Journal of Colloid And Interface Science (v.282, #1)

Demulsification by amphiphilic dendrimer copolymers by Zhiqing Zhang; Guiying Xu; Fang Wang; Shuli Dong; Yijian Chen (1-4).
Amphiphilic block copolymers with dendrimer structures were synthesized by anion polymerization and these dendritic macromolecules exhibited excellent demulsification performance for crude oil emulsion. According to the demulsification experiments, we determined that the copolymers became more efficient with more complex molecular structure due to increased penetrability. The physical model of demulsification intelligibly explained the micromechanism of flocculation and coalescence of water drops in emulsion because of the good adsorption and displacement behaviors of dendrimers.
Keywords: Amphiphilic dendrimer copolymers; Demulsification; Crude oil emulsions;

EDTA effect on the removal of Cu(II) onto TiO2 by Jae-Kyu Yang; Seung-Mok Lee (5-10).
The adsorption of Cu(II) and Cu(II)–EDTA onto TiO2 with variations in the pH, concentration, and molar ratio of Cu(II) to EDTA has been studied. The adsorption of Cu(II) and Cu(II)–EDTA onto TiO2 showed typical cationic- and anionic-type behavior, respectively. The removal of Cu(II) in an EDTA-excess system was less than that in an equimolar Cu(II)/EDTA system due to the competitive adsorption of EDTA and Cu(II)–EDTA onto the TiO2. The removal of Cu(II) was favorable at low pH for both the equimolar and EDTA-excess systems, while significant Cu(II) removal was observed over the entire pH range in a copper-excess system. For model predictions, the MINTEQA2 program employing an inner-sphere complexation and a diffuse layer model was used; the surface complexes used included Ti ―(OH2)O―Cu+, Ti ―(OH)EDTAH2− 2, and Ti ―(OH)EDTA―Cu2−.
Keywords: Adsorption; Copper; Cu(II)–EDTA; EDTA; Surface complexation; TiO2;

To accurately model metal mobility and bioavailability in soils and sediments, systematic adsorption studies are needed in considering heterogeneous, well characterized minerals. Two important surfaces are iron oxide and silica, which are ubiquitous and associated with one another in the environment playing important roles in metal distribution. This study focuses on the synthesis and characterization of such a system, iron oxide-coated silica. A three-level fractional factorial study was used to determine the optimum conditions for producing goethite-coated silica. The amount of coating achieved was between 0.59 and 21.36 mg Fe g−1 solid. The most significant factor in coating using either adsorption or precipitation was the particle size of silica, where Fe increased from an average of 0.85 to 9.6 mg Fe g−1 solid as silica size decreased from 1.5 to 0.2 mm. Other factors investigated, including coating temperature, initial iron concentration, and contact time, were of less importance. The iron oxide coatings were observed to be non-uniform, concentrated in rough concave areas. FTIR revealed a band shift as well as a new band indicating changes in the chemical environment of Fe―O and Si―O bonds; these results along with abrasion studies suggest that the interaction between the oxide coating and silica surface potentially involves chemical forces. Because the nano-sized iron oxide coatings increased surface area, introduced small pores, and changed the surface charge distribution of silica, the coated system demonstrates a greater affinity for Ni compared to that of uncoated silica.
Keywords: Iron oxide-coated sand; Nickel; Adsorption; Coating synthesis and characterization;

Adsorption of Cu(II), Zn(II), Ni(II), Pb(II), and Cd(II) from aqueous solution on Amberlite IR-120 synthetic resin by Ayhan Demirbas; Erol Pehlivan; Fethiye Gode; Turkan Altun; Gulsin Arslan (20-25).
The adsorption of copper(II), zinc(II), nickel(II), lead(II), and cadmium(II) on Amberlite IR-120 synthetic sulfonated resin has been studied at different pH and temperatures by batch process. The effects of parameters such as amount of resin, resin contact time, pH, and temperature on the ion exchange separation have been investigated. For the determination of the adsorption behavior of the resin, the adsorption isotherms of metal ions have also been studied. The concentrations of metal ions have been measured by batch techniques and with AAS analysis. Adsorption analysis results obtained at various concentrations showed that the adsorption pattern on the resin followed Freundlich isotherms. Here we report the method that is applied for the sorption/separation of some toxic metals from their solutions.
Keywords: Cu(II); Zn(II); Ni(II); Pb(II); Cd(II); Amberlite IR-120; Adsorption behavior; Freundlich isotherm;

