Impact dynamics of Newtonian and viscoelastic droplets on heated surfaces at low Weber number

摘要

The mechanism of contact between liquid droplets and hot surfaces is important and attracts many researches recently. Herein, we experimentally investigate the contact of Newtonian and viscoelastic droplets between gradually heated surfaces at low Weber numbers, which has not been explored. To present a detailed analysis of contact line dynamics, experiments were performed across a surface temperature ranging boiling conditions to above Leidenfrost temperature (100°C - 300°C), while various impact phenomena with increasing surface temperature have been observed for Newtonian and viscoelastic droplets. We demonstrate that the polymer additives significantly affect the dynamic contact angle and contact radius on heated hydrophilic surface. In the Leidenfrost regime, the increased velocity causes considerable reduction on contact time of water droplets, especially at the breaks-up mode. However, it does not influence the contact time of impinging polymer droplet. Aqueous polymer droplets with high molecular weight and high concentration suppress secondary atomization, splashing and break-up, but promote droplet foaming and the generation of viscoelastic filaments. The results illustrate how the polymer additives, surface temperature and impact velocity affect the impact outcomes, and original impact phase diagrams are proposed finally.