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Effect of hydrostatic pressure on closed-loop phase behavior of block copolymers
Du Yeol Ryu1, Dong Jun Lee, Jin Kon Kim
1Department of Chemical Engineering and Polymer Research Institute, Electronic and Computer Engineering Divisions, Pohang University of Science and Technology, Kyungbuk 790-784, Korea.
Abstract:
The effect of hydrostatic pressure (P) on closed-loop phase behavior of deuterated polystyrene-block-poly(n-pentyl methacrylate) copolymers [dPS-PnPMA] was investigated by using small-angle neutron scattering and birefringence. For P<20.7 bar, dPS-PnPMA exhibited a lower disorder-to-order transition temperature (T(LDOT)) at 175 degrees C, and then an upper order-to-disorder transition temperature (T(UODT)) at 255 degrees C. With increasing pressure both T(LDOT) and T(UODT) were markedly changed, where dT(LDOT)/dP was 725 degrees C/kbar and dT(UODT)/dP was -725 degrees C/kbar. These are consistent with predictions by the Clausius-Clapeyron equation using measured values of the volume and enthalpy changes of both transitions. The large pressure coefficients imply that the closed-loop phase behavior observed for PS-PnPMA is an entropic-driven phase transition.