Two-dimensional (2D) infrared (IR) correlation spectroscopy for dynamic absorption behavior of oleic acid (OA) onto silica gel

• Absorption dynamics of oleic acid by silica gel is observed by IR spectroscopy.
• Dimers of oleic acid is disintegrated by interaction arising from silica gel.
• Dissociation of the dimer is associated with its liquid crystalline structure.

Dynamic absorption behavior of oleic acid (OA) onto silica gel was probed by infrared (IR) spectroscopy. Once OA is injected into silica gel placed on a horizontal attenuated total reflectance prism, the silica gel starts to absorb the OA molecules due to the molecular-level interaction based on hydrogen bonding between the COOH of OA and the OH of silica gel. The substantial level of variation of spectral feature is readily observed during the absorption of OA onto silica gel. 2D correlation analysis of the time-dependent IR spectra reveals fine details of absorption dynamics of OA molecules depending on the molecular structure. The predominant absorption of the monomers occurs at the onset of the absorption, and it is then quickly followed by the decrease in the dimers. In other words, the dissociation of the liquid crystals occurs via the disuniting of the tightly packed OA dimers.