Journal of Colloid And Interface Science (v.283, #1)


The effect of SiO2 and Al2O3 coating on the surface of TiH2 powders on gas release by Jixiang Fang; Bingjun Ding; Zhimao Yang; Kang Zhao; Chenqing Gu (1-4).
TiH2 particles coated with binary Al2O3 and SiO2 layers were prepared, and the effect of the coating layer on gas release characteristics was investigated. The results show that homogeneous and compact coating layers of SiO2/Al2O3 on the surfaces of TiH2 particles can efficiently delay the starting time of hydrogen release from TiH2 powders to approximately 120 s.
Keywords: Al foams; Coating; SiO2/Al2O3/TiH2 particle; Gas release characteristic;

Adsorption isotherms of associating asphaltenes at oil/water interfaces based on the dependence of interfacial tension on solvent activity by Géza Horváth-Szabó; Jacob H. Masliyah; Janet A.W. Elliott; Harvey W. Yarranton; Jan Czarnecki (5-17).
In the Gibbs adsorption equation, the application of solvent activity for the calculation of the surface/interfacial excess is proposed for nonideal or associating or pseudocomponents such as asphaltenes. For the aforementioned systems, only the mass-based phenomenological interfacial excess can be determined based on interfacial tension versus activity data. The use of the mole fraction is compared to the use of the activity when the adsorbed amount of associating asphaltenes is calculated at a water/toluene interface. Langmuir-type isotherms describe the adsorption of asphaltenes at toluene/water interfaces. Asphaltenes were treated to remove the resins and natural surfactants using cyclic precipitation and dissolution of asphaltenes at a fixed aliphatic/aromatic ratio. Different fractions of asphaltenes were obtained by changing the aliphatic/aromatic ratio of the precipitating solvent. The limiting molar masses of asphaltenes measured by vapor pressure osmometry are different for fractions precipitated at different heptane to toluene ratios. The mass-based adsorbed amounts at the water/toluene interface, at a 0.1 asphaltene-to-toluene mass-ratio, varied in the range of 0.8–2.8 mg/m2, depending on the molar mass of asphaltenes.
Keywords: Adsorption from nonideal mixtures; Adsorption of associating components; Interfacial excess; Activity in Gibbs adsorption equation; Molar mass of asphaltenes; Fractionation of asphaltenes; Interfacial tension of asphaltenes; Molecular area of asphaltenes; Association of asphaltenes;

Sorption kinetics of strontium in porous hydrous ferric oxide aggregates by Wendy van Beinum; Annette Hofmann; Johannes C.L. Meeussen; Ruben Kretzschmar (18-28).
Sorption of ions by hydrous ferric oxide (HFO) often shows a fast initial sorption reaction followed by a much slower sorption process. The second step is diffusion-controlled and can continue for days or months before equilibrium is reached. In this paper, we demonstrate that the diffusion rate may be explained by electrostatic interactions. The internal and external surfaces of HFO are generally positively charged and therefore repel cations. This can result in extremely low cation concentrations in pores, and therefore a significant reduction in pore diffusion rate. The theory is demonstrated here for sorption of Sr2+ in HFO aggregates. The ion concentrations in the pore space are calculated using a Donnan model and diffusion is calculated from the Donnan concentration and potential gradients. This diffusion model is compared with nonelectrostatic pore diffusion, which does not take electrostatic interactions into account. The Donnan model predicts very low concentrations of Sr2+ in the pores and diffusion rates that are up to 8000 times lower than predicted with a nonelectrostatic model.
Keywords: Ferrihydrite; HFO; Iron oxide; Diffusion in pores; Micro-mesoporous aggregates; Donnan diffusion model; Nernst–Planck diffusion; CD-MUSIC; Sorption kinetics;

Sorption kinetics of strontium in porous hydrous ferric oxide aggregates II. Comparison of experimental results and model predictions by Annette Hofmann; Wendy van Beinum; Johannes C.L. Meeussen; Ruben Kretzschmar (29-40).
In a previous paper, we introduced the Donnan diffusion model to describe cation diffusion into microporous solids with variably charged surfaces, such as hydrous ferric oxides (HFO). Here, we present experiments investigating slow diffusion and sorption of strontium by HFO aggregates with well-characterized porosity. Adsorption of protons and strontium at the HFO surface was evaluated by acid–base titration and batch adsorption experiments with dispersed HFO. The experimental data were fitted with a 1-pK basic Stern model including surface ion pair formation of Na+ and NO 3 − and charge distribution for Sr surface complexes. Sorption–diffusion experiments were conducted in flow-through columns at controlled flow rates and at two different pH values, pH 4 and 7. Wet HFO aggregates, which were synthesized using a freezing and thawing method, were packed into chromatographic columns, pre-equilibrated to reach a constant pH, and then Sr breakthrough curves for adsorption and desorption of Sr were recorded. Strong retardation of Sr indicated that diffusion was sufficiently fast in a fraction of pores, so that sorption sites in these pores were rapidly accessible. Based on the analysis of NaNO3 breakthrough curves, this rapidly accessible pore fraction was estimated to be 37% of the total aggregate pore volume at pH 4.0 and 72% at pH 7.0, respectively. Taking this into account, the Donnan diffusion model gave a good description of the experimental Sr breakthrough curves. Cation exclusion was correctly predicted at pH 4.0. At pH 7, the strong tailing of Sr breakthrough curves due to Sr diffusion into the smallest pores was very well simulated. The Donnan diffusion model proved adequate for pore sizes between approximately 2 and 5 nm, depending on pH and ionic strength. This category of pores was dominant in the HFO aggregates used in this work.
Keywords: Strontium; Ferrihydrite; HFO; Surface complexation; CD-music; Micro-mesoporous aggregate; Sorption kinetics; Donnan diffusion model;

