Stored elasticity in flowing solutions of polyisobutylene as measured by recoil

Recoil measurements in capillary flow are performed with solutions of polyisobutylene in toluene and used to calculate a shear modulus G. The shear rate dependence of G is explained in terms of a stiffening function and a network destruction function, the first contribution dominating in the measured range. Good agreement is found for recoil in both the capillary and in a rotational viscometer.