Journal of Colloid And Interface Science (v.319, #2)

EXAFS studies on adsorption irreversibility of Zn(II) on TiO2: Temperature dependence by Wei Li; Gang Pan; Meiyi Zhang; Dongye Zhao; Yuhuan Yang; Hao Chen; Guangzhi He (385-391).
Adsorption irreversibility of Zn(II) on TiO2 at various temperatures was studied using a combination of classical macroscopic methods and extended X-ray absorption fine structure (EXAFS) spectroscopy. When the temperature was increased from 5 to 40 °C, the Zn(II) adsorption capacity increased by 130%, and adsorbed Zn(II) became more reversible. The standard Gibbs free energy change ( Δ G 0 ) of the adsorption reaction at 5, 20, and 40 °C was determined to be − 19.58 ± 0.30 , − 22.28 ± 0.10 , and − 25.14 ± 0.21 kJ mol −1 , respectively. And the standard enthalpy ( Δ H 0 ) and entropy ( Δ S 0 ) were 24.55 ± 2.91 kJ mol −1 and 159.13 ± 0.53 J mol −1 K −1 , respectively. EXAFS spectra results showed that the hydrated Zn(II) was adsorbed through fourfold coordination with an average Zn―O bond distance of 1.98 ± 0.01 Å . Two Zn―Ti atomic distances of 3.25 ± 0.02 and 3.69 ± 0.03 Å were observed, which corresponded to an edge-sharing linkage mode (strong adsorption) and a corner-sharing linkage mode (weak adsorption), respectively. As the temperature increased from 5 to 40 °C, the number of strong adsorption sites ( N 1 ) remained relatively constant while the number for the weak adsorption sites ( N 2 ) increased by 31%. These results indicate that the net gain in adsorption capacity and the decreased adsorption irreversibility at elevated temperatures were due to the increase in available weak adsorption sites ( N 2 ) or the decrease in the ratio of N 1 / N 2 . Both the macroscopic sorption/desorption equilibrium data and the molecular level evidence of this study suggest that in a given environmental system (e.g., soils or natural waters) zinc and other similar heavy metals are likely more mobile at higher temperatures.Zn(II) was adsorbed onto TiO2 as the tetrahedral structure with two linkage modes: corner-sharing (weak adsorption) and edge-sharing (strong adsorption). The increased number of weak adsorption sites was responsible for the increased adsorption capacity and reversibility as temperature increased.
Keywords: Zinc; TiO2; Temperature dependence; EXAFS; Adsorption–desorption; Adsorption mode; Adsorption irreversibility; Hysteresis;

Application of the Polanyi potential theory to phthalates adsorption from aqueous solution with hyper-cross-linked polymer resins by Zhengwen Xu; Weiming Zhang; Bingcai Pan; Changhong Hong; Lu Lv; Qingjian Zhang; Bingjun Pan; Quanxing Zhang (392-397).
The adsorption equilibria of dimethyl phthalate (DMP) and diethyl phthalate (DEP) on two hyper-cross-linked polymer resins (NDA-99 and NDA-150) in aqueous solution were investigated at 298 K. And a coal-based granular activated carbon (AC-750) was chosen for comparison. All the adsorption equilibrium data of DMP were well fitted by the Polanyi-based isotherm modeling (Polanyi–Manes (PM) equation), and the characteristic curves of the three adsorbents were obtained. It is noteworthy that a reasonably good agreement was obtained between the combined micropore and mesopore volume of adsorbents and the corresponding adsorption volume capacity for phthalates. Compared to the granular activated carbon (AC-750), the greater adsorption performances of the two resins (NDA-99 and NDA-150) were assumed to result from their more abundant micro- and mesopore structure, where phthalates can be intensively adsorbed by pore-filling mechanism. According to the exponent b value of the PM equation, NDA-99 and NDA-150 show the more micro- and mesopore heterogeneity than AC-750. On the other hand, the functional groups on the adsorbent surfaces did not take a notable effect on the adsorption equilibria of phthalates. The theory equilibrium adsorption amounts of DEP, predicted by the specific characteristic curve of each adsorbent, agree well with the experimental ones, respectively. The characteristic curve of hyper-cross-linked polymer resins and its prediction of phthalates adsorption calculated by Polanyi-based isotherm modeling have a potential applicability for field applications.The theory DEP adsorption capacities (Figure A), predicted by the characteristic curves obtained from DMP experimental adsorption data (Figure B), agrees well with the experimentally determined values for all the test adsorbents.
Keywords: Characteristic curve; Hyper-cross-linked resins; Pore-filling mechanism; Polanyi-based isotherm; Phthalates adsorption;

