).
Gelation can occur in polymer, hydrogel, and colloid systems that undergo reversible aggregation–fragmentation (crosslinking accompanied by breakage). Gelation, characterized by rapid divergence of weight-average molecular weight and viscosity due to initial network formation, can be reversed if conditions change. In this paper, reversible aggregation and fragmentation in the pre-gelation time period are modeled with distribution kinetics. Moment equations are obtained from the population balance equation, and solved for eight different rate kernels. We identify the cases for which gelation is possible and obtain the critical values for the rate constants that allow gelation. The model provides a good simulation of published experimental data for aggregation and degradation of plasticized wheat gluten during thermo-mechanical treatments. We also evaluate two closure approximations based on Γ and log-normal distributions, and conclude that log-normal closure predicts all five possible steady states, in agreement with the Vigil–Ziff criterion, and Γ closure predicts only three. However, Γ closure approximates the steady state either closely or exactly, whereas log-normal closure only poorly approximates the steady-state distribution.
Keywords: Aggregation; Fragmentation; Reversible; Gelation; Distribution kinetics;
Polymerization contraction of light-cured composite resins containing silica/polymethylmethacrylate bonded microstructured networks by A. Pefferkorn; Y. Haïkel; E. Pefferkorn (388-395).
The adsorption of methylmethacrylate polymer at silica/methylmethacrylate interfaces was determined to provide microstructured networks whose structural characteristics were determined to be controlled by the amount of polymer initially supplied to the system. First, the microstructure was investigated by determining as a function of the amount of polymer (i) the shrinking rate due to evaporation of the methylmethacrylate monomer, (ii) the rate of sedimentation of the silica/polymer complexes in the methylmethacrylate monomer, and (iii) the height of the sediment in the long term. These different characteristics were found to be strongly correlated. Second, the sedimentation characteristics were determined as a function of the amount of polymer initially supplied to the dispersion of the same silica/polymer system in the ethylene glycol dimethacrylate monomer. Then the rate of the polymerization contraction during light-curing of the resin was determined for the sediment recovered after centrifugation. The slowest polymerization contraction and the smallest contraction were obtained with the filler/polymer/resin system composed of aggregates of medium porosity and size.
Keywords: Aggregation of silica particles; Polymerization contraction; Silica/polymer complexes in organic media;
Observations on clear solution silicalite-1 growth by nanoslabs by Ayşe Erdem-Şenatalar; Robert W. Thompson (396-404).
Several research groups have reported the presence of nanometer-sized particles (nanoslabs) in clear solutions, which precipitate the crystalline MFI (ZSM-5) structure. Debate about the growth mechanism for Al-free ZSM-5 (silicalite-1) has revolved around growth by small silicate units (monomers, dimers, etc.) from solution vs growth by nanoslab addition. A model developed for precipitation of uniform sized colloids by addition of sub-colloidal precursor units has been adapted for this zeolite synthesis system. Parameter values were adjusted for the simulation results to match experimental observations from work reported previously, at least to the extent possible. The model involved the simultaneous solution of up to 6000 ordinary differential equations, and required computation times of up to 24 h. The results shed light on the crystal growth mechanism, but pose questions for further investigations of the nucleation mechanism. A model for colloidal particle growth by nanoprecursor addition was applied to silicalite-1 syntheses, and predicted the solution concentration, nucleation rate, and size distribution of particles as functions of time.Display Omitted
Keywords: Crystallization modeling; Growth by nanoslabs; Zeolite synthesis;
Film formation from pure and mixed latices; transient fluorescence study by Şaziye Uğur; Önder Pekcan (405-410).
A fast transient fluorescence technique was used to study latex film formation induced by organic solvent vapor. Mixtures of pyrene (P)- and naphthalene (N)-labeled and/or pure naphthalene-labeled latex films were prepared separately from poly(methyl methacrylate) (PMMA) particles. Then these pure and mixed latex films were exposed to vapor of various chloroform–heptane mixtures in seven different experiments. In both films, fluorescence lifetimes from N were monitored during vapor-induced film formation. It was observed that N lifetimes decreased as the vapor exposure time is increased. A Stern–Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in N lifetimes. A Prager–Tirrell model was employed to obtain back-and-forth frequencies, ν, of reptating PMMA chains during latex film formation induced by solvent vapor. In both pure and mixed latex films, ν values were found to be correlated with the chloroform content in the vapor mixture. It was observed that polymer interdiffusion obeyed a t 1 / 2 law during film formation. Both in pure and mixed latex films back-and-forth frequencies, ν ( B ) , were found to be correlated with the chloroform content in vapour mixture.Display Omitted
Preparation and properties of poly(acrylic acid) oligomer stabilized superparamagnetic ferrofluid by Chia-Lung Lin; Chia-Fen Lee; Wen-Yen Chiu (411-420).
