Journal of Colloid And Interface Science (v.321, #1)
Editorial Board (OFC).
Acknowledgment to reviewers (v-xix).
Arsenic speciation in multiple metal environments by Markus Gräfe; Ryan V. Tappero; Matthew A. Marcus; Donald L. Sparks (1-20).
The speciation of arsenic (As) in a copper-chromated-arsenate (CCA) contaminated soil was investigated using micro-focused X-ray fluorescence ( μ XRF ) and micro-focused X-ray absorption fine structure ( μ XAFS ) spectroscopies to determine if and how the co-contaminating metal cations (Cu, Zn, Cr) influenced the speciation of As. 15 μ XRF images were collected on 30-μm polished thin sections and powder-on-tape samples from which Pearson correlation coefficients ( ρ ) between As and various metal species were determined based on the fluorescence intensity of each element in each image pixel. 29 μ XAFS and two bulk-XAFS spectra were collected from depths of 0–20 cm (LM-A) and 20–40 cm (LM-B) to determine the chemical speciation of As in the soil by target analyses of principal components with circa 52 reference spectra and linear least-square combination fitting of individual experimental spectra with a refined reference phase list (32) of likely As species. Arsenic and metal cations (Cr, Mn, Fe, Cu, Zn) accumulated in distinct, isolated areas often not larger than 50 × 50 μm in which the Pearson correlation between the elements was strongly positive ( ρ > 0.75 ) . The correlation of As to Zn and Cr decreased from >0.9 to <0.8 and increased to Cu from ∼0.6 to >0.8 with depth. Arsenic occurred predominantly in the +5 oxidation state. Abstract factor analysis and linear least square combination fit analysis suggested that As occurred as a continuum of fully and poorly-ordered copper-arsenate precipitates with additional components being characterized by surface adsorption complexes on goethite and gibbsite in the presence and absence of Zn. Precipitates other than copper-based ones, e.g., scorodite, adamite and ojuelaite were also identified. The significant co-localization and chemical speciation of As with Cu suggest that the speciation of As in a contaminated soils is not solely controlled by surface adsorption reactions, but significantly influenced by the co-contaminating metal cation fraction. Future studies into As contaminated soil therefore need to focus on identifying the speciation of As and the co-localizing metal cations.Arsenic speciation in soils is partly controlled by co-sorbing metal cations. Here we show how As(V) co-precipitated with Cu and Zn to form poorly ordered precipitates.
Keywords: μ SXRF ; μ XAFS ; Metal-arsenic co-localisation; Abstract factor analysis; Copper-arsenate precipitates;
Fat retention at the tongue and the role of saliva: Adhesion and spreading of ‘protein-poor’ versus ‘protein-rich’ emulsions by Diane M. Dresselhuis; Martien A. Cohen Stuart; George A. van Aken; Raymond G. Schipper; Els H.A. de Hoog (21-29).
Fat perception of food emulsions has been found to relate to in-mouth friction. Previously, we have shown that friction under mouth-like conditions strongly depends on the sensitivity of protein-stabilized emulsion droplets to coalescence. Here, we investigated whether this also implies that oral fat retention depends in a similar manner on the stability of the emulsion droplets against coalescence. We investigate the separate contributions of droplet adhesion and droplet spreading to fat retention at the tongue, as well as the role of saliva. We perform ex vivo (Confocal Raman Spectroscopy; Confocal Scanning Laser Microscopy) experiments using pig's tongue surfaces in combination with human in vivo experiments. These reveal that protein-poor (unstable) emulsions are retained more at the tongue than protein-rich (stable) emulsions. Furthermore, the layer formed by adhering protein-poor droplets is more stable against rinsing. Saliva is found to be very efficient in removing fat and emulsion droplets from the oral surface but its role in fat retention needs further research. We relate our results to the colloidal forces governing droplet adhesion and spreading.Difference in adhesion energy between a stable ‘protein-rich’ (a) and an unstable ‘protein-poor’ (b) emulsion droplet approaching a hydrophobic surface.
Keywords: Adherence; Coalescence; Wetting; Solid surface; Sensory perception; Particle interaction; Lubrication;
Adsorption and desorption of atrazine on carbon nanotubes by X.M. Yan; B.Y. Shi; J.J. Lu; C.H. Feng; D.S. Wang; H.X. Tang (30-38).
The potential impact of carbon nanotubes (CNTs) on human health and the environment is receiving more and more attention. The high surface area of CNTs tends to adsorb a large variety of toxic chemicals, which may enhance the toxicity of CNTs and/or toxic chemicals. In this study, adsorption and desorption of atrazine on carbon nanotubes from aqueous solution were studied through batch reactors. The adsorption equilibrium isotherms were nonlinear and were fitted by Freundlich, Langmuir, and Polanyi–Manes models. It was found that the Polanyi–Manes model described the adsorption process better than other two isotherm models. Together with the “characteristic curve,” the Polanyi adsorption potential theory is applicable to describe the adsorption process of atrazine on CNTs. Thermodynamic calculations indicated that the adsorption reaction of atrazine on CNTs is spontaneous and exothermic. The desorption data showed that no significant desorption hysteresis occurred. High adsorption capacity and adsorption reversibility of atrazine on CNTs suggest that CNTs have high health and environmental risks, whereas they have potential applications for atrazine removal from water.Repetitive adsorption/desorption of atrazine on CNTs at three initial concentrations: 6.9 (■), 16.2 (▴), and 30.6 mg/L (●), the corresponding open symbols represent the desorption processes after the last adsorption step, respectively: (A) SMWNT20; (B) r-MWNT.
