Electrostatic interactions in dissipative particle dynamics—simulation of polyelectrolytes and anionic surfactants

Electrostatic interactions have been incorporated in dissipative particle dynamics (DPD) simulation. The electrostatic field is solved locally on a grid. Within this formalism, local inhomogeneities in the electrostatic permittivity can be treated without any problem. Key issues like the screening of the potential near a charged surface and the Stillinger–Lovett moment conditions are satisfied. This implies that the method captures the essential features of electrostatic interaction. For the direct simulation of mixed surfactants near oil–water interfaces, or for the simulation of Coulombic polymer–surfactant interactions, this method has all the advantages of DPD over full atomistic molecular dynamics (MD). DPD has proven to be faster than MD by many orders of magnitude, depending on the precise scaling factor chosen for the simulation. This brings phenomena of microseconds in reach of routine simulation, while maintaining a fairly accurate representation of the structure of the molecules. As an example of this simulation tool, the interaction between a cationic polyelectrolyte and anionic surfactant is discussed. Without a surfactant, the polyelectrolyte shows a fractal dimensionality that is in line with the theoretical and experimental values cited in literature, it behaves as a fairly stiff rod, $df∼1.1.$ When salt is replaced by anionic surfactant, the polymer wraps around one or more discrete surfactant micelles, in line with the current understanding of these systems, and scaling invariance in the correlation function is broken.