Multimodal optical device to study dynamics of drying process

Abstract

Imaging and quantification of the drying process find applications in many fields, including the drying of paints. Measurement of different parameters during the drying process leads to accurate identification of the state of the sample under investigation. We propose a multimodal optical technique combining spectroscopy, speckle correlation, and digital holography to analyze and quantify drying process. The developed device is tested in the identification of drying phases of paints. In the developed device, digital holographic interferometry is employed to obtain spatial variation of deformation on the surface coated with paint. Although digital holography is an efficient tool to study drying it is limited to the latter stages of the process. To study initial and intermediate stages laser speckle correlation and spectroscopy are integrated with digital holography. The spectrometer uses an LED source to acquire the reflectance spectrum. The reflectance increases with time and saturates as the water content of paint naturally evaporates. It was observed that this saturation occurs in intermediate stages of the process. To further analyze the drying stages, speckle images of the paint surface are also acquired. The speckle intensity correlation varied from low to high with drying. The combination of laser speckle, digital holography and spectroscopy complement one another and enables the study of all stages of drying process. To the best of our knowledge this is the first time such a multimodal optical device is developed for the complete analysis of drying process.