Executive Summary : | The origin of the proposal lies in mitigating the crack formation observed in surface coatings, paints as well as artworks. Droplets of colloidal suspension drying on solid, rigid substrates have served as the model laboratory system to study crack formation in colloidal films. Herein we explore the strategy of introducing polymers as an additive that may/may not modulate crack formation. This model system of colloid-polymer mixtures is of significant relevance to colloidal science community as they form the base formulations of several commercial products, like, surface coatings, inks, food products and detergents. Particularly we will try to answer the questions as to what is the role of polymeric additive on the onset of crack formation? Can we predict the critical stress for crack propagation and the concomitant critical cracking thickness (maximum crack-free film thickness) for a colloid-polymer system? In continuation, we aim to highlight the polymer rheological properties that may influence the entire process. Experimental evaluation of the in situ stress developed within such drying colloid-polymer films will be correlated with crack propagation dynamics on one end and with rheological changes in microstructure at the other end. This is the first attempt at investigating the drying colloid-polymer mixtures from a holistic viewpoint. Here, holistic implies an approach that outlines the micro-to-macro mechanisms of the drying process. The fundamental question that this study aims to probe is the correlation of rheological changes in a colloid-polymer mixture with colloidal film failure. Microscopic mechanisms of polymer conformations and adsorption or desorption of polymer onto colloidal particle surface control the interaction between the colloid and polymer. This subsequently is responsible for the internal stress evolution and can be employed to predict the failure of the colloidal film. Such insights will be critical to modulation of cracks in surface coatings and paints. |