TRANSIENT-BEHAVIOR OF ASSOCIATING COPOLYMERS IN A SHEAR-FLOW

The transient response of associative copolymer solutions during step shear rate experiments has been characterized. Upon cessation of flow, the stress relaxation modulus is found to decrease faster as the shea r rate increases. Upon start up of the flow, beyond a critical value o f the shear rate, one or several stress overshoots are observed, depen ding on the shear rate value. One of them corresponds to the stress ov ershoot characteristic of entangled polymer systems while the other on es are specific to the presence of hydrophobic units. The critical she ar rate and the accumulated strain position that characterize the appe arance of the overshoots can be most easily explained if the solution is viewed as a loosely connected transient network. Finally, aging phe nomena are also described and are tentatively ascribed to a trend to p hase separation.