Polymer/Au nanoparticle multilayer ultrathin films are fabricated via hydrogen-bonding interaction by a layer-by-layer technique. The Au nanoparticles surface-modified with pyridine groups of poly(4-vinylpyridine) (PVP) are prepared in dimethyl formamide (DMF). Transmission electron microscopy (TEM) image shows that uniform nanoparticles are dispersed in the PVP chains. Poly(3-thiophene acetic acid) (PTAA) and poly(acrylic acid) (PAA) are utilized to form hydrogen bonds with PVP, respectively. Considering the pH-sensitive dissociation behavior of PTAA and PAA, we investigate the release behavior of the Au-containing multilayers at different pH values in this work. UV–vis spectroscopy and atomic force microscopy (AFM) are employed to monitor the buildup and the release of the multilayers. The results indicate that in the films assembled with gold nanoparticles, the polymers are difficult to be removed from the substrate. The interaction between the gold particles and the neighboring PVP chains is responsible for the phenomenon. Gold particles act as physical cross-link points in the multilayers. Due to the additional interaction caused by the gold nanoparticles in the films except the hydrogen-bonding interaction between PTAA (or PAA) and PVP, the stability of the Au-containing multilayer film is ensured even though the changes in pH values may result in the break of the hydrogen bonds.The interaction between the adjacent bilayers induced by the gold nanoparticles serves to maintain the stability of the Au-containing multilayer film.
Keywords: Gold nanoparticle; Layer-by-layer; Hydrogen-bonding interaction;

Using variable substitution, we present a general method for the numerical solution of stiff, ordinary, linear, homogeneous differential equations characteristic of colloid particle adsorption/deposition over an energy barrier. For the example of the radial impinging jet system, we demonstrate the application of this method of calculating the colloid concentration profile and initial particle flux in the presence of repulsive electrostatic interactions between the particle and adsorption surface. We show that our method works well in systems with energy barriers up to the order of hundreds of kT, at which point the adsorption flux vanishes. The numerical results obtained with our method are in good agreement with the known limiting analytical approximations for the particle flux through an energy barrier and for a low Péclet number. The developed numerical code is very stable over a wide range of physical parameters, and its accuracy for the most challenging parameter sets is on the order of 10−4. To achieve this stability, we have derived and employed a single formula for the van der Waals dispersion interaction, working at both a small and a large separation distance. We show that this formula converges to the known available analytical expressions for dispersion forces in the limit of small and large separation distance. We also demonstrate that the maximum deviations between our formula and the other equations appear in the intermediate range of the separation distance and do not exceed 10%.Particle–interface interaction energy (dotted line), colloid concentration (solid line), and normal component of particle flux (dashed line) in a system with a high energy barrier.
Keywords: Colloid particle transport; Colloid particle deposition; Convection–diffusion equation; Van der Waals interaction; Modified empirical formula; DLVO theory; Radial stagnation point flow system;

Adsorption of alpha amino acids at the water/goethite interface by Katarina Norén; John S. Loring; Per Persson (416-428).
The adsorption of amino acids onto mineral surfaces plays an important role in a wide range of areas, e.g., low-temperature aqueous geochemistry, bone formation and protein–bone interactions. In this work, the adsorption of three alpha aminoacids (sarcosine, MIDA and EDDA) onto goethite (α-FeOOH) was studied as a function of pH and background electrolyte concentration at 25.0 °C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The results showed that adsorption of alpha amino acids were strongly dependent on the functionality and structure of the ligands. No adsorption was detected for the zwitterionic sarcosine indicating that simple alpha amino acids without other ionizable and/or functional groups display insignificant affinity for mineral surfaces such as goethite. With respect to the more complex amino acids, which are surface reactive, the number and relative positions of carboxylate and amine groups determine the types of surface interactions. These interactions range from non-specific outer-sphere to specific inner-sphere interactions as shown by the MIDA and EDDA results, respectively. The results presented herein suggest that isomerically-selective adsorption might only occur for amino acids that are capable of specific surface interactions, either through site-specific hydrogen bonding or inner-sphere complexation.The ATR-FTIR spectra and the 2D contour plot reveal two EDDA surface complexes at the water/goethite interface.
Keywords: Adsorption; Amino acids; Water/mineral interface; Goethite; ATR-FTIR spectroscopy;

Enhancement of magnetic resonance contrast effect using ionic magnetic clusters by Sung-Baek Seo; Jaemoon Yang; Tong-Il Lee; Chan-Hwa Chung; Yong Jin Song; Jin-Suck Suh; Ho-Geun Yoon; Yong-Min Huh; Seungjoo Haam (429-434).
Precise diagnosis by magnetic resonance imaging (MRI) requires sensitive magnetic resonance probes to detect low concentrations of magnetic substances. Ionic magnetic clusters (IMCs) as versatile magnetic probes were successfully synthesized for enhancing the magnetic resonance (MR) contrast effect as well as ensuring high water solubility. IMCs with various sizes were prepared by assembly of MNCs using cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS). To synthesize IMCs in the aqueous phase, magnetic nanocrystals in an organic solvent were assembled with CTAB and SDS using the nanoemulsion method, to fabricate cationic magnetic clusters (CMCs) and anionic magnetic clusters (AMCs), respectively. IMCs demonstrated ultrasensitivity by MR imaging and sufficient magnetic mobility under an external magnetic field.Ionic magnetic clusters (IMCs) as versatile magnetic probes were successfully synthesized for enhancing the magnetic resonance (MR) contrast effect as well as ensuring high water solubility.
Keywords: Ionic magnetic clusters; Magnetic cluster size; MR contrast effect;