Ferrofluids, which are stable dispersions of magnetic particles, behave as liquids that have strong magnetic properties. Nanoparticles of magnetite with a mean diameter of 10–15 nm, which are in the range of superparamagnetism, are usually prepared by the traditional method of co-precipitation from ferrous and ferric electrolyte solution. When diluted, the ferrofluid dispersions are not stable if anionic or cationic surfactants are used as the stabilizer. This work presents an efficient way to prepare a stable aqueous nanomagnetite dispersion. A stable ferrofluid containing Fe3O4 nanoparticles was synthesized via co-precipitation in the presence of poly(acrylic acid) oligomer. The mechanism, microstructure, and properties of the ferrofluid were investigated. The results indicate that the PAA oligomers promoted the nucleation and inhibited the growth of the magnetic iron oxide, and the average diameter of each individual Fe3O4 particle was smaller than 10 nm. In addition, the PAA oligomers provided both electrostatic and steric repulsion against particle aggregation, and the stability of dispersions could be controlled by adjusting the pH value of solution. A small amount of Fe2O3 was found in the nanoparticles but the superparamagnetic behavior of the nanoparticles was not affected.
Keywords: Fe3O4; Poly(acrylic acid); Ferrofluid; Superparamagnetic; Nanoparticles;
Modeling of ionic equilibria of trace metals (Cu2+, Zn2+, Cd2+) in concentrated aqueous electrolyte solutions at 25 °C by Sergey Pivovarov (421-432).
This work presents a model of activity coefficients and a database for ionic equilibria of Cu2+, Zn2+, and Cd2+ in (H+, Na+, K+, Mg2+, Ca2+)(OH−, Cl−, NO− 3, ClO− 4, HSO− 4, SO2− 4, HCO− 3, CO2− 3) aqueous media valid up to 6–12 m ionic strength. The activity coefficient of a dissolved species is represented by empirical equation ln γ i = − ( A γ / 2 ) z i 2 ( I − I exp ( − 8 I 0.5 ) ) 1 / 3 + ∑ b i j m j , where A γ is Debye–Hückel constant (1.17 at 25 °C), γ i and z i are activity coefficient and charge of a dissolved species i, I is molal ionic strength, b i j is model parameter, and m j is molal concentration of dissolved species. The model is applicable to the modeling of ionic equilibria, as well as to simulation of solubility of salts in mixed electrolyte solutions.
Keywords: Activity coefficient; Ionic strength; Copper; Zinc; Cadmium; Hydrolysis; Chloride; Sulfate; Carbonate; Complex; Constant;
Enhancement of the electrochemical properties of LiMn2O4 through Al3+ and F− co-substitution by Shu-Juan Bao; Yan-Yu Liang; Wen-Jia Zhou; Ben-Lin He; Hu-Lin Li (433-437).
The cathode-active materials LiMn2O4, LiAl0.1Mn1.9O4, and LiAl0.1Mn1.9O3.9F0.1 were synthesized by a microwave-assisted sol–gel method. The influence of different doping elements on the structural and electrochemical properties of the as-prepared samples was investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical experiments. The results indicated that fluorine plays an important role in controlling the morphology, and the doped aluminum could enhance significantly the stability of spinel-type LiMn2O4. The initial discharge capacity of the Al3+ and F− co-substituted specimen reached 129.8 mA h/g and has a high capacity retention after 40 cycles. The outstanding electrochemical properties of LiAl0.1Mn1.9O3.9F0.1 make it a possible promising cathode material for lithium-ion batteries. The effect of LiF on controlling morphology and particle size, and the material's high specific capacity and good cycleability were discussed.Display Omitted
Keywords: Lithium-ion batteries; LiAl0.1Mn1.9O3.9F0.1; Chemical substitution; Microwave-assisted sol–gel method;
In vitro stability study of organosilane self-assemble monolayers and multilayers by Anfeng Wang; Haiying Tang; Ting Cao; Steven O. Salley; K.Y. Simon Ng (438-447).
