The Excess Heat Capacity in Glass-forming Liquid Systems Containing Molecules

TL;DR

This study investigates the excess heat capacity at glass transition in specific glass-forming systems, revealing how composition and water content influence it, and provides a quantitative model considering atomic and molecular motions.

Contribution

It introduces a quantitative description of excess heat capacity based on atomic and molecular translational motions in glass-forming liquids.

Findings

Excess heat capacity remains constant in Na-K-Ca nitrate systems.

Excess heat capacity increases with water content in hydrate systems.

A model linking atomic/molecular motion to heat capacity is proposed.

Abstract

The excess heat capacity at glass transition temperature in two types of glass-forming systems of [xNaNO3\cdot(1-x)KNO3]60[Ca(NO3)2]40 (0 \leq x \leq 1) and Ca(NO3)2\cdotyH2O (4 \leq y \leq 13) is studied. In the former system, with the replacement of K+ cation with Na+ cation, the excess heat capacity is almost invariable around 65.1 J\cdotmol-1\cdotK-1, while the excess increases by 38.9 J\cdotmol-1\cdotK-1 with the increasing per molar H2O content in latter system. A quantitative description of the excess heat capacity is built up with the consideration of atomic and molecular translational motion in the glass-forming systems. This finding might offer further understanding to the glass transition.