Exciton-mediated optical control of liquid-solid friction

TL;DR

This paper develops a microscopic theory showing how optically generated excitons can control liquid-solid friction in nanofluidic systems, affecting flow and transport properties.

Contribution

It introduces a novel exciton-mediated mechanism for optical control of nanofluidic friction, supported by analytical formulas and experimental data comparison.

Findings

Excitonic friction can significantly reduce slip length in nanochannels.

The theory quantitatively reproduces recent experimental measurements.

Optical excitation of excitons offers a tunable way to control nanofluidic flow.

Abstract

Interfacial friction in nanofluidic systems can arise from fluctuation-induced coupling between liquid charge fluctuations and the internal excitations of the confining solid. Here, we develop a microscopic theory of exciton-mediated solid-liquid friction based on the coupling between optically generated excitons and charge fluctuations in water. We distinguish between static excitons, localized by disorder or functionalization, and dynamic excitons, which interact with water through polarization fluctuations. In both cases, we derive analytical formulas for the excitonic friction, which is experimentally tunable and can significantly reduce the slip length and thereby the hydraulic permeability of nanochannels. Applying our framework to carbon nanotubes, we quantitatively reproduce the recent measurements of Kistwal et al., showing a reduction of nanotube diffusion under optical excitation, without fitting parameters. More broadly, our results establish excitons as a mechanism to optically control nanofluidic transport and suggest that excitonic photoluminescence could provide an optical probe of flow velocity inside nanochannels.