Thermodynamics of polymer solutions under flow: Phase separation and polymer degradation

Abstract

The influence of flow on the free energy of polymer solutions is examined from several points of view both on macroscopic and microscopic bases. Application of non-equilibrium chemical potential to the phenomena of flow-induced phase separation and thermodynamically induced polymer degradation is reviewed. Polymer degradation under elongational flow was extensively covered in a recent review in this series. The thermodynamic theory is compared with the dynamical approaches used in the analysis of stability of solutions and it is seen under which conditions the criteria defining the spinodal line under shear (i.e. the limit of the stability region) are the same in both approaches. The thermodynamic analysis may be useful due to its greater simplicity though, in contrast, the details of the phase segregation or homogenisation and the analysis of the dynamical aspects (viscosity, light scattering) are beyond the reach of a strictly thermodynamic method. A short summary of the phenomenology of flow-induced changes in the phase diagram of polymer solutions under flow is given. Perspectives and open problems are pointed out.