Drop pinning on soft, lubricant-infused silicone elastomers

Soft, slippery surfaces have gained increasing attention due to their wide range of potential applications, for example in biomaterials, self-cleaning, anti-fouling, liquid collection, and more. To prepare a soft, slippery surface, a crosslinked polymer network can be swelled with a compatible lubricant. However, an understanding of how swelling and crosslinking relate to slippery properties is still being developed. In this work, we focus on the influence of polymer network density (i.e. modulus) and degree of swelling on the water drop pinning force. Specifically, we study when a water drop sticks or slides on a vertical, silicone oil–swollen polydimethylsiloxane (PDMS) elastomer, where gravity drives the drop to slide. Our results indicate that the critical water drop volume for sliding is strongly controlled by the degree of swelling, even though a softer substrate may induce a larger wetting ridge that hinders drop sliding. In addition, we show that highly swollen surfaces can recover their slipperiness after they are rinsed with water. This is likely associated with regeneration of an oil-layer on the surface coming from the bulk substrate, demonstrating the durability of lubricant-swollen elastomers for practical uses.