Diffusion in concentrated polystyrene solutions

Abstract

SynopsisThe wedge interferometer technique was used to measure the diffusion coefficients for concentrated solutions of polystyrene. A wide range of molecular weights, all monodisperse except for one, and 14 solvents were studied. Reproducibility of the data was demonstrated in the concentrated region, and good agreement with the sparse literature was observed. The experimental results are discussed and analyzed in terms of current knowledge and theories. In the concentrated region, the solvent type plays a significant role in determining the diffusion coefficient. Its effect cannot be explained simply in terms of hydrodynamics nor the molecular structure of the solvent. In cyclohexanone the diffusion coefficient was found to increase with polymer molecular weight up to 100,000 and to become independent thereafter.

Diffusion in infinitely dilute polystyrene solutions

“…We have conducted diffusion experiments on the polystyrene-1,2,4-trichlorobenzene system and have obtained values of the diffusivity which are approximately one half of those reported by Paul et al 4 These experimental data are still open to question since we have no guarantee that we have eliminated mixing effects. Clearly, the wedge interferometer experiment is sensitive to the initial mixing which takes place a t the start of an experiment.…”

“…This inconsistency is presumably a consequence of the approximate nature of the model, namely, treating segments as point sources of friction. Paul et al 4 presented diffusivity data for polymer solutions which, as is evident below, cannot reasonably be explained within the framework of the Kirkwood-Riseman theory.…”

“…However, since this theory is based on an approximate model of polymer transport and since an a priori value of the draining parameter can not be assigned, experimental confirmation of the validity of the theory is required. Experimental verification of the Kirkwood-Riseman expression for the translational diffusion coefficient is of particular interest in light of the theoretical study of Zwanzig et al3 and the recent experimental investigation of Paul et al 4 Zwanzig et aL3 discovered singularities in the solution of the equations in the Kirkwood-Riseman scheme which lead to negative translational diffusion coefficients. This inconsistency is presumably a consequence of the approximate nature of the model, namely, treating segments as point sources of friction.…”

Cyclohexanone/1,2‐dichloroethane as eluents in GPC of polymers

“…Thus i t can be expected t h a t differences in concentration dependence of diffusion coefficient L ) will be determined by the hydrodynamic term k, being a function of solvent viscosity:D = Do[1 + (211,Mk,) c],where k,ycoefficient characterizing frictioning behaviour of solute, U , Dodiffusion coefficients, A, -second virial coefficient, Mmolecular mass of polymer, cpolymer concentration in the solvent.In CHXN, for example, the hydrodynamic term k,for not very high molecular weights of PS ( M < 1.8 x lo5) exceeds the thermodynamic term 2A2M and, therefore, diffusion coefficient D decreases with the increase of c[32]. Thus i t can be expected t h a t differences in concentration dependence of diffusion coefficient L ) will be determined by the hydrodynamic term k, being a function of solvent viscosity:D = Do[1 + (211,Mk,) c],where k,ycoefficient characterizing frictioning behaviour of solute, U , Dodiffusion coefficients, A, -second virial coefficient, Mmolecular mass of polymer, cpolymer concentration in the solvent.In CHXN, for example, the hydrodynamic term k,for not very high molecular weights of PS ( M < 1.8 x lo5) exceeds the thermodynamic term 2A2M and, therefore, diffusion coefficient D decreases with the increase of c[32].…”