Morphology study of gold–chitosan nanocomposites by Haizhen Huang; Qiang Yuan; Xiurong Yang (26-31).
Gold nanoparticles were prepared in the presence of chitosan via reduction of HAuCl4 with sodium borohydride. The gold–chitosan nanocomposite was formed by adsorbing chitosan molecules onto the gold nanoparticle surfaces. The resulting gold nanoparticles were characterized by transmission electron microscopy and UV–vis spectroscopy. Morphology of gold–chitosan nanocomposite films was investigated by polarized optical microscopy. The morphology of chitosan crystal cast from the prepared nanocomposite was much different from that cast from chitosan solution due to the possible nucleation of gold nanoparticles. A branched-like structure or a cross-linked needle-like structure could be formed in nanocomposite films with different casting volumes.
Keywords: Chitosan; Gold; Nanocomposites; Morphology; POM;

The interaction of copper with three different chitosans having degrees of deacetylation of 77.5, 81.5, and 86.1%, named C, A, and F, respectively, was followed by the batch method at 298 ± 1 K and the values obtained were fitted to a modified Langmuir equation. These interactions were also obtained by calorimetric titration. Experimentally, 50.0 mg of each chitosan was suspended in doubly distilled water at 298.15 ± 0.02 K under mechanical turbine stirring. The titration was performed by adding increments of 10 μl of a 0.10 mol dm3 Cu(NO3)2 aqueous solution and the calorimetric isotherms obtained were adjusted to a modified Langmuir equation. From the net thermal effects K and ΔH values were calculated, also permitting the acquisition of other thermodynamic data for the chitosan–copper interaction at the solid/liquid interface. The exothermic enthalpic values of − 45.65 ± 1.97 , − 49.91 ± 1.57 , and − 48.64 ± 0.82 kJ mol −1 , for chitosans C, A, and F, respectively, reflect the degree of deacetylation. The spontaneity of the systems is shown by the negative ΔG values, − 36.1 ± 0.2 , 36.8 ± 0.1 , and − 38.1 ± 0.3 kJ mol −1 for the same sequence of chitosans. The negative entropic values, −34, −44, and −35 J mol−1 K−1, are in agreement with an ordering of solvent as the complexation occurred. The intensity of the thermal effects and the thermodynamic data obtained from the copper/chitosan interactions can be associated with the ability of these biopolymers to extract copper from aqueous solutions.
Keywords: Chitosan; Degree of acetylation; Copper; Thermodynamics;

Ellipsometric study of nonionic polymer solutions by B.A. Noskov; A.V. Akentiev; D.O. Grigoriev; G. Loglio; R. Miller (38-45).
The thickness and refractive index of adsorption films of poly(vinylpyrrolidone) (PVP) and poly(ethylene glycol) (PEG) were determined by null-ellipsometry at the air–aqueous solution interface. Both parameters, in the same way as the earlier studied dynamic surface elasticity and surface tension, exhibit rather abrupt changes when the concentration approaches the range of semidilute solutions. This behavior can be explained by the worsening of the solvent quality with increasing PEG concentration and by the PVP displacement from the surface by a contamination of high surface activity.
Keywords: Polymer adsorption layers; Ellipsometry; Adsorption kinetics; Adsorbed amount; Adsorption layer thickness;

Method of measuring charge distribution of nanosized aerosols by S.H. Kim; K.S. Woo; B.Y.H. Liu; M.R. Zachariah (46-57).
In this paper, we present the development of a method to accurately measure the positive and negative charge distribution of nanosized aerosols using a tandem differential mobility analyzer (TDMA) system. From the series of TDMA measurements, the charge fraction of nanosized aerosol particles was obtained as a function of equivalent mobility particle diameter ranging from 50 to 200 nm. The capability of this new approach was implemented by sampling from a laminar diffusion flame which provides a source of highly charged particles due to naturally occurring flame ionization process. The results from the TDMA measurement provide the charge distribution of nanosized aerosols which we found to be in reasonable agreement with Boltzmann equilibrium charge distribution theory and a theory based upon charge population balance equation (PBE) combined with Fuchs theory (N.A. Fuchs, Geofis. Pura Appl. 56 (1963) 185). The theoretically estimated charge distribution of aerosol particles based on the PBE provides insight into the charging processes of nanosized aerosols surrounded by bipolar ions and electrons, and agree well with the TDMA results.
Keywords: Nanosized aerosols; Positive ion; Negative ion; Electron; Tandem differential mobility analyzer; Boltzmann theory; Charge population balance equation; Diffusion flame;

Aggregation of paramagnetic particles in the presence of a hydrodynamic shear by E. Brunet; G. Degré; F. Okkels; P. Tabeling (58-68).
We present an experimental study of the aggregation of paramagnetic particles, in the presence of controlled laminar shear flow, conducted in microchannels subjected to an external magnetic field. The microfluidic channels are made of either glass/silicon or polydimethylsiloxane. In ranges of time up to hundreds of seconds, the growth mechanism of the linear chain consists of the accumulation of isolated particles or small clusters onto existing chains, which are all moving at different speeds. In this time regime the chain length increases linearly and has a growth rate that increases as a power law with the shear. At longer times the chain lengths saturate. The Smoluchovski model, which assumes single particle–chain interactions only, closely reproduces the observations both qualitatively and quantitatively. In particular, the evolution of the growth rate of the mean chain length with respect to the shear rate S, predicted as S 1 / 4 , is found to be consistent with the experiments.
Keywords: Orthokinetic aggregation; Paramagnetic particles; Shear flow; Microfluidic;

