Large contact angle hysteresis enhances post-impact droplet oscillations

Abstract

Droplet impact on solid surfaces plays a critical role in a wide range of applications, including inkjet printing, spray cooling, surface coatings, and microdroplet chemistry. Precise control of droplet–surface interactions is essential, but the fundamental mechanisms governing this process are still not fully understood. In this study, we demonstrate that large contact angle hysteresis (CAH) on hydrophobic nanoporous surfaces significantly amplifies post-impact droplet oscillations. This reveals the critical influence of CAH on the redistribution of impact energy and the modulation of droplet–surface interactions. Using shape mode decomposition via Legendre polynomials and fast Fourier transform spectral analysis, we show that surfaces with larger CAH excite and sustain higher-order droplet shape mode oscillations, leading to persistent capillary waves even after contact line pinning. The observed amplitude modulation and multiple frequency components within individual shape modes reveal nonlinear energy transfer between different modes. These amplified and coupled oscillations are shown to promote daughter droplet coalescence. This study presents a framework for understanding the role of CAH in storing and redistributing impact energy through nonlinear mode excitation and establishes CAH as a critical design parameter for controlling fluid dynamics on solid surfaces.