The strength of attractive interaction among particles on a surface, which was studied in our previous work, leads to different degrees of clustering and ordering. A growing structure percolates when all clusters connect and become one and finally the structure is jammed when there is no space large enough to accommodate one more particle. The lowest jamming limit reported is for structures from the random sequential adsorption. We studied here, by means of Monte Carlo simulation, structures built through sequential deposition of particles, into which surface diffusion and various degrees of attractive forces are incorporated and reported jamming limits along with the percolation thresholds. The higher the strength of attractive interactions, the larger the percolation densities and jamming limits are. These results were shown in a diagram as a function of temperature (or equivalently the strength of attractive interaction), ranging from very low temperature to very high temperature (RSA limit).
Keywords: Random sequential adsorption; Percolation; Jamming; Sequential deposition;

Comparisons of porous and adsorption properties of carbons activated by steam and KOH by Feng-Chin Wu; Ru-Ling Tseng; Ruey-Shin Juang (49-56).
In this work, fir woods and pistachio shells were used as source materials to prepare porous carbons, which were activated by physical (steam) and chemical (KOH) methods. Pore properties of these activated carbons including the BET surface area, pore volume, pore size distribution, and pore diameter were first characterized by a t-plot method based on N2 adsorption isotherms. Highly porous activated carbons with BET surface area up to 1009–1096 m2/g were obtained. The steam and KOH activation methods produced carbons with mesopore content in the range 9–15 and 33–49%, respectively. The adsorption equilibria and kinetics of tannic acid, methylene blue, 4-chlorophenol, and phenol from water on such carbons at 30 °C were then investigated to check their chemical characteristics. The Freundlich equation gave a better fit to all adsorption isotherms than the Langmuir equation. On the other hand, the intraparticle diffusion model could best follow all adsorption processes. In comparison with KOH-activated carbons, it was shown that the rate of external surface adsorption with steam-activated carbons was significantly higher but the rate of intraparticle diffusion was much lower.
Keywords: Activated carbons; Steam activation; KOH activation; Porous properties; Adsorption equilibrium; Kinetics;

Adsorption of gaseous formaldehyde and carboxylic acids by ammonium-ion-exchanged α-zirconium phosphate by A. Hayashi; Y. Fujimoto; Y. Ogawa; H. Nakayama; M. Tsuhako (57-63).
Ammonium-ion-exchanged α-Zr(HPO4)2⋅H2O (α-ZrP) was obtained as a single phase with the interlayer distance of 9.4 Å by the ion-exchange of proton with ammonium ion. The ammonium ion-exchanged α-ZrP could adsorb ill-smelling gases, such as formaldehyde and carboxylic acids (formic acid, acetic acid, propionic acid, and butyric acid). The adsorption amounts of carboxylic acids increased in the order, butyric acid < propionic acid < acetic acid < formic acid, whereas the adsorption amount of formaldehyde was the same as that of butyric acid. It was cleared that the adsorbed formaldehyde was partially decomposed to formic acid and methanol by self oxidation–reduction reaction in the interlayer region as evidenced by solid-state NMR. Thereby the interlayer distance after the adsorption of formaldehyde expanded to 14.4 Å. In the case of formic acid, it was cointercalated into the interlayer region, and the interlayer distance expanded to 11.1 Å. On the other hand, the interlayer distance of the other carboxylic acid-adsorbed compounds decreased to 7.6 Å due to release by the evacuation.
Keywords: Layered zirconium phosphate; Adsorption; Formaldehyde; Carboxylic acid; Solid-state NMR;

Polymer-protected platinum/ruthenium colloidal dispersions were prepared by refluxing mixed solutions of hexachloroplatinic(IV) acid and ruthenium(III) chloride in a mixture of ethanol/water (1/1 v/v) in the presence of poly(N-vinyl-2-pyrrolidone). The electronic spectra and transmission electron micrographs suggested that the colloidal dispersions are almost composed of the mixture of the small monometallic Pt and Ru clusters over all the ratio of Pt/Ru compositions. Extended X-ray absorption fine structure analyses and high resolution electron microprobe analyses indicated that no Pt/Ru alloy clusters exist in the dispersions, and the aggregation occurs between small monometallic Pt clusters (diameter ca. 15 Å) and partially oxidized Ru microclusters (diameter less than 10 Å). Electron diffraction measurements also suggested that the diffraction pattern of aggregated Pt/Ru cluster particles prepared by the simultaneous reduction of Pt and Ru ions is the same as that of the physical mixture of the small monometallic Pt and Ru clusters separately prepared. Therefore, it can be concluded that the aggregated Pt/Ru cluster particles, with 10 to 60 Å in diameter, are built up by small monometallic Pt clusters and partially oxidized Ru microclusters, and that Pt/Ru alloy clusters are not formed.
Keywords: Colloidal dispersions; Pt/Ru bimetallic clusters; Alloy; Aggregation; Coagulation; Agglomeration; Microclusters; EXAFS; Platinum; Ruthenium;