Low-Knudsen-number photophoresis of aerosol spheroids by Chang L. Ou; Huan J. Keh (69-79).
The photophoretic motion of a freely suspended aerosol spheroid exposed to a radiative heat flux that is oriented arbitrarily with respect to its axis of revolution is analytically studied. The Knudsen number is assumed to be so small that the fluid flow can be described by a continuum model with a thermal slip at the particle surface. In the limit of small Peclet and Reynolds numbers, the appropriate energy and momentum equations are solved using the bifocal-coordinate transformations. Expressions for the photophoretic velocity and force are obtained in closed form for various cases of prolate and oblate spheroidal particles. The average photophoretic velocity and force for an ensemble of identical, noninteracting spheroids with random orientation distribution are also determined. The results indicate that the aspect ratio and relative thermal conductivity of a spheroidal particle and its orientation with respect to the incident light can have significant effects on its photophoretic behavior.
Keywords: Photophoresis; Aerosol spheroids; Continuum regime; Thermal slip;

We have developed a cleaning procedure for aluminum alloys for effective minimization of surface-adsorbed sub-micrometer particles and nonvolatile residue. The procedure consists of a phosphoric acid etch followed by an alkaline detergent wash. To better understand the mechanism whereby this procedure reduces surface contaminants, we characterized the aluminum surface as a function of cleaning step using surface enhanced Raman spectroscopy (SERS). SERS indicates that phosphoric acid etching re-establishes a surface oxide of different characteristics, including deposition of phosphate and increased hydration, while the subsequent alkaline detergent wash appears to remove the phosphate and modify the new surface oxide, possibly leading to a more compact surface oxide. We also studied the zeta potential of <5 μm pure aluminum and aluminum alloy 6061-T6 particles to determine how surface electrostatics may be affected during the cleaning process. The particles show a decrease in the magnitude of their zeta potential in the presence of detergent, and this effect is most pronounced for particles that have been etched with phosphoric acid.
Keywords: Aluminum surfaces; Metal cleaning; Surface enhanced Raman spectroscopy; Zeta potential;

Photocatalytic degradation of methylene blue by a combination of TiO2 and activated carbon fibers by Rusheng Yuan; Rongbo Guan; Wenzhong Shen; Jingtang Zheng (87-91).
Photocatalytic degradation of methylene blue (MB) in aqueous solution was investigated using TiO2 immobilized on activated carbon fibers (ACFs). The TiO2 and ACF combination (TiO2/ACF) was prepared by using epoxy as the precursor of the link between TiO2 and ACFs, followed by calcination at 460 °C in a N2 atmosphere. The TiO2/ACF composite prepared was easier to handle than the original TiO2 powder in suspension. More significantly, the TiO2/ACF composite can be used repeatedly without a decline in photodegradation ability. After six cycles, the amount of MB removal for the TiO2/ACF composite was still slightly higher than that for fresh P25 TiO2 in suspension. Through measurement of chemical oxygen demand in the solution and the concentration of ammonium generated during degradation of MB, it was confirmed that MB molecules are mineralized instead of adsorbed by ACFs.
Keywords: Titanium dioxide; Activated carbon fibers; Photodegradation; Methylene blue;

Anion-induced adsorption of thallium complex on silver electrodes by T.C. Girija; M.V. Sangaranarayanan (92-101).
The interfacial behavior of thallium ions on polycrystalline silver electrodes is analyzed using cyclic voltammetric and chronocoulometric and impedance studies. The specificity associated with bromide ions leading to the anion-induced adsorption of the thallium complex is pointed out and the stoichiometry of the thallium complex is deduced.
Keywords: Anion-induced adsorption; Thallium complex; Silver electrodes; Cyclic voltammetry; Chronocoulometry; Impedance spectroscopy;

A study of the reason for the early ignition of coconut-based impregnated carbon in comparison with the peat-based impregnated carbon was conducted. The surface features of carbons were evaluated using various physicochemical methods. The metal analysis of the initial carbon indicated that the content of potassium was higher in the coconut-based carbon. The surface functional group analysis revealed the presence of similar surface species; however, the peat-based carbon was more acidic in its chemical nature. Since the oxygen content was higher in the peat-based carbon, the early ignition of the coconut-based material was attributed to its higher affinity to chemisorb oxygen, which leads to exothermic effects. This conclusion was confirmed by performing oxidation of coconut-based carbon prior to impregnation. This process increased the ignition temperature for Cu/Cr impregnated coconut-based material from 186 to 289 °C and for the Cu/Zn/Mo impregnated carbon from 235 to 324 °C.
Keywords: Activated carbon; Combustion; Impregnation; Surface treatment; Surface properties;

