期刊
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
卷 467, 期 2131, 页码 1939-1958出版社
ROYAL SOC
DOI: 10.1098/rspa.2010.0516
关键词
emulsions; foams; micro-emulsions; sodium dodecyl sulphate; surface tension; bending modulus
资金
- Royal Society
- Direccion General de Investigacion
- Ministerio de Ciencia y Tecnologia of Spain [FIS2007-65869-C03]
- Comunidad Autonoma de Madrid [MODELICO-CM/S2009ESP-1691]
Using computer simulations, we investigate the interfacial structure of sodium dodecyl sulphate (SDS) monolayers adsorbed at the water surface and water-oil interfaces. Using an algorithm that removes the averaging effect of the capillary waves, we obtain a detailed view of the solvation structure of water around the monolayer. We investigate surface concentrations between 45 and 33 angstrom(2) per surfactant, which are near experimental conditions corresponding to the critical micellar concentration and the formation of Newton black films. The surfactants induce a layering structure in water, which disappears at approximately 1 nm from the monolayer plane. The water molecules exhibit a preferred orientation with the dipoles pointing towards the monolayer. The orientational order decays slowly, but it does not influence the hydrogen bond structure of water, which is significantly disrupted in the interfacial region only. These structural changes are qualitatively the same in SDS-water and oil-SDS-water interfaces. In the latter case, we find a small degree of penetration of oil in the monolayer (between 0.2 and 0.25 molecules per SDS). This small penetration has a measurable effect on the monolayer, which increases its thickness by approximately 10 per cent. The bending modulus of the SDS monolayers is of the order of the thermal energy, k(B)T.
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