Blends of ethylene vinyl alcohol (EVOH; 44 mol% ethylene) and polyamide 6/66 (PA; 75 mol% PA 6) random copolymers were studied in the entire composition range. Specific interaction between the components was analyzed by IR spectroscopy; furthermore, coefficients related to the Flory–Huggins interaction parameter were derived from equilibrium water uptake and tensile strength. Morphology of the blends was investigated by thermal analysis (DSC), density measurements, and SEM micrographs. The two polymers form heterogeneous blends in each composition. Although the components crystallize in separate phases, the morphology and the mechanical properties are greatly affected by the association of OH and NH groups. Crystallization is restricted in the blends, and the increase of the amorphous fraction, as well as specific interaction between the components, results in essential improvement in the mechanical properties.
Keywords: EVOH; PA; Blends; Miscibility; Specific interaction;

A study has been made of the effect of urea upon the hydrolysis of 2-naphthyl acetate (2-NA) catalyzed by lipase from Rhizopus arrhizus in AOT–heptane–water reverse micellar solutions at pH 7. The partition constants, K, of 2-NA between n-heptane and aqueous urea solutions in the absence of micelles were also determined. It was found that K decreases when the concentration of urea increases. In aqueous solution the rate of hydrolysis of 2-NA catalyzed by lipase is dependent on the concentration of urea (at a given 2-NA concentration). This result can be due to a decrease in the magnitude of the association of lipase with 2-NA and/or to changes in the reaction rate of the lipase–2-NA complex. The modifications of the enzymatic activities elicited by addition of urea show a lineal correlation with K, emphasizing the relevance of hydrophobic effects in the loss of activity. Nevertheless, the slope of the line is higher than one, suggesting that changes in the conformation of the enzyme would be also important. Addition of urea to the micellar solutions provokes a decrease of the enzyme activity. From the dependence of the reaction rate with AOT concentration, the partition constant of 2-NA between n-heptane and the micelles, K p , was obtained. In the presence of 2 M urea a value of K p = 0.33   M −1 was derived. This value is lower than that measured in the absence of urea (Aguilar et al., Arch. Biochem. Biophys. 388 (2001) 231), indicating that incorporation of urea to the micellar interface produces a decrease of the association of 2-NA with the micelles. From a comparison of the results obtained in the micellar solution and in aqueous solution, it is concluded that the enzyme is more resistant to denaturation by urea in the micellar solution than in aqueous solution. Furthermore, at intermediate urea concentrations (2 M), the additive produces an increase in the Michaelis constant ( K M ) without a significant decrease (or even a small increase) in the catalytic rate constant ( k cat ).
Keywords: AOT reverse micelles; Lipase; Enzyme activity; 2-Naphthyl acetate;

Small-angle X-ray scattering (SAXS) has been widely used to investigate the organization of clay colloids in response to the particle concentration and ionic strength of the suspending medium. In such investigations, measuring the interparticle distance and/or spacing is usually attempted. In random or short-range ordered clay–water systems, the interparticle distances are often derived from the experimental structure factor maximum; however, the validity of such practice has never been theoretically or experimentally evaluated. The experimental structure factors of several clay–water systems with and without polyphosphate treatment to block the edge charges of clay particles were obtained from SAXS data in order to understand the physical meaning of this property. The results show that the polyphosphate treatment eliminated the experimental structure factor maximum and that the particle concentration effects were correlated with the depression on the curve in a random clay–water system (e.g., illite and laponite). For clay particles with greater anisotropy (i.e., montmorillonite), polyphosphate treatment enhanced the ordering of clay layers at high particle concentrations forming long-range ordered crystals showing Bragg reflections. In this ordered system, distinctive and symmetrical peaks representing the interparticle spacing were obtained by using a Fourier transform of the scattering curves. Thus, we conclude that the experimental structure factor maximum is induced by the edge–face oriented interactions, which may not be in direct contact as in a house-of-cards structure, and the position of the maximum should not be interpreted as an averaged interparticle distance in a clay–water system unless particles orient along the same direction.
Keywords: Clay minerals; Interparticle distance; SAXS; Structure factor;

