Thermodynamic slowing down of mutual diffusion in isotopic polymer mixtures (original) (raw)

The mutual diffusion coefficient, D(9), determined at finite blend compositions, 9, in blends of normal (hydrogenated) and deuteriated polystyrene was found to be highly dependent on composition. D (9) experiences a minimum, or "thermodynamic slowing down", in the vicinity of the critical composition, 9'c. This effect increases with decreasing temperature. This result is consistent with recent small-angle neutron-scattering measurements which indicate that this system exhibits an upper critical solution temperature. The temperature dependence of the Flory interaction parameter, x, was extracted from the data by using a mean field prediction for the compositional dependence of D. We found that x = 0.22(&0.06)/T-3.2(*1.2) x 10-4. 5, 519. There is a second prediction for D(Q) (Brochard, F.; Jouffory, J.; Levinston, P. Macromolecules 1984, 17, 2925) which differs from eq 3 such that Q (Q) = 2O(1-3)[(1-O)/ DD*ND + O./DH*NJ1. Since we have chosen N H = N D , both predictions for D(O) yield essentially the same result.

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