Determination of thermal and optical parameters of melanins by photopyroelectric spectroscopy

TL;DR

This study employs photopyroelectric spectroscopy to accurately determine the thermal and optical properties of electropolymerized melanins, including thermal diffusivity, conductivity, specific heat, and optical gap.

Contribution

It introduces a novel application of PPE to measure thermal and optical parameters of melanins with high accuracy, including the first determination of the optical gap.

Findings

Thermal diffusivity coefficient measured accurately

Thermal conductivity and specific heat determined

Optical gap of 1.70 eV identified

Abstract

Photopyroelectric spectroscopy (PPE) was used to study the thermal and optical properties of electropolymerized melanins. The photopyroelectric intensity signal and its phase were independently measured as a function of wavelength, as well as a function of chopping frequency for a given wavelength in the saturation part of the PPE spectrum. Equations for both the intensity and the phase of the PPE signal were used to fit the experimental results. From the fittings we obtained for the first time, with great accuracy, the thermal diffusivity coefficient, the thermal conductivity and the specific heat of the samples, as well as a value for the condensed phase optical gap, which we found to be 1.70 eV.