Using a Stochastic Kinetic Theory to quantify the fluctuations and correlations in charged systems

The behavior of systems containing multiple charged species in high concentrations is affected by correlations arising from the long-ranged electrostatic interactions, other short-ranged interactions (such as excluded volume), and fluctuations. This is important for systems that include colloidal suspensions, electrolytes, polymers, and proteins, where the interactions alter phenomena such as precipitation, phase separation, or coacervation. The high concentrations motivate using a field-based approach but traditional models of electrostatic interactions (e.g. Debye Huckel) work best when at least one of the objects in the system is dilute and may not accurately capture ion-ion correlations or fluctuations. The task of simulating such systems can become more difficult when flow is involved, which can alter structure formation. We present the results of applying a stochastic kinetic theory approach which is inherently applicable to non-equilibrium situations and can capture fluctuations and correlations in the system. It is a coarse-grained field-based approach where the particles and ions are described using number-density equations. The results show how underscreening in concentrated systems and the effect of excluded volume due to the finite size of the particles affect correlations and structure formation.