Retention ratio and thermal diffusion parameters such as thermal diffusion factor and coefficient for polystyrene in toluene are examined by using Thermal Field Flow Fractionation(T.F.F.F) method.
Retention ratio is reduced by increasing solute polystyrene molecular weight and channel temperature difference, and increased by increasing cold wall temperature and independent of solvent flow rate. These results are well interpreted by means of a theoretical calculation of the influence of both ordinary and thermal diffusions.
Thermal diffusion factor is obtained from experimental value of retention ratio. Like the Ham's theory, thermal diffusion factor shows a marked temperature dependence proportional to the inverse of mean temperature of the channel and a polymer molecular weight dependence proportional to $(M.W)^0.553$.
Using the equation for ordinary diffusion coefficient developed by Flory's method, thermal diffusion coefficient is calculated from the values of thermal diffusion factors.
Themal diffusion coefficient is increased with molecular weight below 240,000 but constant above it. It is independent of concentration of polymer sample.
Therefore, thermal diffusion coefficient cannot be responsible for the thermofractionation effect on polymers. On the other hand, ordinary diffusion coefficient, which is of pronounced dependence on the molecular weight, seems to be the governing factor for T.F.F.F.
