High Speed Imagery Analysis of Droplet Impact on Soft Oil Infused Surface

Droplet impact on solid liquid-infused surfaces (LIS) has been widely explored due to its significant scientific implications and industrial relevance. In most studies, the predominant impact behavior observed is complete droplet rebound. In This study we investigated the influence of octadecyltrichlorosilane (OTS) functionalization and oil coatings on the droplet impact dynamics of smooth polydimethylsiloxane (PDMS) surfaces. We conducted droplet impact experiments on smooth PDMS functionalized with OTS and subsequently coated or absorbed with two different oils, silicone oil (5cSt) and hexadecane, to create Van der Waals and non-Van der Waals SLIP surfaces. Contact angle measurements revealed that OTS functionalization reduced adhesion and increased water repellency, facilitating partial droplet rebound upon impact. Oil-coated surfaces exhibited reduced droplet spreading due to viscous resistance, while absorbed oils altered surface flexibility, influencing impact dynamics. PDMS samples absorbed with silicone oil demonstrated complete droplet rebound at all Weber numbers, whereas hexadecane-absorbed surfaces exhibited limited spreading and no rebound, highlighting the significance of oil-PDMS interactions. High-speed imaging and quantitative analysis confirmed that surface functionalization and oil interactions critically affect droplet spreading, recoil, and rebound behavior. These findings provide insights into optimizing liquid-repellent surfaces for applications such as self-cleaning coatings and droplet transport systems.