Electro-optic techniques were used to investigate the influence of poly(ethylene oxide) (PEO) on the surface electric state of positively charged oxide particles. The variations in particle electrophoretic mobility of β-FeOOH particles in the presence of PEO indicate significant changes in the surface electric state of the particles in the concentration interval of PEO 10−2–10−1 g dm−3. The electro-optic results for the same conditions were unexpected: no significant difference is observed in the value and the relaxation frequency of particle electric polarizability in the frequency domain of the α-relaxation (detected in the kilohertz range); particle rotational relaxation time also remains unchanged; considerable changes are detected only in the relaxation interval of particle rotation (detected in the hertz range). The obtained results reject the possibility of the formation on the particle surface of a thick polymer layer. A thin adsorption layer cannot explain the significant decrease in particle electrophoretic mobility. The variations in electrophoretic mobility are well correlated with the effects in the domain of particle rotation. A possible explanation of the observed effects is proposed, based on our previous investigations of the effects in the low-frequency domain. The presented results demonstrate that the important information on the electrokinetic charge distribution is not found in the domain of the α-dispersion, but in the domain of particle rotation.
Keywords: Polymer coated colloidal particles;

We report an electrical impedance spectroscopy (EIS) characterization of composite systems formed by emulsion polymerization of polypyrrole (PPY) in concentrated aqueous solutions of sodium dodecyl sulfate (SDS) containing dispersed magnetite particles. SDS–(Fe3O4)–(conducting polymer) microaggregates with different iron contents were prepared by varying in a reciprocal manner the relative amounts of the metal oxide and PPY. We have measured the zeta-potential and the average size of the corresponding dispersed particles and examined their relative composition through energy dispersive X-ray (EDX) microanalysis and Fourier transform infrared (FTIR) spectroscopy. Important aspects of the charge transport in these composite particles can be identified by mapping the real and imaginary parts of their complex impedance as a function of the frequency of the applied external electric field. For instance, for binary composites SDS–(Fe3O4) polarization effects are dominant at the low-frequency regime, with a well-defined dielectric relaxation easily identifiable. On the other hand, when the relative amount of PPY is progressively increased in the ternary SDS–(Fe3O4)–PPY composites, a transition between different charge transport mechanisms is observed at higher frequencies. The EIS results suggest that in these ternary aggregates the PPY chains envelop the metal oxide clusters and effectively shield them from the external field, and that only in binary samples that do not contain PPY is that the surfactant molecules can directly enclose the magnetite particles. These results are consistent with the fact that the average size of the aggregates in the ternary composites is in general larger than those of either SDS–PPY or SDS–magnetite binary particles.Real part of the impedance measured at 1 MHz of the SDS–Fe3O4–PPY, indicating the existence of two different sets of electrical—and possibly structural—characteristics for the SDS–Fe3O4–PPY aggregates dispersed in solution, mainly associated with the reciprocal change in the relative contents of the polymer and magnetite.
Keywords: Emulsion polymerization; Polypyrrole; Magnetic iron particles; Organic–inorganic hybrid composites; Electrical impedance spectroscopy;

This work reports the fabrication and characterization of multilayered gold nanoparticle (AuNP) thin films on aminosilane functionalized substrates. The films are fabricated via layer-by-layer (LbL) assembly using as-synthesized, un-modified AuNPs and poly(allylamine hydrochloride) as the building blocks. While most literature reports that AuNP based LbL assemblies are constructed with a single interlayer binding force, this work shows that both coordination and electrostatic interaction are involved in the process of assembly based on X-ray photoelectron spectroscopic results. The stepwise film growth behavior is demonstrated by atomic force spectroscopy and UV–vis spectroscopy. It is found that the particles agglomerate with each other and form large clusters when the number of assembled layers increases.This work focuses on the combined interlayer binding force ant the particle growth behavior for multilayered gold nanoparticle thin films fabricated via layer-by-layer assembly.
Keywords: Gold nanoparticles; Layer-by-layer assembly; Coordination-electrostatic coexistence; Agglomeration;

Transmission X-ray microscopy reveals the clay aggregate discrete structure in aqueous environment by Marek S. Żbik; Ray L. Frost; Yen-Fang Song; Yi-Ming Chen; Jian-Hua Chen (457-461).
The utilization of new transmission X-ray microscopy (TXM) using the synchrotron photon source enable for the first time the study in three dimensions microsize clay particles in aggregates in their natural aqueous environment. This technique makes possible remarkable accurate images of nanosize mineral interparticle structure which forms a new nanocomposite. The Birdwood kaolinite/LDH aggregates observed in the TXM are much more compact than observed before in pure Birdwood kaolinite suspension and similar to aggregates formed after treatment by positively charged surfactant. Kaolinite/LDH aggregates in water reveal complex structure of larger kaolinite platelets connected together by gelled nanoparticles which are most probably LDH colloidal plates. Comparisons of the transmission electron microscope (TEM) and TXM techniques show similarities in particle morphology. The ability to study particles and aggregates in their natural aqueous environment and in 3-dimensions make this technique superior to the TEM technique.
Keywords: Clay aggregates; Transmission X-ray microscopy; Kaolinite; Hydrotalcite; Halloysite;

