(382a) Aggregation, Gelation, and Glass Formation in Nanoparticle Dispersions with Adhesive Interactions

Colloidal dispersions exist in nearly every area of our daily lives from the paint applied to protect our homes to toothpaste. Hence, understanding the delicate interplay between the interparticle forces and structural states and phases is an important challenge to industry and scientists alike. Interestingly enough, experiments and simulations of model colloidal systems have shown that colloids can behave as ?big atoms?. That is, colloidal systems can exist in various distinct states analogous to molecular systems such as an isolated gas or condensed liquid. Additionally, these systems can exhibit a wide range of equilibrium phases and non-equilibrium states [gels, attractive driven glasses (ADGs), repulsive driven glasses (RDGs), etc.] and coexistence regions [gas-liquid, liquid-crystal, etc.]. In this work we use a well characterized simple system (particle radius, a ~ 15 nm) in which we control a short-range attraction via temperature to study the fluid-gel phase transition. We define gelation as the point when particles first percolate through the system to form a continuous network which is in a state of dynamical arrest. We use a combination of small-amplitude oscillatory rheology and fiber optic quasi-elastic light scattering (FOQELS) to characterize the temperature at which dynamical arrest occurs for a given dispersion. We then use small-angle neutron scattering (SANS) to probe the nanostructure of the dispersion at and around the gel temperature. Analysis of the SANS scattering profiles provides an accurate method to extract the interparticle potential at the gel point. The experimental results demonstrate a connection between the gel and ADG lines defining the onset of dynamical arrest. Furthermore, the results show that the gel line intersects the liquid-vapor coexistence region at concentrations below the critical point. Monte Carlo (MC) simulations of the equilibrium structure using the experimentally determined interparticle potential allows for a direct visualization of the structure and a detailed numerical study of dynamic arrest.