Pattern formation during the impact of a partially-frozen binary droplet on a cold surface

TL;DR

This study investigates the complex impact dynamics of a partially frozen binary droplet on a cold surface, revealing a novel fingered solid-phase growth caused by pre-solidification affecting flow and pattern formation.

Contribution

It uncovers the phenomenon of fingered solid-phase growth during droplet impact, highlighting the role of pre-solidified material in altering flow and pattern development.

Findings

Pre-solidified material induces fingered growth patterns.

Impact speed influences pattern formation and phase growth.

Solid-phase growth affects flow stability and contact line dynamics.

Abstract

Impact of a droplet on an undercooled surface is a complex phenomenon as it simultaneously instigates several physical processes that cover a broad spectrum of transport phenomena and phase-transition. Here, we report and explain an unexpected but highly relevant phenomenon of fingered growth of the solid-phase. It emerges during the impact of a binary droplet that freezes from the outside prior to the impact on the undercooled surface. We establish that the presence of pre-solidified material at the advancing contact line fundamentally changes the resulting dynamics, namely by modifying the local flow mobility that leads to an instability analogous to viscous fingering. Moreover, we delineate the interplay between the interfacial deformations of the impacting droplet and patterned growth of the solid-phase as disconnected patterns emerge at faster impacts.