Colloids and Surfaces最新文献

To reveal the interaction between cationic fluorocarbon and cationic hydrocarbon surfactants, the mixed critical micelle concentration (CMC) of diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMAC) and dodecyltrimethylammonium chloride (DTAC) in aqueous solution was determined using electrical conductivity measurements. An interaction parameter, β, of 1 was obtained by applying a regular solution theory (RST) to the mixed CMC. Further, partition coefficients of alcohols and pyrene-3-carboxaldehyde between the micelles and the aqueous phase were measured. All these data were interpretable using RST with β = 1, indicating a rather small repulsive interaction between DEFUMAC and DTAC compared with anionic fluorocarbon and hydrocarbon surfactant mixtures. This is due to the large different CMC values of the two surfactants.

Detailed molecular modelling of surfactant micelles is, in spite of enormous efforts during the last decade, still a formidable task. Exact description by molecular dynamics is, for the time being, computationally not feasible. Recently, we developed a self-consistent field theory to describe the self-assembly of surfactants into micelles, in which we used a Markov approximation for the chain statistics on a lattice with a spherical geometry. In this paper we extend our previous work by using a more exact anisotropic excluded-volume term in combination with a rotational isomeric state scheme in the chain statistics (referred to as the self-consistent anisotropic field (SCAF) theory). One of the most remarkable new results of our SCAF analysis is that the tails in the micelle are not “melt” like; the amount of order in the micelle is higher on the outer part of the core and lower in the micelle centre. The inefficient packing in the central part of the micelle has the effect that the tail density is locally reduced as compared to the outer region of the core.

It was observed that the micropore volume of active carbon decreases with increasing amount of metal (Ni, Cu, Cd, Zn) in the carbon lattice. A temperature programmed reduction study indicated that active carbon acts as a dispersing agent and metal residues are present on the surface in dispersed form. A detailed examination of nitrogen adsorption indicated differences in the mode of dispersion of these metals. The effect of metal on the adsorption behavior of active carbon for acetaldehyde was also studied as a function of temperature. From the adsorption data, thermodynamic parameters such as free energy, entropy and enthalpy of adsorption were calculated from a virial isotherm expression. It was observed that supported metal/active-carbon systems exhibit greater adsorption affinity than expected from the sum of the individual constituents.

Alumina for adsorption chromatography was subjected to chemical pretreatment with HClO₄ and HCl of various concentrations, and samples of surface-phase pH 1.0–9.0 were prepared. The surface area, CiO⁻₄ and Cl⁻ ion content and OH⁻ ion-exchange capacity of the samples were determired. A sorption—desorption study of the nitrophenols, 2,4-dinitrophenol and 2,4,6-trinitrophenol, from aqueous solutions, under a variety of experimental conditions was carried out on the substrates. The sorption was found to depend on the pH of the substrate and on the acid used for the pretreatment. Maximum sorption was observed in the pH range 4.5–5.5. The process was fast (10 min–24 h) and exothermic (30–60°C), with low values of isosteric heat of adsorption (−6 to −31 kJ mol⁻¹). The desorption efficiency and retarding influence of the anions on adsorption was in the order: PO³⁻₄ > C₂O²⁻₄ > SO²⁻₄ > CH₃COO⁻ > NO⁻₃. The a treatment, and hence, the anion present (ClO⁻₄ or Cl⁻), appears to modify the sorption properties of alumina significantly. Anion-exchange sorption and weak chemical interactions (hydrogen bonding and π-electron interaction) appear to control the sorption of the solutes on pretreated alumina.

The distribution coefficients for adsorption and desorption were determined, and on the basis of these data, the elution behaviour and column chromatography were studied.

The equilibrium exchange of Sr²⁺ and Cs⁺ ions with the hydrogen forms of cerium(IV) antimonate (CeSb) and tin(IV) antimonate (SnSb) have been studied at 25, 45 and 60°C. The exchange isotherms have been measured for both forward and reverse reactions, at a solution ionic strength or 0.1, by the bath technique. Tin(IV) antimonate has a pronounced selectivity for Sr²⁺ and Cs⁺ in acid medium compared with CeSb. On the basis of the exchange isotherms, various thermodynamic parameters have been calculated and some predictions made for the exchange process taking place in the materials.