Keywords: Carbon nanotubes; Adsorption; Desorption; Hysteresis; Atrazine;
Preparation and characterization of organoclays based on an amphoteric surfactant by A.R. McLauchlin; N.L. Thomas (39-43).
The uptake of the amphoteric surfactant, cocamidopropyl betaine (CAB) by a sodium montmorillonite clay was studied with respect to concentration and pH. A series of organoclays was prepared in which the basal spacings were found to depend on both parameters. Adjusting the solution pH during preparation influenced the adoption of either 1.8 or 2.0 nm spacing, whereas the 3.9 nm spacing in the same sample was unaffected. The presence of the carboxyl group in the CAB molecule enabled dispersion of the clay at higher pH by which means pure organoclays of high spacing could be obtained, whereas, without dispersing the clay, mixed populations were obtained. The results indicate the optimum parameters for preparing organoclays of desired spacings for use in clay-reinforced nanocomposites.The interlayer spacing of organomontmorillonites containing cocamidopropyl betaine depends both on the pH and timing of pH adjustment.
Keywords: Organoclay; Amphoteric surfactant; Montmorillonite; Cocamidopropyl betaine;
Influence of polymeric additives on biomimetic silica deposition on patterned microstructures by Olaf Helmecke; Alexander Hirsch; Peter Behrens; Henning Menzel (44-51).
Microstructured polymer films prepared by photochemical grafting of different polymers were used as restricted reaction areas in silica deposition experiments. Linear and branched poly(alkyleneimines) and poly(allylamine hydrochloride) in pure aqueous or phosphate-containing solutions were used as additives to silica precursor solutions. The silica deposits obtained by spin-coating these solutions onto microstructured polymer films were investigated by scanning electron microscopy and atomic force microscopy. Experiments with poly(alkylene imines) in the silica precursor solution show the deposition of smooth and granular silica structures that closely mimic the natural patterns. The structure formation can be explained by physicochemical processes. Hypotheses that have been made for the natural silification processes can be evaluated on this basis.Differently shaped structures coated with different polymer films have been applied in silica mineralization experiments. Some of the obtained silica structures are closely mimicking the natural patterns of diatoms.
Keywords: Surface patterning; Photochemical grafting; Silica deposition; Diatoms; Polyamines;
Studies on the exchange of early pellicle proteins by mucin and whole saliva by Ida E. Svendsen; Liselott Lindh; Ulla Elofsson; Thomas Arnebrant (52-59).
Adsorption of small pellicle proteins statherin or proline-rich protein 1 (PRP1), respectively, and subsequent adsorption of human whole saliva (HWS) or salivary mucin MUC5B, respectively, was studied using ellipsometry and total internal reflectance fluorescence. Differences in elution (using sodium dodecyl sulphate (SDS) solutions) between mixed and single protein films were also investigated. On both hydrophilic and hydrophobized surfaces HWS and MUC5B were found to adsorb to pre-adsorbed layers of statherin and PRP1, respectively. Statherin adsorption on both substrate types showed no or minor exchange by HWS or MUC5B and no change in SDS elution between mixed and single protein films. Small amounts of PRP1 were exchanged by HWS on both surface types and the SDS elutable fractions were similar or larger for mixed films compared to single protein films. PRP1 and MUC5B in sequence showed minor exchange of PRP1 on hydrophilic surfaces, while no exchange could be established on hydrophobized substrates. SDS elutable fractions decreased for PRP1 and MUC5B mixed films compared to single protein films. In conclusion, minor amounts of statherin and PRP1 are exchanged during the time course of the experiments, which indicates that these proteins may to a large extent remain incorporated in the pellicle.Data on sequential adsorption obtained by total internal reflectance fluorescence and ellipsometry shows minor exchange of salivary protein PRP1 by whole saliva on hydrophilic substrates.
Keywords: Total internal reflectance fluorescence; Ellipsometry; Hydrophilic surfaces; Hydrophobic surfaces; FITC; SDS; MUC5B; Proline-rich protein; Statherin;
A facile and simple method for the preparation of copoly(TEAMPS/VP)/silver nanocomposites for the humidity-sensing membranes by Min-Su Park; Tae-Ho Lim; Young-Min Jeon; Jong-Gyu Kim; Sang-Woo Joo; Myoung-Seon Gong (60-66).
