Solvent effect on monomer-dimer equilibrium in supercritical fluid: Spectroscopic and thermodynamic studies

The monomer-dimer equilibrium of lauric acid in supercritical CO2 was studied at different temperatures and pressures using FTIR spectroscopy. The equilibrium constant and thermodynamic properties of the dimerization were obtained based on the spectroscopic determinations. It has been found that fluid density plays an important role on the dimerization. Thermodynamic studies on the equilibrium suggested that there may be differential solvent effects on the monomer and dimer. At lower density, the solvent aggregates about the solute and, therefore, the differential solvent effect is significant. With increase in density the solvent-solute clustering and differential solvent effect decrease, and the supercritical solution becomes more homogeneous.