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

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.