A rotating catalyst contact reactor (RCCR) was developed which consisted of palladized bacterial cellulose immobilized on acrylic discs for hydrodechlorination of pentachlorophenol (PCP). More than 99% of 40 mg L−1 PCP was dechlorinated to phenol in the presence of hydrogen in batch mode at initial pH values of 5.5 and 6.5 within 2 h of reaction with stoichiometric release of free chloride. The rate of PCP dechlorination was found to be independent of rotational speed of discs. PCP (40 mg L−1) hydrodechlorination experiments were also conducted using RCCR in continuous flow mode at hydraulic retention times of 1 and 2 h. The average outlet PCP concentrations revealed that liquid phase in RCCR closely resembled that of a continuous flow complete mix reactor (CFMR). Approximately 12 and 11 L of 40 mg L−1 PCP (pH 6.5) could be treated in RCCR with 99 and 80% efficiencies in batch and continuous flow modes, respectively without any appreciable loss of the catalytic activity. These results suggested reusability of palladized bacterial cellulose which in turn is expected to substantially reduce the cost of treatment process. Thus RCCR seems to have high potential for treatment of ground water contaminated with chlorinated organic compounds. Dried palladized bacterial cellulose has been used as a material for electrodes in a fuel cell. However, its application as a hydrodechlorination catalyst in a reactor operating under room temperature and atmospheric pressure has not been reported to the best of our knowledge. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analyses suggested the irreversible deposition of palladium (Pd0) particles on the bacterial cellulose fibrils.The figure shows the schematic diagram of RCCR (rotating catalyst contact reactor) used for treating pentachlorophenol (PCP). Palladized bacterial cellulose immobilized on the surface of the rotating acrylic discs in RCCR interacts with molecular hydrogen to generate palladium hydride (Pd-H) which in turn reductively dehalogenates sorbed PCP to the hydrocarbon product, phenol with the stoichiometric release of free chloride ions. Phenol may be further degraded to produce ring cleavage products.
Keywords: Hydrodechlorination; Pentachlorophenol; Palladium; Bacterial cellulose; Rotating catalyst contact reactor;

Effect of nickel deposition on hydrogen permeation behavior of mesoporous γ-alumina composite membranes by Chang-Yeol Yu; Bong-Kuk Sea; Dong-Wook Lee; Sang-Jun Park; Kwan-Young Lee; Kew-Ho Lee (470-476).
Ni/alumina composite membranes were prepared and investigated for hydrogen separation at high temperature. α-Alumina-supported γ-alumina composite membranes were prepared by soaking-rolling method. In order to improve H2 selectivity and permeance of the γ-alumina membranes, Ni was deposited by a soaking process. As a result of a single gas permeation test of the Ni/alumina composite membranes, hydrogen permeance and H2/N2 selectivity at permeation temperature of 450 °C were 6.29 × 10 −7 mol / m 2 s Pa and 5.2 which exceeded theoretical Knudsen selectivity. Contribution of surface diffusion was investigated by temperature dependence of H2 permeance. The surface diffusion was observed at higher temperature above 250 °C. The Ni deposition on surface of the γ-alumina composite membrane led to hydrogen permeation via Knudsen diffusion combined with surface diffusion, which gave high H2 selectivity exceeding the Knudsen diffusion mechanism.Temperature dependence of H2/N2 selectivity of Ni/γ-alumina/α-alumina composite membranes according to variation of Ni concentration (wt%).
Keywords: Composite membrane; Nickel; Hydrogen separation; Surface diffusion;

