Effect of external high pressures on the clay mineral sodium montmorillonite intercalated with methylated octadecylammonium bromide surfactants

► A high-pressure Raman microprobe spectroscopic study of surfactant-intercalated clay minerals. ► Interesting behavior of the CH2 stretching modes under high pressure. ► Pressure-induced gauche-to-trans conformational changes in the orientation of the CH2 chains of the surfactants are observed. ► The pressure-induced changes are completely reversible.