Compressive elasticity in polymer Couette flow

Abstract

Accepted models of polymers in flow assume that the polymer chains stretch with the elastic energy stored as a reduced entropy of the chain. The first optical measurement of changes in the Polydiacetylene 4- Butoxycarbonylmethylurethane (4-BCMU) polymer Kuhn segment lengths in Couette flow are reported. This polymer in semi-dilute solution shows a reducing conjugated segment length with increasing flow rate. The visco-elasticity for this polymer is attributed to compressive entropy loss in the chain. This is a reversal of the physics assumed in models of polymer flow based on the Kühn model. The restricted volume of the chain due to the presence of the neighbouring polymers results in compre..