Drop Impact on Heated Nanostructures

Drop
impact on a heated surface not only displays intriguing flow
motion but also plays a crucial role in various applications and processes.
We examine the impact dynamics of a water drop on both heated flat
and nanostructured surfaces, with a wide range of impact velocity
(V) and surface temperature (Ts) values. Via high-speed imaging and temperature measurements,
we construct phase diagrams of different impact outcomes on these
heated surfaces. Like those on the heated flat surface, water drops
can deposit, spread, rebound, or break-up with atomizing on the heated
nanostructures as V and Ts are increased. We find a significant influence of nanostructures
on the impact dynamics by generating particular events in specific
parameter ranges. For example, events of splashing, gentle central
jetting, and violent central jetting are observed on and thus triggered
by the heated nanostructures. The heated nanotextures with high roughness
can easily trigger the splashing and the central jetting. Our data
of the normalized maximum spreading diameter for the heated surfaces
display distinct trends at low and high Weber number (We) ranges, where We compares the kinetic to surface
energy of the impacting droplet. Finally, compared with the flat surface,
the dynamic Leidenfrost temperature (TLD) for We ≈ 10 is decreased (by ≈60 °C) by the high-roughness
nanotextures. In addition, our experimental data of TLD is consistent
with a model prediction proposed by balancing the droplet dynamic
and vapor pressure.