Journal of Colloid And Interface Science (v.317, #2)

A review of the literature of kinetic and mechanistic studies of transition-metal nanocluster nucleation and growth is presented; the focus is on nucleation processes. A brief survey of nucleation theory is given first, with an emphasis on classical nucleation theory, as this is the logical starting point of transition-metal nanocluster nucleation and growth studies. The main experimental methods for following nanocluster formation are examined next—dynamic light scattering, UV–visible spectroscopy, electron microscopy, and X-ray spectroscopies—with special attention paid to their strengths and weaknesses. Several specific examples of transition-metal nanocluster formation are then given, beginning with LaMer's classic sulfur sol system and including the Finke–Watzky mechanism of slow continuous nucleation A → B followed by fast autocatalytic surface growth A + B → 2 B . Finally, brief overviews of semiconductor nanoparticle preparations, solid-state nucleation studies—emanating from Avrami's work—and protein agglomeration mechanistic studies are also provided, as these processes are relevant, conceptually and in a general sense, to the field of transition-metal nanocluster nucleation and growth mechanisms.A review of transition-metal nanocluster nucleation and growth is presented with attention given to the nucleation process. Key studies and insights from the literature are provided, with a look toward needed future studies.
Keywords: Nanoclusters; Nucleation; Growth; Kinetics and mechanism;

Effect of ozonolysis on the pore structure, surface chemistry, and bundling of single-walled carbon nanotubes by Tirandai Hemraj-Benny; Teresa J. Bandosz; Stanislaus S. Wong (375-382).
An ozonolysis protocol has recently been developed that cannot only purify nanotubes but also achieve rational spatial and molecular control over chemical derivatization in single-walled carbon nanotubes (SWCNTs). Ozonolysis likely opens end caps and introduces holes into the sidewalls of tubes, which may occur through an oxidation of carbon atoms located on the nanotube surface, resulting in the formation of oxygen-containing functional groups. Overall, it was demonstrated by analysis of nitrogen adsorption and TGA/DTG that the total surface area, micropore volume, and mesopore volume of SWCNTs depend on several, intertwined factors including the degree of purity, surface functionality, density of surface groups, as well as the state of aggregation of the carbon tubes. Hydrogen bonding in these systems plays a role too. Data suggest that complete removal of surface functionalities would lead to a greater total surface area and higher micropore volume.The total surface area, micropore volume, and mesopore volume of nanotubes are dependent on several, intertwined factors including purity, surface functionality, density of surface groups, and the state of aggregation of the tubes.
Keywords: Carbon nanotubes; Oxidation; Heat treatment; Adsorption; BET surface area;

Adsorption characteristics of zwitterionic diblock copolymers at the silica/aqueous solution interface by Kenichi Sakai; Maria Vamvakaki; Emelyn G. Smith; Erica J. Wanless; Steven P. Armes; Simon Biggs (383-394).
The adsorption of a zwitterionic diblock copolymer, poly(2-(diethylamino)ethyl methacrylate)–block–poly(methacrylic acid) (PDEA59–PMAA50), at the silica/aqueous solution interface has been characterised as a function of pH. In acidic solution, this copolymer forms core–shell micelles with the neutral PMAA chains being located in the hydrophobic cores and the protonated PDEA chains forming the cationic micelle coronas. In alkaline solution, the copolymer forms the analogous inverted micelles with anionic PMAA coronas and hydrophobic PDEA cores. The morphology of the adsorbed layer was observed in situ using soft-contact atomic force microscopy (AFM): this technique suggests the formation of a thin adsorbed layer at pH 4 due to the adsorption of individual copolymer chains (unimers) rather than micelle aggregates. This is supported by the remarkably low dissipation values and the relatively low degrees of hydration for the adsorbed layers, as estimated using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and optical reflectometry (OR). In alkaline solution, analysis of the adsorption data suggests a conformation for the adsorbed copolymers where one block projects normal to the solid/liquid interface; this layer consists of a hydrophobic PDEA anchor block adsorbed on the silica surface and an anionic PMAA buoy block extending into the solution phase. Tapping mode AFM studies were also carried out on the silica surfaces after removal from the copolymer solutions and subsequent drying. Interestingly, in these cases micelle-like surface aggregates were observed from both acidic and alkaline solutions. The lateral dimension of the aggregates seen is consistent with the corresponding hydrodynamic diameter of the copolymer micelles in bulk solution. The combination of the in situ and ex situ AFM data provides evidence that, for this copolymer, micelle aggregates are only seen in the ex situ dry state as a result of the substrate withdrawal and drying process. It remains unclear whether these aggregates are caused by micelle deposition at the surface during the substrate withdrawal from the solution or as a result of unimer rearrangements at the drying front as the liquid recedes from the surface.The adsorption of a zwitterionic diblock copolymer, poly(2-(diethylamino)ethyl methacrylate)–block–poly(methacrylic acid) (PDEA–PMAA), at the silica/aqueous solution interface has been characterised as a function of pH.
Keywords: Zwitterionic diblock copolymers; Adsorption; In situ soft-contact AFM; Tapping mode AFM;