Design of nanocatalysts for efficient heterogeneous catalytic systems is needed to high ingredients for environmental cleanup of organic pollutant species. Here, well-defined order NiO–silica monolithic catalysts with hexagonal P6mm and cubic Pm3n mesostructures were successfully fabricated by using an instant direct-templating method of lyotropic and microemulsion phases of Brij 76 (C18H37(OCH2CH2)10OH, C18EO10). Ordered hexagonal P6mm NiO/HOM-2 monoliths could be fabricated in lyotropic system of Brij 76 at phase composition domains of TMOS/Brij 76 (50 wt%). However, periodically ordered cubic Pm3n NiO-supported monoliths were synthesized in microemulsion system formed by addition of C12-alkane to the hexagonal phase domains. This synthetic strategy also revealed that the NiO particles were well-dispersed into the silicate pore surface matrices of mesostructures. Monolithic NiO–silica composites with 2D hexagonal and 3D cubic geometries and with large particle morphologies show promise to act as catalysts. The current study revealed evidence of the advantages of nanoscale pore geometry and shape, and particle morphology of the supported silica monoliths in the design of nanocatalysts that can efficiently enhance the catalytic functionality in terms of stability, reversibility and reactivity. Furthermore, a key finding in our study was that 2D hexagonal and 3D cubic mesostructured NiO–silica catalysts retained the specific activity towards the oxidation reaction even after several regeneration/reuse cycles. Significant study of the mechanistic cyclization of the organic reactant using the density functional (DFT) calculations provided evidence of the key components of conformations of the functional model during the formation of the oxidation product.Well-defined order NiO–silica composites with large particle size-like monoliths, channel- and cage-like pores, and 2D hexagonal P6mm and 3D cubic Pm3n mesostructures were used as nanocatalysts to reproducibly oxidized pollutants such as aminophenols in aqueous solution. A key finding in our study was that our mesostructured NiO–silica catalysts retained the specific activity towards the oxidation reaction even after several regeneration/reuse cycles.
Keywords: Synthesis; Brij 76; Hexagonal and cubic monoliths; NiO–silica catalysts; Nanoscale pores;

Calcium–phosphorus interactions at a nano-structured silicate surface by Daniel C. Southam; Trevor W. Lewis; Andrew J. McFarlane; T. Borrmann; Jim H. Johnston (489-497).
Nano-structured calcium silicate (NCS), a highly porous material synthesized by controlled precipitation from geothermal fluids or sodium silicate solution, was developed as filler for use in paper manufacture. NCS has been shown to chemisorb orthophosphate from an aqueous solution probably obeying a Freundlich isotherm with high selectivity compared to other common environmental anions. Microanalysis of the products of chemisorption indicated there was significant change from the porous and nano-structured morphology of pristine NCS to fibrous and crystalline morphologies and non-porous detritus. X-ray diffraction analysis of the crystalline products showed it to be brushite, CaHPO4⋅2H2O, while the largely X-ray amorphous component was a mixture of calcium phosphates. A two-step mechanism was proposed for the chemisorption of phosphate from an aqueous solution by NCS. The first step, which was highly dependent on pH, was thought to be desorption of hydroxide ions from the NCS surface. This was kinetically favoured at lower initial pH, where the predominant form of phosphate present was H2PO 4, and led to decreased phosphorus uptake with increasing pH. The second step was thought to be a continuing chemisorption process after stabilization of the pH-value. The formation of brushite as the primary chemisorption product was found to be consistent with the proposed mechanism.A porous nano-structured calcium silicate (NCS) was shown on to produce CaHPO4⋅2H2O on exposure to phosphate. A temperature- and pH-dependent mechanism was proposed for the chemisorption of phosphate by NCS.
Keywords: Nano-structured calcium silicate; Phosphate sequestration; Chemisorption; Calcium phosphate; Hydroxyapatite inhibition;

In situ synthesis of surfactant/silane-modified hydrotalcites by Jianxi Zhu; Peng Yuan; Hongping He; Ray Frost; Qi Tao; Wei Shen; Thor Bostrom (498-504).
In this study, anionic surfactant and silane-modified hydrotalcites were synthesized through a soft chemical in situ method. The resulting materials were characterized using X-ray diffraction (XRD), high-resolution thermogravimetric analysis (HRTG), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N2 adsorption–desorption. The Mg–Al hydrotalcite (LDH) and the only surfactant-modified hydrotalcite (LDH-2) display similar XRD patterns while both surfactant and silane-modified hydrotalcite (LDH-3) show two distinct series of reflections, corresponding to hydrotalcite and smectite-like materials, respectively. The smectite-like materials show a series of regular (001) reflections with d 001 = 12.58 Å . Further supporting evidence was obtained from FTIR and TG, for example, the vibration at 1198 cm−1 corresponds to Si―O―Si-stretching mode and the mass loss at ca. 861 °C to dehydroxylation. In LDH-2, the loaded surfactants are located in both the interlayer space and the interparticle pores with a “house of cards” structure as supported by FTIR, TG, and N2 adsorption–desorption isotherms. Both electron microscopy (SEM and TEM) micrographs and N2 adsorption–desorption isotherms show that in situ modification with surfactant and silane has a significant influence on the morphology and porous parameters of the resulting hydrotalcite materials.The XRD pattern of the both surfactant- and silane-modified hydrotalcite (LDH-3) shows a coexistence of two phases, hydrotalcite and smectite-like layered materials.
Keywords: Hydrotalcite; In situ synthesis; Anionic surfactant; Silane; Nanochemistry;

