Application of supercritical fluid solvents to new technologies: Development of a high-pressure surface plasmon resonance spectroscopy sensor to monitor polymer adsorption

The importance of solvent quality and polymer structure on polymer-supercritical fluid (SCF) solution behavior for multiple industrially relevant systems is studied with phase behavior measurements. These measurements provide a macroscopic description and qualitative understanding of the chemistry and physics that control the location and the shape of the phase boundaries. For a more detailed microscopic description of the polymer-SCF behavior, a high-pressure surface plasmon resonance spectroscopy (SPR) technique has been developed. This novel adaptation of an optical technique has been used in a thorough study of solvent refractive indices as a function of pressure, and also has been used for preliminary studies of polymer adsorption from an SCF environment. The adsorption experiments lay the framework for developing an understanding as to the driving forces and physicochemical constraints of polymer adsorption by using tunable SCF solvents.; Phase behavior data are presented for fluorinated polymers and copolymers containing tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene in supercritical CO₂ and halogenated solvents. Data are also presented for a polyester resin in supercritical dimethyl ether, chlorodifluoromethane, and CO₂ with several cosolvents, and for poly(lactide-co-glycolide) copolymers of varying composition in supercritical CO₂and halogenated solvents. CO₂ is a weak solvent that can not dissolve nonpolar polymers without extreme temperature and pressure, and that has temperature sensitive energetic mismatches with polar polymers. However, CO₂ does exhibit specific interactions with fluoropolymers enabling solubility at moderate pressures and temperatures. Polymer solubility can be increased by the introduction of a liquid or SCF cosolvent to tune the energetics of the system. Halogenated solvents are also used with polar polymers as a comparison to CO₂ and to elucidate the role of the solvent in the phase behavior.; SPR studies are performed with multiple experimental designs, each being critically analyzed for drawbacks and sources of error. The optimal design based on a retroreflector is used for measuring the refractive indices and dispersion curves of several liquid and compressed gas solvents up to 15,000 psia. A correction is required to account for the stress-induced changes in the optical properties of the SPR sensor itself. The incorporation of this correction leads to an extremely favorable comparison to refractive index literature data for several of the solvents. The SPR retroreflector technique is also used to probe polymer adsorption. Experiments were performed with carboxyl-terminated-polystyrene, polyvinyl acetate (PVAc) and Fluorel (poly(vinylidene fluoride-co-22 mol% hexafluoropropylene)) in acetone at ambient conditions. The magnitude of the time scales for the experiments are found to be very large (∼7 days). The sensitivity of the experimental technique is enhanced by a large difference between the solvent's and the polymer's refractive index. The Fluorel/acetone system is also studied at 5,000 psia. The application of the hydrostatic pressure to the system does not change the final adsorbed amount but has a significant effect on, the rate of adsorption due to pressure-induced changes in the adsorption mechanism itself.