The sedimentation velocity of a gelled polymer

Analytical Ultracentrifuge Technologies for the Characterization of Biopolymer Gels and Microgels

“…it was stated that the maximum gel sedimentation rate alone is not sufficient to completely characterize the sedimentation of the gel as no relationship between this sedimentation rate and the induction period could be found. If the movement of the centre of mass is taken to calculate the sedimentation coefficient of the gel (Borchard and Hinsken, 1997). no induction period is observed anymore which shows that the definition of the gel sedimentation coefficient of the gel via the movement of the centre of mass is more correct.…”

“…a sedimentation velocity experiment can be performed in analogy to a sedimentation velocity run with a polymer solution. In this case the movement of the boundary gel/sol towards the cell bottom can be measured as a function of time although recently it has been pointed out that the movement of the centre of mass has to be considered rather than that of the meniscus gel/sol (Steensgard et at., 1992;Borchard and Hinsken. 1997;Hinsken, 1998).…”

“…Nowadays, it is known that the movement ofthece1l1re of mass has to be considered (Borchard and Hinsken, 1997). Nevertheless Johnson used this plot to define the 1.18,--------------------------------------, conditions under which the gel interface behaves like a solution boundary.…”

“…The independence of the sedimentation coefficient from the presence of a water layer on top of the gel column had already demonstrated that the total hydrostatic pressure has a negligible influence on the sedimentation behaviour of the gel, as was also shown theoretically later . However, the observed dependence of the sedimentation coefficient of the gel on the column length indicates an error in the definition of gel sedimentation as the sedimentation of a gel has to be treated as a movement of its centre of mass rather than a movement of the meniscus gelJsol (Borchard and Hinsken, 1997). Therefore, all results based on the effective sedimentation coefficient from the movement of the meniscus gelJsol have to be treated with care, especially as the reported gel sedimentation coefficients are generally of the same order of magnitude of soluble polymers and not a factor of 10 lower, which has been found recently (Borchard and Hinsken, 1997).…”

“…The sedimentation velocity of a gel was subject of a recent paper by Borchard and Hinsken (1997). In contrast to the treatment so far that the movement of the meniscus gel/sol must be used for the calculation of the sedimentation coefficient, they could show that the movement of the center of mass has to be considered.…”