Monitoring of a drying process in polymer water and methanol solutions by dynamic speckle metrology

Abstract

Observation of speed of processes by dynamic speckle metrology has been applied to different samples of industrial or biological nature. The method allows for detecting regions of lower or higher activity on the sample surface through statistical processing of the speckle patterns formed on this surface under laser illumination. The aim of the paper is to check applicability of this dynamic speckle technique for monitoring of the drying process in polymer water and methanol solutions. For the purpose, we recorded several sets of 256 correlated in time speckle patterns of a transparent drop of PAZO water solution and PAZO methanol solution on a glass plate illuminated by a He-Ne laser. The sets were separated by intervals of several minutes, and the last set was recorded 100 minutes after the start of the experiment. For statistical description of activity on the observed sample we applied pointwise correlation-based algorithms to binary patterns formed by comparison of intensities at each point to a sign threshold. The obtained two-dimensional maps of the used statistical estimator at different time lags clearly indicated the difference between water and methanol solutions and proved efficiency of dynamic speckle analysis for monitoring of drying processes in polymer solutions.