We developed a simple method for the preparation of polyelectrolyte/silver nanocomposites, where silver nanoparticles were dispersed in a polyelectrolyte. Copoly(TEAMPS/VP)/silver (w/w = 100/0, 100/1, 100/2, 100/3 and 100/4) nanocomposites were obtained by a thermal decomposition reaction of silver carbamate complex at 130 °C, and well-dispersed silver colloids were stabilized by copolymer of tetraethylammonium 2-acrylamido-2-methyl-1-propanesulfonate (TEAMPS) and N-vinylpyrrolidone (VP). A dark brown solution in its UV–vis absorption spectrum showed surface plasmon resonance absorption bands at 420 nm in solution. The silver precursor and the resulting polyelectrolyte/Ag nanocomposite was characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), infrared (IR), transmission electron microscopy (TEM). In addition the humidity-sensing properties using copoly(TEAMPS/VP)/Ag nanocomposite films were examined.Dependence of impedance on the relative humidity of copoly(TEAMPS/VP)/Ag nanocomposite films obtained by thermal heating of the mixtures of copoly(TEAMPS/VP) and silver carbamate complex solution at 130 °C.
Keywords: Polyelectrolyte/silver nanocomposite; Silver alkylcarbamate complex; Humidity-sensitive membrane;
Fabrication of hollow silica spheres using droplet templates derived from a miniemulsion technique by Bo Peng; Min Chen; Shuxue Zhou; Limin Wu; Xiaohua Ma (67-73).
Hollow silica spheres have been successfully fabricated by means of a miniemulsion technique, in which miniemulsion droplets of tetraethoxysilane (TEOS) and octane were prepared with cetyltrimethylammonium bromide as a surfactant and hexadecane as a costabilizer and used as templates. As the TEOS diffused out from the droplets, it was hydrolyzed and condensed to form a silica shell at the oil/water interface. In this way, hollow silica spheres could be obtained directly since the miniemulsion droplets of octane could be evaporated very easily during the reaction process or the drying process; neither an additional dissolution nor a calcination process or additional surface modification of the templates were needed.Hollow silica spheres have been synthesized by a miniemulsion technique by using the oil droplet (mixture of TEOS and octane) as template at room temperature.
Keywords: Silica; Hollow spheres; Miniemulsion;
Effect of particle size and natural organic matter on the migration of nano- and microscale latex particles in saturated porous media by Andrew J. Pelley; Nathalie Tufenkji (74-83).
In the interest of fully assessing the potential environmental risks linked to “nanolitter,” we need to be able to predict the persistence, toxicity, and mobility of engineered nanomaterials in the natural subsurface environment. To examine the effects of particle size and natural organic matter on nanoparticle mobility, laboratory-scale filtration experiments were performed using different sized model nanomaterials (i.e., latex colloids having diameters of 50, 110, and 1500 nm) in the presence and absence of 5.0 mg/L Suwannee River humic acid (SRHA). At low ionic strengths (1–10 mM KCl), an increase in attachment efficiency (α) with increasing particle size was observed. This result contrasts with predictions of particle filtration based on attachment in the primary energy minimum of the particle–grain interaction energy profile evaluated using Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The presence of SRHA generally resulted in a decrease in α over the range of experimental conditions investigated. Results of particle transport experiments combined with particle characterization measurements suggest that the decrease in colloid attachment in the presence of SRHA is related to the combined influence of the mechanisms of charge stabilization and steric stabilization.
Keywords: Nanoparticle; Filtration; Groundwater; Contamination; Humic acid; Steric stabilization; Particle size; Zeta potential;
Oxidation of FeS by oxygen-bearing acidic solutions by Paul Chiriţă; Michaël Descostes; Michel L. Schlegel (84-95).
Oxidation of FeS in oxygen-bearing acidic solutions was investigated at different temperatures (25 to 45 °C) and pH (2.75 to 3.45). The rate of the oxidative dissolution of FeS is strongly dependent on pH. The reaction order with respect to hydrogen ions has been found to be 1.03 ± 0.02 at 25 °C, and the apparent activation energy ( E a ) is 41.6 ± 10.7 kJ mol−1 at initial pH 3.00, suggesting that the FeS oxidative dissolution is controlled by the diffusion of oxidant species across a sulfur-rich layer (SRL) that undergoes chemical transformations leading to an increase in the mean number of sulfur atoms in polysulfide chains and the rearrangement of these chains. Fourier transform infrared spectroscopy and X-ray diffraction results obtained for the FeS samples reacted for 72 h at 25 °C and pH between 2.75 and 3.45 indicate the formation of goethite, of lepidocrocite, and of poorly ordered solid phases (assigned as SRL) on initial surfaces. The experimental data suggest a mechanism based on the protonation of FeS surfaces followed by oxidation of FeS by dissolved oxygen to produce Fe2+, S0, and S2− n . Fe2+ is unstable under oxidative conditions and transforms into Fe(OH)3(s), goethite and lepidocrocite.The reaction order of FeS oxidative dissolution with respect to H+ is 1.03 ± 0.02 at 25 °C. E a = 41.6 ± 10.7 kJ mol −1 at pH 3.00 suggesting a reaction controlled by the diffusion of O2 across a SRL.
