Orientational fluctuations and phase transitions of long chain molecules at the air/water interface

Abstract

Orientational fluctuations in long chain molecules at the air/water interface were detected by second-harmonic spectroscopy. The flucutations depend on the polarization of the incident (\ensuremath{\omega}) and detected (2\ensuremath{\omega}) light showing that the fluctuations are orientational rather than density in origin. The phenomenon is attributed to an orientational phase transition that is dependent on chain length, head group, and charge. Scaling experiments based on increasing the laser beam area indicated a correlation length (domain size) greater than 6 \ensuremath{\mu}m near the transition point.