The stability of self-assembled monolayers (SAMs) and multilayers formed on silicon surface by amino-terminated silanes and SAMs formed by alkyl and glycidyl terminated silanes were investigated in vitro with saline solution at 37 °C for up to 10 days. FTIR and XPS results indicated that amino-terminated SAMs and multilayers are very unstable if the alkyl chain is short ((CH2)3), while stable if the alkyl chain is long ((CH2)11). On the other hand, alkyl-terminated SAMs are very stable regardless of the alkyl chain length, and glycidyl terminated SAM retained approximately 77% of the organosilane molecules after 10 days. Hydrogen bonding between the organosilane monomer and silicon surface and among the organosilane monomers is believed to contribute to the instability of the SAM and multilayer formed by amino-terminated silane with a short alkyl chain ((CH2)3). Therefore, the widely used (3-aminopropyl) trimethoxysilane (APTMS) SAM and multilayer may not be suitable for implantable biomedical applications. The stability of self-assembled monolayers and multilayers formed on silicon surface by various organosilanes was investigated in vitro with saline solution at 37 °C.Display Omitted
Keywords: Self-assembled monolayer; Multilayer; Organosilane; Silicon; Stability; In vitro;
Effects of self-assembly process of latex spheres on the final topology of macroporous silica by Djalma A. Barros Filho; Cíntia Hisano; Roberto Bertholdo; Matheus G. Schiavetto; Celso Santilli; Sidney J.L. Ribeiro; Younés Messaddeq (448-464).
This paper surveys the topology of macroporous silica prepared using latex templates covering the submicrometric range (0.1–0.7 μm). The behavior of latex spheres in aqueous dispersion has been analyzed by dynamic light scattering (DLS) measurement indicating the most appropriate conditions to form well-defined cubic arrays. The optical behavior of latex spheres has been analyzed by transmittance and reflectance measurements in order to determine their diameter and filling factor when they were assembled in bidimensional arrays. Macroscopic templates have been obtained by a centrifugation process and their crystalline ordering has been confirmed by porosimetry and scanning electron microscopy. These self-assembled structures have been used to produce macroporous silica, whose final topology depends on the pore size distribution of the original template. It has been seen that latex spheres are ordered in a predominant fcc arrangement with slipping of tetragonal pores due to the action of attractive electrostatic interactions. The main effect is to change the spherical shape of voids in macroporous silica into a hexagonal configuration with possible applications to fabricate photonic devices with novel optical properties.
Keywords: Latex spheres; Photonic crystals; Chemical template; Macroporous silica; Porous material; Self-assembly; Thin films; Colloid stability;
Incorporation of porphyrins into mesopores of MCM-41 by Hidekazu Tanaka; Tomomi Usui; Shinichiro Sugiyama; Shingo Horibe; Hideo Shiratori; Ryozi Hino (465-470).
To introduce porphyrins such as the alcoholic-hydroxyl-group-appended free base porphyrin derivative (HP) of 5-[4-(3-hydroxylpropyloxycabonyl)phenyl]-10,15,20-triphenylphorphine into mesopores of MCM-41, samples were treated with 0–4.0 mmol dm−3 HP toluene solutions and the materials obtained were characterized by various means. The framework structure of MCM-41 was not altered by the treatment. With increasing HP concentration, the specific surface area and pore size decreased; in contrast, the number of HP molecules in the material increased almost linearly from 0 to 0.17 groups nm−2. These facts reveal that the HP molecules are incorporated into mesopores of MCM-41. IR results indicated that the hydroxyl group of the HP molecule reacts with surface free Si―OH groups of the MCM-41 by a dehydration reaction. Diffuse reflection UV–vis spectra of the HP-introduced material were almost the same as that of pure HP molecules. The Beers plot suggested that the HP molecules in the material are dispersed at an HP concentration less than 1.0 mmol dm−3, and above that concentration, aggregation or flattening of the HP molecules on the MCM-41 surface takes place.
Keywords: MCM-41; Mesopores; Porphyrin; UV–vis spectrum; Surface Si―OH group;
Rapid adsorption and entrapment of benzoic acid molecules onto mesoporous silica (FSM-16) by Yuichi Tozuka; Sara Sasaoka; Ayako Nagae; Kunikazu Moribe; Toshio Oguchi; Keiji Yamamoto (471-476).
Changes in the molecular state of benzoic acid (BA) in the presence of folded sheet mesoporous material (FSM-16), which has uniformly sized cylindrical mesopores and a large surface area, were assessed with several analyses. When BA was blended with FSM-16 for 5 min (BA content = 30%), the X-ray diffraction peaks of BA crystals disappeared, suggesting an amorphous state. Fluorescence analysis of the mixture showed a new fluorescence emission peak for BA at 386 nm after mixing with FSM-16. Fluorescence lifetime analysis of the BA component in the mixture at 386 nm showed a longer lifetime in comparison with that of BA crystals. The solid-state 13C CP/MAS and PST/MAS NMR spectra of the mixture with FSM-16 showed a significantly different spectral pattern from the mixture with nonporous glass, whose NMR spectra were identical to those of BA crystals. These results indicate that BA molecules disperse quickly into the hexagonal channels of FSM-16 by a simple blending procedure and adsorbed BA molecules had clearly different physicochemical properties to BA crystals.