Adsorption of alkyl trimethylammonium bromides at the air/water interface by Tibor Gilányi; Imre Varga; Cosima Stubenrauch; Róbert Mészáros (395-401).
A number of features of the adsorption of alkyl trimethylammonium bromides with n c = 10 , 12 , 14 , and 16 at the air/water interface were studied. First, the adsorption isotherms were calculated from experimental surface tension vs concentration curves by means of the Gibbs equation. Second, a novel method was used to estimate the adsorption free energy change. From the analysis of these data it was concluded that the hydrophobic driving force for the adsorption first increases with increasing adsorbed amount and then levels off in a plateau, which holds true for all four homologues. This peculiar behavior was interpreted by the formation of a thin liquid-like alkane film at the air/water interface once a certain adsorbed amount is exceeded. The hydrophobic contribution to the standard free energy change of adsorption was compared with those values previously determined for alkyl sulfate homologues. This comparison suggests that the alkyl trimethylammonium type surfactants behave as if their alkyl chain was approximately one methylene group shorter than those of the corresponding alkyl sulfates.The analysis of the adsorption isotherms suggests that the alkyl trimethylammonium type surfactants behave as if their alkyl chains were approximately one methylene group shorter than the corresponding alkyl sulfates.
Keywords: Adsorption; Surfactants; Adsorption free energy; Alkyl trimethylammonium bromides;

Heavy metal contamination of waters and soils is particularly dangerous to the living organisms. Different studies have demonstrated that hydroxyapatite has a high removal capacity for divalent heavy metal ions in contaminated waters and soils. The removal of Cd from aqueous solutions by hydroxyapatite was investigated in batch conditions at 25 ± 2 ° C . Cadmium was applied both as single- or multi-metal ( Cd + Pb + Zn + Cu ) systems with initial concentrations from 0 to 8 mmol L−1. The adsorption capacity of hydroxyapatite in single-metal system ranged from 0.058 to 1.681 mmol of Cd/g of hydroxyapatite. In the multi-metal system competitive metal sorption reduced the removal capacity by 63–83% compared to the single-metal system. The sorption of Cd by hydroxyapatite follows the Langmuir model. Cadmium immobilization occurs through a two-step mechanism: rapid surface complexation followed by partial dissolution of hydroxyapatite and ion exchange with Ca resulting in the formation of a cadmium-containing hydroxyapatite.The sorption of Cd by hydroxyapatite occurs through a two-step mechanism: rapid surface complexation followed by partial dissolution of hydroxyapatite and ion exchange with Ca.
Keywords: Cadmium; Hydroxyapatite; Competitive sorption; Surface complexation; Ion exchange;

Adsorption of lanthanides on mordenite from nitrate medium by Agnieszka Gładysz-Płaska; Marek Majdan; Stanisław Pikus (409-423).
The adsorption of lanthanides (except for Pm) on mordenite was investigated under various solution conditions of nitrate ion concentrations ([NO 3]: 0.001–2 mol/dm3) and total lanthanide concentrations (0.0005 mol/dm3). Solutions of lanthanide nitrates were equilibrated with zeolite samples at 296 K. A concave tetrad effect was evident in the change of log K d values within the lanthanide series and an explanation by a comparison of covalence in Ln―O bonds existing in Al―O(1/3Ln)―Si species found in the zeolite phase and in Ln(H2O)3+ x or Ln(NO3) n−3 n complexes formed in the aqueous phase is presented. The decreasing trend in C 1 and C 3 coefficients, which are the function of E 1 and E 3 Racah f-interelectron repulsion parameters, is evidence of the magnification of covalence in Ln―O bond in the series Si―O(1/3Ln)―Al  < Ln(H2O)3+ x  < Ln(NO3) n−3 n . The adsorption isotherms of the lanthanides, registered for total lanthanide nitrate concentrations (0.0001–0.001 mol/dm3), were found to be a Freundlich type. The obtained adsorption capacity K and adsorption intensity n parameters show odd–even changes in the lanthanide series, indicating the importance of covalence effects in the lanthanides adsorption mechanism. The mordenite samples loaded with lanthanide nitrates were investigated using diffusive reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray diffraction (XRD), and scanning electron microscopy (SEM) methods. Negative correlations between E = ( [ Al ] − [ Na ] ) / [ Ln ] and [Ln]/[Al], and negative correlations for [Ln] and [Na] on the zeolite surface, resulting from the interaction (ion exchange) of lanthanide ions with Si―O(Na)―Al and Si―OH―Al groups within the mordenite framework were found. DRIFT spectra showed the sensitivity of the framework vibration band T―O―T for Ln3+ ion interactions with negative oxygen of the mordenite structure.Tetrad effect in the distribution constants log K d of the lanthanides in the system with mordenite (numbers denote the molar concentrations of nitrates in the aqueous phase).
Keywords: Lanthanides; Mordenite; Adsorption; Tetrad effect; Racah parameters;

Association of humic acid with metal (hydr)oxide-coated sands at solid–water interfaces by Jin Chul Joo; Charles D. Shackelford; Kenneth F. Reardon (424-433).
Mineral-bound humic acid (HA) can significantly modify the physicochemical properties of the mineral surfaces and vice versa, thereby influencing the fate and transport of organic pollutants in the subsurface. The effect of various mineral surfaces on the adsorption–desorption of dissolved bulk, terrestrial HA was evaluated using three model sorbents [uncoated, α-FeO(OH)-coated, and Al2O3-coated sands] at two equilibrium pH values. The results of SEM/EDS and XPS analyses revealed relatively uniform and stable metal (hydr)oxide coatings on quartz surface and the presence of the HA coating. Strong hysteresis effects were observed for both metal (hydr)oxide-coated sands whereas a weaker hysteresis effect was observed for uncoated sand, suggesting that the adsorption–desorption of HA to model sorbents is dependent on the affinity of chemical interactions between the HA and surface composition of model sorbents. Adsorption of HA molecules onto metal (hydr)oxide-coated sands can be attributed to ligand exchange for lower molecular weight (MW) HA fractions and hydrophobic interaction for higher MW HA fractions, illustrating that both kinetic and fractional adsorption–desorption of HA subcomponents are important considerations.Strong hysteresis effects were observed for metal (hydr)oxide-coated sands, whereas weaker hysteresis effects were observed for uncoated sand, suggesting that sorption reversibility of humic acid to the sorbents was dependent on the affinity of chemical interactions between them.
Keywords: Adsorption; Desorption; Hysteresis; Metal (hydr)oxide-coated sands; Molecular weight fraction; Terrestrial humic acid;