Surface free energy of sulfur—Revisited by Emil Chibowski; Konrad Terpilowski (505-513).
Surface free energy of two different samples of solidified sulfur (yellow and orange) was investigated, using several approaches for its determination. It was found that values determined about two decades ago for surface free energy of sulfur were overestimated. From current studies the apparent value of this energy ranges between 30 and 60 mJ/m2, depending on the kind and age of the sulfur samples (up to 1 year old) and/or the probe liquid used for the advancing and receding contact angle measurements. The energy has been calculated from van Oss et al.'s approach (Lifshitz–van der Walls, electron-donor, and electron-acceptor components), the contact angle hysteresis approach proposed by Chibowski, the equation of Owens and Wendt (dispersion and polar components), and Neumann et al.'s equation of state, as well as from equilibrium contact angle using Tadmor's procedure. The lowest values of the energy for 3-day- and 3-month-old samples of sulfur were calculated from the equation of state; they were below the range mentioned above.Surface free energy of two different samples of sulfur was investigated using several approaches for its determination. Thus determined the apparent energy ranges between 30 and 60 mJ/m2.
Keywords: Sulfur; Different samples; Surface free energy; Various approaches;

Surface free energy of sulfur—Revisited by Konrad Terpilowski; Lucyna Holysz; Emil Chibowski (514-519).
The apparent surface free energy of yellow and orange samples of sulfur crystallized at the surface of gold, silicon, and Teflon and in air was evaluated from the advancing and receding contact angles of water. The samples were prepared by casting melted rhombic mineralogical specimen sulfur onto the surface of the above-noted solids. Yellow samples were obtained when just melted sulfur (ca. 120 °C) was cast onto the surfaces, and the orange ones, when the melted sulfur was heated longer to a higher temperature (ca. 160 °C) and then cast onto the surfaces. The obtained results show that the apparent surface free energy depends on which surface it crystallized. The greatest value is for the sample crystallized at the gold surface, which is 35% higher than that crystallized in air. Generally, the surface free energy of orange samples is slightly higher than that of yellow ones. It is believed that the differences in the energy result from changes in the packing and structural orientation of sulfur atoms on the surfaces.
Keywords: Sulfur; Different samples; Surface free energy;

Calorimetric study of the α-tocopherol solubility in reversed AOT micelles by H. Wilczura-Wachnik; A.G. Yavuz; A. Myslinski (520-525).
The experimental data of heat of mixing (Q) for heterogeneous system α-tocopherol/AOT/n-heptane with and without water at 25 °C are presented. The Q dependence on AOT (sodium bis (2-ethylhexyl) sulfosuccinate) concentration, and R parameter defined as R=[H2O]/[AOT] with flow calorimetric method were investigated. Using the D'Aprano model (which is formally identical to that used earlier by Magid et al.) the binding constant (K), the distribution constant of α-tocopherol ( K distr ) between hydrocarbon and the micellar phase, and the standard enthalpy of transfer ( Δ H tr 0 ) of α-tocopherol from the hydrocarbon to AOT reversed micelles were calculated. The solubility of α-tocopherol in AOT reversed micelles explored with the calorimetric technique was compared to the literature data obtained respectively with UV spectrophotometry for reversed micelles and by other techniques for the phospholipid bilayer.The nonlinear regression (blue line) of the heat of mixing data of α-tocopherol/n-heptane +AOT/n-heptane solutions (dots) involved to evaluate Δ H tr 0 of α-tocopherol from n-heptane to AOT reversed micelles.
Keywords: α-Tocopherol; AOT-reversed micelles; Flow calorimetry;

Self-assembly properties of some chiral N-palmitoyl amino acid surfactants in aqueous solution by Mariana Gerova; Fernanda Rodrigues; Jean-François Lamère; Alexander Dobrev; Suzanne Fery-Forgues (526-533).
Various chiral N-palmitoyl amino acid surfactants (AAS) derived from methionine, proline, leucine, threonine, phenylalanine and phenylglycine were prepared and converted to their sodium salt. The properties of the aggregates formed in aqueous solution were studied for both the optically-active compounds and their racemic mixture. Characterization was made by surface tensiometry, fluorimetry, dynamic light scattering, circular dichroism (CD) and transmission electron microscopy. It appeared that most of the AAS studied in this work spontaneously formed different types of aggregates, including micrometer-sized aggregates. No significant difference could be found between the critical aggregation concentration (cac) value of pure enantiomers and that of the racemic forms. CD spectra did not reveal any aggregation-induced chirality.
Keywords: N-acyl amino acids; Critical aggregation concentration; Chirality; Microscopy; Microfiber;

