Surface Viscoelastic Properties Of Spread Ferroelectric Liquid Crystal Monolayer On Air-Water Interface

摘要

Ferroelectric Liquid crystal having Smectic C* phase at room temperature was capable of forming Langmuir monolayer due to presence of both hydrophilic and hydrophobic groups in it. Surface viscoelasticity properties of FLC monolayer spread on water surface had been determined by dynamic oscillation method and discussed as a function of surface pressure. Dynamic viscoelastic properties such as G (Elastic modulus), G' (storage (elastic) modulus), G" (Loss (viscous) modulus) and phase change with sinusoidal oscillation had been measure at phase changing surface pressure values. As monolayer was becoming condensed, increasing trend was observed in G" values while G' was decreasing. At higher frequencies, viscous modulus G" had negative values. This relaxation phenomenon was probably caused by conformational rearrangements that acted to fluidize monolayer. Phase change tanθ was positive, response in surface pressure was ahead of the de-formation in area and the monolayer had positive dilatational viscosity. Phase change tan θ was negative, response in surface pressure was hysteretic to the deformation in area, and negative dilatational viscosity had been observed. Studies of monolayer in barrier oscillating mode provided us the surface pressure which was most suitable for Langmuir Blodgett monolayer deposition.