Fabrication of rutile rod-like particle by hydrothermal method: an insight into HNO3 peptization by Juan Yang; Sen Mei; José M.F. Ferreira; Poul Norby; Sandra Quaresmâ (102-106).
In this work, well-crystallized and well-dispersed rod-like TiO2 rutile particles were prepared by hydrothermally treating acid-peptized TiO2 sols at relatively low temperatures of 200 and 240 °C. Raman spectra, transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize the peptized sols before and after hydrothermal treatment. The results showed that HNO3 peptization of amorphous TiO2 was able to promote, at room temperature, the formation of crystalline phases of anatase or rutile, at low ( HNO 3 /Ti = 1 ) or at high ( HNO 3 /Ti = 4 ) concentrations of peptizer, respectively. However, after hydrothermal treatment, well-crystalline rutile developed independent of the starting concentration of the peptizer. The formation of well-dispersed rutile particles is attributed to high long-range electrostatic forces between particles in the presence of the high concentration of the peptizer. The acid peptization would easily break the oxolation bonds between Ti―O―Ti, promote the formation of titanium species with fewer oxolation bonds depending on the amount of acid, and create conditions for the formation of rutile nuclei after structural rearrangements.
Keywords: Rutile; Raman; Peptization; Hydrothermal treatment;

Natural chrysotile fibers and pegmatitic phlogopite were acid-leached under controlled conditions. The resulting products were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, 29Si nuclear magnetic resonance, transmission electron microscopy, and selected area electron diffraction. The leached products derived of the two clays are similar, consisting of layered hydrated disordered silica with a “distorted” structure resembling the silicate layer existing in the original minerals. A simple model of the “disordered” silica structure is presented.
Keywords: Chrysotile; Phlogopite; Silica; Layered materials; Silicates;

Small-angle X-ray scattering from a dual-component organogel to exhibit a charge transfer interaction by Yeonhwan Jeong; Arianna Friggeri; Isamu Akiba; Hiroyasu Masunaga; Kazuo Sakurai; Shinichi Sakurai; Shigeru Okamoto; Katuaki Inoue; Seiji Shinkai (113-122).
The structure of a dual-component organogel consisting of methyl 4,6-O-(p-aminobenzylidene)-α-d-glucopyranoside and methyl 4,6-O-(p-nitrobenzylidene)-α-d-glucopyranoside in diphenyl ether was investigated with small-angle X-ray scattering (SAXS). The individual components gelatinized the solvent to yield a colorless gel and the gel fiber consisted of the crystal, providing the crystalline peaks at the same diffraction angles as those of the solid samples. When the components were mixed in equimolar ratio and dissolved in diphenyl ether, a yellow gel was formed and the crystalline peaks disappeared. For all compositions, the SAXS profiles were well fitted by a cylinder model. The cross-sectional radius of gyration, r c , was determined from the cross-sectional Guinier plot (qI vs q 2 , where I and q are the scattering intensity and the magnitude of the scattering vector). The value of r c reached a minimum of 3.0 nm at the equimolar composition. By correcting the data for the thermal scattering background, we obtained the entire SAXS profile for the equimolar dual-component gel. From this profile, the radial electron density distribution was determined and the radius of the cylinder was estimated to be 2.6 nm. The electron density distribution thus obtained revealed that four gelator molecules are packed in the sectional direction. This model was consistent with the size of the gelator molecules.
Keywords: Small-angle X-ray scattering (SAXS); Dual-component organogel; Cross-sectional radius of gyration; Radial electron density distribution;

The rate of the copper(II)/iron cementation reaction in the presence of surfactant (SAS) was determined by measuring the rate of cementation of copper on a rotating Fe cylinder from a CuSO4 solution in the absence and the presence of SAS using an atomic absorption spectrophotometer. The rate of cementation reaction is decreased by an increasing concentration of SAS, temperature and number of rotation. It is found that the order of the rate of decrease of the cementation reaction in the presence of SAS is as follows, Triton X-100 < SDS < SOS. The rate of the cementation reaction was also found to decrease with the addition of small amounts of alcohol. In the presence of alcohol, the amount of decrease ranged from 11.47 to 47.8% depending on the type and as well as the concentration of alcohol used. The effect of mixed surfactant (SAS) on cementation reaction was given. Thermodynamic parameters Δ H * , Δ S * , and Δ G * were calculated.
Keywords: Cementation; Inhibitors; Alcohols; Thermodynamic parameters; Iron cylinder;

Intercalation and functionalization of zinc hydroxide nitrate with mono- and dicarboxylic acids by Fernando Wypych; Gregorio Guadalupe Carbajal Arízaga; José Eduardo Ferreira da Costa Gardolinski (130-138).
The intercalation of ions derived from succinic, glutaric, and adipic acid into layered zinc hydroxide nitrate by ionic exchange reaction is reported. Different reaction conditions are investigated and the materials are characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis (simultaneous thermogravimetry and differential scanning calorimetry) and elemental analysis. The dicarboxylic acids can be grafted to the matrix slab by one carboxylate group and the second hydrated carboxylate group is hanging between the layers. Benzoate ions have also been intercalated by both ionic exchange reaction and stirring in acetonitrile. The two benzoate-intercalated materials exchange the organic moiety by sulfate ions if stirred in magnesium sulfate solution, but the sample obtained by anion exchange also allows the unusual incorporation of neutral magnesium sulfate in addition to free solvated sulfate ion. A schematic arrangement of the intercalated species between the layers is presented.
Keywords: Zinc hydroxide nitrate; Intercalation; Carboxylic acid; Grafting;

