A Water Droplet Impact on a Hydrophobic Soft Surface

Impacting water droplet on a hydrophobic soft surface is investigated and impacting droplet behavior during the spreading and retraction phases is examined. Polyisoprene elastomer surface is hydrophobized via deposition with functionalized nanosilica particles using the dip coating method. Hydrophobized surface results in the contact angle of 135 ± 3 deg with a hysteresis of 2 ± 1 deg, and stretching and stretch relaxing of the coated samples do not alter the wetting state of the surfaces. Pressure variation, spreading, and retraction rates of droplet are simulated and findings are validated through the experimental data obtained from high-speed video system. The findings are also compared to those obtained for the impacting droplet on the hydrophobized glass surfaces. It is observed that predictions of droplet height and droplet shape agree well with the experimental data. Spreading period of the impacting droplet on the hydrophobized elastomer surface is longer than the hydrophobic glass surface; contrary, the retraction period of the impacting droplet is shorter on the elastomer surface than the glass surface. Impacting droplet generates large amplitude oscillatory surface waves on the elastomer surface and as the time progresses the wave amplitude reduces considerably, particularly along the surface (x-axis).