Dynamic Light Scattering Studies of Ternary Polymer Solutions in Porous Media

The tracer diffusion of probe polystyrene (PS) molecules in a matrix polymer solution confined in a porous medium has been studied by using dynamic light scattering (DLS). In these experiments, a sample of controlled pore glass was equilibrated with a ternary solution consisting of PS, polytetrahydrofuran (PTHF), and the common solvent 2-fluorotoluene (2FT); PTHF and 2FT are isorefractive with the porous glass. The PS concentration was held low, whereas the PTHF concentration cm exterior to the pore was systematically increased within the homogeneous regime. The tracer diffusion coefficient Dp of PS in the interior of the pore decreased more rapidly than did the tracer diffusion coefficient D_fin the exterior as c_m increased in the range below the overlap concentration c_m^*; this is ascribed to the enhanced polymer-polymer interactions in the narrow pore channels. However, D_p showed a weaker dependence on c_m than D_f as c_m exceeded c_m ^*. This result is ascribed to the smaller topological constraint exerted by PTHF macromolecules in the interior of the pore than in the exterior free solution because of the lower interior PTHF concentration. The short-time characteristics of the DLS autocorrelation function are also reported.