Effect of interfaces on the nearby Brownian motion

TL;DR

This study uses large-scale molecular dynamics simulations to investigate how interfaces alter the long-time decay behavior of Brownian motion, revealing a breakdown of the no-slip boundary condition and implications for nanoscale sensing.

Contribution

It introduces a new Green-Kubo relation for interface friction and uncovers the modified decay law of velocity autocorrelation near boundaries.

Findings

Velocity autocorrelation decay changes from t^(-3/2) to t^(-5/2) near interfaces.

Breakdown of no-slip boundary condition at short times.

Potential application in nanoscale interface wettability sensing.

Abstract

Near-boundary Brownian motion is a classic hydrodynamic problem of great importance in a variety of fields, from biophysics to micro-/nanofluidics. However, due to challenges in experimental measurements of near-boundary dynamics, the effect of interfaces on Brownian motion has remained elusive. Here, we report a computational study of this effect using microsecond-long large-scale molecular dynamics simulations and our newly developed Green-Kubo relation for friction at the liquid-solid interface. Our computer experiment unambiguously reveals that the t^(-3/2) long-time decay of the velocity autocorrelation function of a Brownian particle in bulk liquid is replaced by a t^(-5/2) decay near a boundary. We discover a general breakdown of traditional no-slip boundary condition at short time scales and we show that this breakdown has a profound impact on the near-boundary Brownian motion. Our results demonstrate the potential of Brownian-particle based micro-/nano-sonar to probe the local wettability of liquid-solid interfaces.