Analysis of dielectric relaxation phenomena with molecular orientational ordering in monolayers at the liquid-air interface.

Abstract

Starting from the Debye theory of rotational Brownian motion, we analyzed the dielectric relaxation phenomena with molecular orientational ordering in Langm\uir film on a water surface, assuming that the orientational distribution of the constituent rodlike polar molecules is ruled by Boltzmann statistics. The transient behavior of the polar molecules induced by the application of step compression at the molecular area $A={A}_{i}(l{A}_{c})$ is discussed with taking account of the friction constant of monolayer $\ensuremath{\xi}$, and the dielectric relaxation time $\ensuremath{\tau}$. Here ${A}_{c}$ is the critical molecular area defined as $\ensuremath{\pi}{l}^{2}$ ($l$: the length of rodlike polar molecule). The orientational order parameter $S$ of monolayers and Maxwell displacement current (MDC) at the dielectric relaxation process were obtained, for the first time, with the consideration of $\ensuremath{\xi}$ and $\ensuremath{\tau}$. On the basis of the analysis developed here, we examined the generation of MDC across 4-cyano-4\ensuremath{'}-5-alkyl-biphenyl (5CB) Langm\uir film by monolayer compression.