This paper presents the gelation results of a variety of organic fluids and supercritical carbon dioxide with 12-hydroxy stearic acid (HSA). At low concentration (0.75 wt%), HSA caused thermoreversible gelation of a variety of organic fluids such as aliphatic, alicyclic, aromatic hydrocarbon liquids, chlorinated fluids, and mixture such as Soltrol-130.
As low as 0.75 wt% of HSA also gelled high pressure solutions of dense CO2 and the selected organic fluids such as alcohols and chlorinated fluids. In the absence of any cosolvent, HSA was insoluble in dense CO2 at 1800 psig and 34°C. However, with 10-15% ethanol, HSA was found to be totally soluble in CO2 at the above experimental conditions. Results indicate the mixture of HSA/ethanol or chloroform gels CO2. The ungelled mixture of HSA/cosolvent and CO2 is clear whereas it turns to translucent or opaque when it gels. Viscosity measurements were made of mixtures of HSA with ethanol in dense CO2 at 1800 psig between 21 to 34°C, using a high pressure capillary viscometer equipped with a sapphire cell for visual observations. These showed that the gelation of CO2 with HSA depends on the temperature and concentration of both HSA and cosolvents, which affect the gel temperature (Tg) and viscosity of CO2. The presence of cosolvent enhances the solubility of HSA in CO2 and increases its viscosity.