Keywords: FeS; Oxygen; Kinetics; Reaction mechanism;
Structure evolution and optimization in the fabrication of PVA-based activated carbon fibers by Shu-Juan Zhang; Hui-Min Feng; Jian-Ping Wang; Han-Qing Yu (96-102).
The structure and composition evolution of polyvinyl alcohol (PVA) fibers during the fabrication of activated carbon fibers (ACF) by a newly developed method were systematically elucidated. The pore structure of the fibers was significantly influenced by the carbonization and activation conditions. The elemental composition and chemical structure evolution of the fibers during the heat treatment processes were evaluated by elemental analysis, Fourier transform infrared spectrophotometry (FTIR), and X-ray photoelectron spectroscopy (XPS). Crystal structure evolution of the fibers during the heat treatment processes was elucidated by X-ray diffraction (XRD) analysis. Based on these understandings, the process conditions were optimized using an L 9 ( 3 ) 4 orthogonal array design matrix. Appropriate process parameters for the fabrication of PVA-ACFs were established as carbonizing the dehydrated fiber at 300 °C for 60 min, and then lifting the temperature to 900 °C with a heating speed of 10 °C/min in an inert atmosphere, thereafter keeping the fiber at 900 °C for 60 min in an oxidizing atmosphere.The pore structure of PVA-ACF was significantly influenced by the carbonization and activation conditions. Based on such this understanding, the process conditions for the fabrication of PVA-ACF were optimized.
Keywords: Activated carbon fiber; Fabrication; Optimization; Structure;
Complex conductivity of water-saturated packs of glass beads by P. Leroy; A. Revil; A. Kemna; P. Cosenza; A. Ghorbani (103-117).
The low-frequency conductivity response of water-saturated packs of glass beads reflects a combination of two processes. One process corresponds to the polarization of the mineral/water interface coating the surface of the grains. The other process corresponds to the Maxwell–Wagner polarization associated with accumulation of the electrical charges in the pore space of the composite medium. A model of low-frequency conductivity dispersion is proposed. This model is connected to a triple-layer model of electrochemical processes occurring at the surface of silica. This model accounts for the partition of the counterions between the Stern and the diffuse layers. The polarization of the mineral/water interface is modeled by the electrochemical polarization model of Schurr for a spherical grain. We take into account also the DC surface conductivity contribution of protons of the sorbed water and the contribution of the diffuse layer. At the scale of a macroscopic representative elementary volume of the porous material, the electrochemical polarization of a single grain is convoluted with the grain size distribution of the porous material. Finally, the Maxwell–Wagner polarization is modeled using the complex conductivity of a granular porous medium obtained from the differential effective medium theory. The predictions of this model agree well with experimental data of spectral induced polarization. Two peaks are observed at low frequencies in the spectrum of the phase. The first peak corresponds to the distribution of the size of the beads and the second peak is due to the roughness of the grains.Phase of the complex conductivity as a function of the frequency for a pack of glass beads with a rough surface at different salinities and comparison with the prediction of the model.
Keywords: Spectral impedance; Porous media; Induced polarization; Complex conductivity; Double layer; Particle size distribution;
The effect of evaporation on the wicking of liquids into a metallic weave by N. Fries; K. Odic; M. Conrath; M. Dreyer (118-129).
Wicking of liquids into porous media is of great importance to many applications. One example are propellant management devices (PMD) used in spacecraft tanks. PMDs are designed to ensure gas free delivery of propellant during all acceleration conditions of the flight. This might be achieved by a metallic weave which is wetted by the propellant and thus prevents gas from entering below a critical bubble point pressure. In the case of cryogenic or volatile liquids the weave may dry out and refilling of the structure becomes an important issue. In this study we analyze the wicking of different liquids into a dry Dutch twilled weave (DTW 200 × 1400 ) by combining experimental and analytical approaches. Experiments were performed under isothermal and terrestrial conditions to investigate the role of evaporation for the capillary rise. The standard wicking model from Lucas and Washburn is enhanced to account for evaporation and gravity effects, too. By comparing the experimental results with the enhanced wicking model we find good qualitative agreement. It is also noted that evaporation may have a major impact on the wicking process.An experimental investigation and a comparison with an analytic model.
Keywords: Capillary rise; Evaporation; Dutch twilled weave; Liquid penetration; Porous medium; Imbibition; Wicking; Lucas–Washburn equation; Washburn equation; Heat pipe mesh;
Some aspects of hydrate formation and wetting by P. Fotland; K.M. Askvik (130-141).
