Microfluidic Surface Shields: Control of Flow and Diffusion over Sensitive Surfaces

Abstract

Selective shielding of surfaces from flow and diffusion is essential in many domains of physics and engineering. We propose and characterize experimentally a framework to shield both flow and diffusion simultaneously within a reshapable fluid volume. To do so, we directly use flow singularities to generate conformal transforms of the diffusion profile, taking inspiration from classical cloaking devices. The properties of microfluidic surface shields as open-space diffusion filters (O-filters) are further investigated. An analytical model is provided, which yields an outstanding match with experimental measurements of both flow and tracer diffusion. Via conformal mapping, these measurements reveal a strong topological link with classical H-filters in microfluidics.