Interfacial Dynamics of Macromolecular Liquids

This thesis presents theoretical studies of two aspects of the interfacial dynamics of polymeric liquids: In the first study, a coupled two-fluid model for hydrodynamic surface modes on concentrated polymer solutions and polymer gels is presented. This model is used to investigate such surface modes in the limit of strong coupling. The surface mode dispersion relation omega(k) and the structure factor S(k,omega) of thermally induced surface fluctuations are derived in this limit for materials with a general constitutive relation eta(omega). I argue for the existence of several types of surface modes, including Rayleigh elastic waves, capillary waves, and overdamped modes resulting from viscous dissipation in the solvent as well as from polymer diffusion in the case of polymer solutions. The properties of surface modes are discussed separately for the cases of polymer gels and concentrated polymer solutions. Detailed predictions for the form of the normal modes omega(k), and the surface model structure factor S(k,omega ) are given and their dependence on relevant material properties are discussed in each case. Possible experimental scenarios are anticipated and discussed. Finally, I discuss some of the limitations of the model presented and future directions to be explored. In the second study, a mean field model of interface formation between two weakly incompatible polymer blends is used to investigate the time development of interfacial composition. The interface width as a function of time exhibits two power law growth regimes; a t^ {1over 2} growth law at early times crosses over to a t^{1over 4 } growth law before relaxing towards the equilibrium interfacial profile. The results of this model are compared critically to recent experimental data on interface formation kinetics for incompatible blends of protonated and deuterated polystyrenes. Finally, limitations of the model and suggested future directions for theoretical investigation are discussed.