Detection of phase transition of 4-alkoxy-4′- n-cyanobiphenyl Langmuir films by Maxwell displacement current and optical second-harmonic generation measurements

Abstract

Monolayers of 4-alkoxy-4′- n-cyanobiphenyl ( nOCB, n=5–8) at the air–water interface have been investigated using Maxwell displacement current (MDC) and optical second-harmonic generation (SHG) measurements by monolayer compression. The generation of MDC and SHG from 5, 6 and 7OCB monolayers was similar, but different from that of 8OCB monolayers, possibly due to the strong interaction between 8OCB molecules leading to aggregation. That is, p-p and s-p SH signals were generated by monolayer compression and p-s and s-s SH signals were generated by further compression of 5, 6 and 7OCB monolayers, but these four signals were simultaneously generated for 8OCB monolayers. We could also detect p-s and s-s SH signals due to shear induced reorientation by monolayer compression.