One attractive feature of supercritical fluids is that their physical properties can vary significantly with just a small change in temperature or pressure relatively close to the critical point.   We utilize the unique properties of supercritical fluid in this laboratory to develop environmentally benign chemical processes and to produce nanomaterials. 

For example, supercritical carbon dioxide is being used to create self-assembled monolayers (SAMs) and polymeric films on various metal surfaces for corrosion resistance and electrochemical modifications.  This environmentally friendly solvent is also being used to make drug delivery devices by implanting various pharmaceuticals into biocompatible polymeric devices as well as chewing gum.  Various reactions and nanomaterial synthesis processes are also being explored in sub- and supercritical carbon dioxide in attempts to better understand these unique fluids. 

Dr. Weinstein has 10 different high pressure reaction vessels (3 mL up to 500 mL) for use with this work.  Six vessels have visual access through sapphire windows which allow for in situ spectroscopic measurements.  All vessels have methods for stirring and controlling temperature.  One vessel has a movable piston to allow for solubility measurements through cloud point observation.  Two hand pumps and 4 ISCO syringe pumps provide methods for pressurization of the vessels up to 7000 psi.  For chemical analysis in solution, Dr. Weinstein has a Cary 50 UV-Vis spectrophotometer, a Spectrasystem UV3000 HPLC system with autoinjector and UV detector, and a 6890 Agilient Technologies GC with FID and autoinjector with 100 sample tray.  He also frequently makes use of other analytical equipment on campus (TEM, SEM, NMR, etc.) which is not dedicated to this laboratory.

The critical point of a pure fluid marks the end of the vapor-liquid coexistence curve, as shown in the figure below. A pure fluid is considered supercritical when both its temperature and pressure are greater than those at the critical point. In the supercritical region, no matter how much pressure is applied, the fluid will not go through a phase transition as its density increases to a liquid-like state.