Deformation and bursting of nonspherical polysiloxane microcapsules in a spinning-drop apparatus by M. Husmann; H. Rehage; E. Dhenin; D. Barthès-Biesel (109-119).
We analyze the deformation and bursting process of nonspherical organosiloxane capsules in centrifugal fields. Measurements were performed in a commercial spinning-drop tensiometer at different values of tube rotation. A theoretical analysis of the mechanics of initially ellipsoidal elastic shells subjected to centrifugal forces is developed where the deformation of the capsule is predicted as a function of the initial geometry and membrane elastic properties. For different types of organosiloxane membranes the Poisson number varies between 0 and 0.9. This phenomenon points to a considerable reduction of the membrane thickness at the onset of mechanical stress. Membrane-breaking processes always initiated at one of the pole ends of the capsules. Such rupture processes can be interpreted in terms of the derived theoretical model.
Keywords: Capsule; Spinning-drop tensiometer; Surface shear modulus;

The purpose of this work is the numerical resolution, in the case of anisotropic elasticity, of the problem of a misfit dislocation located between an infinite substrate and two-layer composite. This case is obtained where the period of a network of misfit dislocations is taken as much greater than the thickness of the two foils. As a result, in the vicinity of the dislocation, the limiting boundary conditions will be close to those of Volterra translation dislocation. The elastic fields of displacement and stress are calculated for various orientations of the burger's vector, by inversion of a 30 × 30 computed matrix. Before this calculation, we tested the precision of the results of the program by comparing the interfacial relative displacement obtained from it with the results of the analytical expression describing this same displacement. The composite NiSi2/Si/(001)GaAs the subject of several investigations, is treated as an example.
Keywords: Dislocation; Misfit; Interface; Networks;

In this study, activated carbon fibers (ACFs), onto which silver (Ag) nanoparticles have been introduced by an electroplating technique, were used to remove NO. Surface properties of the ACFs were determined by X-ray diffraction and scanning electron microscopy. N2 adsorption isotherms at 77 K were investigated by BET and t-plot methods to characterize the specific surface areas and pore volumes, and NO removal efficiency was confirmed by a gas chromatographic technique. As for the experimental results, Ag content on the ACFs increased with plating time. However, adsorption properties such as the BET specific surface area and the total pore volume were somewhat decreased in the presence of Ag nanoparticles. NO removal efficiency of all Ag–ACFs was higher than that of untreated ACFs and increased with Ag content. However, a decrease in the extent of NO removal was shown in the excessively plated ACFs, which might be associated with the blocking of the micropores in the carbon; therefore, an optimal Ag content needs to exist in the presence of initially well-developed micropores to lead to an increase in the efficient NO removal ability of the ACF.
Keywords: Activated carbon fibers; Electroplating; Silver nanoparticles; NO removal;

The oscillating drop/bubble technique is increasingly popular for measuring the interfacial dilatational properties of surfactant/polymer-laden fluid/fluid interfaces. A caveat of this technique, however, is that viscous forces are important at higher oscillation frequencies or fluid viscosities; these can affect determination of the interfacial tension. Here, we experimentally quantify the effect of viscous forces on the interfacial-tension measurement by oscillating 100 and 200 cSt poly(dimethylsiloxane) (PDMS) droplets in water at small amplitudes and frequencies ranging between 0.01 and 1 Hz. Due to viscous forces, the measured interfacial tension oscillates sinusoidally with the same frequency as the oscillation of the drop volume. The tension oscillation precedes that of the drop volume, and the amplitude varies linearly with Capillary number, Ca = Δ μ ω Δ V / γ a 2 , where Δ μ = μ D − μ is the difference between the bulk Newtonian viscosities of the drop and surrounding continuous fluid, ω is the oscillation frequency of the drop, ΔV is the amplitude of volume oscillation, γ is the equilibrium interfacial tension between the PDMS drop and water, and a is the radius of the capillary. A simplified model of a freely suspended spherical oscillating-drop well explains these observations. Viscous forces distort the drop shape at Ca > 0.002 , although this criterion is apparatus dependent.
Keywords: Oscillating drop; Oscillating bubble; Tensiometry; Interfacial rheology; Axisymmetric drop shape analysis; Interfacial tension; Surface tension; Viscous forces;

