Effect of HPAM hydrolysis degree on catanionic mixtures of DTAB/HPAM: A coarse-grained molecular dynamic simulation

Abstract

Self-assembly of polymer and surfactant mixtures has attracted great interests because of its potential applications, ranging from tertiary oil recovery to drug delivery. However, the mechanism by which the hydrolysis degree of polymers promotes morphology transition is still experimentally challenging. In this study, self-assembly of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) and anionic polyelectrolyte partially hydrolyzed polyacrylamide (HPAM) mixture was investigated by coarse-grained molecular dynamics (CG MD) simulation. In the polymer-surfactant mixtures, a sphere-to-rod transition of aggregates was obtained with the increasing concentration of DTAB. The increase of HPAM hydrolysis degree can promote the morphological transition from spherical into rod-like aggregates. Our simulation revealed that the flexibility of HPAM chain and the electrostatic attraction between DTAB headgroups (N(CH3)3+) and HPAM carboxylate ions (COO−) exerted a crucial role in promoting the morphological transition of aggregates. These simulation results brought to light the molecular-level information of sphere-to-rod transitions in polymer-surfactant aggregates. This work is expected to trigger further studies on morphology transition of polymer-surfactant mixtures.