Macroporous crosslinked poly(p-vinylbenzylaniline) (PVBA) was synthesized and its adsorption isotherms for phenol in hexane and in aqueous solution were comparatively measured. It was shown that the adsorption isotherms in hexane were straight lines and passed through the origin, whereas those in aqueous solution could be simulated by Freundlich isotherms. Adsorption enthalpies of phenol onto PVBA were calculated, and the results indicated that the adsorption was an exothermic process. Comparison of the adsorption behaviors of PVBA, poly(p-vinylbenzylmethylamine) (PVBMA), and poly(p-vinylbenzyl-p-nitroaniline) (PVBNA) for phenol in hexane suggested that hydrogen bonding and π – π stacking were primarily responsible for the adsorption, the nitrogen atom and benzene ring of PVBA acted as hydrogen bonding acceptors and formed hydrogen bonding with the hydrogen atom of hydroxyl group of phenol. Investigation of the adsorption mechanism in aqueous solution revealed that hydrogen bonding and hydrophobic interaction were the main driving forces.Adsorption isotherms of phenol onto PVBA in hexane and aqueous solution with the temperature at 293, 298, 303, and 308 K, respectively.
Keywords: Aniline modified polystyrene resin; Phenol; Adsorption; Hydrogen bonding; π – π stacking; Hydrophobic interaction;

Determination of the space between closed multiwalled carbon nanotubes by GCMC simulation of nitrogen adsorption by S. Furmaniak; A.P. Terzyk; P.A. Gauden; K. Lota; E. Frąckowiak; F. Béguin; P. Kowalczyk (442-448).
We present a new determination method of the porosity created by the adsorption space between closed multiwalled carbon nanotubes. Using the grand canonical Monte Carlo (GCMC) simulation of nitrogen adsorption at 77 K and applying the “Karolina” algorithm, local isotherms were simulated for different distances between parallel nanotubes and finally the equation of the global adsorption isotherm was solved. This methodology leads to a satisfactory description of the experimental nitrogen adsorption data showing that the distance between nanotubes is in the range between 4 and 14 nm.
Keywords: Adsorption; Carbon nanotubes; Pore-size distribution;

Protein–surfactant interactions at hydrophobic interfaces studied with total internal reflection fluorescence correlation spectroscopy (TIR-FCS) by Andreas W. Sonesson; Hans Blom; Kai Hassler; Ulla M. Elofsson; Thomas H. Callisen; Jerker Widengren; Hjalmar Brismar (449-457).
The aim of this work was to study the dynamics of proteins near solid surfaces in the presence or absence of competing surfactants by means of total internal reflection fluorescence correlation spectroscopy (TIR-FCS). Two different proteins were studied, bovine serum albumin (BSA) and Thermomyces lanuginosus lipase (TLL). A nonionic/anionic (C12E6/LAS) surfactant composition was used to mimic a detergent formulation and the surfaces used were C18 terminated glass. It was found that with increasing surfactant concentrations the term in the autocorrelation function (ACF) representing surface binding decreased. This suggested that the proteins were competed off the hydrophobic surface by the surfactant. When fitting the measured ACF to a model for surface kinetics, it was seen that with raised C12E6/LAS concentration, the surface interaction rate increased for both proteins. Under these experimental conditions this meant that the time the protein was bound to the surface decreased. At 10 μM C12E6/LAS the surface interaction was not visible for BSA, whereas it was still distinguishable in the ACF for TLL. This indicated that TLL had a higher affinity than BSA for the C18 surface. The study showed that TIR-FCS provides a useful tool to quantify the surfactant effect on proteins adsorption.
Keywords: Protein–surfactant interactions; TIR-FCS; Lipase; BSA; C12E6/LAS; Hydrophobic surface;

Mechanism of nanocapsules formation by the emulsion–diffusion process by Delphine Moinard-Chécot; Yves Chevalier; Stéphanie Briançon; Laurent Beney; Hatem Fessi (458-468).
A detailed investigation into the mechanisms of nanocapsule formation by means of the two stages “emulsion–diffusion” process is reported. Such widely used process is still poorly understood. An emulsion of oil, polymer and ethyl acetate is fabricated as a first step; dilution with pure water allows ethyl acetate to diffuse out from the droplets, leaving a suspension of nanocapsules at the end. It has been shown that the size of nanocapsules was related to the chemical composition of the organic phase and the size of primary emulsion through a simple geometrical relationship. As a consequence, most of the properties of the nanocapsules were decided at the emulsification step. The influence of several formulation and processing parameters of the primary emulsion was studied accordingly. The thin polymer membrane of nanocapsules was observed by means of cryo-fracture electron microscopy. Finally two experiments were designed for a mechanistic investigation of the diffusion step. A step-by-step diffusion of the organic solvent takes place by successive partition equilibria of ethyl acetate between the droplets and aqueous phase. A time-resolved experiment shows the fast diffusion (less than 20 ms) related to the small droplet size of the emulsion.
Keywords: Nanocapsule; Emulsion; Process; Emulsion–diffusion; Polycaprolactone;

