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Hydration of a spherical micelles of C12E6 in solution is studied by molecular dynamics simulation. The interface is found to be separated in an inner part composed of water and hydrophobic and hydrophilic moieties and an outer part with hydrophilic moiety and water only. Hydration numbers in the inner and in the outer parts are in excellent agreement with experimental data from various different methods. Temperature dehydration occurs in the inner region only and is related to the presence of water molecules directly in contact with the hydrophobic core at low temperature.

We present molecular dynamics simulations of three spherical aggregates constituted of the same number of monomeric chains of increasing hydrophilic character in water solution. The three different chains are dodecane, CH3(CH2)10CH3; dodecan-1-ol, CH3(CH2)10CH2OH; and oligoethylenoxide, CH3(CH2)11(OCH2CH2)3OH, and the systems are denoted C12, C12E0, and C12E3, respectively. The three solutions are simulated at the same temperature and pressure and at about the same concentration in weight of the solute. We investigate the structural changes of the aggregate and the conformational changes of its chains after increasing the hydrophilicity of the monomers. In the C12 system, the density of the aggregate is higher than the density of the pure hydrocarbon liquid in the same thermodynamic conditions. Dodecane chains are quite rigid and mostly in the all-trans conformation. This is an effect of the strong hydrophobic repulsion exerted on the aggregate by the water. A density depletion develops at the interface between the oil core and the solvent because of the mismatch between the two components. This extra pressure is gradually released after increasing the hydrophilicity of the monomers. In the C12E3 system, the density depletion at the interface is completely canceled, and the system is homogeneous through the interface. In this system, the interfacial regions appear to be divided into an inner part, where methylene groups, oxyethylene groups, and water molecules are present, and into an outer region formed by a mixture of oxyethylene groups and water only. The local density of oxyethylene groups in the interfacial region is strongly fluctuating, and its histogram shows an effective attraction among those groups. Thus, a considerable portion of the interfacial volume is filled by the solvent only. We observe a strong tendency for the OCCO dihedrals in the hydrophilic tails to be in the gauche state, and at the same time, we observe the presence of H-bond bridges that stabilize this structure.

The dielectric permittivity, viscosity, and density of octyl β-d-glucopyranoside (OBG) and glycine (G) aqueous solutions, with different OBG/G molecular ratios, were measured as a function of surfactant concentration and temperature in order to investigate the effect of the amino acid on the surface of glucoside micelles. The amino acid shows an appreciable influence on the thermodynamic stability of the surfactant aggregates. However viscometric, volumetric, and dielectric results indicate that glycine is not involved in the micellar surface. Such a result indicates that the stabilization of the OBG micellar assemblies, previously observed, is mainly due to the reduction of the solubility of the hydrocarbon tail and/or to an increase of the interfacial tension between the micellar oil core and the solvent rather than to short-range interactions between glycine and OBG polar head groups.