MASS DIFFUSION-COEFFICIENTS OF POLYMER-FILMS USING REAL-TIME HOLOGRAPHIC-INTERFEROMETRY

The mass diffusion coefficient is obtained using real-time holographic interferometry. The stresses induced during desorption and absorption of moisture are monitored as a function of time at various relative h umidities. A mathematical relationship is applied to relate these stre sses to the moisture diffusion through the thickness of the films. The advantage of the holographic interferometry technique is that both th e swelling stress as a function of time and the mass diffusion coeffic ient can be quantified simultaneously during the same experiment. Seve ral films and coatings were investigated: polyimides (PMDA-ODA and BPD A-PAA), photographic gelatin, and cellulose acetate. Each exhibited ch aracteristic Fickian diffusion behavior. A gravimetric technique was e mployed to validate the holographic interferometry results. The moistu re diffusion coefficients determined by holographic interferometry agr eed well with reported Literature values. (C) 1996 John Wiley & Sons, Inc.