A series of anionic sulfonate gemini surfactants with the general structure of [(C n H2n+1)(C3H6SO 3) NC s N(C3H6SO 3)(C n H2n+1)]⋅2Na+ have been synthesized. While the spacer group C s represents p-xylyl or (CH2)3, the surfactants are abbreviated as C n CpxC n (SO3)2 ( n = 8 , 10 , 12 ) or C12C3C12(SO3)2 ( n = 12 ) , respectively. A corresponding monomeric surfactant C12H25N(CH3)(C3H6SO 3)⋅Na+(C12NSO3) has also been prepared. The aggregation behavior of these surfactants has been studied at pH 9.2 and ionic strength of 30 mM. The gemini surfactants exhibit stronger aggregation tendencies and much less endothermic enthalpy changes of micellization ( Δ H mic ) compared with the monomeric surfactant. The critical micelle concentrations (CMC) of the gemini surfactants decrease with the increase of the hydrophobic chain length from C8CpxC8(SO3)2 to C10CpxC10(SO3)2, but the CMC values of C10CpxC10(SO3)2 and C12CpxC12(SO3)2 are very close. The Δ H mic values vary from endothermic for C8CpxC8(SO3)2 to almost zero for C12CpxC12(SO3)2. Besides, vesicles are observed above the CMC for all these surfactants. The water-mediated intermolecular hydrogen bonding between the tertiary nitrogen groups may assist C12NSO3 and C12C3C12(SO3)2 in their vesicle formation, while the ππ interaction between aromatic rings should be another additional driving force for the vesicle formation of C n CpxC n (SO3)2. Meanwhile, the hydrogen bonding, ππ interaction, and strong hydrophobic interaction provide the possibility of a multilayer formation for C12CpxC12(SO3)2 and C12C3C12(SO3)2 at the air/water interface, which is a possible reason for the extremely small minimum area occupied per surfactant molecule at the air/water interface for these two gemini surfactants.
Keywords: Gemini surfactant; Sulfonate surfactant; Aggregation behavior; Vesicle;

Role of the surfactant headgroup on the counterion specificity in the micelle-to-vesicle transition through salt addition by Nina Vlachy; Markus Drechsler; Jean-Marc Verbavatz; Didier Touraud; Werner Kunz (542-548).
A transition from micelles to vesicles is reported when salts are added to a catanionic micellar solution composed of sodium dodecylcarboxylate (SL) and dodecyltrimethylammonium bromide (DTAB), with an excess of SL. The counterion binding and increase in aggregate size was monitored by mass spectrometry, rheology and dynamic light scattering measurements, whereas the vesicles were characterized by freeze-fracture and cryo-transmission microscopy experiments. The effect of counterions on the formation of vesicles was studied and compared to a previously studied catanionic system with a sulfate head group, SDS/DTAB. As in the latter case, no anion specificity was found, while large differences in the hydrodynamic radii of the formed objects were observed, when the cation of the added salt was varied. A classification of the cations could be made according to their ability to increase the measured hydrodynamic radii. It is observed that, if the sulfate headgroup of the anionic surfactant is replaced by a carboxylic group, the order of the ions is reversed, i.e. it follows the reversed Hofmeister series. Different morphologies are observed as the ionic strength of the system is increased. The aggregates are analogous to those found in the SDS/DTAB system.The formation of vesicles upon the addition of chloride salts to a SL/DTAB micellar solution.
Keywords: Specific-ion effects; Micelle-to-vesicle transition; Catanionic surfactant mixtures;

Universal electro-osmosis formulae for porous media by A. Gupta; D. Coelho; P.M. Adler (549-554).
Approximate analytical formulae valid for any porous media with elongated pores are derived for the electro-osmotic coefficient α and for the average ionic concentration n ¯ . A macroscopic Debye–Hückel length κ ¯ −1 based on n ¯ is introduced. Simultaneously, the electro-osmotic coefficient α is systematically calculated for various media, zeta potentials and electrolyte concentrations by solving the local equations. Numerical results show that κ ¯ −1 and α follow universal curves valid whatever the porous medium; these curves can be approximated by the analytical formulae previously derived. These formulae can be used to provide a priori estimates of the electro-osmotic coefficient.Electro-osmotic coefficients calculated for any porous media, any zeta potentials and any electrolyte concentrations are shown to follow a universal curve when the macroscopic Debye–Hückel length based on the average concentration is used.
Keywords: Porous media; Electrokinetics; Zeta potential; Electro-osmosis; Non-linearity;

The concentration dependence of a polyelectrolyte diffusion coefficient in aqueous low salt solution (KCl, 1 mM) is determined from a single dynamic gradient experiment. The Boltzmann method is applied to calculate the diffusion coefficient. A special diffusion cell is constructed that minimizes aberrations in the optical detection of the polyion concentration profile. Bovine serum albumin (BSA) is chosen as a model polyion. To get information about the diffusion process down to very small polyion concentrations, the BSA molecule is fluorescently labeled. The fluorescence intensity is used as a measure of the polyion concentration. The change of the polyion net charge caused by labeling is discussed. The cell is illuminated by an LED, and the fluorescence intensity profile is detected by a CCD camera. Experiments at 5 and 17 °C show that the diffusion coefficient of labeled BSA remains constant in the very low polyion concentration range below a threshold of about 1.5 g/l. This is in contradiction to the linear concentration dependence of polyion diffusion coefficients at very low concentrations often postulated in the literature without reference to direct experimental evidence. Our finding is confirmed by dynamic light scattering experiments published recently. An explanation for this behavior based on a modified Donnan osmotic compressibility approach is given.Boltzmann's method is used to determine the concentration dependence of the diffusion coefficient (right) of a fluorescently labeled polyelectrolyte (BSA) in a low salt solution at very small polyion concentrations from a single concentration profile, here taken after 9 h (left).
Keywords: Polyion diffusion coefficient; Concentration dependence of the diffusion coefficient; BSA; Effective net charge; Fluorescence label; Boltzmann gradient method; Diffusion cell;