Encapsulation of protein drugs in biodegradable microparticles by co-axial electrospray by Jingwei Xie; Wei Jun Ng; Lai Yeng Lee; Chi-Hwa Wang (469-476).
A co-axial electrospray process was developed to encapsulate protein-based drugs in biodegradable polymeric microparticles eliminating the key problem faced by other conventional methods of protein encapsulation—the primary emulsion being a major cause for protein denaturation and aggregation. Bovine serum albumin (BSA) and lysozyme were chosen as model protein drugs for this study. Scanning electron microscopy observation of the morphology of particles showed spherical microparticles of several microns could be achieved. In vitro release profiles measured using Micro-BCA assay indicated sustained release of proteins for more than 30 days. The results of circular dichroism suggested that the secondary structure of released BSA can be retained. The bioactivity of released lysozyme was found to be more than 90% which is higher than the values reported from most literatures. Therefore, co-axial electrospray could be a very promising approach to encapsulate biomacromolecules such as proteins, enzymes, DNA plasmids or living cells inside microparticles for controlled release drug delivery applications.A co-axial electrospray process was developed to encapsulate protein-based drugs in biodegradable polymeric microparticles. The bioactivity of released lysozyme from microparticles was found to be more than 90%.
Keywords: Co-axial electrospray; Microparticles; Protein; Encapsulation;

We describe the construction of hepatic-targeting microcapsules by self-assembly of chemo-enzymatic synthesized poly(vinyl galactose ester-co-methacryloxyethyl trimethylammonium chloride) (PGEDMC) containing galactose branches, which can be specifically recognized by membrane bound galactose receptors (ASGPR), for acyclovir (ACV) controlled release system. Alternate deposition of PGEDMC and poly(sodium 4-styrenesulfonate) (PSS) was carried out on ACV microcrystals. It was revealed that the drug release rate decreases with the increase of coated layer number and a microcapsule-drying treatment would enhance the sustained release effect probably because of a multilayer shrink and tightness during the process. The complete release of ACV yielded a hollow PGEDMC/PSS multilayered network with favorable integrity and nano-thickness by TEM and SEM. The potential targetability of the system was proved in vitro by PNA lectin recognition. Lectin hardly adsorbed on the film where the outmost layer was a polyanion or a polycation without galactose component. Whilst the galactose-containing layer (PGEDMC) was the outmost layer, a significant lectin combination was observed. This technique could provide a promising way to encapsulate and deliver various target substances in biological and pharmaceutical applications.Hepatic targeting multilayer drug delivery system: layer-by-layer assembly of PGEDMC and PSS on drug crystal to control the release in buffer. The multilayer bearing galactose residues outside can be recognized by PNA lectin.
Keywords: Drug delivery; Galactose; Hepatic targeting; Lectin; LbL assembly; Microcapsule; Polyelectrolyte;

Synthesis of faceted and cubic Ag2S nanocrystals in aqueous solutions by Lihong Dong; Ying Chu; Yang Liu; Lili Li (485-492).
With thiourea (Tu) as sulfur source and the assistance of CTAB, faceted and cubic Ag2S nanocrystals have been synthesized successfully via a simple hydrothermal route by modulating the ratio of Tu and AgNO3, respectively. It is the first report that the fabrication of faceted and cubic Ag2S nanocrystals takes place in aqueous medium, which makes the synthesis environmentally benign, user-friendly, economical and practicable to industry production. It is also found that the cooperation effect of CTAB and Tu should be responsible for the formation of the as-obtained Ag2S nanocrystals. The UV–vis absorption spectrum of the products shows obvious blue shift.With thiourea as sulfur source and the assistance of CTAB, faceted and cubic Ag2S nanocrystals have been synthesized via hydrothermal route by modulating the ratio of Tu and AgNO3, respectively.
Keywords: Ag2S; Faceted and cubic nanocrystals; Thiourea; CTAB; Cooperation effect;

Piperidine as a new free OH organic base has been successfully used to prepare Zn5(OH)8(Ac)2⋅2H2O particles (named Zn-HDS) or concentrated alcoholic ZnO sols. Considering the applications of Zn-HDS and ZnO compounds, as well as interests of these synthesis mechanisms for fundamental chemistry, such investigations are of importance. This strategy not only allows preparing Zn-HDS compounds at room temperature but also brings evidence of some new nucleation-growth, and permits the preparation of well crystalline ZnO nanocrystals at low temperature (maximum 60 °C). It was possible to convincingly prove that the formation of Zn-HDS phase is concomitant to the ZnO nanocrystals formation and that Zn-HDS could be considered as an intermediate initiator of ZnO nanocrystals. A parallel approach was used for the fast screening of the synthesis progress.
Keywords: Zinc oxide; Nanocolloids; Zn-HDS; Nucleation; Growth; Piperidine; Parallel screening;

Surface activity of solid particles with extremely rough surfaces by Yoshimune Nonomura; Shigeyuki Komura (501-506).
The solid particles are adsorbed at liquid–liquid interfaces and form self-assembled structures when the particles have suitable wettability to both liquids. Here, we show theoretically how the extreme roughness on the particle surface affects their adsorption properties. In our previous work, we discussed the adsorption behavior of the solid particles with microstructured surfaces using the so-called Wenzel model [Y. Nonomura et al., J. Phys. Chem. B 110 (2006) 13124]. In the present study, the wettability and the adsorbed position of the particles with extremely rough surfaces are studied based on the Cassie–Baxter model. We predict that the adsorbed position and the interfacial energy depend on the interfacial tensions between the solid and liquid phases, the radius of the particle, and the fraction of the particle surface area that is in contact with the external liquid phase. Interestingly, the initial state of the system governs whether the particle is adsorbed at the interface or not. The shape of the particle is also an important factor which governs the adsorbed position. The disk-shaped particle and the spherical particle which is partially covered with the extremely rough surface, i.e. Janus particle, are adsorbed at the liquid–liquid interface in an oriented state. We should consider not only the interfacial tensions, but also the surface structure and the particle shape to control the adsorption behavior of the particle.
Keywords: Solid particle; Surface activity; Adsorption; Surface roughness; Wettability;

Submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles (averaged diameter: 200 nm) as a template in conjunction with the sol–gel method. Utilization of 0.20 mol/L titanium tetrabutoxide and 25 g/L latex led to the formation of anatase particles having shell thickness of about 15 nm and void diameter of about 150 nm. Photocatalytic activity of the titania hollow spheres was examined by focusing on its enhancement by electron scavengers in the photocatalytic decomposition of methylene blue (MB). The electron scavengers employed were inorganic oxidants such as ClO 3, BrO 3, IO 4, H2O2, and S2O2− 8. Differences in electronegativity, atomic radius of the halogens, and the number of highly reactive radical and nonradical intermediates were proven to be important criteria for an electron scavenger to yield high efficiency in the MB photodecomposition. Based on the results, the effect of the oxidants used were found to be in the order of S 2 O 8 2 − > IO 4 − > BrO 3 − > H 2 O 2 > ClO 3 − .Submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles as a template in sol–gel method. Photocatalytic activity of the hollow spheres was investigated by focusing on its enhancement by utilizing various electron scavengers. The effect of all oxidants used in UV/TiO2 system on enhancing photodecomposition of MB was found to be in the order of S 2 O 8 2 − > IO 4 − > BrO 3 − > H 2 O 2 > ClO 3 − .
Keywords: Titania hollow spheres; Sol–gel method; Photocatalytic activity; Electron scavenger; Methylene blue; Halogens; Radical;

Many carbonate oil reservoirs are oil-wet and fractured; waterflood recovery is very low. Dilute surfactant solution injection into the fractures can improve oil production from the matrix by altering the wettability of the rock to a water-wetting state. A 2D, two-phase, multicomponent, finite-volume, fully-implicit numerical simulator calibrated with our laboratory results is used to assess the sensitivity of the process to wettability alteration, IFT reduction, oil viscosity, surfactant diffusivity, matrix block dimensions, and permeability heterogeneity. Capillarity drives the oil production at the early stage, but gravity is the major driving force afterwards. Surfactants which alter the wettability to a water-wet regime give higher recovery rates for higher IFT systems. Surfactants which cannot alter wettability give higher recovery for lower IFT systems. As the wettability alteration increases the rate of oil recovery increases. Recovery rate decreases with permeability significantly for a low tension system, but only mildly for high tension systems. Increasing the block dimensions and increasing oil viscosity decreases the rate of oil recovery and is in accordance with the scaling group for a gravity driven process. Heterogeneous layers in a porous medium can increase or decrease the rate of oil recovery depending on the permeability and the aspect ratio of the matrix block.When an oil-wet, oil saturated porous rock is immersed in a dilute (∼0.05 wt% anionic) surfactant solution, surfactant solution imbibes and oil comes out as drops on the top side of the rock (as shown in the figure). This paper studies the sensitivity of this process to various parameters.
Keywords: Wettability alteration; Fractured carbonates; Dilute surfactant treatment; Enhanced oil recovery; Compositional simulation; Imbibition; Gravity drainage;

Investigation of mechanochemically modified kaolinite surfaces by thermoanalytical and spectroscopic methods by Veronika Vágvölgyi; József Kovács; Erzsébet Horváth; János Kristóf; Éva Makó (523-529).
The effect of mechanochemical activation (dry grinding), formamide intercalation, and thermal deintercalation on high- and low-defect kaolinite surfaces was studied by thermogravimetry and diffuse reflectance Fourier transform infrared spectroscopy. These investigations were completed with specific surface area and pore size distribution measurements. The surface acidity of the ground and the ground-and-intercalated kaolinites was probed with ammonia adsorption. The surface area and the pore volume as well as the amount of adsorbed ammonia increased with the rate of mechanochemical activation. At the same time the thermally deintercalated minerals showed increased surface area but decreased pore volume with the time of grinding. Adsorbed ammonia was detected as ammonium ion in the 1400–1500 cm−1 spectral range.The pore size distribution curves of kaolinite ground for 0, 1, 3, and 6 h show an increase in intensity and a shift toward higher pore size values after formamide intercalation followed by thermal deintercalation.
Keywords: Kaolinite; Intercalation; Mechanochemical activation; Adsorption; Infrared spectroscopy; Thermal analysis;

Preparation and magnetic properties of Cu-ferrite nanorods and nanowires by Zhongbing Huang; Guangfu Yin; Xiaoming Liao; Yadong Yao; Yunqing Kang (530-535).
An aqueous solution method has been developed for preparing Cu-ferrite nanorods (NRs) array and nanowires (NWs) on Cu substrate. The Cu-ferrite NRs exhibit a clear uniaxial anisotropy with the easy axis along rods. The decrease of the reduced remanence from 0.24 in the parallel magnetic field to almost zero in the perpendicular field shows a strong effect of the demagnetizing field perpendicular to the rod axis. The weaker uniaxial anisotropy makes NWs the lower saturation magnetization.(a) SEM image of Cu-ferrite nanorods array film on Cu substrate. (b) TEM image of Cu-ferrite nanowires and partially hollow nanotubes.
Keywords: Cu-ferrite nanorods; Magnetic nanowires; Quasi-aligned; Anisotropy; Saturation magnetization;

