Badiger, M., Wolf, B. A.
"Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly(N-isopropyl acrylamide)"
Macromolecular Chemistry and Physics 2003, 204,600-606.
Abstract: The interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight (MW = 1 600 kg/mol) poly(N-isopropyl acrylamide) was investigated. The system demixes upon heating and the cloud point temperature, Tcp decrease steadily with rising polymer concentration up to 10 wt-%. The application of shear supports phase separation and reduces Tcp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, h at higher polymer concentrations are closely connected with the thermodynamic conditions. [h] decreases by almost two orders of magnitude upon heating, whereas the corresponding increase of kH is less pronounced. The h values (constant shear rate) of the moderately concentrated solutions as function of T pass a maximum at the corresponding phase separation temperatures. The existence of clusters also manifests in terms of stress overshoot and of particularities observed with solutions that are sheared for the first time.
preprint number: 240