Experimental observations of gas hydrate formation have shown that, in the initial nucleation and crystallization process, water–oil emulsions may be generated, destabilized or even inverted. These phenomena are consistent with the effects of particles on emulsions. In this work we relate experimental observations of hydrate formation to the phenomenon of wettability. It is shown that details of hydrate wetting are important for both the morphology and the kinetics of the formed hydrates. For the cases of hydrate lenses and spheres, it is shown that the various wetting states can be illustrated and analyzed by using wetting diagrams. Metastability is a function of the surface energies of the hydrate formation, i.e., the wetting state, and it is shown that in some cases metastability vanishes, and thus hydrates nucleates instantly at all positive driving forces. The magnitude of buoyancy and turbulence forces acting on a hydrate sphere are compared to the capillary force and it is concluded that capillary energy dominates when the hydrate spheres is less than 1 mm.The effective energy of hydrate formation at an interface or in bulk phases can be mapped in a wetting diagram, and used to describe both hydrate morphology and sub-cooling.
Keywords: Hydrates; Wettability; Metastability; Agglomeration;
Effect of non-homogeneous surface viscosity on the Marangoni migration of a droplet in viscous fluid by O. Manor; O. Lavrenteva; A. Nir (142-153).
Marangoni migration of a single droplet in an unbounded viscous fluid under the additional effect of variable surface viscosity is studied. The surface tension and the surface viscosity depend on concentration of dissolved species. Cases of the motion induced by the presence of a point source and by a given constant concentration gradient are considered. The dependence of the migration velocity on the governing parameters is computed under quasi-stationary approximation. The effect of weak advective transport is studied making use of singular perturbations in the Peclet number, Pe. It is shown that, when the source is time dependent a Basset-type history term appears in the expansion of the concentration and, as a result, the leading order correction to the flow and to the migration velocity is of O ( Pe 1 / 2 ) . If the source of active substance driving the flow is steady, the effect of convective transport on the migration is weaker.Marangoni migration of a droplet under the effect of variable surface viscosity is studied. Surface properties depend on a concentration of dissolved species undergoing diffusive and weak advective transport.
Keywords: Surface viscosity; Surface tension; Surfactant; Surface-active substance; Non-homogeneous distribution; Marangoni effect; Viscous drop; Advective transport; Singular perturbations; Matched asymptotic expansion;
Enzymatically prepared n-alkyl esters of glucuronic acid: The effect of freeze-drying conditions and hydrophobic chain length on thermal behavior by C. Blecker; S. Danthine; M. Pétré; G. Lognay; B. Moreau; L. Vander Elst; M. Paquot; C. Deroanne (154-158).
In this work, some of the physicochemical properties of enzymatically prepared n-alkyl esters of glucuronic acid are presented. Two questions are addressed. The first concerns the influence of post-purification freeze-drying conditions on octyl glucuronate thermotropic behavior. Depending on the amount of water added before freeze-drying, the α / β anomeric ratio determined by 1H NMR is affected and differences are observed in DSC thermograms probably due to polymorphism. The second question concerns the effect of hydrophobic chain length on the thermal behavior. An increase of both transition temperature and transition enthalpy is observed by increasing the number of carbon atoms in the alkyl chain (C8 < C10 < C12 < C14). This kind of results can provide relevant information for the processing and the practical use of these nonionic surfactants.
Keywords: Nonionic surfactants; Glucuronic acid; Biosurfactants; Enzymatic synthesis; Lipase; DSC; X-ray diffraction; 1H NMR;
Lyotropic liquid crystalline phases formed in ternary mixtures of 1-cetyl-3-methylimidazolium bromide/p-xylene/water: A SAXS, POM, and rheology study by Jin Zhang; Bin Dong; Liqiang Zheng; Na Li; Xinwei Li (159-165).
The phase behavior of ternary mixtures of 1-cetyl-3-methylimidazolium bromide (C16mim-Br)/p-xylene/water is studied by small-angle X-ray scattering (SAXS), polarized optical microscopy (POM), and rheology measurements. Two types of lyotropic liquid crystalline phases are formed in the mixtures: hexagonal and lamellar. The structural parameters of the lyotropic liquid crystalline phases are calculated. Greater surfactant content in the sample leads to denser aggregation of the cylindrical units in the hexagonal liquid crystalline phase. The increase in lattice parameter and thickness of the water layer in lamellar phase are attributed to the increase of water content, and the area per surfactant molecule at the hydrophobic/hydrophilic interface for lamellar phase is found to be larger than that for hexagonal phase. The structural parameters of the liquid crystalline phases formed from the cetyltrimethylammonium bromide (CTAB) system are larger than those for the C16mim-Br system. The rheological properties of the samples are also found to be related to the structure of the liquid crystalline phases.The phase behavior of the ternary mixtures of 1-cetyl-3-methylimidazolium bromide/p-xylene/water is studied by small angle X-ray scattering, polarized optical microscopy and rheology measurements.
Keywords: Long-chained imidazolium ionic liquid; Lyotropic liquid crystalline phase; Pseudo-ternary phase diagram; SAXS; POM; Rheology;
On structural transitions in a discontinuous micellar cubic phase loaded with sodium diclofenac by R. Efrat; A. Aserin; N. Garti (166-176).