Behaviour of wetting films of sodium hyaluronate saline solutions by Walkíria Ribeiro; Marta Orfão; José Luís Mata; Benilde Saramago (536-543).
The behaviour of wetting films of sodium hyaluronate (NaHA) saline solutions, at physiological conditions, is investigated using interferometry. Concentrations in the range of dilute and semi-dilute regimes were chosen to assess the role of bulk molecular interactions on the surface forces. The transition from dilute to semi-dilute solutions is known to occur at c ∗ = 0.59   mg mL −1 . Dilute solutions form stable films whose behaviour is explained by van der Waals interactions. For semi-dilute solutions, the disjoining pressure vs film thickness isotherms show branches attributed to stepwise thinning or film stratification, which is interpreted in terms of a network as predicted by the theory of semi-dilute polyelectrolyte solutions. The distance between branches is 16 nm for the NaHA concentration of 2 mg mL−1 and 12 nm for the concentration of 3.5 mg mL−1, in agreement with the calculated correlation lengths of the polymeric network. Since no experimental evidence exists for the presence of a stable network in the bulk, this tendency for self-association should be the result of the liquid confinement. To our knowledge, the existence of oscillatory disjoining pressure isotherms in the presence of excess salt was never observed for other polyelectrolyte solutions.
Keywords: Sodium hyaluronate; Wetting films; Disjoining pressure isotherms; Interferometry; Polyelectrolytes;

Monolayer properties of surface-active metalorganic complexes with a tunable headgroup by R. Mallouri; A.D. Keramidas; G. Brezesinski; E. Leontidis (544-555).
Surface-active metalorganic complexes can be used to construct organic thin films with excellent electronic and catalytic properties. We have recently introduced a new versatile surface-active ligand, which can efficiently coordinate a wide range of transition metals. In the present work we report an investigation of Langmuir monolayers of VV, MoVI and TiIV complexes of this ligand, using surface pressure–area isotherms, Brewster-angle microscopy, and Grazing incidence X-ray diffraction. The monolayers of these complexes are stable enough over broad temperature ranges to allow efficient transfer to solid substrates.
Keywords: Langmuir monolayer; Metalorganic complex; Brewster angle microscopy; Langmuir–Blodgett film; GIXD;

Wetting kinetics of oil mixtures on fluorinated model cellulose surfaces by Christian Aulin; Andrei Shchukarev; Josefina Lindqvist; Eva Malmström; Lars Wågberg; Tom Lindström (556-567).
The wetting of two different model cellulose surfaces has been studied; a regenerated cellulose (RG) surface prepared by spin-coating, and a novel multilayer film of poly(ethyleneimine) and a carboxymethylated microfibrillated cellulose (MFC). The cellulose films were characterized in detail using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM indicates smooth and continuous films on a nanometer scale and the RMS roughness of the RG cellulose and MFC surfaces was determined to be 3 and 6 nm, respectively. The cellulose films were modified by coating with various amounts of an anionic fluorosurfactant, perfluorooctadecanoic acid, or covalently modified with pentadecafluorooctanyl chloride. The fluorinated cellulose films were used to follow the spreading mechanisms of three different oil mixtures. The viscosity and surface tension of the oils were found to be essential parameters governing the spreading kinetics on these surfaces. XPS and dispersive surface energy measurements were made on the cellulose films coated with perfluorooctadecanoic acid. A strong correlation was found between the surface concentration of fluorine, the dispersive surface energy and the contact angle of castor oil on the surface. A dispersive surface energy less than 18 mN/m was required in order for the cellulose surface to be non-wetting ( θ e > 90 ° ) by castor oil.AFM tapping mode image of a bilayer of PEI/MFC on silica in the height mode. The scanned surface area was 1 μm2 (left) and dispersive surface energy of fluorinated regenerated cellulose surfaces vs atomic fluorine concentration (right).
Keywords: MFC; Adsorption; Fluorosurfactant; XPS; AFM; Multilayer; Wetting; Oil resistance; Cellulose surface; Contact angle;

Interaction of methemoglobin with GDA/n-C5H11OH/water assemblies by Yongsheng Wang; Xia Guo; Rong Guo (568-576).
In the present paper, we studied the interaction between n-dodecylammonium α-glutamate (GDA)/n-C5H11OH/H2O assemblies and methemoglobin by UV–vis spectroscopy, X-ray diffraction, electron spin resonance (ESR), rheology, and freeze-fractured transmission electron microscopy (FF-TEM). It is found that W/O microemulsion forms at a lower n-pentanol content and O/W microemulsion forms at a lower water content with the addition of methemoglobin. The existence of methemoglobin reduces the hexagonal liquid crystal region, while the lamellar liquid crystal region is little changed in the presence of methemoglobin. Moreover, methemoglobin and GDA/n-C5H11OH/H2O assemblies can affect their structures and properties and the change in behavior is dependent on the content of methemoglobin and the composition and structure of the GDA/n-C5H11OH/H2O system. The relationship among the changes in the structure and properties of GDA/n-C5H11OH/H2O assemblies, the content of methemoglobin, and the composition and structure of GDA/n-C5H11OH/H2O assemblies may provide some important theoretical information for elucidation of the interaction between methemoglobin and blood cell membrane and may also be helpful for the cure of some blood diseases.
Keywords: Methemoglobin; n-Dodecylammonium α-glutamate; ESR; Viscosity; Small-angle X-ray diffraction;

