The sedimentation velocity of a gelled polymer

Abstract

In a centrifugal field a gel is a continuous system with a radial concentration gradient due to the volume force of the field and diffusion. In contrary to the known definition of the sedimentation coefficient of a gel where the movement of the gel meniscus is related to the driving force, the velocity of the center of mass of the polymer with respect to its acceleration has been introduced using irreversible thermodynamics. It is shown that there will be no induction period of this velocity although the meniscus does not move. From extrapolation to times where the selected rotor speed had just been reached, the sedimentation coefficient of the polymer of a κ-carrageenan/water gel could be determined. In addition to the sedimentation coefficient, the phenomenological and the diffusion coefficients were also calculated from the data. Differences between the sedimentation of a sol and a gel are pointed out and discussed.