Micro-rheology Using Multi Speckle DWS with Video Camera. Application to Film Formation, Drying and Rheological Stability

Abstract

We present in this work two applications of microrheology: the monitoring of film formation and the rheological stability. Microrheology is based on the Diffusing Wave Spectroscopy (DWS) method [1] that relates the particle dynamics to the speckle field dynamics, and further to the visco‐elastic moduli G′ and G″ with respect to frequency [2]. Our technology uses the Multi Speckle DWS (MS‐DWS) set‐up in backscattering with a video camera. For film formation and drying application, we present a new algorithm called “Adaptive Speckle Imaging Interferometry” (ASII) that extracts a simple kinetics from the speckle field dynamics [3,4]. Different film forming and drying have been investigated (water‐based, solvent and solvent‐free paints, inks, adhesives, varnishes, …) on various types of substrates and at different thickness (few to hundreds microns). For rheological stability we show that the robust measurement of speckle correlation using the inter image distance [3] can bring useful information for industry...