Entropy of Activation of Viscous Flow in Dilute Solutions of High Polymers

Abstract

IT has been previously shown1,2 that the entropy of activation of viscous flow, ΔS, of dilute solutions of flexible chain high polymers decreases with increasing concentration c and molecular weight M of the polymer. In contrast, ΔS for dilute solutions of cellulose derivatives, the chains of which are stiffer and more extended in solution3, generally increases with increase of c and M (refs. 1, 2 and 4). An interpretation in terms of positive and negative contributions to ΔS was tentatively advanced2. The positive contribution was assumed to be proportional to Q/T, where Q is the apparent activation energy of viscous flow of the solution and T the absolute temperature. The negative contribution was assumed to be not primarily dependent on Q and to result from synchronization between movements necessary for a successful unit act of flow5. The effects of variation in c and M on Q are relatively small for dilute solutions of flexible chain high polymers and it was suggested that the negative contribution was the greater. The marked increases in Q with increase of C or M, observed with dilute solutions of cellulose derivatives, led to the suggestion that in such cases increases in the positive contribution outweighed any increases in the negative one.