Keywords: Porous material; Adsorption; Solid-state NMR; Fluorescence spectra; Benzoic acid; FSM-16;
Influence of templating latex on spray dried nanocomposite powders studied by small angle scattering by A. Thill; O. Spalla (477-488).
Nanoporous powders are prepared in a single step by spray-drying mixtures of small inorganic and larger organic nanoparticles. The structure of these powders has been studied as a function of the mixture's composition using silica and polybromostyrene nanoparticles. Scanning electron microscopy reveals the presence of an increasing concentration of mesopores as the concentration of polybromostyrene increases. By coupling thermogravimetric analysis and ultra-small-angle X-ray scattering, the structure is quantitatively linked to the composition of the porous grains. Experimental USAXS intensities are compared to scattering models for the composite powders. It allows to demonstrate that (i) all mesopores are empty even in the center of the grains, (ii) part of the polymer remains in the micropores of the dried grains. A quantification of the fraction of micropores filled by residual polymer is presented. Such a synthesis procedure can be used to produce hydrophobic porous powders in a one-step process.
Keywords: SAXS; USAXS; Spray drying; Confined colloids; Nanoparticles; Porous powders;
Effect of sodium dodecylbenzene sulfonate on the motion of three-phase contact lines on the Wilhelmy plate surface by Stoyan I. Karakashev; Chi M. Phan; Anh V. Nguyen (489-496).
The combined approach of the molecular-kinetic and hydrodynamic theories for description of the motion of three-phase gas–liquid–solid contact lines has been examined using the Wilhelmy plate method. The whole dynamic meniscus has been divided into molecular, hydrodynamic, and static-like regions. The Young–Laplace equation and the molecular-kinetic and hydrodynamic dewetting theories have been applied to describe the meniscus profiles and contact angle. The dissipative forces accompanying the dynamic dewetting have also been investigated. The experiments with a Wilhelmy plate made from an acrylic polymer sheet were carried out using a computerized apparatus for contact angle analysis (OCA 20, DataPhysics, Germany). The extrapolated dynamic contact angle versus velocity of the three-phase contact line for Milli-Q water and 5 × 10 −4 M SDBS solution was experimentally obtained and compared with the combined MHD models with low and moderate Reynolds numbers. The models predict similar results for the extrapolated contact angle. SDBS decreases the equilibrium contact angle and increases the molecular jumping length but does not affect the molecular frequency significantly. The hydrodynamic deformation of the meniscus, viscous dissipation, and friction were also influenced by the SDBS surfactant.
Keywords: Three-phase contact line; Dynamic meniscus; Contact angle; Wilhelmy plate;
Interpretation of contact angle measurements on two different fluoropolymers for the determination of solid surface tension by H. Tavana; F. Simon; K. Grundke; D.Y. Kwok; M.L. Hair; A.W. Neumann (497-506).
Contact angle measurements with a large number of liquids on the semi-fluorinated acryl polymer EGC-1700 films are reported. The surface tension was determined to be γ sv = 13.84 mJ / m 2 from contact angles of octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS). Inertness of these two liquids makes them ideal for determination of surface tension of low-energy fluoropolymers. On the other hand, contact angles of many other liquids deviated somewhat from a smooth contact angle pattern that represents the EGC-1700 surface tension. It is argued that noninertness of the molecules of these liquids gives rise to specific interactions with the polymer film, causing the deviations. Furthermore, contact angles of a series of n-alkanes (n-hexane to n-hexadecane) showed systematic deviations from this curve, similar to the trend observed for n-alkanes/Teflon AF 1600 systems studied earlier. Adsorption of vapor of short-chain liquids onto the polymer film caused their contact angles to fall above the γ sv = 13.84 mJ / m 2 curve, and a parallel alignment of molecules of the long-chain n-alkanes in the vicinity of the solid was the explanation for the deviation of their contact angles below it. It is found that vapor adsorption effect is more significant in the case of Teflon AF 1600, while the alignment of liquid molecules close to the surface is more pronounced for EGC-1700. Films of two fluoropolymers show very different properties upon contact with a liquid. Teflon AF 1600 is inert but EGC-1700 chains are reoriented.Display Omitted
Keywords: Solid surface tension; Contact angle; Fluoropolymers; n-Alkanes; ADAS-P; Specific interactions;
Wetting of a particle in a thin film by Jennifer Fiegel; Fang Jin; Justin Hanes; Kathleen Stebe (507-514).
