Simulation of scattering properties of gels

Brownian dynamics simulations of a simple model of a polymer gel were perfo rmed to investigate the conditions under which gels show nonergodicity, the presence of frozen density fluctuations which do not relax completely, and to explore possible connections between nonergodicity and the existence of density fluctuations of large spatial extent which are observed in many re al gels. The gel was modeled by a random two-dimensional network of springs , formed by bond dilution of a regular triangular lattice. Scatterers locat ed at the nodes of the network moved in Brownian motion. Average scattered intensities and time correlation functions of the intensities were calculat ed for different gel connectivities and spring constants. These well-define d model systems exhibited both large-scale inhomogeneities and nonergodicit y, but no unambiguous connection between the two was found. Nevertheless, i n some cases scattering behavior very similar to that of real gels was obse rved.