Brownian Motion near Soft Interfaces

Soft and wet contacts are ubiquitous across scales from geology to physiology and are crucial for engineering. Furthermore, many processes of physics and biology at small scales are governed by the mobility of microscopic entities in soft and confined environments, with the aim of reaching specific targets. Interestingly, an emergent elastohydrodynamic (EHD) lift force was theoretically predicted recently for an immersed object moving near an elastic wall. An active community, including the PI, has started to explore this striking effect with various deterministic models and experiments, showing its relevance for nanoscale and biomimetic systems. In this context, and moving beyond the deterministic, the PIs central claim is that such EHD effects can be spontaneously triggered by thermal fluctuations. The result would be an original migration scenario in complex and confined environments with enormous implications. However, studies are scarce on the topic. The ambition of EMetBrown is thus to address this challenge at the interface between two mature fields, by solving a fundamental problem involving both continuum and statistical mechanics: Brownian motion near soft interfaces. The three objectives are to reveal, explore and harvest the signatures of such motion, paving the way towards the future design of methods for particle transport, surface patterning, confined reactions and nanorheology. These objectives will be reached using a combination of experiments, theory and numerics, domains in which the PI has extensive experience. EMetBrown involves three core experimental setups (free colloids, optical trapping and atomic-force microscopy), three core theoretical models (soft lubrication, stochastic theory and Langevin simulations) and three exploratory tools (microfluidics, suspension rheometry and molecular dynamics). These complementary methods will be employed through four work packages covering various viscous, hard, soft materials, as well as applied flow.