A Snapshot of Liquid State

Liquid is one the three principal states of matter and its properties are known to be intermediate between gaseous and solid phases. Several types of intermolecular forces, categorised into long range and short range, play important roles in defining liquid structure. Long range forces are of three types, namely electrostatic, induction and dispersion, whilst the short range forces are of quantum chemical nature, due to exchange of electrons. A wide range of materials, including elements, oxides, mixtures of salts and dilute acids, are known to form glasses, which are non−crystalline, amorphous matter. Methods such as lattice theories have been devised long time back to understand the structure of liquids. Several other theories have been put forward as well in order to explain complex behaviour of liquids at lower temperature such as formation of highly viscous glassy materials. Most notable theoretical propositions include Adam – Gibbs theory, Mode Coupling Theory and Energy Landscape theory. Inherent Structure (IS) analysis is a powerful tool to identify the fundamental structures of the system under investigation, and to obtain a pictorial characterisation of the energetics between strong and fragile glasses. Relaxation times exhibit two distinct kinetics, alpha and beta relaxations, which can be properly explained by Mode Coupling Theory. Aqueous solutions of sugars and alkali salts such as lithium chloride are known to be good glass formers, which require only low cooling rates in order to form glasses, bypassing crystallisation.

Keywords: Atactic polymer, Expansion coefficient, Fragile, Freezing, Glass transition, Hole theory, Inherent structures, Kauzmann’s paradox, Lindemann ratio, London forces, Metastable, Strong liquids.