Laser interferometry: A measurement technique for diffusion studies in thin polymer films

Laser interferometric techniques have many applications in the area of thin film science and technology due to their sensitivity, simplicity, and low cost. Typically, changes in thickness and/or refractive index of a transparent polymer film sample are detected from changes in film reflectivity, as measured by variations in the intensity of reflected laser light. Diffusion related properties such as solvent uptake/swelling, dissolution, and drying rates are accessible with laser interferometry since each of these processes involves a change in the film's thickness and/or refractive index. The principles and basic experimental considerations common to these three applications will be discussed. Illustrative examples from our lab will include n‐methyl‐2‐pyrrolidone diffusion in polyimide, and methanol diffusion in poly(methyl methacrylate). Copyright © 1991 Society of Plastics Engineers