Thermal Physical Fundamentals

Abstract

This chapter discusses mainly about five important physical concepts in liquid and gas systems, which are phase equilibrium, phase transition, interface, contact angle, and cluster. Phase refers to the physically distinctive form of a substance. From the view of thermodynamics, the states and conditions for phase equilibrium are described and some fundamentals for phase transition are introduced. A liquid-vapor interface is considered to be a very thin region having rapid changes in fluid or material properties from the bulk liquid to bulk vapor. Using surface excess quantity, the thermodynamic analysis can be conducted to explore the interfacial effects. Interface tension and Young-Laplace equation are discussed here. The contact angle, which is used to quantify the wettability of liquid, is defined as the angle between the liquid-vapor interface and the solid surface at the contact line. Contact angle equilibrium, hysteresis and dynamic are discussed. Clusters consisting of tens and hundred of atoms or molecules are a new class of compounds called atomic or molecular clusters. The number balance equation is formulated for activated molecules in clusters, with a comprehensive investigation of the dynamics of clusters formed with internal or external perturbations.