Molecular dynamics study of the aggregation rate for zwitterionic dodecyldimethylamine oxide and cationic dodecyltrimethylammonium chloride micelles

Abstract

We studied dynamic scaling law for the early stage domain growth in the micelle aggregation process of dispersed surfactant molecules in water for zwitterionic dodecyldimethylamine oxide (DDAO) and cationic dodecyltrimethylammonium chloride (DTAC) based on all-atomistic molecular dynamics calculations. For both surfactants, the aggregation number N increases in proportion to t^α′, where t and α′ are the simulation time and exponent of the dynamic scaling, respectively. When the aggregation is controlled by diffusion, it follows the well-known Lifshitz–Slyozov (LS) law giving the exponent α′ = 1. The values of α′ obtained for DDAO and DTAC are 0.6 and 0.3, respectively, indicating that the aggregation rate is suppressed compared with purely diffusion controlled LS process. The aggregation of DDAO and DTAC may be partly controlled by electrostatic interaction between the aggregates.