Spreading, encapsulation and transition to arrested shapes during drop impact onto hydrophobic powders

We present findings from an experimental study of the impact of liquid droplets onto powder surfaces, where the particulates are hydrophobic. We vary both the size of the drop and impact speed coupled with the size range of the powder in order to assess the critical conditions for the formation of liquid marbles, where the drop becomes completely encapsulated by the powder, and arrested shapes where the drop cannot regain its spherical shape.By using different hydrophobization agents we find that a lower particle mobility may aid in promoting liquid marble formation at lower impact kinetic energies. From observations of the arrested shape formations, we propose that simple surface tensions may be inadequate to describe deformation dynamics in liquid marbles.

Arrested shape formed during the impact of a 2 mm water droplet onto hydrophobic 25 μμm particles.Figure optionsDownload high-quality image (30 K)Download as PowerPoint slide