Determination of thermodynamic parameters from light intensity signals obtained from oxygen optical sensors

Abstract

A quite simple and inexpensive experimental set up using a platinum porphine/polysulfone-based oxygen optical sensor was used for determining thermodynamic parameters characterising polymers and luminophores constituting optical sensing membranes. In particular, the activation energies of the non-radiative, ΔEnr, and diffusion, ΔED, processes and the gas solubility enthalpy inside the polymeric layer, ΔEs, were computed. They were determined by expressing the Stern–Volmer constant, K′SV, in terms of luminophore life-time, diffusion coefficient and solubility of the analyte gas. The dependence of the three parameters on temperature ranging between 40 and 90°C was accounted for with suitable physical models used to obtain the cited parameters by regression procedures starting from experimental data. The found values are: ΔED=2.8(0.3)kJ/mol, and ΔEs=13(3)kJ/mol. These results are in agreement with literature data relative to similar layers. The experimental set-up of the sensor required the sensing membrane supported on optical fibers. Structural information about the membrane was also obtained by monitoring K′SV variations with time during the conditioning time, determining how long the polymeric structure takes for reaching equilibrium conditions.