Drop coalescence during condensation on viscous slippery and viscoelastic coatings

Coatings of viscous oil or viscoelastic polymer on a rigid surface transform the condensation phenomena differently. When the viscous oil is infused on low-energy rigid surfaces, the surface shows excellent water repellent behavior. On the other hand, the viscoelastic material coating exhibits a high affinity with water drop resulting in more contact angle hysteresis (CAH). We focused on the drop coalescence phenomena during condensation on viscous slippery and viscoelastic coated metallic samples in this work. We have observed that the drop coalescence on lubricant infused surfaces (LIS) significantly depends on the viscosity of the lubricant and the stability of droplet interface bilayers between the drops. The lifetime of the non-coalescence event of the droplets during condensation on high viscous liquid infused surfaces (50 cst and 500 cst) surfaces was found to be in 1–3 orders of magnitude longer compared to low viscous liquid infused surface (5 cst). Coalescence induced motion during condensation was significantly observed in high viscous liquid infused surfaces (50 cst and 500 cst) compared to low viscous lubricant infused surface (5 cst). On soft viscoelastic coating, drop coalescence during condensation event undergoes through merging of the droplets followed by relaxation of the coalesced drop by the capillary induced movement of the contact line. Key findings of this work would be helpful to comprehend the drop coalescence phenomena on viscous slippery and viscoelastic coatings in a detailed manner.