When a particle is placed in a thin liquid film on a planar substrate, the liquid either climbs or descends the particle surface to satisfy its wetting boundary condition. Analytical solutions for the film shape, the degree of particle immersion, and the downward force exerted by the wetting meniscus on the particle are presented in the limit of small Bond number. When line tension is significant, multiple solutions for the equilibrium meniscus position emerge. When the substrate is unyielding, a dewetting transition is predicted; that is, it is energetically favorable for the particle to rest on top of the film rather than remain immersed in it. If the substrate can bend, the energy to drive this bending is found in the limits of slow or rapid solid deflection. These results are significant in a wide array of disciplines, including controlled delivery of drugs to pulmonary airways, the probing of liquid film/particle interface properties using particles affixed to AFM tips and the positioning of small particles in thin films to create patterned media.
Nonlinear stability analysis of a two-layer thin liquid film: Dewetting and autophobic behavior by L.S. Fisher; A.A. Golovin (515-528).
The nonlinear stability analysis of a liquid film composed of two superposed thin layers of immiscible liquids resting on a solid substrate is performed. It is shown that the coupling of van der Waals interactions in the two layers can lead to an autophobic behavior in the form of spinodal decomposition of two planar liquid layers into a system of localized drops divided by almost planar wetting layers. The results of the weakly nonlinear analysis near the instability threshold are confirmed by the numerical solution of a system of two strongly nonlinear evolution equations for the liquid–liquid and liquid–gas interfaces. The kinetics of the drop coarsening at late stages is studied and is found to be close to that reported for a one-layer film. It is also shown that gravity effects can become significant even for very thin two-layer films.
Keywords: Thin liquid films; Van der Waals interactions; Dewetting; Spinodal decomposition;
Micellization of AOT in aqueous sodium chloride, sodium acetate, sodium propionate, and sodium butyrate media: A case of two different concentration regions of counterion binding by I.M. Umlong; K. Ismail (529-536).
Critical micelle concentrations of AOT in water in the presence of sodium chloride, sodium acetate, sodium propionate, and sodium butyrate were determined at 25 °C by the surface tension method. The co-ions do not have any effect on the value of critical micelle concentration. The surface density of AOT at the air–water interface increases in the presence of added electrolyte and attains a maximum value of 2.5 ± 0.1 mol m−2 at a particular electrolyte concentration which is different for sodium chloride and the other three electrolytes. From the Corrin–Harkins plot it has been found that for AOT micelles the counterion binding constant has values 0.40 and 0.82 below and above ∼0.015 mol kg−1 electrolyte concentration ( c ∗ ), respectively. Measurement of sodium ion activity from the EMF method has confirmed such a shift in the counterion binding constant of AOT at c ∗ . The higher value of the counterion binding constant for AOT has been reported for the first time. From fluorescence spectroscopy it has been found that the aggregation number of AOT is 22 in water and its average aggregation numbers in the presence of electrolytes are about 34 and 136 below and above c ∗ , respectively. The increase by a factor of 2 in the counterion binding constant is shown to be due to a change in the shape of the AOT micelles around c ∗ . The shape of AOT micelles in the electrolyte concentration range ⩽ c ∗ is inferred to be oblate spheroid and a change from this shape appears to occur above c ∗ . A sudden increase in the polarity of the micelle–solution interface is also observed above c ∗ . For AOT micelles the counter ion binding constant has values 0.40 and 0.82 below and above ∼0.015 mol kg−1 electrolyte concentration, respectively. The higher value of the counterion binding constant for AOT has been reported for the first time.Display Omitted
Keywords: AOT; Sodium chloride; Sodium acetate; Sodium propionate; Sodium butyrate; Surface tension; EMF; Critical micelle concentration; Fluorescence spectra; Counterion binding constant; Polarity;
Studies of dynamic interactions between a pyrene-labeled polyelectrolyte and an oppositely charged rodlike micelle by a fluorescence quenching technique with use of a hydrophobic quencher by Tatsuyoshi Kawamoto; Akihito Hashidzume; Yotaro Morishima (537-542).