An intermediate mesophase of lyotropic liquid crystalline structure from the ternary mixtures of glycerol monooleate, water, and ethanol was recently characterized in our lab. This mesophase, termed Q L , consists of discrete discontinuous micelles arranged in a cubic array. The Q L phase can solubilize very significant loads of water-insoluble anti-inflamatory drug sodium diclofenac (Na-DFC). Close examination of the internal structures of the lyotropic liquid structure upon increasing the solubilization loads reveals the existence of three structural transitions controlled by the Na-DFC levels. Up to 0.4 wt% Na-DFC, the Q L structure remains intact with some influence on the hydration of the headgroups and on the intermicellar forces. However, at 0.8 to 1.2 wt% Na-DFC, the discontinuous micellar cubic phase is transformed into a more condensed mesophase of a bicontinuous cubic phase. At > 1.2 wt% Na-DFC, the cubic phase is converted into a lamellar phase ( L α ). Within 5.5 to 7.3 wt% Na-DFC the mesophase is progressively transformed into a less ordered lamellar structure. At ⩾ 12 wt% Na-DFC crystals tend to precipitate out. At low Na-DFC concentrations the drug behaves like a lyotropic or kosmotropic salt and can salt-out the surfactant from its water layer, but at higher levels it behaves like a hydrotropic, chaotropic salt and can salt-in the surfactant. The Na-DFC location and position within the interface as well as its polarization and partial ionization are strongly affected by its solubilization contents and the structure that it is inducing. In the cubic phase the drug is located less close to the hydration layer while once transition occurs it is exposed more to the water layer and the surfactant headgroups.
Keywords: Lyotropic liquid crystals; Mesophases; Sodium diclofenac; Solubilization; Phase transformations; Kosmotropic; Chaotropic salt;
Lyotropic liquid crystal behaviour of azelate and succinate monoester surfactants based on fragrance alcohols by Frédéric Marchal; Véronique Nardello-Rataj; Nelly Chailloux; Jean-Marie Aubry; Gordon J.T. Tiddy (177-185).
Azelaic acid was used as a starting material for the preparation of new monoester surfactants based on fragrance alcohols. Sodium monocitronellyl azelate (citroC9Na) and sodium monomenthyl azelate (menC9Na) were synthesized and their aqueous phase behaviour was studied. For comparison, monoesters derived from succinic anhydride, i.e. sodium monocitronellyl succinate (citroC4Na) and sodium monomenthyl succinate (menC4Na), were also prepared as well as sodium monodecyl succinate (C10C4Na) and sodium monodecyl azelate (C10C9Na) in order to study the effect of the position of the ester function inside the hydrophobic tail and of branching and unsaturation respectively. Liquid crystal structures were examined by optical polarising microscopy and schematic partial binary phase diagrams (surfactant + water, 0–100 wt%, 10–90 °C) of the surfactants were established. Succinate surfactants behave as longer alkyl chain surfactants than their azelate counterparts, meaning that these last ones probably adopt a more folded conformation, with the ester function more frequently present at the micelle surface. This conformation would result in a rougher micelle surface, making it slightly less easy for micelles to pack in liquid crystalline phases. It was also shown that the tendency to adopt a more folded conformation and to form smaller micelles is ranked in this order: monomenthyl > monocitronellyl > monodecyl.
Keywords: Surfactant; Azelate; Succinate; Optical polarising microscopy; Lyotropic behaviour; Liquid crystal; Menthol; Citronellol;
Interfacial and stability study of microbubbles coated with a monostearin/monopalmitin-rich food emulsifier and PEG40 stearate by Yuyi Shen; Robert L. Powell; Marjorie L. Longo (186-194).
The stability and presence of micron-scale bubbles (microbubbles) is of considerable interest in environmental, biomedical, and food sciences. Here we show that microbubbles can be formed and stabilized in a solution of low cost food-grade emulsifier (a mixture of saturated long-chain monoglycerides, diglycerides and sodium stearoyl-2-lactylate) in combination with polyethylene glycol (PEG)-40 stearate. Langmuir trough methods and fluorescence microscopy were combined to investigate the surface tension, interfacial elastic modulus, phase behavior and microstructure of monolayer shells coating these microbubbles. Our results strongly suggest that although the PEG40S is necessary to form microbubbles this component, as well as sodium stearoyl-2-lactylate, are “squeezed out” in the form of collapse aggregates. This process leaves a microbubble shell, composed of a condensed-phase low surface tension mono- and diglycerides mixure with some of the PEG40S and SSL2 remaining trapped between the condensed-phase domains. We find that other commercially available emulsifiers, containing unsaturated or bulky components unable to form condensed phases, do not to form or stabilize a microbubble layer, although they may form a foam, a finding that we relate to differences in surface tension. π – A isotherm combined with fluorescence microscopy show the monolayer of each stable microbubble was composed of condensed phase monostearin/monopalmitin-rich domains with expanded phase entrapped between compressed domains.
