Polymer-Mediated\nCrack Suppression in Deposit of Nanoellipsoids

Uniform\ndistribution of particles and crack suppression in dried\nparticulate deposits are major challenges for applications in coating\nand printing technologies. To address this, we investigated the impact\nof the addition of a water-soluble polymer, poly(vinyl alcohol) (PVA),\non the evaporative self-assembly and kinetics of crack formation in\ndeposits of anisotropic colloids. The fluid flow inside the drying\ndrop is significantly altered due to polymer-mediated adsorption of\nellipsoids to the drop surface. The competition between outward capillary\nflow and Marangoni flow developed in the drying colloid–polymer\ndispersion drop dictates the distribution of particles in the final\ndried patterns. The deposits formed by drying drops of ellipsoids\ndispersed in PVA solutions show three distinct patterns depending\non the PVA concentration. A transition from ring-like deposit to uniform\ndeposition with intermittent cracks was observed for a critical PVA\nconcentration of 0.3 wt %. Radial as well as annular cracks were observed\nin the case of no PVA, while only annular cracks were formed in the\ndried patterns as the PVA content increased, thus indicating the change\nof capillary stresses in the films. Analyses of the particle dynamics\nand deposition patterns confirmed the effectiveness of gelation-driven\ncrack prevention. This method offers a facile and straightforward\nsolution for obtaining crack-free coatings in drying-mediated colloidal\nnanoparticle assembly.