THERMAL-DIFFUSION OF DILUTE POLYMER-SOLUTIONS

In this paper diffusion of a dilute solution of elastic dumbbell model macromolecules under nonisothermal conditions is studied. Using the c enter of mass definition for the local polymer concentration, the diff usive flux contains a thermal diffusion dyadic d(T). To get some idea of thermal diffusion d(T) is evaluated for steady state isothermal con ditions. Explicit results are presented for some homogeneous flows. It is shown that if the polymeric number density is defined via the bead s (of the dumbbell) - termed n(b) - then the diffusive flux j contains partial derivative/partial derivative r . tau(c), where tau(c) is the intramolecular contribution to the bulk stress. Though the form of th e diffusion equation for nh thus differs from the corresponding one fo r n, it is shown that for essentially unbounded systems differences be tween n and nb are small. Since the results involve the translational diffusion coefficient they can readily be taken over for Rouse coils.