Structural characterisation of polyurethane dispersion and their transformation into films Ellen Quane 1 , Anna Newman 1 , Thomas Neal 1 , Neal Williams 2 , Niels Elders 2 , Anthony Ryan 1 and Oleksandr Mykhaylyk 1 1 University of Sheffield, UK, 2 AkzoNobel Ltd.,UK/NL Interest in aqueous dispersions is growing as industry strives to produce environmentally friendly products. In particular, incorporation of hydrophilic monomers into polyurethane (PU) gives aqueous dispersions that provide low VOC, high performance coatings. 1 Controlling the phase separation within the PU film is fundamental for targeting specific coating properties. It is, therefore, essential to understand the morphology of PU particles in dispersion and morphological transformations taking place during the drying process that forms the final PU film. 2 Small angle x-ray scattering (SAXS) is exploited in this study as a non-intrusive method for probing the morphology of polyether-based PU, colloidally stabilised by inclusion of acidic monomers. Effects of chemical composition on the particle morphology are studied systematically. Structural models developed in this work for SAXS analysis of PU dispersions enable a relationship between particle size, composition and water content to be established. SAXS analysis of PU films shows that some particle interfaces remain during drying forming a periodic structure dictated by the size of the original particles, in addition to phase separation. In situ studies of the drying process by time-resolved grazing incidence SAXS reveals morphological rearrangement that is triggered in the bulk after particle coalescence. Results are confirmed using atomic force microscopy by trapping the particle morphology using spin-coating from dilute solution and comparing with air-dried films. This suggests that the confinement imposed by the size of the PU nanoparticles in dispersion causes frustration of phase separation that is released during drying, allowing chain rearrangement to more thermodynamically favourable length scales. A relationship between polyether Mn, polyether content and phase separation is established. References 1. H. Honarkar, J. Dispers. Sci. Technol. , 2018 , 39, 507–516. 2. R. Satguru, J. McMahon, J. C. Padget and R. G. Coogan, J. Coatings Technol. , 1994 , 66, 47–55.
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