Pressure-induced association of oleic acid (OA) under varying temperature studied by multiple-perturbation two-dimensional (2D) IR correlation spectroscopy

Pressure-induced association of oleic acid (OA) under varying temperature was studied by multiple-perturbation two-dimensional (2D) IR correlation spectroscopy. Pressure-dependent ATR-IR spectra of OA were measured by imposing the static pressure ranging up to 12 MPa. Then variations of the IR spectra were captured over the temperature range of 20–40 °C. Multiple-perturbation 2D correlation analysis, coupled with the ATR-IR measurements, reveals association dynamics of OA molecules caused by the applied pressure. The compression first generates the liquid crystalline structure by aggregating the disordered dimer units. Further compression induces the development of the dimer via the assembling of the isolated monomers. In addition, the variation of the partial asynchronous correlation intensities induced by the change in temperature reveals the way the association dynamics is influenced by temperature. The increase in the temperature increased segmental motion of the alkyl chain, which in turn restricts the generation of the liquid crystalline structure based on the tightly packed dimer units.