The investigation on the pressure-induced phase transition in linoleic acid by in situ Raman spectroscopy

• Linoleic acid undergoes two pressure-induced phase transitions below 1.29 GPa.
• The first transition from liquid phase to solid phase takes place in 0.07–0.12 GPa.
• The second phase transition occurs in 0.31-0.53 GPa.
• Some conformational characters of the two high-pressure phases were determined.
• The pressure-induced phase transitions in linoleic acid are reversible.

With diamond anvil cell as a high-pressure apparatus, the in situ Raman spectra of linoleic acid from normal pressure to 1.29 GPa were measured to investigate the effect of pressure on the structural changes. In the pressure ranges of 0.07–0.12 GPa and 0.31–0.53 GPa, the significant changes in Raman spectra show that linoleic acid undergoes two pressure-induced phase transitions. Spectral analysis indicates that the polymethylene chain of linoleic acid molecule transforms from the disordered gauche conformation to the ordered trans conformation in the range of 0.07–0.12 GPa. And the polymethylene chain of linoleic acid molecule remains the ordered trans conformation whereas the conformation of the olefin group significantly changes and the degree of conformational order increases in the range of 0.31–0.53 GPa. The pressure-induced phase transitions in linoleic acid are reversible.

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