Thermal Diffusivity and Conductivity of Polyolefins by Thermal Lens Technique

Abstract

A mode-mismatched thermal lens spectrometry (TLS) technique, in a pump–probe two-laser-beam configuration, was employed for the experimental determination of the thermal properties of four selected well-characterized polyolefin homopolymer films. We investigated the thermal diffusivity (D) and thermal conductivity (κ) of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and polypropylene. We also measured the structural properties (i.e., average molecular weight, polydispersity index, branching number), along with the rheological and thermal properties (i.e., melting point, specific heat capacity Cp, degree of crystallinity) of samples by high-temperature gel permeation chromatography (HT-GPC), rheometric mechanical spectrometry (RMS), differential scanning calorimetry (DSC), and densitometry. The relationship between microstructural properties such as degree of crystallinity, D, and κ was investigated. The results show that there is good correlation between the degree of crystallinity and D. The TL technique enables measurement of D in semitransparent thin films within an uncertainty of 4%.

Thermal Diffusivity of Aqueous Dispersions of Silicon Oxide Nanoparticles by Dual-Beam Thermal Lens Spectrometry

“…Still, TLS has some disadvantages that limit the method applicability, including work with optically transparent media and low absorbances [ 22 ], as well as a need for frequent adjustments of the spectrometer [ 23 ]. The impossibility of direct measurements of C p and k also limits the use of TLS [ 24 ].…”