Keywords: Bubbles; Condensed phase; Monoglyceride; Diglyceride;
Micellar aggregation for ionic surfactant in pure solvent and electrolyte solution: Nonextensive thermodynamics approach by Pierre Letellier; Alain Mayaffre; Mireille Turmine (195-204).
We show in this study that the concepts of nonextensive thermodynamics introduced and applied in a series of previous studies can be used to describe the behaviour of ionic surfactant solutions at concentrations higher than the critical micelle concentration (cmc) in pure solvents and in the presence of electrolytes. We supposed that the aggregated amphiphiles and their counter ions form two interpenetrated nonextensive phases of the same thermodynamic dimension, m, characterised by two parameters A am and A CI related to the aggregated amphiphile and the counter ion, respectively. Our experimental results and those published in the literature indicate that logarithms of the activities of the amphiphile and of its counterion vary with the quantity of aggregated monomer according to a power law. Thus, we demonstrate a linear relation between the logarithms of the activities of the two ions beyond the cmc in pure solvents (“micellization product”). An original relation, different from the Corrin–Harkins relation, can thus be established to describe the effects of salt on the cmc of ionic surfactants. According to this relation the cmc of charged surfactant in some systems can increase in the presence of an electrolyte with a common ion.In this approach, amphiphilic ions and their counterions are supposed to form two nonextensive phases of the same dimension, m. They are in equilibrium with the monomers in the solution at the temperature T. The interfaces with the surrounding medium are “fuzzy interfaces.”
Keywords: Nonextensive thermodynamics; Micelle; Surfactant behaviour; Fuzzy interface;
Stabilization of the mesomorphic phase in a self-assembled two-component system by Yifeng Zhou; Miao Xu; Tingcheng Li; Yilu Guo; Tao Yi; Shuzhang Xiao; Fuyou Li; Chunhui Huang (205-211).
We reported here the two-component self-assembling building blocks capable of forming lyotropic liquid crystal and liquid-crystalline physical gel. One of the components has a molecular characteristic of C 3 -symmetrical trisureas containing three azobenzene groups, which can form liquid-crystal phase in a temperature range of 133–215 °C. Another one has a trisamide core, which can self-aggregate to fibrous network through hydrogen bonds of amide moieties. The mixture of these two components performs lyotropic liquid crystal as well as liquid-crystalline physical gel in a temperature range larger than that of sole compound, suggesting that the cooperation of hydrogen bonds between these components stabilizes the mesophase of the assembly. The mechanism of formation of the mesophase was investigated by infrared spectra and small-angle X-ray scatterings.The cooperation of intermolecular interaction between C 3 -symmetrical trisurea compounds and trisamide gelator stabilizes the mesophases of the assembly; thus performs LCs and LC physical gel in a large temperature range.
Keywords: Hydrogen bonds; Liquid crystals; Self-assemble; Thermotropic properties;
Adsorption of fluorescent R6G dye into organophilic C12TMA laponite films by S. Salleres; F. López Arbeloa; V. Martínez; T. Arbeloa; I. López Arbeloa (212-219).
The absorption and fluorescence properties of rhodamine 6G (R6G) in organophilic laponite (Lap) clay films are studied. For this purpose, organo-Lap clays are synthesized by the incorporation of dodecyltrimethylammonium (C12TMA) as surfactant into the interlayer space of Lap clays. Two organo-Lap clays are prepared: one with moderate surfactant content (around 70% of the total cation-exchange capacity (CEC) of the clay) and a second with a high surfactant loading (about 130% CEC). Supported films are elaborated by the spin-coating technique and characterized by several techniques such as atomic force microscopy, elemental CHN analysis, X-ray diffraction, and thermogravimetry. IR spectroscopy reveals that the intercalation of R6G into organo-Lap films takes place at the detriment of the adsorbed C12TMA molecules. The photophysical properties of R6G monomers in the interlayer space of Lap films are improved by the presence of surfactant molecules. Moreover, organophilic environments can reduce the dye aggregation and favor the formation of fluorescent J-type aggregates, enhancing the fluorescence ability of dye/clay films with high dye contents. This improvement depends on the surfactant content.
Keywords: Organophilic clays; Surfactants; Rhodamine 6G adsorption; Thin films; Absorption and fluorescence properties; Dye aggregation;
The effect of molecular structure on the surface properties of selected quaternary ammonium salts by Katarzyna Dopierala; Krystyna Prochaska (220-226).
