title: Effect of hydrostatic pressure on closed-loop phase behavior of block copolymers.
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.
authors.affiliation: Department of Chemical Engineering and Polymer Research Institute, Electronic and Computer Engineering Divisions, Pohang University of Science and Technology, Kyungbuk 790-784, Korea.
authors.forename: Du Yeol
authors.initials: DY
authors.lastname: Ryu
authors.forename: Dong Jun
authors.initials: DJ
authors.lastname: Lee
authors.forename: Jin Kon
authors.initials: JK
authors.lastname: Kim
authors.forename: Kristopher A
authors.initials: KA
authors.lastname: Lavery
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Russell
authors.forename: Young Soo
authors.initials: YS
authors.lastname: Han
authors.forename: Baek Seok
authors.initials: BS
authors.lastname: Seong
authors.forename: Chang Hee
authors.initials: CH
authors.lastname: Lee
authors.forename: P
authors.initials: P
authors.lastname: Thiyagarajan