Interfacial properties of acidified skim milk by E. Cases; C. Rampini; Ph. Cayot (133-141).
The purpose of this study is to investigate the tension properties and dilatational viscoelastic modulus of various skim milk proteins (whole milk, EDTA-treated milk, β-casein, and β-lactoglobulin) at an oil/water interface at 20 °C. Measurements are performed using a dynamic drop tensiometer for 15,000 s. The aqueous bulk phase is a skim milk simulated ultrafiltrate containing 11 × 10 −3   g L −1 milk protein. At pH 6.7, β-casein appears as the best to decrease the interfacial tension, whereas β-lactoglobulin leads to the highest interfacial viscoelastic modulus value. Whole milk was almost as surface-active as individual β-casein in terms of the final (steady-state) lowering of the interfacial tension, but the rate of tension lowering was smaller. EDTA treatment improved the rate of tension lowering of whole milk. The acidification of milk, from previous measurements, would lead to the enhancement of surface activity. At t = 15 , 000   s , the order of effectiveness is pH 4.3 > pH 5.3 = pH 5.6 > pH 6.7 whole milk, suggesting that pH 4.3 whole milk is the best surface active. As compared to pH 6.7 whole milk, the use of pH 5.3 and pH 5.6 milk as surface active would result in the use of milk containing more free β-casein born of pH-dissociated casein micelles.
Keywords: Acidified whole milk; β-Casein; β-Lactoglobulin; Interfacial properties; Interfacial tension; Interfacial viscoelastic modulus;

The adsorption and micellar behavior of diethylene glycol mono-n-tetradecyl ether (C14E2), sodium 3,6,9,12-tetraoxaoctacosanoate (TOOCNa), and their mixture at a 1:1 molar ratio have been studied by film balance, Brewster angle microscopy (BAM), and surface tensiometry at different temperatures. The monolayers of pure C14E2 and its mixture with TOOCNa show a first-order phase transition with a conspicuous cusp point in their respective adsorption isotherms. This is further confirmed by the observation of bright two-dimensional condensed phase domains visualized by BAM just after the appearance of the phase transition. It is interesting to note here that for C14E2, condensed domains are observed up to 19 °C, while in the mixed system, they are observed up to 22 °C. To understand why in the mixed system the domains are observed at higher temperatures than for pure C14E2, we have measured the temperature dependency of the equilibrium surface tension at ⩾cmc ( γ cmc ) values of both the pure and the mixed systems. The γ cmc values of pure C14E2 remain almost constant, while those of pure TOOCNa and its mixture with C14E2 decrease appreciably with increasing temperature. It is concluded that higher degree of dehydration of the ethylene oxide (EO) chain reduces the head-group size of TOOCNa, which outweighs the combined effect of the repulsive interactions between the head-groups and the thermal motion of the adsorbed molecules. Furthermore, C14E2 being inserted into the TOOCNa monolayer reduces the electrostatic repulsions between the charged heads, and consequently, the adsorbed monolayers attain closer molecular packing. As a result, the γ cmc values of both pure TOOCNa and its mixture with C14E2 decrease with increasing temperature. This facilitates the formation of condensed domains in the mixed system at higher temperatures, whereas none of the individual members can show any indicative feature of phase transition under the same experimental conditions.
Keywords: Nonionic surfactant; Anionic surfactant; Phase transition; Brewster angle microscopy; Adsorbed monolayer; Critical micelle concentration;

Effects of interactions on the formation of mixed micelles of 1,2-diheptanoyl-sn-glycero-3-phosphocholine with sodium dodecyl sulfate and dodecyltrimethylammonium bromide by Carolina Vautier-Giongo; Mandeep Singh Bakshi; Jasmeet Singh; Radha Ranganathan; Joseph Hajdu; Barney L. Bales (149-155).
Mixed micelles of the phospholipid 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) with sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) in aqueous solutions and the effects of interactions between the components were studied by fluorescence and NMR measurements. The regular solution theory (RST) was applied to analyze the experimental critical micelle concentration values determined from the fluorescence spectra of pyrene in the mixed micelles. Negative values for the interaction parameter ( β 12 ) were obtained for both DHPC + SDS and DHPC + DTAB mixtures, with the value being more negative in the former case. The negative β 12 values for the two systems imply that the interaction between the phospholipid and the two ionic surfactants is attractive in nature, being more intense in the case of DHPC + SDS. The interaction parameter, β 12 , varies with composition of the mixtures indicating changes in packing. The proton NMR shifts are quite different for the two systems and also vary with composition. An interpretation of these experimentally determined chemical shifts in terms of the degree of compactness attributed to electrostatic and steric interactions in the mixed micelle supports the conclusions derived from the fluorescence cmc experiments.
Keywords: Diheptanoyl phosphatidylcholine; Mixed micelles; Sodium dodecyl sulfate; Dodecyltrimethylammonium bromide;

