Elasto-viscoplastic spreading: From plastocapillarity to elastocapillarity

We study the spreading of elasto-viscoplastic (EVP) droplets under surface tension effects. The non-Newtonian material flows like a viscoelastic liquid above the yield stress and behaves like a viscoelastic solid below it. Hence, the droplet initially flows under surface tension forces but eventually reaches a final equilibrium shape when the stress everywhere inside the droplet falls below the resisting rheological stresses. We use numerical simulations and combine volume-of-fluid (VOF) method and an EVP constitutive model to systematically study the dynamics of spreading and the final shape of the droplets. The spreading process explored in this study finds applications in coating, droplet-based inkjet printing, and 3D printing, where complex fluids such as paints, thermoplastic filaments, or bio-inks are deposited onto surfaces. Additionally, the computational framework enables the study of a wide range of multiphase interfacial phenomena, from elastocapillarity to plastocapillarity.