Translucency and negative temperature-dependence for the slip length of water on graphene

TL;DR

This study measures how water slip length varies with graphene layer thickness and temperature, revealing translucency effects and negative temperature dependence, crucial for nanofluidic device design.

Contribution

First experimental determination of water slip length on supported few-layer graphene, showing thickness-dependent translucency and negative temperature dependence.

Findings

Slip length on single-layer graphene varies with substrate.

Slip length decreases significantly with temperature increase.

Thickness influences slip length, approaching graphite values.

Abstract

Carbonous materials, such as graphene and carbon nanotube, have attracted tremendous attention in the fields of nanofluidics due to the slip at the interface between solid and liquid. The dependence of slip length for water on the types of supporting substrates and thickness of carbonous layer, which is critical for applications such as sustainable cooling of electronic devices, remains unknown. In this paper, using colloidal probe atomic force microscope, we measured the slip length of water on graphene ls supported by hydrophilic and hydrophobic substrates, i.e., SiO2 and octadecyltrimethoxysilane (OTS). The ls on single-layer graphene supported by SiO2 is found to be 1.6~1.9 nm, and by OTS is 8.5~0.9 nm. With the thickness of few-layer graphene increases to 3~4 layers, both ls gradually converge to the value of graphite (4.3~3.5 nm). Such thickness dependence is termed slip length translucency. Further, ls is found to decrease by about 70% with the temperature increases from 300 K to 350 K for 2-layer graphene supported by SiO2. These observations are explained by analysis based on Green-Kubo relation and McLachlan theory. Our results provide the first set of reference values for the slip length of water on supported few-layer graphene. They can not only serve as a direct experimental reference for solid-liquid interaction, but also provide guideline for the design of nanofluidics-based devices, for example the thermo-mechanical nanofluidic devices.