Oscillatory phenomena at liquid–liquid interfaces by R.P. Rastogi; R.C. Srivastava; Sharwan Kumar (139-143).
The mechanism of (i) Yoshikawa and Matsubara liquid–liquid interface oscillators and (ii) density/salt-water oscillators has been investigated. A modified simple mathematical formalism of both has been presented. Qualitative support for the model is provided by the available experimental results.
Keywords: Density/salt-water oscillators; Liquid–liquid interface oscillators; Instability;

Langmuir monolayers of the zwitterionic surfactant hexadecyl 1-N-l-tryptophan glycerol ether by M. Mercedes Velázquez; Francisco Ortega; Francisco Monroy; Ramón G. Rubio; Sofía Pegiadou; Lourdes Pérez; Maria Rosa Infante (144-152).
We report the formation of Langmuir monolayers of pure zwitterionic hexadecyl 1-N-l-tryptophan glycerol ether (C16-TGE) surfactant and mixed monolayers of cationic–zwitterionic surfactant obtained modifying the pH of the subphase. The pressure–area and surface potential–area isotherms and fluorescence microscopy measurements have been used to characterize the surface phase transitions in the monolayers. These transitions appeared at larger areas as the pH decreased from 6.0 to 2.0 and almost disappeared as the pH decreased further. The analysis of the surface potential and the infrared reflection–absorption spectroscopy data suggests that the phase transition is associated with a change of orientation of both the hydrocarbon chain and the aromatic group of the surfactant with respect to the air–water surface. The surface rheology of the monolayers was studied by quasielastic light scattering and by the oscillatory barrier technique. The results indicate that there is at least one relaxation process in the monolayer.
Keywords: Langmuir monolayers; Hexadecyl 1-N-l-tryptophan glycerol ether; Surface potential; Fluorescence microscopy; Infrared reflection–absorption spectroscopy (IRRAS); Quasielastic light scattering (SQELS);

A polyaniline-containing filter paper that acts as a sensor, acid, base, and endpoint indicator and also filters acids and bases by Dipak Dutta; Tridib Kumar Sarma; Devasish Chowdhury; Arun Chattopadhyay (153-159).
In this paper we report a new idea for synthesizing polyaniline in an ordinary filter paper. The synthesis was carried out by a process in which aqueous acidic aniline solution and the oxidizing agent H2O2 was added to the paper drop by drop and in sequence. Uniform polymerization could be obtained with the addition of reagents in either sequence. The polymer formation led to a green coloration of the paper. Formation of the emeraldine salt of polyaniline was confirmed by UV–vis and FTIR spectroscopy. Scanning electron microscopic measurements were made for surface characterization of the polymer formed in the paper. The same paper was used as a sensor for ammonia in vapor and in solution, for acid and base as well as endpoint indication, and also to filter acids and bases. We found that, using the polymer-containing paper, ammonia concentrations in a solution as low as 14 ppm could be measured.
Keywords: Polymerization; Filter paper; Conducting polyaniline; Sensor; Spectroscopic methods; Materials;

Sorption of the antibiotic ofloxacin to mesoporous and nonporous alumina and silica by Keith W. Goyne; Jon Chorover; James D. Kubicki; Andrew R. Zimmerman; Susan L. Brantley (160-170).
Mesoporous and nonporous SiO2 and Al2O3 adsorbents were reacted with the fluoroquinolone carboxylic acid ofloxacin over a range of pH values (2–10) and initial concentrations (0.03–8 mM) to investigate the effects of adsorbent type and intraparticle mesopores on adsorption/desorption. Maximum ofloxacin adsorption to SiO2 surfaces occurs slightly below the p K a 2 (pH 8.28) of the antibiotic and sorption diminishes rapidly at pH > p K a 2 . For Al2O3, maximum sorption is observed at pH values slightly higher than the adsorbent's point of zero net charge (p.z.n.c.) and less than midway between the p K a values of ofloxacin. The effects of pH on adsorption and ATR–FTIR spectra suggest that the zwitterionic compound adsorbs to SiO2 solids through the protonated N4 in the piperazinyl group and, possibly, a cation bridge; whereas the antibiotic sorbs to Al2O3 solids through the ketone and carboxylate functional groups via a ligand exchange mechanism. Sorption edge and isotherm experiments show that ofloxacin exhibits a higher affinity for mesoporous SiO2 and nonporous Al2O3, relative to their counterparts. It is hypothesized that decreased ofloxacin sorption to mesoporous Al2O3 occurs due to electrostatic repulsion within pore confines. In contrast, it appears that the environment within SiO2 mesopores promotes sorption by inducing formation of ofloxacin–Ca complexes, thus increasing electrostatic attraction to SiO2 surfaces.
Keywords: Ofloxacin; Fluoroquinolone carboxylic acid; Mesoporosity; Sorption edge; Adsorption/desorption isotherms; ATR–FTIR spectroscopy; Molecular modeling; Mineral–organic interactions;