Unusual micellar properties of multiheaded cationic surfactants in the presence of strong charge neutralizing salts by Jayanta Haldar; Vinod K. Aswal; Prem S. Goyal; Santanu Bhattacharya (156-161).
The aggregation properties of single-chain surfactants bearing one (H1), two (H2), and three (H3) trimethylammonium head groups have been studied by small-angle neutron scattering (SANS). Growth of aggregates was observed to decrease dramatically with an increase in the number of head groups in the surfactants. The micelles grow progressively smaller with every increase in the number of head groups of the surfactants. Aggregation number (N) continuously decreases and the fractional charge (α) gradually increases with the increase in the number of head groups. The semiminor axis (a) and semimajor axis ( b = c ) of the micelle decrease strongly with the increase in the number of head groups. In the case of H1, dramatic micellar growth is observed on addition of salts such as KBr and sodium salicylate, but this type of micellar growth is not observed in the cases of H2 and H3 when the above salts are added to their micellar solutions. Aggregation number and size of the micelles remain almost the same, even after addition of KBr at a concentration as high as 100 mM. This observation with multiheaded cationic surfactants is unusual. Clearly, the charge density at the head group level of surfactants markedly influences their micellar aggregation properties.
Keywords: Multiheaded surfactants; Micelles; Small-angle neutron scattering; Viscoelasticity;

Critical parameters playing a role in oil recovery by capillary imbibition of surfactant solutions were studied. Experiments conducted on sandstone and carbonate samples using different oil and surfactant types were evaluated for surfactant selection. In this evaluation interfacial tension (IFT), surfactant type, solubility characteristics of surfactants, rock type, initial water (pre-wet rock), and surfactant concentration were considered. In addition to these, a new technique was adopted to facilitate the surfactant screening process. This technique is based on assigning inorganic and organic property values and plotting organic conception diagrams (OCD) for surfactants. OCD defines the property of a compound in terms of physical chemistry in such a way that the property that depends much on the van der Waals force is called “organic” and the one that depends much on electric affinity is called “inorganic.” Correlations between the capillary imbibition recovery performance and the properties of surfactant and oil (organic value (OV), inorganic value (IV), and IFT of surfactant solutions, oil viscosity, and surfactant type) were obtained. These correlations are expected to be useful in selecting the proper surfactant for improved oil recovery as well as identifying the effects of surfactant properties on the capillary imbibition performance.
Keywords: Capillary imbibition; Interfacial tension; Oil recovery; Organic conception diagram; Correlation between oil recovery and surfactant properties; Critical micelle concentration; Initial water; Solubility of surfactants;

Phase diagram studies in two-surfactant ternary systems employing positron annihilation spectroscopy by K. Chandramani Singh; P.H. Khani; R. Yadav; P.C. Jain (176-181).
Positron annihilation lifetime parameters in condensed media are sensitive to structural and conformational changes. This property has been exploited to study the phase diagrams of two ternary cationic surfactant systems. Positron lifetime measurements were performed in cetyltrimethylammonium bromide (CTAB)/water/hexanol and tetradecyltrimethylammonium bromide (TTAB)/water/pentanol systems having varying concentrations of hexanol and pentanol respectively. For both the systems, changes were observed in the positron lifetime parameters whenever a phase transformation occurred. The various phase boundaries demarcated by this technique agrees well with those obtained by other conventional techniques. Besides this, the present work suggests the existence of two kinds of lamellar structures referred to as DI and DII phases in both the systems, which were otherwise considered to be a single D phase by other conventional techniques. The existence of such lamellar structures has been demonstrated by a change in the trend of o-Ps lifetime when the system passes from one type of lamellar structure to the other type. The results of these investigations are presented.
Keywords: Positron; Surfactant; Phase transitions; Lamellar structure; Aggregates;

The capillary number is used to quantify the mobilization potential of organic phases trapped within porous media. The capillary number has been defined in three different forms, according to types of flow velocity and viscosity used in its definition. This study evaluated the suitability of the capillary number definitions representing surfactant and surfactant foam floods by constructing capillary number–TCE saturation relationships. The results implied that the capillary number should be correctly employed, according to scale and fluid flow behavior. This study suggests that the pore-scale capillary number should be used only for investigating the organic-phase mobilization at the pore scale because it is defined by the pore velocity and the dynamic viscosity. The Newtonian-fluid capillary number using the Darcy velocity and the dynamic viscosity may be suitable for quantifying flood systems representing Newtonian fluid behavior. For viscous-force modified flood systems such as surfactant-foam floods, the apparent capillary number definition employing macroscopic properties (permeability and potential gradient) may be used to appropriately represent the desaturation of organic phases from porous media.
Keywords: Capillary number; Foam; Surfactant; Trichloroethylene; Remediation; DNAPL; Porous media;