Structure and dynamics of a sponge phase in the methyl δ-aminolevulinate/monoolein/water/propylene glycol system by Johanna Bender; Patrik Jarvoll; Magnus Nydén; Sven Engström (577-584).
The structural effect caused by the addition of up to 16% (w/w) of the hydrochloride salt of δ-aminolevulinic acid (ALA, HOOC–CH2–CH2–CO–CH2–NH2⋅HCl) or its methyl ester (m-ALA) to the sponge phase formed of monoolein/water/propylene glycol was investigated by means of crossed polarizers, small angle X-ray diffraction (SAXD) and nuclear magnetic resonance diffusometry (NMRD). Inspection with crossed polarizers revealed that additions of 4–16% (w/w) m-ALA transformed the isotropic bicontinuous sponge phase partly (4–10%) or completely (13 and 16%) into an anisotropic lamellar phase, indicating that m-ALA has a flattening effect on the bilayer curvature. The addition of 16% (w/w) ALA did not show any effect on the sponge phase. By addition of water to the anisotropic m-ALA samples, isotropic liquids were re-formed. The SAXD data for the isotropic liquids showed a diffuse Bragg peak and the NMRD self-diffusion coefficients for the drug (m-ALA) and the components of the original sponge phase (monoolein, water and propylene glycol) were shown to be essentially constant for 0–16% (w/w) added m-ALA. These results confirmed the hypothesis that the re-formed isotropic phases were indeed sponge phases. Water, for example, showed a diffusion coefficient of 3.1 – 3.9 × 10 −10 m 2 s −1 in the sponge phase, compared to 5.3 – 5.7 × 10 −10 m 2 s −1 in relevant water/propylene glycol solutions or 2.3 × 10 −9 m 2 s −1 in pure water. The reduction can be explained as a consequence of the microstructure (congruent monoolein bilayer) of the sponge phase and of the viscosity effect caused by propylene glycol and m-ALA.
Keywords: Sponge phase; Self-diffusion; NMRD; SAXD; m-ALA; ALA; Monoolein; Propylene glycol;

Incorporation of sparingly soluble species in mesostructured surfactant–polymer films by Benjamin M.D. O'Driscoll; Adrian M. Hawley; Karen J. Edler (585-592).
Recently we have investigated the formation of novel thick, solid, mesostructured films of polymer/surfactant mixtures which form spontaneously at the air–solution interface. Here we report studies of the effect of adding a series of sparingly soluble species to the precursor solution, to alter the mesostructure of cetyltrimethylammonium bromide/polyethylenimine films and to investigate the incorporation of small molecules within the films. Small-angle neutron scattering confirmed that cyclohexane and decane evenly swell the micelles in film forming solutions, while cyclohexanol extends the prolate micelles along their long axis. Although the presence of these additives in solution did not greatly affect the formation of the film, it was observed that they did influence the structure of the films. Films produced with decane consisted of a cubic phase rather the conventional 2-D hexagonal phase, whilst both cyclohexane and cyclohexanol enhance the level of ordering in low MW polymer films. Benzene was found to have no significant effect on the film.
Keywords: Surfactant–polyelectrolyte interactions; Film; Nanostructure; SANS; Reflectivity; Encapsulation;

A microfluidic electrochemical detection technique for assessing stability of thin films and emulsions by Farshid Mostowfi; Jan Czarnecki; Jacob Masliyah; Subir Bhattacharjee (593-603).
An experimental technique is developed for assessing stability of thin liquid films by application of electric potential to compress the liquid film and to simultaneously measure the electrical properties of the system. The concept involves creating a thin film at the intersection of two microchannels etched onto a glass substrate. A ramped DC potential difference is applied across the film, which develops an electrical stress across the film. Increasing the potential to a critical value leads to the rupture of the film. The critical potential is used to assess the stability of the liquid film. Small channel dimensions in this microfluidic platform allow characterization of thin films formed between micron-sized droplets representing systems with high capillary pressures, analysis of which are typically beyond the scope of conventional thin film characterization techniques. The results of DC potential breakdown of films show that critical potential can be considered as a measure of thin film stability.A microfluidic system for creating a thin liquid film followed by electrical break up of the film.
Keywords: Thin liquid film; Water-in-oil emulsion; Electrochemical destabilization; Microfluidics; Surfactant; De-emulsifier;

Interfacial tension in aqueous biopolymer–surfactant mixtures by F. Spyropoulos; P. Ding; W.J. Frith; I.T. Norton; B. Wolf; A.W. Pacek (604-610).
The current study offers a first insight into the interfacial properties of pullulan–sodium dodecyl sulphate (SDS) aqueous two-phase systems (ATPS) in the presence of sodium chloride (NaCl). The effect of composition on the interfacial tension (σ) in these ATPS was investigated over a wide range of pullulan, SDS and NaCl concentrations. An increase in the interfacial tension was observed with increasing pullulan and SDS concentrations and a small increase was also observed as the NaCl concentration was increased. In both cases the interfacial tension increases were closely related to the phase behaviour of these systems; as a consequence of increasing the pullulan, SDS and/or NaCl concentrations, the system moves further away from the critical point. In all systems interfacial tensions (of the order of μN/m) were comparable with those reported for polymer–polymer ATPS. Interfacial tensions σ can be well correlated with the difference in pullulan and SDS concentrations between the phases ( Δ C pul and Δ C SDS ) and also the tie-line length (TLL); all yield straight lines on a log–log scale.Modified retracting drop method was used for measuring interfacial tension in biopolymer–surfactant ATPS. By analysing the drop retraction and plotting deformation parameter D (Eq. (1)) against time t (Fig. 1), interfacial tension can be calculated using Eqs. (2)–(3). D = a − b a + b ( 1 ) , ln D ( t ) = ln D 0 − t τ ( 2 ) , τ = μ c R 0 σ ( 19 λ + 16 ) ( 2 λ + 3 ) 40 ( λ + 1 ) ( 3 ) .
Keywords: Aqueous two-phase systems; Interfacial tension; Retracting drop method; Polymer–surfactant mixtures; Pullulan; SDS; NaCl;

