Quantitative analysis of small angle neutron scattering (SANS) data from homogeneous multicomponent mixtures of supercritical carbon dioxide (scCO 2) and two polymers is presented for the first time. The two polymers used in this study were styrene-acrylonitrile copolymer (SAN) and deuterated poly(methyl methacrylate) (dPMMA). Model polymers were used to facilitate comparisons between theory and experiment. The random phase approximation (RPA) was used to derive a simple expression to describe SANS profiles. The scCO 2-free binary blend was studied to determine the temperature dependence of the polymer-polymer interaction parameter. scCO 2-polymer solubility data was used to relate polymer-solvent interaction parameters. Comparisons between SANS profiles from multicomponent mixtures and the RPA expression provided an estimate of the interaction parameter between scCO2 and PMMA, χ13. The addition of scCO2 at a modest pressure results in a decrease of phase separation temperature Ts by 127 K. The analysis indicates that the change in Ts is caused by an increase in χ13 with increasing scCO2 pressure. © 2013 American Chemical Society.

Small-angle neutron scattering (SANS) was used to probe the phase behavior of multicomponent mixtures of supercritical carbon dioxide (scCO2), styrene-acrylonitrile 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 °C. An expression based on the multicomponent random phase approximation was used to determine the interaction parameters between polymer and scCO2 from a combination of SANS experiments on homogeneous ternary mixtures and measurements of scCO2 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 scCO2 density.