It's harder to splash on soft solids

TL;DR

This study demonstrates that softer substrates significantly increase the energy threshold for droplet splashing, with implications for splash prevention and understanding impact dynamics.

Contribution

It reveals how substrate stiffness influences splashing thresholds and introduces soft gels as a tool for studying splash formation mechanisms.

Findings

Soft substrates increase splashing energy threshold by over 70%.

Young's modulus below 100 kPa reduces splashing.

Soft gels can serve as coatings for splash prevention.

Abstract

Droplets splash when they impact dry, flat substrates above a critical velocity that depends on parameters such as droplet size, viscosity and air pressure. By imaging ethanol drops impacting silicone gels of different stiffnesses we show that substrate stiffness also affects the splashing threshold. Splashing is reduced or even eliminated: droplets on the softest substrates need over 70\% more kinetic energy to splash than they do on rigid substrates. We show that this is due to energy losses caused by deformations of soft substrates during the first few microseconds of impact. We find that solids with Young's moduli $\lesssim 100$kPa reduce splashing, in agreement with simple scaling arguments. Thus materials like soft gels and elastomers can be used as simple coatings for effective splash prevention. Soft substrates also serve as a useful system for testing splash-formation theories and sheet-ejection mechanisms, as they allow the characteristics of ejection sheets to be controlled independently of the bulk impact dynamics of droplets.