Investigation of the Nanoscale Morphology in Industrially Relevant Clearcoats of Waterborne Polymer Colloids by Means of Variable-Angle Grazing Incidence Small-Angle X-ray Scattering AITranslate

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DOI：https://doi.org/10.1021/acsapm.9b00601

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Soft polymer colloidal water suspensions are extremely important formulations for industrial applications such as water-based environmental-friendly coatings, paints, and adhesives. Homogeneity of the final coating at the micrometer and nanoscale is a crucial factor for optimal coating performance, such as barrier properties against solvent permeation. Here, we investigated the remnant nanostructure in slot-die-coated micrometer-sized thick clear coating films (clearcoats) of three different waterborne polymer colloids (pure soft, pure hard, and soft/hard multiphase), commonly utilized as primers in paint formulations [Mader et al. Prog. Org. Coat.2011, 71, 123–135], using variable-angle grazing incidence small-angle X-ray scattering (GISAXS) complemented with cross-sectional atomic force microscopy (cs-AFM). After complete macroscopic drying, the coating films exhibit the presence of residual nanostructure with characteristic distance (d*) smaller than the original particle size and even smaller (≪d*) heterogeneity dimensions. These nanostructural heterogeneities (i) develop due to partial particle coalescence, (ii) are preferentially located close to the air–film interface and (iii) demonstrate the tendency to align perpendicular to the air–film interface, implying vertical gradient in hydroplasticization effects having occurred earlier during film formation. The extent and size of the nanostructural heterogeneities, driven by the slot-die coating application, strongly depend on the polymer chemistry (glass transition temperature, Tg) and the colloidal architecture. Last, solvent exposure has a significant impact on the nanostructure, causing the removal of these heterogeneities and leading to a more strongly coalesced film.