NOTES ON THE FORMULATION OF CONCENTRATION FLUCTUATION IN MODERATELY CONCENTRATED POLYMER-SOLUTIONS

The dynamic structure factor of moderately concentrated polymer soluti ons is often multimodal, roughly consisting of fast and slow modes. Wa ng's formulation of concentration fluctuations predicts that the slow mode disappears when the polymer and solvent components have identical partial specific volumes, but the prediction is not supported by the formulation of Onuki (J. Non-crystalline Solids, 1994, 172-174, 1151) and that of Doi and Onuki as well (J. Phys. II (Paris), 1992, 2, 1631) . The present paper shows that the primary origin of the disagreement is the difference in the basic equations of the two theories, in contr ast to the prevailing notion that attributes it to the different const itutive equations assumed by the two theories for the partial stresses generated by concentration fluctuation. (C) 1998 Elsevier Science Ltd . All rights reserved.