Quantum-mechanically enhanced water flow in sub-nanometer carbon nanotubes

TL;DR

This paper investigates the quantum-mechanical mechanisms behind water flow in sub-nanometer carbon nanotubes, revealing how weak water-phonon interactions protect superflow and differ from classical and semi-classical models, with implications for nanofluidics.

Contribution

It introduces a quantum-mechanical framework for understanding water-CNT friction, explaining superflow protection and discrepancies with classical theories.

Findings

Quantum effects hinder water-CNT scattering, enabling superflow.

Comparison shows quantum predictions are much lower than semi-classical models.

Potential applications include minimally-invasive cellular injections and water filtration.

Abstract

Water-flow in carbon nanotubes (CNT's) starkly contradicts classical fluid mechanics, with permeabilities that can exceed no-slip Haagen-Poiseuille predictions by two to five orders of magnitude. Semi-classical molecular dynamics accounts for enhanced flow-rates, that are attributed to curvature-dependent lattice mismatch. However, the steeper permeability-enhancement observed experimentally at $\sim$nm-size radii remains poorly understood, and suggests emergence of puzzling non-classical mechanisms. Here we address water-CNT friction from a quantum-mechanical perspective, in terms of water-energy loss upon phonon excitation. We find that combined weak water-phonon coupling and selection rules hinder water-CNT scattering, providing effective protection to water superflow, whereas comparison with a semiclassical theory evidences a friction increase that can exceed the quantum-mechanical prediction by more than two orders of magnitude. Quasi-frictionless flow up to sub-nm CNT's opens new pathways towards minimally-invasive trans-membrane cellular injections, single-water fluidics and efficient water filtration.