THEORETICAL-STUDY ON THE STRUCTURE AND INTERFACIAL-AREAS OF NONYL PHENOL ETHOXYLATED SURFACTANTS

A structural, molecular mechanics and molecular dynamics study of the properties of nonyl phenol ethoxylated surfactants (NPE) is presented. In the first part, structural AM1 calculations on CH3(CH2)(8)-C6H4-O- (CH2CH2O)(m)-H(NPE(m)) surfactants, where m = 2, 5, 8, 9, 11, 12, 13 a nd 14 units, were carried out, and the variation of the molecular prop erties was observed as a function of the molecular length. The magnitu de of the intermolecular energies between pairs of NPE(m), NE(m), and aryl-substituted NPE(m) surfactant molecules has also been studied, an d the effect of the ionization potential on the intermolecular interac tion between these surfactants is discussed. In the second part, the i nterfacial areas of nonyl phenol triethoxylated surfactants were deter mined using short-time molecular dynamics calculations on ternary syst ems composed of a surfactant monolayer located at a heptane/water inte rface. A novel energetic description of a surfactant monolayer at an o il/water interface is presented. This expression can be simply paramet rized with the aid of molecular dynamics simulations.