SANS-OCT of directed organisation of colloid-polymer films

Colloid-polymer blends are integral to product applications like paints, coatings, and the electrodes of high-energy-density batteries; the polymer chains are used as a binder, to enhance mechanical properties and stability. However, during film formation a polymer can preferentially move through the spaces left in a colloidal film, by a process known as binder migration. Accumulating at the drying surface of the film, it can form into a skin that hinders evaporation, while weakening the rest of the coating. Building on progress made using small-angle scattering techniques to better understand film formation of colloidal materials, we propose to use SANS to characterise polymer transport during the drying of aqueous dispersions of colloid-polymer mixtures. Using colloidal silica and polyvinyl alcohol as common, industrially relevant products, we will adjust the D2O:H2O ratio of the dispersant to match out the different phases, allowing their transport to be observed in isolation. We will make use of a unique non-invasive capability, combining SANS with a bespoke Optical Coherence Tomography, to simultaneously monitor structural changes at nano and micro scales. Hence, we will provide a high-spatial-resolution mapping of the optical changes during film formation. Together, our results will provide a detailed view of the effects of polymer characteristics, using polymer chain length as an initial parameter, on binder migration in colloid-polymer films.