Frequency Dependent Specific Heat from Thermal Effusion in Spherical Geometry

TL;DR

This paper introduces a new spherical effusion method to measure frequency-dependent specific heat near the glass transition, allowing independent determination of thermal properties with high sensitivity within a specific frequency range.

Contribution

The paper presents a novel spherical thermal effusion technique that accurately measures frequency-dependent specific heat and thermal conductivity, accounting for mechanical boundary conditions.

Findings

Successfully measured frequency-dependent specific heat of 5-polyphenyl-4-ether.

Method isolates longitudinal specific heat from isobaric heat.

Achieved high sensitivity within a 2-3 decade frequency range.

Abstract

We present a novel method of measuring the frequency dependent specific heat at the glass transition applied to 5-polyphenyl-4-ether. The method employs thermal waves effusing radially out from the surface of a spherical thermistor that acts as both a heat generator and thermometer. It is a merit of the method compared to planar effusion methods that the influence of the mechanical boundary conditions are analytically known. This implies that it is the longitudinal rather than the isobaric specific heat that is measured. As another merit the thermal conductivity and specific heat can be found independently. The method has highest sensitivity at a frequency where the thermal diffusion length is comparable to the radius of the heat generator. This limits in practise the frequency range to 2-3 decades. An account of the 3omega-technique used including higher order terms in the temperature dependency of the thermistor and in the power generated is furthermore given.