Study of Complex Fluids via Mesoscopic Simulation
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)Abstract
Dissipative particle dynamics (DPD) simulation method was developed to accomplish the task of reaching larger lengths and longer time scales than atomistic molecular dynamics simulations (MD) resulting in a mesoscopic description of the system. This approach has been successfully applied to study a wide variety of complex fluids including polymeric solutions, colloidal suspensions, surfactants and biological membranes where different lengths and time scales are involved. For all these systems the electrostatic interactions play a key role in understanding phenomena that do not occur in uncharged systems. Therefore, the inclusion of these interactions in DPD simulations is essential to capture phenomena at mesoscopic level such as formation of polyelectrolite-surfactant aggregates, charge stabilization, colloidal suspension and the formation of complexes driven by charged species in biological systems.
In this work, the electrostatic interactions in dissipative particle dynamics (DPD) simulations are calculated using the standard Ewald sum method. With this method we reproduce the experimental results of a polyelectrolite in a salt solution as a function of pH and degree of ionization of the chain; the radius of gyration increases with the net charge of the polymer in agreement with the experimental trend found in static light scattering experiments of polysterene sulfonate solutions.
Additionally, we simulated an amphoteric biological polyelectrolite, that acquires a positive or negative charge, depending on the pH of the solution. In this case the radius of gyration increases or decreases depending on the net charge in the polymeric chain. Our results reproduce the experimental trend.
Finally, we study the scaling properties of the radius of gyration of a polyelectrolyte as a function of its chain length at a fixed pH and ionic strength.