Low polydispersed copper-sulfide nanocrystals derived from various Cu–alkyl amine complexes by Toshihiro Kuzuya; Keiichi Itoh; Kenji Sumiyama (565-571).
Copper-sulfides, Cu2−x S nanocrystals (NCs) have been synthesized using the reaction between a Cu–alkyl amine complex and a sulfur/1-dodecanethiol. Here, 1-dodecanthiol plays an important role to reduce the reaction temperature of sulfuration. The Cu/S composition (the Cu-defect density) of Cu2−x S NCs depends on the stability of Cu–alkyl amine complex. XPS analyses reveal that the substance of Cu-defect is attributed to an introducing of Cu+ 2S2− 2 species. There is a good correlation between an intensity of a near IR absorption peak and a Cu-defect density estimated by XPS analyses. These results demonstrate that optical properties of Cu2−x S NCs in a near IR region are tunable.
Keywords: Copper sulfide; Nanocrystal; Near-IR absorption; Intraband transition;

Chemically stable silver nanoparticle-crosslinked polymer microspheres by Abdiaziz A. Farah; Ramon A. Alvarez-Puebla; Hicham Fenniri (572-576).
Stabilization of metal nanoparticles (MNP) is a prerequisite for any application in sensor design, optoelectronics, catalysis, spectroscopic labeling, and nanomedicine. However, MNPs produced by most currently available synthetic approaches tend to undergo aggregation into large clusters, thus reducing their accessibility and compromising properties associated with their nanoscale dimensions. To circumvent the agglomeration problem and enhance their chemical and physical stability, we developed an efficient strategy for the preparation of MNP/polymer composites in which silver nanoparticles coated with 4-mercaptomethylstyrene act as crosslinkers in a suspension polymerization. The resulting microspheres were characterized by Raman, SERS and XPS spectroscopies, DSC, SEM and TEM. Their chemical and physical stability was also established.
Keywords: Silver nanoparticles; Suspension polymerization; Nanocomposite;

Effect of shear rate on aggregate size and morphology investigated under turbulent conditions in stirred tank by Miroslav Soos; Amgad S. Moussa; Lyonel Ehrl; Jan Sefcik; Hua Wu; Massimo Morbidelli (577-589).
Aggregation and breakage of aggregates produced from fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tank. Detailed investigation of the initial kinetics showed that the collision efficiency, α, depends on the shear rate according to α ∝ G − b , with a power law exponent, b, equal to 0.18. After steady state was reached the dynamic response of the system on a change in stirring speed and solid volume fraction was investigated. It was found that the steady-state values of two measured moments of the cluster mass distribution (CMD) are fully reversible upon a change in stirring speed. This indicates that although the moments of CMD at steady-state depend on the applied shear rate, the aggregate structure is independent of the shear rate in the given range of stirring speeds. This was proved by independent measurement of the fractal dimension, d f , using image analysis which provided a d f equal to 2.62 ± 0.18 independent of applied stirring speed. The critical aggregate size, below which breakage is negligible, determined by dilution experiments was consequently used to evaluate the aggregate cohesive force holding the aggregate together, which was found to be independent of the aggregate size and equal to 6.2 ± 1.0 nN.
Keywords: Aggregation; Breakage; Turbulent conditions; Polystyrene particles; Shear rate effect; Solid volume fraction effect; Aggregation efficiency; Steady-state reversibility; Aggregate morphology; Light scattering; Image analysis; Aggregate cohesive force;

Pollution of soils and sediments by heavy metals is an environmental concern. Among the remedial techniques, soil washing is proving to be reliable. Biosurfactant rhamnolipid has shown its potential as a washing agent. In this research, small angle neutron scattering (SANS) was employed to investigate the size and morphology of rhamnolipid aggregates and micelle structure in the presence of heavy metals Cu, Zn, and Ni. The results indicate the importance of the pH of the system in the morphology of the aggregates in the rhamnolipid solution. Creation of a basic condition by addition of 1% NaOH led to the formation of large aggregates (>2000 Å) + micelles with R G ∼ 17   Å while in the acidic environment with 1% NaCl, large polydisperse vesicles with a radius about 550–600 Å were formed. The size of the aggregates in both acidic and basic condition is fine enough to ease the flow of the rhamnolipid solution through the porous media with the pore sizes as small as 200 nm.Morphological transformations of the rhamnolipid biosurfactant from large vesicles to small vesicles to micelles (coexisting with large aggregates) occurred upon increasing the pH value.
Keywords: SANS; Rhamnolipids; Heavy metals; Soil remediation; Micelle structure;