Analysis of stress-induced phase separations in polymer solutions

Abstract

The free energy of polymer solutions must depend upon the conformation of the macromolecules, and hence upon the deformation state imposed on the system, as well as upon the more familiar thermodynamic state variables of temperature and composition. As one consequence of the importance of this additional thermodynamic state variable, the precipitation temperature (cloud point) of polymer solutions may be increased by several tens of degrees Centigrade by imposition of steady shearing at low deformation rates. As a second consequence, the precipitated phase is sometimes found to be a solid of new morphology, and one which is quite refractory to re-solution. In this work a quantitative theoretical analysis of solubility phenomena in deforming solutions is given. The free energy of macromolecules in stagnant solutions is obtained from the Flory-Huggins theory, and changes with deformation state are computed from Marrucci's analysis for dilute solutions of elastic dumbbells. The parameters in the theoretical analysis were evaluated, using solutions of polystyrene in dioctyl phthalate, by measurements of the thermodynamic interaction parameter and of the rheological properties. The theory, which contains no adjustable parameters, was used to make a priori predictions of the change in cloud point with deformation state. The experimentally observed changes, of 3-28 °C, were predicted with a mean deviation of about 3 °C.

Rheo-Optical Evidence of a Flow-Induced Isotropic−Nematic Transition in a Thermotropic Liquid-Crystalline Polymer

“…Experimental evidence has shown that application of shearing promotes phase separation (i.e., the shear-induced demixing effect). [3][4][5] Such experimental observations are predicted by theory. 6,7 On the contrary, other research workers have presented experimental evidence that homogenization (i.e., flow-induced mixing effect) is promoted when a two-phase mixture of polymers is subjected to a shear flow field.…”

“…This observation supports our view that the morphology of the specimen remained unchanged during the same period. After the total rest period of 80 min the specimen was subjected to oscillatory shear flow over a range of ω, and the results are also plotted in Figure 16 (4). For comparison, plots of log G′ and log G′′ at 192°C in the isotropic state are also included in Figure 16 (O).…”

Small-angle neutron scattering study of shear-induced phase separation in aqueous poly(N-isopropylacrylamide) solutions

“…It is well known that shear flow can influence the phase separation of polymer solutions [1]. Several techniques have been employed to study the influence of shear on demixing of solutions of linear-chain polystyrene (PS) in dioctyl phthalate (DOP) including turbidity, dichroism, small-angle light scattering (SALS) and small-angle neutron scattering (SANS) [2][3][4].…”

Flow-induced conformational changes and phase behavior of aqueous poly-L-lysine solutions

“…Theoretical and experimental studies of such structuring include studies of concentration complexation is believed to involve secondary interactions between dissimilar macromolecules that fluctuations, liquid-liquid demixing, gelation, and complexation or network formation under flow. [1][2][3][4] have the ability to form intermacromolecular interactions. [5][6][7] To date, only qualitative explanations of In most cases, these phenomena have been documented for shearing flows wherein the rheological flow-induced gelation have been offered, and the effect of flow on such macromolecular interactions ethylene glycol (15% in H 2 O) destabilizes the bsheet, as it is a better solvent than water for the is not well understood.…”