Electrostatic interactions of poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) (PyPAMPS) labeled with pyrene and a rodlike micelle of dimethyloleylamine oxide (DMOAO), an amine oxide type surfactant, mixed with varying mole fractions (Y) of hexadecyltrimethylammonium chloride (CTAC), a cationic surfactant, were investigated by a fluorescence quenching technique using 3, 4 ′ -dimethylbenzophenone (DBP), a hydrophobic quencher, that can only reside in the micellar phase. Fluorescence measurements were performed under homogeneous conditions in the region 0 < Y < Y p , where Y p is the critical mole fraction of CTAC at which macroscopic phase separation of resulting polymer–micelle complexes occurs. There was no fluorescence quenching and hence no interaction occurred between PyPAMPS and the DMOAO/CTAC mixed micelle when Y was below a certain value ( Y c ) depending on the ionic strength ( μ ) , e.g., Y c ≈ 0.005 at μ = 0.05 . When Y > Y c , the fluorescence was efficiently quenched by DBP-carrying DMOAO/CTAC mixed micelles, both steady-state and time-dependent fluorescence data indicating that the degree of the quenching and hence the extent of the complex formation increased significantly with increasing Y. Applying a kinetic model to the steady-state and time-dependent fluorescence data, the residence time for PyPAMPS in the polymer–micelle complex was calculated. The residence time was found to depend on both Y and μ, e.g., when Y was increased from 0.01 to 0.03, the residence time increased from 4 to 80 μs at μ = 0.05 whereas little or no increase in the residence time was observed in this range of Y at μ = 0.20 . At this higher ionic strength, the residence time increased only moderately from 3 to 10 μs when Y was increased from 0.01 to 0.09.
Keywords: Dynamic interaction; Polyelectrolytes; Rodlike micelles; Fluorescence quenching; Poly(sodium 2-(acrylamido)-2-propanesulfonate); Dimethyloleylamine oxide; Hexadecylammonium chloride;
Solubility of sodium soaps in aqueous salt solutions by Bin Lin; Alon V. McCormick; H. Ted Davis; Reinhard Strey (543-549).
The solubility of sodium soaps in dilute aqueous salt solutions has been systematically investigated by direct visual phase behavior observations. The added electrolytes, including simple inorganic salts and bulky organic salts, influence the solubility of sodium soaps in water, as represented by the varied soap Krafft point. Two inorganic salts, sodium chloride and sodium perchlorate, demonstrate a “salting-out” property. On the other hand, tetraalkylammonium bromides show an excellent ability to depress the soap Krafft point and enhance the soap solubility in water. With increasing the tetraalkylammonium ionic size, the degree of “salting-in” of soaps in water increases. However, solubility of pure tetraalkylammonium bromide in water decreases as the length of the alkyl chains increases. Furthermore, in the ternary water-tetrapentylammonium bromide (TPeAB)-sodium myristate (NaMy) system, we observed an upper cloud point phenomenon, which greatly shrinks the 1-phase micellar solution region in the phase diagram. This miscibility gap, together with the organic salt solubility limitation, restricts the use of tetraalkylammonium bromides with alkyl chains longer than 4 carbon atoms as effective soap solubility enhancement electrolytes. We also found that for sodium soap with a longer hydrocarbon chain, more tetrabutylammonium salt is required to reduce the soap Krafft point to room temperature.
Keywords: Sodium soaps; Solubility; Tetraalkylammonium bromides; Phase behavior; Krafft point;
Effect of temperature and salt on the phase behavior of nonionic and mixed nonionic–ionic microemulsions with fish-tail diagrams by Rajib K. Mitra; Bidyut K. Paul (550-559).
The phase behavior of Brij-56/1-butanol/n-heptane/water is investigated at 30 °C with α [weight fraction of oil in (oil + water)] = 0.5, wherein a 2 ̲ → 3 → 2 ¯ phase transition occurs with increasing W 1 (weight fraction of 1-butanol in total amphiphile) at low X (weight fraction of both the amphiphiles in the mixture) and a 2 ̲ → 1 → 2 ¯ phase transition occurs at higher X. Addition of an ionic surfactant, sodium dodecylbenzene sulfonate, destroys the three-phase body and decreases the solubilization capacity of the system at different δ (weight fraction of ionic surfactant in total surfactant). A three-phase body appears at α = 0.25 , but not at α = 0.75 for the single system. No three-phase body appears with the mixed system at either α value. Increased temperature increases the solubilization capacity of the Brij-56 system; on the other hand, a negligible effect of temperature on the Brij-56/SDBS mixed system has been observed. Addition of salt (NaCl) produces a three-phase body for both single and mixed systems and increases their solubilization capacities. The monomeric solubility of 1-butanol in oil ( S 1 ) and at the interface ( S 1 s ) has been calculated using the equation hydrophile–lipophile balance plane for both singles- and mixed-surfactant systems. These parameters have been utilized to explain the increase in solubilization capacity of these systems in the presence of NaCl.
