Thermodynamic Interactions and Phase Behavior of Multicomponent Blends Containing Supercritical Carbon Dioxide, Styrene-Acrylonitrile Random Copolymer, and Deuterated Poly(methyl methacrylate)

Small-angle neutron scattering (SANS) was used to probe the phase behavior of multicomponent mixtures of supercritical carbon dioxide (scCO(2)), styreneacrylonitrile random copolymer, and deuterated poly(methyl methacrylate). Ternary mixtures were homogeneous at low carbon dioxide pressures (PCO2) but phase separated as PCO2 was increased at constant temperature (T). Phase separation pressure was found to be a nonmonotonic function of T with a minimum at T = 60 degrees C. An expression based on the multicomponent random phase approximation was used to determine the interaction parameters between polymer and scCO(2) from a combination of SANS experiments on homogeneous ternary mixtures and measurements of scCO(2) uptake by the neat polymers. Interaction parameters that underlie the nonmonotonic phase behavior described above collapse onto a straight line when plotted as a function of scCO(2) density.