Brownian motion near soft interfaces – EMetBrown

Soft and wet contacts are ubiquitous from geology to biology and are crucial for engineering. Furthermore, many key processes of life are governed by microscopic motility in soft and confined environments with the aim of reaching specific targets. In soft matter, an emergent elastohydrodynamic (EHD) lift force was theoretically predicted recently for elastic bodies moving past each other in a fluid. An active community, including the PI, has thus explored this striking effect with various deterministic models and experiments, showing its potential relevance for biological and nanoscale systems. In this context, and moving beyond the deterministic, the PI’s claim is that such EHD forces are even spontaneously triggered by thermal fluctuations. The result is an original migration scenario at small scales – with enormous implications. However, it is intriguing to note that studies are scarce on the topic.

The ambition of EMetBrown is to address this frontier challenge and set the ground for a new physical description of biological motility by solving a fundamental problem at the boundary between 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 toward the design of new methods for the rheology of biological and nanoscale materials, surface patterning and medical research.

These objectives will be reached by a combination of experiments, theory and numerics – all of which are familiar to the PI from past research. 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 methods will be employed in four work packages, covering hard, soft, biological and fluctuating interfaces, as well as directive flow.