Keywords: Phase transitions; Fish-tail diagram; Mixed surfactants; SDBS; Brij-56; Hydrophile–lipophile balance;
Wormlike micelles and microemulsions in aqueous mixtures of sucrose esters and nonionic cosurfactants by Carlos Rodriguez-Abreu; Kenji Aramaki; Yusuke Tanaka; M. Arturo Lopez-Quintela; Masahiko Ishitobi; Hironobu Kunieda (560-569).
A study of the phase and rheological behavior of sucrose hexadecanoate (C16SE)/cosurfactant/water systems in the presence of solubilized oil, using complementary techniques such as dynamic light scattering and small angle X-ray scattering, is presented. Viscoelastic wormlike micellar solutions are found when a nonionic lipophilic cosurfactant is added to C16SE aqueous systems. Contrary to previous reports, the effect of oil solubilization on these wormlike micelles is not unique and depends on several factors. Linear alkyl chain oils that tend to solubilize in the micellar core have a disrupting effect, decreasing the relaxation time and the viscosity of the systems. This effect is larger as the molecular volume of oil increases and as the solubility of the cosurfactant in oil increases. On the other hand, oils that penetrate in the palisade layer, such as p-xylene, induce micellar growth and have a thickening effect at a given micellar composition. Thermodynamic considerations are used to explain the experimental results.
Hydrolyzable nonionic surfactants: Stability and physicochemical properties of surfactants containing carbonate, ester, and amide bonds by Maria Stjerndahl; Krister Holmberg (570-576).
A linear and a branched nonionic cleavable surfactants containing a carbonate bond have been prepared from tetra(ethylene glycol) and an alkylchloroformate. The stability of these carbonate surfactants was determined by investigating their hydrolysis and biodegradability characteristics. The hydrolysis was catalyzed by alkali or enzymes (esterase from porcine liver and lipases from Mucor miehei and Candida antarctica B) and was monitored using 1H NMR. It was found that the stability toward alkali was higher for a carbonate surfactant than for a corresponding surfactant with an ester as weak bond. Biodegradation tests resulted in more than 60% degradation after 28 days for both carbonate surfactants. Physicochemical properties, such as critical micelle concentration (CMC), cloud point, area per molecule, and surface tension at the CMC, were determined and compared to those obtained from similar surfactants containing ester, amide, or ether bonds. It was found that the carbonate linkage is hydrophobic and that the oxycarbonyl part of the carbonate group is equivalent, in a formal sense, to an extra methylene group in the alkyl chain of the surfactant.
Keywords: Cleavable surfactant; Nonionic surfactant; Hydrolysis; Carbonate; Biodegradation; CMC; Amide; Ester;
On the Lagrangian/Eulerian modeling of dispersed droplet inertia: Internal circulation transition by G.F. Naterer; M. Milanez; G. Venn (577-584).
This article addresses a limitation of Lagrangian methods for droplet tracking, when approaching the transition point of internal circulation within droplets. Laminar multiphase flow with dispersed droplets in a co-flowing airstream is considered. Analytical and numerical formulations of droplet motion are developed based on a Lagrangian finite difference method of droplet tracking. Cases of both high and low relative Reynolds numbers are formulated. The role of interfacial drag in cross-phase momentum exchange increases at higher relative Reynolds numbers. A new transition criterion is developed to characterize conditions leading to shear-driven non-uniformities of velocity within a droplet. This criterion entails a momentum Biot number, in analogy with the Biot number criterion for conjugate heat transfer problems involving conduction and convection. At sufficiently high momentum Biot numbers, appreciable changes of velocity within a droplet imply that Lagrangian methods become unsuitable and transition to Eulerian volume averaging is needed. Predicted results of Lagrangian modeling of droplet motion in a co-flowing airstream are presented and discussed.
Keywords: Multiphase flow; Lagrangian/Eulerian tracking; Droplet inertia; Droplet/air interface; Shear driven velocity non-uniformities; Transition to internal circulation; Momentum Biot number criterion;
NO removal of Ni-electroplated activated carbon fibers by Soo-Jin Park; Gyu-Hong Shim; Hak-Yong Kim (585-587).