Interactions between sodium poly(acrylate) (NaPAA) and dodecyltrimethyl/ethyl/propyl/butylammonium bromide (C12NM, C12NE, C12NP, and C12NB) were studied. Variation of the physicochemical properties of the surfactants and polyelectrolyte–surfactant mixtures, such as critical micelle concentration (cmc), critical aggregation concentration (cac), micellar micropolarity, aggregation number, and pyrene lifetime, were determined by steady-state and time-resolved fluorescence methods. It is shown that the surfactant head group size has a striking effect on the interaction between surfactant and polyelectrolyte. The interaction is weakened gradually when the surfactant head group is increased from trimethyl to tripropyl, which might be owing to the increase of the steric hindrance between the polyelectrolyte chain and micellar surface. But when the head group is tributyl, the interaction is enhanced and stronger than that between C12NP and NaPAA. This might be explained by the self-association of the C12NB head groups.
Keywords: Polyelectrolyte; Surfactant; Polyelectrolyte–surfactant interaction; Surfactant head group size; Fluorescence;

The storage modulus, G ′ , together with the yield stress, is an essential quantity characterizing the rheological properties of magnetic field-responsive suspensions (magnetorheological fluids or MRF). In this work, we present both experimental and theoretical results on the viscoelastic properties of MRFs. Two MRFs are used: In one the solid phase consists of cobalt ferrite particles + silica gel, with silicone oil as liquid phase. The second system is formed by carbonyl iron + silica gel also dispersed in silicone oil. The cobalt ferrite particles are synthesized as monodisperse colloidal spheres with an average diameter of 850 nm. We describe a new model based on the slender-body approach for hydrodynamic interactions. The predictions of the model are compared to preliminary experimental G ′ data obtained in a controlled stress plate–plate rheometer. It is found that the model gives the correct order of magnitude for the highest fields in iron suspensions, but underestimates the experimental results obtained in ferrite ones. In the case of high permeability materials such as carbonyl iron, by the inclusion of high-order multipolar interactions and saturation effects we also predict the order of magnitude of the experimental results. When dealing with low permeability cobalt ferrite based MRFs, other effects, such as remanence (at low fields) and saturation (at high fields), must be considered.
Keywords: Slender-body approach; Magnetic colloids; Magnetorheological fluids; Rheology; Viscoelasticity; Oscillometry;

Modeling of the linear viscoelastic properties of oil-in-water emulsions by Sylvie Dagréou; Bruno Mendiboure; Ahmed Allal; Gérard Marin; Jean Lachaise; Philippe Marchal; Lionel Choplin (202-211).
The aim of this work is to use a recently developed statistical model of dispersions with nonhydrodynamic interactions to describe the linear viscoelastic properties of emulsions of Newtonian liquids. None of the existing models can describe the rheological behavior of such systems, particularly the elastic properties, in the linear regime. We first present the results of numerical simulations of our model applied to emulsions. We show that taking nonhydrodynamic interactions into account allows to predict that emulsions of two purely viscous liquids have a complex viscoelastic behavior. We then compare the model to experimental results on oil/water emulsions, stabilized with ionic and nonionic surfactants. We find out that our statistical mechanical approach gives a much better description of the viscoelastic behavior of these samples than purely hydrodynamic models do. However, the elasticity observed is underestimated by our model. We indicate further theoretical developments which could improve the description of the viscoelastic properties of emulsions.
Keywords: Emulsions; Rheology; Linear viscoelasticity; Statistical model; Nonhydrodynamic interactions; Elasticity;

Separation of colloidal particles of different sizes is becoming increasingly important due to rapid developments in the area of proteomics, genetic engineering, drug discovery, etc. In particular, there is a need to accomplish these separations on a microscale in ‘lab-on-a-chip’ devices. In this paper, we propose a new method for accomplishing separation of charged colloids of different sizes in a microchannel. This method involves a combination of pulses of lateral electric fields and Poiseuille flow in the axial direction. We develop a model for this separation technique and obtain closed form solutions for the mean velocity and the dispersion coefficient for a pulse of molecules introduced into the channel. These expressions are then utilized to determine the channel length and the separation time. For reasonable value of design constants, the proposed technique can separate molecules of different sizes that have diffusivities of 10−10 and 0.5 × 10 −10  m 2 / s in 15.7 s in a 3.7 mm long channel. The length and the time increase to 5.45 cm and 231 s if the ratio of the diffusivities is reduced from 2 to 1.2, i.e., the latter diffusivity is increased to 0.835 × 10 −10  m 2 / s , while keeping all the other parameters the same. If the diffusivities are about 10 −9  m 2 / s , the length and the time for separation are 1 cm and 17.5 s for D 1 / D 2 = 2 , and 16 cm and 269 s for D 1 / D 2 = 1.2 .
Keywords: Pulsating lateral electric fields; Separation; Microchannel;

