Abstract
Drop interaction with solid surfaces upon impact has been attracting a growing community of researchers who are focusing more and more on ‘complex’ surfaces and ‘complex’ drops. Recently, we are observing an emerging research trend related to the investigation of compound drop impact. Compound drops consist of two or more distinct continuous phases sharing common interfaces, surrounded by a third phase. Examples are core–shell and Janus drops. In this review, we address the fundamental aspects of compound drop impact and discuss the current challenges related to experimental testing and numerical simulation of multiphase fluid systems. Furthermore, we provide a perspective on the technological relevance of understanding and controlling compound drop impact, ranging from 3D printing to liquid separation for water cleaning and oil remediation.
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•A perspective on compound drop impact studies in the last 3 years is presented.•Compound drops consist of at least two distinct phases sharing common interfaces.•Compound drops belong to the more general class of complex drops.•Self-lubrication, enhanced splashing and fine radial jetting are discussed.•Technological prospects, e.g. 3D printing and oil–water separation, are presented.