摘要：

A consideration of the motion of a particle in an ultracentrifuge from the Langevin equation shows that the concentration dependence of sedimentation should involve only the concentration dependence of the frictional coefficient. The coefficient K appearing in the expansion of the frictional coefficient, F = F 0(1 + KC + … +) has been evaluated from sedimentation data in the case of four fractions of polystyrene in methyl ethyl ketone, toluene, and chloroform. K was found to be proportional to the square root of the molecular weight over the range investigated in the three solvents mentioned. More fundamentally, K was found to be proportional to the average molecular extension in a manner nearly independent of solvent. A parallelism noted for our fractions between K and the intrinsic viscosity is discussed. The relationship between the concentration dependence of diffusion and K is briefly treated. The molecular weight region for polystyrene in methyl ethyl ketone in which the concentration dependence of diffusion should change from positive to negative is predicted.

展开