Sedimentation and diffusion coefficients in polymer solutions and gels

Abstract

Recently Lamm’s differential equation, which frequently was applied in ultracentrifugal sedimentation experiments of polymer solutions, was extended to cross-linked swollen polymers. If a polymer solution is chemically cross-linked to a swollen polymer network (gel), the transport of a solvent in a gel in a centrifugal field consists of velocities due to sedimentation, diffusion and deformation. It was shown that the elastically active coefficient describing the deformation velocity has the same units as the diffusion coefficient. The sum of both coefficients in a gel is proportional to the mobility of the polymer and the thermodynamic factor. The latter can be found in the literature in papers of G. Rehage and coworkers. As diffusion coefficients are also known for some systems, the sedimentation coefficients for solutions and gels can be calculated and compared at the same concentrations and temperatures. The transport coefficients in thermodynamically good and bad solvents are discussed.