| Knowing the rate at which chemicals migrate in various media, such as polymers, leads to novel consumer products and provides the information necessary to design more environmentally safe processes. Time-controlled release patches used to treat heart disease, for example, were tailored by studying how nitroglycerine diffuses in polymers. Although acquiring data directly is extremely important, complementary theoretical studies are essential so that transport rates in the many possible polymer/solvent combinations can be predicted a priori.; Free-volume (FV) diffusion models are most likely to attain predictive status in the future since most of the parameters can already be estimated from pure component properties. In this work, attention is focused on a particular FV diffusion model, developed by Vrentas and Duda, in the hopes of rendering the model completely predictive. To achieve this goal several studies were conducted: (1) solvent free-volume parameters are shown to be obtainable from both low temperature viscosity studies as well as variable temperature {dollar}sp{lcub}13{rcub}{dollar}C NMR T{dollar}sb1{dollar} relaxation measurements, (2) a correlation is proposed for estimating the polymer unit involved in a diffusive jump, (3) the importance of the energy required to overcome local attractive forces is quantified, and (4) experimentally obtained diffusion coefficients as well as equilibrium solubilities are provided for organic solvents in both linear low density polyethylene (LLDPE) and poly(ethylene-co-propylene) (EPR). Besides these main studies, the Vrentas/Duda FV diffusion model is extended to describe diffusion in homogeneous solvent/block copolymer systems. |