Influence of anisotropy on the dynamic wetting and permeation of paper coatings by Paul A. Bodurtha; G. Peter Matthews; John P. Kettle; Ian M. Roy (171-189).
A void network model, named Pore-Cor, has been used to study the permeation of an ink solvent into paper coating formulations coated onto a synthetic substrate. The network model generated anisotropic void networks of rectangular cross-sectional pores connected by elliptical cross-sectional throats. These structures had porosities and mercury intrusion properties which closely matched those of the experimental samples. The permeation of hexadecane, used as an analogue for the experimental test oil, was then simulated through these void structures. The simulations were compared to measurements of the permeation of mineral oil into four types of paper coating formulation. The simulations showed that the inertia of the fluid as it enters void features causes a considerable change in wetting over a few milliseconds, a timescale relevant to printing in a modern press. They also showed that in the more anisotropic samples, fast advance wetting occurred through narrow void features. It was found that the match between experimental and simulated wetting could be improved by correcting the simulation for the number of surface throats. The simulations showed a more realistic experimental trend, and much greater preferential flow, than the traditional Lucas–Washburn and effective hydraulic radius approaches.
Keywords: Anisotropy; Paper coatings; Absorption; Porous media; Modelling; Wetting; Permeation; Mercury porosimetry; Pore-Cor; Shale;

Effect of surface oxyfluorination on the dyeability of polyethylene film by Soo-Jin Park; Si-Yong Song; Jun-Sik Shin; John-Moon Rhee (190-195).
The effect of surface oxyfluorination on low-density polyethylene (LDPE) film was studied in terms of surface functionality and surface energetics of the film surfaces, which can be attributed to improvement of the dyeability. The growth of functional groups and surface free energy was confirmed by FTIR-ATR, XPS, and contact angle methods. As a result, the total surface free energy was increased with oxyfluorination time, as a progressive increase of the polar component together with a small decrease of the dispersive component of surface free energy. From the dyeability test using the Kubelka–Munk equation, it was found that the oxyfluorination treatment plays an important role in the growth of oxygen-containing functional groups of LDPE film, resulting in improving the dyeability with a basic dyeing agent. A direct linear relationship is shown between the specific component of surface free energy and the K / S value for this work.
Keywords: Oxyfluorination; LDPE; Dyeability; Surface free energy; Contact angle;

In this work a generalized hydrodynamic theory for water flow into a mesoporous matrix from hydrophobized silica gel is suggested. Although we examine a fluid dynamics problem, the motion of the water–gas–solid contact line past a hydrophobized silica gel surface, motivation for such research derives from the investigation of a novel principle of mechanical energy dissipation, called surface dissipation, and its attached machine element, named a colloidal damper (CD). Similar to a hydraulic damper, this absorber has a cylinder–piston structure, but oil is replaced by a colloid consisting of a mesoporous matrix and a lyophobic liquid. Here, the mesoporous matrix is from silica gel modified by linear chains of alkyldimethylchlorosilanes and water is the associated lyophobic liquid. Mainly, the colloidal damper energy loss can be explained by the dynamic contact angle hysteresis in advancing (liquid displaces gas) and receding motion (gas displaces liquid); such hysteresis occurs due to the geometrical and chemical heterogeneities of the solid surface. Although this new kind of dissipation could be attractive for many applications, the subject remains almost unexplored in the scientific literature. Many different, complex, and interconnected aspects are related to this subject: capillary hydrodynamics, slippage effect, contact angle hysteresis, estimation of dissipated energy, thickness optimization of the grafted layer on the surface of the mesoporous matrix, etc. For this reason, a novel and global approach to all the complex and interconnected phenomena related to the contact line movement past a solid surface from hydrophobized silica gel is proposed. Our approach has a modest experimental basis but this is compensated for with rich references to other experimental and theoretical work oriented to the study of surface phenomena in such systems. We tried to sort the existing results and to find the right place for each in building our global view of the problem. This work is structured as follows. The measurement technique of the hysteresis loop is described. From experimental data one calculates the dissipated energy versus length of the grafted molecule on the silica gel surface. These results are justified by flow analysis. Generalized hydrodynamic theory means here that the basic structure of the Navier–Stokes equations is kept, but in order to include the relation between macroscopic flow and molecular interactions, slip is allowed on the solid wall. The nanopillar architecture of the silica gel hydrophobic coating is described. Concepts of slip and contact angle hysteresis are detailed and their connection is revealed. During adsorption, water penetrates the pore space by maintaining contact with the top of the coating molecules (region of ―CH3 groups); after that, water is forced into and partially or totally fills the space between molecules (region of ―CH2 groups). In such circumstances, at the release of the external pressure, desorption occurs. An original energetic-barriers approach is proposed to understand the filling of the nanosize canals which occur in the hydrophobic grafted layer. Employing this energetic-barriers approach, one finds the optimum length of the grafted molecule which maximizes the dissipated energy of the CD reversible cycle. Such results are useful for the appropriate design of ultrahydrophobic surfaces in general, and for the optimal design of a hydrophobic coating of a mesoporous matrix destined for CD use.
Keywords: Colloid; Damping; Nanotechnology; Hydrophobic porous silica gel; Contact angle hysteresis; Slip; Generalized Cassie–Wenzel model; Energetic barriers; Optimization;

