Driving force of water entry into hydrophobic channels of carbon nanotubes: entropy or energy?

TL;DR

This study uses molecular dynamics simulations to analyze the thermodynamics of water entering single-wall carbon nanotubes, revealing that both energy and entropy favor the process across various temperatures and interaction strengths.

Contribution

It provides a detailed thermodynamic analysis of water entry into SWCNTs, highlighting the roles of energy and entropy, which was not comprehensively understood before.

Findings

Both energy and entropy decrease with increasing temperature.

Reducing nanotube-water attraction increases energy of transfer.

Both energy and entropy favor water entry into SWCNTs.

Abstract

Spontaneous entry of water molecules inside single-wall carbon nanotubes (SWCNTs) has been confirmed by both simulations and experiments. Using molecular dynamics simulations, we have studied the thermodynamics of filling of a (6,6) carbon nanotube in a temperature range from 273 to 353 K and with different strengths of the nanotube-water interaction. From explicit energy and entropy calculations using the two-phase thermodynamics method, we have presented a thermodynamic understanding of the filling behaviour of a nanotube. We show that both the energy and the entropy of transfer decrease with increasing temperature. On the other hand, scaling down the attractive part of the carbon-oxygen interaction results in increased energy of transfer while the entropy of transfer increases slowly with decreasing the interaction strength. Our results indicate that both energy and entropy favour water entry into (6,6) SWCNTs. Our results are compared with those of several recent studies of water entry into carbon nanotubes.