In this study, activated carbon fibers (ACFs) were treated by a Ni-electroplating technique in order to remove nitric oxide (NO). The surface properties of the ACFs were investigated by XPS measurement. N2/77 K adsorption isotherm characteristics were determined by the BET equation. Also, NO-removal efficiency was confirmed by gas chromatography. For experimental results, Ni2p was introduced on ACFs during the Ni-electroplating technique. The nickel deposited on ACFs appeared to increase the NO removal despite the decrease in the BET specific surface areas and micropore volumes compared to nontreated ACFs. Consequently, it was found that NO conversion of ACFs was significantly improved due to the catalytic reaction of nickel deposited on ACFs.
Keywords: Activated carbon fibers; Ni electroplating; Surface properties; NO removal; Catalytic reaction;
Thermodynamic parameters for adsorption equilibrium of heavy metals and dyes from wastewater with low-cost adsorbents by A. Ramesh; D.J. Lee; J.W.C. Wong (588-592).
This note revisits the literature evaluating the thermodynamic parameters of adsorption equilibrium uptakes of heavy metals and dyes from water and wastewater streams using low-cost adsorbents derived from agricultural waste, industrial wastes, inorganic particulates, or some natural products. We highlighted the possible flaws in some adsorption studies when their thermodynamic parameters were assessed, since compensation effects during enthalpy and entropy evaluation were possibly overlooked.
Keywords: Adsorption; Thermodynamics; Heavy metal; Dye; Low-cost adsorbent; Equilibrium;
Three-phase contact line profile between a large air bubble and a flat solid surface by M. Mukherjee; A.K. Lahiri (593-596).
The spreading of the three-phase contact (TPC) line after rupture of the thin film between a large air bubble and a flat solid surface was experimentally studied by means of a CCD high-speed video technique. The present study shows that the TPC line profile is noncircular for a deformed bubble.
Keywords: Bubble; Spreading; Three-phase contact line; Profile; Asymmetry;
Ammonia removal of activated carbon fibers produced by oxyfluorination by Soo-Jin Park; Byung-Joo Kim (597-599).
In this study, activated carbon fibers (ACFs) were produced by an oxyfluorination treatment to enhance the capacity of ammonia gas removal. The introduction of polar groups, such as C―F, C―O, and COOH, on the ACFs was confirmed by a XPS analysis, and N2/77 K adsorption isotherm characteristics including specific surface area and total and micropore volumes were studied by the BET and t-plot methods. The ammonia-removal efficiency was confirmed by a gas-detecting tube technique. As a result, the specific surface area and micropore volume of ACFs were slightly destroyed as the surface treatment time was increased. However, the oxyfluorinated ACFs led to an increase of fluorine and oxygen-containing polar functional groups in ACF surfaces, resulting in an increase in the ammonia-removal efficiency of the ACFs produced. In this study, activated carbon fibers (ACFs) were produced by an oxyfluorination treatment to enhance the capacity of ammonia gas removal. The introduction of polar groups, such as C―F, C―O, and COOH, on the ACFs was confirmed by a XPS analysis, and N2/77 K adsorption isotherm characteristics including specific surface area and total and micropore volumes were studied by the BET and t-plot methods. The ammonia-removal efficiency was confirmed by a gas-detecting tube technique. As a result, the specific surface area and micropore volume of ACFs were slightly destroyed as the surface treatment time was increased. However, the oxyfluorinated ACFs led to an increase of fluorine and oxygen-containing polar functional groups in ACF surfaces, resulting in an increase in the ammonia-removal efficiency of the ACFs produced.Display Omitted
Keywords: Activated carbon; Oxyfluorination; Surface oxygen complexes; Ammonia removal;
Parameterization of the corrected Dubinin–Serpinsky adsorption isotherm equation by Sylwester Furmaniak; Artur P. Terzyk; Piotr A. Gauden; Gerhard Rychlicki (600-605).
A recently proposed new modification of the Dubinin–Serpinsky adsorption isotherm equation, the CDS formula, is analyzed. We develop the equation describing the isosteric enthalpy of adsorption, and we give the meaning of the empirical parameters occurring in the CDS model. Finally the application of the CDS equation and related enthalpy formula describing experimental water adsorption and enthalpy data measured on two microporous carbons is shown. The simultaneous fit of the theoretical CDS isotherm and related enthalpy formula to experimental data is very good.
Keywords: Adsorption; Activated carbon; Water; Dubinin–Serpinsky equation;
Some historical ruminations on the ACS Colloid and Surface Chemistry Symposium by Milton Kerker (606-609).
Author Index for Volume 291 (610-611).