Flat-cupped transition in freezing drop impacts

TL;DR

This study investigates how alkane drops impact a liquid bath and undergo a morphological transition from flat to cupped shapes, influenced mainly by melting temperature and thermal shock, with implications for understanding impact-induced solidification.

Contribution

The paper reveals a morphological transition in freezing drops during impact and identifies the key factors controlling this transition, providing a unified phase diagram for different liquids.

Findings

Transition depends on melting temperature and thermal shock

Impact dynamics are unaffected by thermal shock prior to solidification

Solidification onset is governed by formation of a thin solid layer

Abstract

We present an experimental study on the freezing of alkane drops impacted on a liquid bath. More specifically, for drops of hexadecane and tetradecane on brine, we found a morphological transition of the solid between a flat disk and a cupped shape. We show that this transition depends mainly on melting temperature and thermal shock, and varies weakly with impact velocity. We observed that the impact dynamics does not depend on the thermal shock before the drop starts to solid ify, which allows a rationalization of the solid size by models established for impact without phase change. Finally, we show that the relevant timescale setting the onset of solidification is associated with the formation of a thin solid layer between the drop and the bath, a timescale much shorter than the total solidification time. These findings offer the possibility to collapse the data for both liquids in a single phase diagram.