Generalized Taylor Dispersion for Translationally Invariant Microfluidic Systems

We consider Taylor dispersion for tracer particles in microfluidic planar channels with strong confinement. In this context, the channel walls modify the local diffusivity tensor and also interactions between the tracer particles and the walls become important. We provide a simple and general formula for the effective diffusion constant along the channel as well as the first non-trivial finite time correction for arbitrary flows along the channel, arbitrary interaction potentials with the walls, and arbitrary expressions for the diffusion tensor. The formulas are in particular amenable to a straightforward numerical implementation, rendering them extremely useful for comparison with experiments. We present a number of applications, notably for systems that have parabolically varying diffusivity profiles, to systems with attractive interactions with the walls as well as electro-osmotic flows between plates with differing surface charges within the Debye–Hückel approximation.