The effect of added liposomes on the rheological properties of a hydrogel: A systematic study by Spyridon Mourtas; Maria Haikou; Maria Theodoropoulou; Christos Tsakiroglou; Sophia G. Antimisiaris (611-619).
Rheological characteristics of liposome-containing-hydrogels were studied. Sonicated unilamellar vesicles (SUV), prepared by probe sonication and multilamellar vesicles (MLV) prepared by thin film hydration were loaded in a hydrogel containing carbopol 974 NF and hydroxyethylcellulose (Natrosol 250 HX). Phosphatidylcholine (PC) or hydrogenated-PC (HPC) liposomes, plain or mixed with cholesterol (chol) were used. Static (steady-stress sweep-tests) and dynamic (frequency sweep-tests) rheological measurements were carried out. All gels had a shear thinning behaviour (fitted well by Cross model). Zero-rate shear viscosity and power law index values, revealed that PC liposome addition in the hydrogel had minimum effect on its rheological properties even at the highest lipid concentration used (20 mg/ml). Oppositely, HPC (or HPC/chol) liposome addition resulted in significant modulations of the same rheological characteristics (which increased with increasing lipid concentration). HPC liposomes also caused a significant increase in gel relaxation time, which indicates that the elastic character of the gel strengthens as HPC liposome concentration increases. Concluding, liposome composition (membrane rigidity) and lipid concentration, but not liposome size, seem to be very important factors that determine the rheological modulations caused by liposome addition in gels.The effect of adding different types and concentrations of liposomes in a gel on the gel rheological characteristics was studied.
Keywords: Rheological properties; Hydrogels; Gels; Liposomes; Lipid composition; Topical administration; Vaginal;

Motion of a spherical particle in a cylindrical channel using arbitrary Lagrangian–Eulerian method by Noor Al Quddus; Walied A. Moussa; Subir Bhattacharjee (620-630).
A finite element particle transport model, consisting of Navier–Stokes and continuity equations defined in arbitrary Lagrangian–Eulerian (ALE) kinematics, is employed to describe the motion of a rigid uncharged spherical particle in a cylindrical channel of uniform cross-section. The wall correction factors for the spherical particle moving with a fluid confined in an infinitely long cylindrical channel, as well as in finite length channels are presented. Two finite channel effects are considered, namely, motion of the particle at the entrance and exit of an open channel, and the motion of a particle toward the capped end of the channel. The numerical model demonstrates good agreement with many existing analytical results for infinite channels in the Stokes flow regime. Simple correlations for the hindrance factors are presented.Fluid and particle motion in a tightly fitting cylindrical capillary obtained from a solution of the Navier–Stokes and continuity equations in the arbitrary Lagrangian–Eulerian framework.
Keywords: Wall correction factor; Particle motion; Cylindrical capillary; Finite channel; Arbitrary Lagrangian–Eulerian;

Many biofluids such as blood and DNA solutions are viscoelastic and exhibit extraordinary flow behaviors, not existing in Newtonian fluids. Adopting appropriate constitutive equations these exotic flow behaviors can be modeled and predicted reasonably using various numerical methods. However, the governing equations for viscoelastic flows are not easily solvable, especially for electroosmotic flows where the streamwise velocity varies rapidly from zero at the wall to a nearly uniform velocity at the outside of the very thin electric double layer. In the present investigation, we have devised a simple method to find the volumetric flow rate of viscoelastic electroosmotic flows through microchannels. It is based on the concept of the Helmholtz–Smoluchowski velocity which is widely adopted in the electroosmotic flows of Newtonian fluids. It is shown that the Helmholtz–Smoluchowski velocity for viscoelastic fluids can be found by solving a simple cubic algebraic equation. The volumetric flow rate obtained using this Helmholtz–Smoluchowski velocity is found to be almost the same as that obtained by solving the governing partial differential equations for various viscoelastic fluids.A simple method is devised to find the volumetric flow rate of viscoelastic electroosmotic flows through microchannels, employing the concept of the Helmholtz–Smoluchowski velocity. (a) Microchannel under consideration, (b) comparison of the Helmholtz–Smoluchowski velocity ( U HS ) with the solution of the viscoelastic Navier–Stokes equation.
Keywords: Helmholtz–Smoluchowski velocity; Electroosmotic flow; Viscoelasticity;

The unusual aggregation behavior of poly(N-isopropylacrylamide)-based amphiphilic block copolymers was investigated by a combination of dynamic and static laser light scattering, AFM, and 1H NMR. The results revealed that PS-b-PNIPAM always forms large micelle aggregates in the transition process from an organic solvent to water due to the cononsolvency effect of PNIPAM. The cononsolvency effect of PNIPAM can be avoided to obtain classical micelles with PS29-b-PNIPAM27 in acetone–water at low temperatures (below 20 °C).AFM images of PS29-b-PNIPAM27 micelles formed in the THF–water system without dialysis of THF and after dialysis of THF.
Keywords: PNIPAM; Cononsolvency effect; Classical micelles;

The Kelvin equation by A.Ch. Mitropoulos (643-648).
The capillary condensation/evaporation process is studied in conjunction with small angle X-ray scattering measurements. The scattering data are analyzed with the indirect Fourier transformation technique and the results are compared with the predictions of the Kelvin equation. It is found that the Kelvin equation is obeyed by menisci with mean radius of curvature as low as 40 Å. For smaller radii, in particular from 40 to 30 Å, the two methods differ by ∼25%. Broekhoff and de Boer analysis may improve the prediction. The hysteresis region of an adsorption step is presented schematically.The predictions of the Kelvin/Cohan equation are compared with small angle X-ray scattering data that have been analyzed with the indirect Fourier transformation method. It is found that the two methods are in agreement when the mean radius of curvature is as low as 40 Å. For smaller radii, in particular from 40 to 30 Å, the two methods differ by ∼25%.
Keywords: Kelvin equation; Capillary condensation/evaporation; Vycor; Unduloidal surfaces; Small angle X-ray scattering;