Understanding the pH-responsive behaviour of alkylamine surfactants

Alkylamine surfactants exhibit interesting pH-responsive behaviour, which can be attributed to changes in the protonation state of the primary amine group. This behaviour is important to their use in a broad variety of applications, but it is challenging to isolate experimentally due to the need to add acid to control system pH. In this work, we achieve this by applying multi-scale computational modelling to study the self-assembly and phase behaviour of the alkylamine surfactant dodecylamine (DDA), validating our model against available experimental phase diagrams for DDA. Our results show that the degree of charge of the surfactant controls the delicate balance between hydrophilic/hydrophobic interactions and hence the interplay between self-assembly and solubility that is responsible for the rich phase behaviour observed in these systems. These findings have important implications as to how pH can be used to control the behaviour of alkylamine surfactants in various applications.