Dynamic and phase transition studies of ionic surfactant-stabilized oil/water microemulsion: Effects of volume fraction, polymer grafting, and temperature

Abstract

In this work, we study the dynamic/phase transition relationship of a system composed of spherical particles of oil/water microemulsion, stabilised by an ionic surfactant based on cetylpyridinium chloride (CpCl) and an octanol-based cosurfactant, and dispersed in salt water. We examine a large range of volume fractions Φ. To do this, we use molecular dynamics simulations with an appropriate interaction potential that accounts for Van der Waals and electrostatic interactions. We also graft different numbers of dodecyl-(polyethylene oxide)227-dodecyltriblock copolymers onto the microemulsion nanodroplets, which we denote (n(D−PEO227−D)), where n varies from 0 to 12. Specifically, we treat the dynamic properties, using the mean square displacement (MSD) and diffusion coefficients, and then use Arrhenius law to determine the activation energy. In our study, we vary three main parameters: the volume fraction, the number of polymer added to the n(D−PEO227−D) microemulsion, and the temperature. The result shows a transition from the sol to the gel state of the bare microemulsion as the volume fraction increases or as the temperature decreases. Also, it proves that when a D-PEO-D polymer is added to the microemulsion, the system rapidly changes its state either as the volume fraction Φ increases or as the temperature T decreases. We also calculate the activation energy of the bare particles in the microemulsion at different volume fractions (ϕ) using the Arrhenius equation.