Effect of inorganic electrolyte concentration on anionic-cationic adsorption films. Part 3: Dodecylpyridinium chloride + sodium octylsulfonate + sodium chloride

Computer Simulations of Catanionic Surfactants Adsorbed at Air/Water Interfaces

Structural properties pertaining to the solvation of mixtures of dodecytrimethylammonium/dodecylsulfate adsorbed at water/air interfaces were studied using molecular dynamics techniques. Two different surfactant coverages, both in the submonolayer regime, were considered: an infinite-diluted catanionic pair and an equimolar mixture, at a surface concentration of 78.7 A2/headgroup. The most stable solvated structures for the single surfactant pair correspond to contact-head-ion-pairs (CHIP) at a distance close to 5 A. In addition, marginally stable solvent-separated-head-ion-pairs (SSHIP) at distances approximately 7 A were also observed. The mean free energy for the dissociation of CHIP was estimated to be approximately 1 kcal/mol. At finite surfactant concentrations, one observes a considerable degree of clustering between the amphiphiles, due to the strong Coulomb coupling between headgroups. The resulting spatial domains show asymmetric structures with linear dimensions comparable to the simulation box, suggesting the onset of percolative structures. The connectivity pattern of these domains was interpreted in terms of a simplified model consisting of two-dimensional charged Lennard-Jones spheres.

Removal of copper metal by cementation using a rotating iron cylinder

The rate of the copper(II)/iron cementation reaction in the presence of surfactant (SAS) was determined by measuring the rate of cementation of copper on a rotating Fe cylinder from a CuSO(4) solution in the absence and the presence of SAS using an atomic absorption spectrophotometer. The rate of cementation reaction is decreased by an increasing concentration of SAS, temperature and number of rotation. It is found that the order of the rate of decrease of the cementation reaction in the presence of SAS is as follows, Triton X-100 < SDS < SOS. The rate of the cementation reaction was also found to decrease with the addition of small amounts of alcohol. In the presence of alcohol, the amount of decrease ranged from 11.47 to 47.8% depending on the type and as well as the concentration of alcohol used. The effect of mixed surfactant (SAS) on cementation reaction was given. Thermodynamic parameters Delta H(*), Delta S(*), and Delta G(*) were calculated.

Observation of a Liquid−Gas Phase Transition in Monolayers of Alkyltrimethylammonium Alkyl Sulfates Adsorbed at the Air/Water Interface

The equilibrium adsorption layers of symmetric chain alkyltrimethylammonium alkyl sulfates (Cn+.Cn- for n = 8, 12) were investigated at the air/water interface by sum-frequency vibrational spectroscopy in the function of the bulk surfactant concentration. To ensure the surface purity of the solutions investigated, an improved version of the foam fractionation method was used for the purification of the constituent ionic surfactants and the surface purity of the solutions was also checked. In the monolayer of the C12+.C12- surfactant, a two-dimensional first-order gas/liquid phase transition was observed. At surfactant bulk concentrations just exceeding the concentration corresponding to the phase transition, the monolayer is conformationally disordered, liquidlike, but with increasing bulk surfactant concentration the conformational order of the monolayer increases. The SFG spectra of the C8+.C8- monolayer did not indicate the occurrence of phase transition at room temperature.