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.

Keywords:

• Micelle formation
• Lifshitz–Slyozov law
• zwitterionic DDAO
• cationic DTAC
• molecular dynamics calculation

Acknowledgments

This work was supported by the FLAGSHIP2020, MEXT within priority study 5 (Development of new fundamental technologies for high-efficiency energy creation, conversion/storage and use), using computational resources of the K computer provided by the RIKEN Advanced Institute for Computational Science through the HPCI System Research project [grant number hp160225] and MEXT KAKENHI [grant number 26410012(N.Y.)]. Calculations were mainly performed at the Research Centre for Computational Science, Okazaki, Japan, partially at the Information Technology Centre of Nagoya University, and partially at the Institute for Solid State Physics, the University of Tokyo.