Molecular dynamics approach to investigate the coupling of the hydrophilic-lipophilic balance with the configuration distribution function in biosurfactant-based emulsions.

Emulsion stability has been characterized by macroscopic variables such as the hydrophilic-lipophilic balance, with the aim being to predict the surfactant properties of molecules. Nevertheless, this parameter does not take the topology of the molecule into account, as it only considers its lipophilic degree. On the other hand, the classical Derjaguin-Landau-Verwey-Overbeek approach (based on the continuum model), which has been widely utilized to evaluate the stabilities of colloids, polymers, and surfactants, takes some bulk macroscopic parameters such as the shear viscosity coefficient and the dielectric permittivity into account. In the work reported here, molecular dynamics simulations were used to elucidate the mechanism of layer formation and micellar structure for different combinations of valine-aspartic acid peptides in dodecane-water emulsions, as well as their associations with the hydrophilic-lipophilic balance. The peptide-dodecane radial distribution function showed that the first peak intensity was inversely correlated with the hydrophilic-lipophilic balance; moreover, the oscillatory structural forces became increasingly prominent when the hydrophilic-lipophilic balance was decreased. Our results seem to indicate that the radial distribution function could be utilized to evaluate the stabilities of emulsions of peptides via molecular simulations.