Electroviscoelasticity of liquid/liquid interfaces: fractional-order model by Aleksandar M. Spasic; Mihailo P. Lazarevic (223-230).
A number of theories that describe the behavior of liquid–liquid interfaces have been developed and applied to various dispersed systems, e.g., Stokes, Reiner–Rivelin, Ericksen, Einstein, Smoluchowski, and Kinch. A new theory of electroviscoelasticity describes the behavior of electrified liquid–liquid interfaces in fine dispersed systems and is based on a new constitutive model of liquids. According to this model liquid–liquid droplet or droplet–film structure (collective of particles) is considered as a macroscopic system with internal structure determined by the way the molecules (ions) are tuned (structured) into the primary components of a cluster configuration. How the tuning/structuring occurs depends on the physical fields involved, both potential (elastic forces) and nonpotential (resistance forces). All these microelements of the primary structure can be considered as electromechanical oscillators assembled into groups, so that excitation by an external physical field may cause oscillations at the resonant/characteristic frequency of the system itself (coupling at the characteristic frequency). Up to now, three possible mathematical formalisms have been discussed related to the theory of electroviscoelasticity. The first is the tension tensor model, where the normal and tangential forces are considered, only in mathematical formalism, regardless of their origin (mechanical and/or electrical). The second is the Van der Pol derivative model, presented by linear and nonlinear differential equations. Finally, the third model presents an effort to generalize the previous Van der Pol equation: the ordinary time derivative and integral are now replaced with the corresponding fractional-order time derivative and integral of order p < 1 .
Keywords: Electroviscoelasticity; Fractional-order model; Deformable interfaces; Finely dispersed systems; Emulsions; Double emulsions;

Electrophoretic mobilities and primary electroviscous coefficients are determined for “hard” prolate ellipsoids of axial ratio less than or equal to 4 in KCl, NaCl, and Tris–glycine salt solutions. Account is taken of the steady state distortion of the ion atmosphere around the ellipsoid by numerical solution of the coupled Poisson, low-Reynolds-number Navier–Stokes, and ion transport equations. This is accomplished by a boundary element procedure. Results are presented as ratios of mobilities and primary electroviscous coefficients of ellipsoids to those of corresponding spheres. It is shown that the electrophoretic mobility of an ellipsoid is very similar to that of a sphere under similar conditions of size, ionic strength, salt type, and zeta potential. Other factors being equal, shape has little effect on electrophoretic mobility. For the primary electroviscous coefficient, on the other hand, there is a substantial shape effect. It is argued that the complementary techniques of electrophoresis and viscosity together provide an effective means of studying the size, charge, and shape of macroions and colloidal particles.
Keywords: Prolate ellipsoids; Electrophoresis; Viscosity; Boundary element; Electrokinetic transport;

In this study, the effects of fluorine treatment on surface properties, surface free energies, and dielectric constants of polyimide thin films were studied using X-ray photoelectron spectroscopy, contact angles, and dielectric characteristics, respectively. The glass transition temperature of fluorinated polyimide film gradually decreases with increasing fluorine pressure. The surface free energies and dielectric constants of the film decreased with increasing amount of the treatment fluorine gas. It was explained that the replacement of fluorine led to a decrease of the local electron polarization of polyimide and an increase of the free volume, which could be attributed to the relatively large volume of fluorine.
Keywords: Polyimide thin film; Fluorination; XPS; Glass transition temperature; Dielectric constant;

Pattern formation through selective chemical transformation of self-assembled benzaldimine monolayer by soft X-ray irradiation by Yu Jin Jung; Jung-Im Kim; Tai-Hee Kang; Kyuwook Ihm; Ki-Jeong Kim; Bongsoo Kim; Joon Won Park (241-247).
Benzaldimine monolayer was exposed to soft X-rays, and the involved chemical transformation was investigated using X-ray photoelectron spectra and near-edge X-ray absorption fine structure spectroscopy. The spectroscopy indicated that irradiation of soft X-ray (550 eV)-induced selective transformation of the imine group into a nonhydrolyzable one, i.e., the amine group. Utilizing the selective chemical transformation of the imine group with the soft X-ray irradiation, we were able to generate a micropattern. AFM images showed that the patterning with alternating surface topology was effective. The patterned monolayer was further modified with biotin and Cy3-tagged Streptavidin sequentially. Fluorescence images showed that the above molecules were selectively immobilized onto the amine-terminated region of the patterned surface. The current system is found to be more efficient than the predecessor, 4-nitrobenzaldimine monolayer.
Keywords: Soft X-ray; Benzaldimine monolayer; X-ray photoelectron spectra (XPS); Near edge X-ray absorption fine structure (NEXAFS) spectroscopy; Pattern; AFM image; Fluorescence image;

by Arthur Hubbard (248).