Effect of electric fields on contact angle and surface tension of drops by A. Bateni; S. Laughton; H. Tavana; S.S. Susnar; A. Amirfazli; A.W. Neumann (215-222).
Contact angles of sessile drops were experimentally investigated in the electric field. The experimental setup was designed such that the electric field was applied to all three interfaces. The advanced Automated Polynomial Fitting (APF) methodology was employed to measure contact angles with high accuracy. The significance of the observations and trends was examined by conducting statistical tests of hypothesis. It was found that contact angles of polar liquids such as alcohols increase in the electric field. However, no significant trend was observed for nonpolar liquids such as alkanes. The change in the contact angle was found to be stronger for liquids with longer molecules. It was shown that the polarity of the electric field is not an underlying factor in the observed trends. Using the equation of state for interfacial tensions, the observed shift in contact angles was translated into a corresponding change in surface tension of the liquids. The results suggest that the surface tension of alcohols increases by one to two percent (depending on the size of molecules) when an electric field of the order of magnitude of 10 6  V / m is applied.
Keywords: Contact angle; Surface tension; Electric field; Sessile drops; Automated Polynomial Fitting (APF);

The influence of additives and metal rods on the nucleation and growth of gas hydrates by Jinping Li; Deqing Liang; Kaihua Guo; Ruzhu Wang (223-230).
A major technical issue in industrial applications of the gas hydrate storage process is to develop a practical means for rapid hydrate formation. In this paper, the formation processes of HCFC141b (CH3CCl2F) gas hydrate in a column of water with additives and with an iron rod that was placed in the center of the column have been studied to reveal the influence of the additives and the iron rod on the nucleation and growth of the gas hydrate. The water solution column, in a cylindrical glass container, was placed in a thermostatic bath at 274.15–280.15 K and under atmospheric pressure. The experimental results show that, compared to the pure water and the HCFC141b system, the properly placed iron rod combined with proper concentrations of lauryl sodium sulfonate, lauryl sodium sulfate, and sodium dodecylbenzenesulfonate-6 considerably reduces the hydrate nucleation time and promotes formation speed. The formation rate of HCFC141b gas hydrate increases with increasing concentration of sodium dodecylbenzenesulfonate-6 in the water solution, while the addition of potassium oxalate monohydrate in water has shown no effect on the nucleation and growth of HCFC141b gas hydrate. Under the experimental conditions, both the anion surfactants and the iron rod strongly induce the first nucleation of HCFC141b gas hydrate, while the following growth of the HCFC141b gas hydrate is primarily influenced by the anion surfactant. This experiment suggests a new way of fast formation of clathrate hydrate, which may be much easier for practical application of the gas hydrate for cold storage in air conditioning systems.
Keywords: Gas hydrate; Nucleation; Growth; Surfactants; Interface; Wettability; Interfacial tension;

The effect of dl-homocysteic acid (dl-2-amino-4-sulfonobutyric acid) on W/O microemulsion of potassium naphthenate (80%) and naphthenic acid (20%) in mixed solvent (1-octanol and n-heptane) has been found in four phases: (1) Interaction between the amino acid molecules and the polar head groups of the surfactant through hydrogen bonding enhances solubilization in the aqueous cores. (2) The interaction results in the growth of the microemulsion droplets and the homogenization of the particle size distribution. (3) The microstructure of the solubilized water remains unchanged, except that the polarity of the interface is affected. (4) The transition point is reduced to lower water content. A possible mechanism is proposed.
Keywords: dl-Homocysteic acid; Naphthenic acid; Reversed micelles; W/O microemulsion;

Complex formation in alkyldimethylamine oxide/sodium palmitate/water mixtures by Shimon Tanaka; Hideya Kawasaki; Hiroshi Maeda (238-244).
The complex formation between nonionic alkyldimethylamine oxide (CnDMAO, n = 14 , 16, and 18) and sodium palmitate (NaPa) in the solid phase of CnDMAO/NaPa mixtures and the dependence of the interaction parameter β of the regular solution theory (RST) on the mixed micelle composition of C16DMAO/NaPa mixtures were investigated. The dissolution temperature showed a maximum at a NaPa mole fraction X Pa * of 0.3–0.4 for C16DMAO/NaPa and 0.2 for C18DMAO/NaPa. The compositions of the complexes suggested by X Pa * are C16DMAO: NaPa = 3:2 or 2:1 and C18DMAO:NaPa = 4:1. The composition X Pa * depended on the chain length of the amine oxides. The maximum was not observed in the case of the C14DMAO/NaPa/water system. In the range 0.7 ⩽ X Pa ⩽ 1.0 , dissolution temperature depression was observed with decreasing X Pa . The dissolution temperature depression was analyzed by taking into account the nonideal behavior in the mixed micelles and the counterion binding on the mixed micelle surface. The negative β values were obtained for all three mixed systems. It was shown that the counterion activity remained practically constant in the range of 0.7 ⩽ X Pa ⩽ 1.0 . The cmc values of C16DMAO/NaPa mixtures were determined by pyrene fluorescence measurement. For C16DMAO/NaPa mixtures, the dependence of the RST interaction parameter β on the mixed micelle composition X Pa was determined for a wide range ( 0.2 ⩽ X Pa ⩽ 0.9 ). In the range 0.2 ⩽ X Pa ⩽ 0.5 , the β values were obtained from an analysis of cmc based on the RST. In the range 0.7 ⩽ X Pa ⩽ 0.9 , the β values were obtained from an analysis of the dissolution temperature depression. From the analysis of the micelle composition dependence of the β values, a short-range attractive interaction between the headgroup of C16DMAO and palmitate anion is suggested.
Keywords: Alkyldimethylamine oxide; Sodium palmitate; Complex formation; Mixed micelles; Dissolution temperature; Interaction parameter of the regular solution theory;

