| The static and dynamic behavior of polyelectrolyte solutions was studied by using various computer simulations and theories of a simple bead-spring model. Polymer chains were modeled as flexible bead-spring chains composed of uniformly charged monomers, and small ions like counterions and co-ions as charged spheres of the same size as the monomers of the polymer chains. Although the primitive model ignored all the chemical details, most polyelectrolyte properties such as the liquid-like ordering of the solution structure, the enhanced collective diffusion, and the abnormal osmotic behavior were captured in the model, which implies that the chain connectivity and the long-range electrostatic interaction are mainly responsible for those interesting properties. Using the simple but essential nature of the bead-spring model we were able to analyze (and sometimes predict) experiments and to test theories with meaningful statistics. Examples include the effect of the counterion valence on polyelectrolyte properties such as polymer size and diffusion, the behavior of the osmotic pressure, the properties of polyelectrolyte adsorption on charged surfaces, and the effect of the hydrophobic interaction on conformation and dynamics.; Fluid diffusion in disordered media was also investigated with the same level of the molecular model used in the study of polyelectrolyte solutions. In this work, unlike previous simulation studies for the random walk of a single particle at infinitely dilute concentration, the effects of fluid and medium concentrations, medium structure, and particle size on translational and rotational diffusions were examined in a systematic way. Some interesting properties including the slowdown of the rotation diffusion and the strong molecular weight dependence of the translational diffusion were also found. Since conventional theories for fluids without disordered media were not appropriate to predict the fluid behavior in disordered media, we hope that this simulation will serve as a guide for the development of new theoretical attempts. |