Equilibrium and dynamics of adsorption at the air/water interface of cationic surfactants belonging in the group of quaternary ammonium bromides was studied. Static surface tension of aqueous surfactants' solutions was measured in a wide range of surfactant concentrations using du Noüy ring method. Quaternary ammonium salts with different alkyl chain numbers and hydrophobicities were investigated. The Frumkin equation and reorientation model were used for a quantitative description of the process of their adsorption. The adsorption dynamics of the considered salts was described as a supplement to the equilibrium study. It was found that four short alkyl chains in tetraalkylammonium salt build a molecule which is weakly surface active. The number of alkyl chains as well as the symmetry of the molecules are important factors, determining the behavior of the surfactants at the interface and in the bulk solution. Surfactants with asymmetrical structure, like TTABr or MTOABr, show a strong tendency to reorientation, in opposite to tetraalkylammonium bromides and DDABr. Measurements of the dynamic surface tension revealed also strong dependence of the dynamics of adsorption on the chemical structure of the molecules. Measurements of the particle size by the dynamic light scattering method enabled the presence or lack of the micelles in the selected solutions to be confirmed.Surface and micellar properties of the selected quaternary ammonium salts were discussed. Effect of the molecular structure on the adsorption properties was shown. Apparent aggregate sizes for TBABr solutions at concentrations: (—) 0.1 M, (– –) 0.05 M, (- - -) 0.0005 M as determined by dynamic light scattering.
Keywords: Quaternary ammonium salts; Tetraalkylammonium bromides; Adsorption at air/water interface; Dynamics of adsorption; Reorientation at the interface;
Active control of surface properties and aggregation behavior in amino acid-based Gemini surfactant systems by Haiming Fan; Feng Han; Zhuang Liu; Lang Qin; Zichen Li; Dehai Liang; Fuyou Ke; Jianbin Huang; Honglan Fu (227-234).
Two types of Gemini surfactants containing a disulfide bond in the spacer, sodium dilauroyl cystine (SDLC) and sodium didecamino cystine (SDDC), were synthesized, and their surface properties and aggregation behavior in aqueous solution were studied by means of surface tension measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM), and fluorescence. During the transition of the Gemini surfactants to their corresponding monomers through the reduction of disulfide bonds, the surface tensions of their aqueous solutions, as well as their aggregation behavior, changed greatly. The reduction of SDLC and SDDC led to disruption of the vesicle, and the oxidation of corresponding monomers to Gemini surfactants led to vesicle re-formation. These results demonstrated the control of surface properties and aggregation behavior by the reversible transition between the Gemini surfactant and its monomer via reduction/oxidation reactions.Surface properties and aggregation behavior of two amino acid-based Gemini surfactants were studied. Active control of surface properties and aggregation behavior was achieved by utilizing reduction/oxidation reactions.
Keywords: Gemini surfactant; Reduction/oxidation reactions; Transition between Gemini and its monomer; Surface tension; Vesicle;
Vapor-phase self-assembled monolayers of aminosilane on plasma-activated silicon substrates by S. Fiorilli; P. Rivolo; E. Descrovi; C. Ricciardi; L. Pasquardini; L. Lunelli; L. Vanzetti; C. Pederzolli; B. Onida; E. Garrone (235-241).
Aminosilane self-assembled monolayers on silicon substrates have been prepared via a gas-phase procedure based on the consecutive reactions of the aminosilane precursor and water vapor. X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements have been used to characterize the aminosilane layers. For comparison, substrates modified with aminosilane through a liquid-phase procedure have been prepared and characterized by means of the same techniques. The vapor-based procedure was found to yield more uniform layers characterized by fewer and smaller aggregates as compared with liquid-treated substrates. Grazing angles reflection Fourier transform infrared measurements were carried out on the vapor-treated substrates before and after water exposure to investigate the hydrolysis of the alkoxy groups and further reaction to form siloxane bonds. The surface density of amino groups, as estimated through a colorimetric method, is very similar for vapor- and liquid-treated substrates, suggesting a similar reactivity and accessibility of the functional groups on the surface.Uniform and reproducible aminosilane self-assembled monolayers on silicon substrates have been prepared via a gas-phase procedure, based on the consecutive reactions of the aminosilane precursor and water vapor.
Keywords: Self-assembled monolayer; Vapor phase; Aminosilane;
Loading–unloading of an elastic–plastic adhesive spherical microcontact by Y. Kadin; Y. Kligerman; I. Etsion (242-250).
A numerical solution is presented for a single load–unload cycle of an adhesive contact between an elastic–plastic sphere and a rigid flat. The interacting forces between the sphere and the flat are obtained through connecting nonlinear spring elements having force-displacement behavior that obeys the Lennard-Jones potential. Kinematic, rather than isotropic, hardening is assumed for the sphere material to account for possible secondary plastification during the unloading. The well-known Tabor parameter and a plasticity parameter are shown to be the two main dimensionless parameters governing the problem. The effects of these two parameters on the load-approach curves, on the plastically deformed sphere profiles, and on the plastic strain fields inside the sphere are presented, showing different modes of separation during the unloading.An original, yet undeformed, hemisphere has an initial approach, ω, which denotes the distance between its summit and a rigid flat. The spherical surface is allowed to deform due to surface atomic interaction.
Keywords: Adhesion; Surface forces; Lennard-Jones potential; Elastic–plastic contact; Load–unload cycle; Ductile separation; Kinematic hardening;