How Surface Functional Groups Influence Fracturation in Nanofluid Droplet Dry-Outs

In this study of drying water-based nanofluid droplets, we report the influence of surface functional groups and substrate surface energies on crack formation and dry-out shape. These two key parameters are investigated by allowing nanofluids with several functional groups grafted on polystyrene nanoparticle surfaces to dry on various substrates. These experiments result in a variety of regular crack patterns with identical nanoparticle diameter, material, concentration, and drying conditions. We demonstrate that, despite the various patterns observed, the crack spacing/deposit height ratio is constant for similar substrate surface energies and linearly increases with this parameter. Moreover, this study shows that the crack shape is strongly influenced by surface functional groups as a result of particle interactions (depending on the particle surface potentials) and compaction during solvent evaporation.