The yield stress of Na-montmorillonite suspension in an electrostatically dispersed state was studied to confirm the validity of previously proposed equation for the dependency of the yield stress on the volume fraction of clay and ionic strength. In the derivation of the equation, it is assumed that (1) clay layers array in parallel, and (2) the yield stress is equivalent to the strength of electrostatic repulsion when it reaches the yield stress. Measurements of the yield stress were performed with the vane method, varying the volume fraction of clay, ϕ, under controlled ionic strength for the region of 0.008 < ϕ < 0.023 and 10 −2 < NaCl < 10 −5   M . Experimental data qualitatively agreed with theoretical predictions; however, quantitative differences were found to range from 0.1 to 1000 times. This discrepancy can be eliminated if we introduce a correction factor. Reasonable agreement was obtained when the factor was proportional to n 0 −0.256 .
Keywords: Yield stress; Vane method; Gouy–Chapman theory; Montmorillonite; Ionic strength;

In order to investigate the validity of the dissipative particle dynamics method, which is a mesoscopic simulation technique, we have derived an expression for viscosity from the equation of motion of dissipative particles. In the concrete, we have shown the Fokker–Planck equation in phase space, and macroscopic conservation equations such as the equation of continuity and the equation of momentum conservation. The basic equations of the single-particle and pair distribution functions have been derived using the Fokker–Planck equation. The solutions of these distribution functions have approximately been solved by the perturbation method under the assumption of molecular chaos. The expressions of the viscosity due to momentum and dissipative forces have been obtained using the approximate solutions of the distribution functions. Also, we have conducted nonequilibrium dynamics simulations to investigate the influence of the parameters, which have appeared in defining the equation of motion in the dissipative particle dynamics method. The theoretical values of the viscosity due to dissipative forces in the Hoogerbrugge–Koelman theory are in good agreement with the simulation results obtained by the nonequilibrium dynamics method, except in the range of small number densities. There are restriction conditions for taking appropriate values of the number density, number of particles, time interval, shear rate, etc., to obtain physically reasonable results by means of dissipative particle dynamics simulations.
Keywords: Dissipative particle dynamics method; Mesoscopic approach; Nonequilibrium dynamics method; Transport coefficients; Viscosity;

In order to obtain a wide set of test cases for numerical methods to solve Smoluchowski's coagulation equation the exact solutions for the constant, sum or product kernel, with gamma distributions as initial size spectra, are generalized by allowing size distributions with a singularity at zero volume.
Keywords: Smoluchowski's coagulation equation; Exact solutions; Gamma distribution;

A paper contributes not only by its originality and creativity, but also by its continuity and development toward subsequent research. Referencing and quotation accuracy are an important part of a scientific article. This study presents a literature review concerning the precision of 50 first authors' publications, which originally cited Ho's pseudo-second-order kinetic expression paper in kinetics model for solute sorption on various sorbents. This model applies to a range of solid–liquid systems such as metal ions, dyestuffs, herbicides, oil, and organic substances in aqueous systems onto various sorbents. In addition, citations of Lagergren and Elovich rate equations are also discussed. This comment offers information for citing the original idea of Ho's pseudo-second-order kinetic expression and Lagergren's pseudo-first-order kinetic equation. It is also suggested that the cited paper should be accurately quoted.
Keywords: Sorption; Kinetics; Pseudo-second-order; Pseudo-first-order; Citation;

The removal of humic acids from water by solvent sublation by Yujuan Lu; Jianhong Liu; Jie Tang; Bo Wei; Xueli Zhang (278-284).
The application of solvent sublation in the removal of humic acids was investigated in the present study. The humic acids (HA) were removed from an aqueous solution by solvent sublation of humic acid–hexadecylpyridium chloride (HPC) complex (sublate) into isopentanol. Several parameters were examined towards the optimization of humic acid removal; the dosage of a surfactant was found to be the major one, controlling the overall efficiency of the progress. The removal rate was somewhat enhanced by higher airflow rate and almost independent of the volume of the organic solvent floating on the top of the aqueous column. The effects of electrolytes (e.g., NaCl), nonhydrophobic organics (e.g., ethanol), and pH of the solution upon the process were studied. Under the optimized condition, the treatment performance was found to be very efficient, reaching almost 100%, indicating that solvent sublation can serve as a possible alternative technology for the removal of humic acids. The solvent sublation process follows first-order kinetics. A characteristic parameter, apparent activation energy of attachment of the sublate to bubbles, was estimated at a value of 9.48 kJ/mol. Furthermore, the simulation of a mathematical model with the experiments on the solvent sublation of humic acid–HPC was described here.
Keywords: Solvent sublation; Humic acids; Kinetics; Thermodynamics; Simulation;

by Arthur Hubbard (285).