Photothermal configuration applied to the study of water vapor permeability in biodegradable films under several water activities

Application of photothermal configuration to the study of water vapor permeability in biodegradable films under several water activities was presented. The light beam of a 250 W tungsten lamp was mechanically modulated and focused onto a cylindrical photoacoustic cell, which was closed at the outer front side by a quartz window. Measurements were performed at a modulation frequency of 22 Hz and the water vapor diffusion coefficient was determined as a function of relative humidity. The normalized photoacoustic signal amplitude showed a linear behavior as a function of relative humidity for the studied samples.