Modeling the effect of structural details of nonionic surfactant on micellization in solution and adsorption onto hydrophobic surfaces

Applying the classical one-gradient self-consistent-field (SCF) theory for adsorption and/or association, we can show that the molecular architecture of nonionic surfactants influences strongly the micellization in solution and the adsorption on solid-liquid interfaces. This is illustrated by using two models for the molecule with the same overall structure, one with a linear and one with a more realistic branched hydrocarbon tail. The critical micelle concentration is computed for several lengths of the poly(oxyethylene) headgroup. In addition, the adsorption isotherms of these small surfactants on hydrophobic surfaces were studied. Theoretical results are critically compared to the experimental results for critical micelle concentrations and adsorption isotherms of Triton X-100 and Triton X-405 onto a polystyrene latex dispersion. From this comparison, it was concluded that a SCF model in which homogeneous adsorbed layers are preassumed fails to reproduce experimental findings. It is speculated that lateral inhomogeneities must. be included in the SCF model to improve its performance.