Analysis of dielectric polarization of organic monolayer at the air–water interface by MDC and SHG spectroscopy

With Maxwell displacement current (MDC) measurement coupled with optical second harmonic generation (SHG) measurement, the dielectric polarization phenomena of monolayers can be examined. We have been developing a novel MDC–SHG experimental system, and analyzing the dielectric monolayers at the air–water interface. From theoretical side, based on a rod molecule model, formula to express the linear and nonlinear polarization of monolayers with C∞-symmetry have been derived using orientational order parameters. On the other hand, using the developed experimental system, the orientational order parameter has been determined with surface pressure–molecular area isotherm (π–A isotherm) for liquid crystalline monolayers. Further, phase transitions of monolayers that accompanies the monolayer structural change has been successfully detected.