Condensation and structural transitions in thin films at interfaces

Abstract

A phase is a state of matter in which the macroscopic physical properties of the substance newlineare uniform on a macroscopic length scale [1]. A phase is characterized by a newlinethermodynamic function called the free energy which depends on the intensive variables newlinesuch as temperature, pressure, concentration etc. Each phase can be transformed from one newlineform to the other by varying these parameters called as phase transition [1-3]. A phase newlinetransition is represented by a non-analytic point (singularity) of the free energy function. newlinePhase transitions can be of first-order or second-order depending on the first derivative of newlinethe free energy function (e.g., entropy) being discontinuous or continuous, respectively [4, newline5]. newlineThe thermodynamic properties of a system are governed by conservation laws and newlinebroken symmetries [5, 6]. The order parameter is associated with the breaking of symmetry newlineof the system. For instance, condensation is a phase transition involving the change of the newlinephysical state of matter from gaseous to liquid phase. The symmetry of the two phases, gas newlineand liquid, on either side of this phase transition is the same. This explains that there is no newlineloss of symmetry in going from the high-temperature gas (vapor) phase to the lowtemperature newlineliquid phase. But the liquid phase varies from the gaseous phase in terms of newlinedensity and compressibility. In two-dimensional systems like Langmuir monolayers (at the newlineair-water (A-W) interface), rich phase diagrams are obtained [7, 8]. We have studied the newlinecondensation occurring in the Langmuir monolayers of a liquid crystal at charged newlineinterfaces and the factors responsible for the same. newline