Modeling transport processes in polymers: Application of free-volume concepts and numerical solution techniques

This thesis addresses several problems involving the general area of transport in polymeric materials, the unifying theme of which is the application of free-volume concepts and numerical techniques. The problems covered in this thesis fall into two major categories. In the first category methods to correlate and predict diffusion and conduction processes are studied.; The applicability of free-volume concepts to describe diffusion below the glass transition temperature was studied. Two approaches based on free-volume concepts are discussed and their differences are elucidated using diffusivity data for styrene diffusing in polystyrene.; The development of a new approach which combines the free-volume concepts and unique transport characteristics of ionic systems to describe ion-conduction in polymeric is described. The model incorporates the unique features of ion transport and can not only correlate the molecular transport characteristics, but the correlating parameters have physical significance and are at least qualitatively consistent with the anticipated physical phenomena.; Finally, a method to predict diffusion of a solvent of unknown characteristics in a polymer when diffusion data for other solvents in the same polymer are available is considered by combining the activation energy and free-volume approaches.; In the next category, free-volume ideas are combined with continuum species equations to model transport processes in polymers. Heat effects in sorption, non-instantaneous boundary condition changes other effects that can cause errors in the determination of diffusion behavior are studied and approximate correction procedures are proposed. Results indicate that sigmoidal uptake curves at low solvent activities result from non-instantaneous boundary condition changes, while heat effects can give rise to sigmoidal uptake curves at high solvent activities.; Crystal formation in polymers in the presence of a solvent is studied. Crystal formation is described using a mobility term related to the nature of the polymer and the plasticizing ability of the solvent. A convection term arises on account of the volume change which accompanies phase change is incorporated. The model indicates that solvent overshoot is observed when the rate of crystal formation is slow compared to diffusion, while typical Fickian behavior is witnessed when crystal formation is fast compared to diffusion.