(102a) Small Scale Wetting and Adhesive Friction on Soft and Swollen Elastomers

Understanding the behavior of very soft interfaces is an ongoing challenge. When materials are sufficiently soft, or the characteristic size scale is small, crosslinked solids can display liquid-like characteristics, like capillarity. When these crosslinked polymers are infused with a fluid (i.e., swollen gels), the fluid itself can also provide true liquid behavior, creating multi-phase situations that are even more complex. In this talk, we show how combinations of solid and liquid characteristics relate to the wetting behavior of soft, swollen interfaces. In addition to the polymer elasticity, we demonstrate that surface tension, phase separation, and osmotic pressure are essential to describe the wetting physics. Experimentally, we employ confocal microscopy methods to study this behavior using silicone-based elastomers. In the second part of this talk, we combine colloidal-probe, lateral force measurements with confocal microscopy to explore how a stiff microparticle starts to move laterally on a soft, adhesive surface. Our current knowledge suggests that surface creases emerge when pulling the particle, governed by interfacial strength. The crease moves in a Schallamach wave-like manner, which requires a sticky but slippery crease interface.