Nanorheology : an Investigation of the Boundary Condition at Hydrophobic and Hydrophilic Interfaces

TL;DR

This study investigates how polar liquids like water and glycerol behave at hydrophilic and hydrophobic interfaces, revealing no-slip conditions on hydrophilic surfaces and significant slip on hydrophobic ones using nanometer-resolution measurements.

Contribution

It provides experimental evidence of slip boundary conditions at hydrophobic interfaces for polar liquids, using a novel nanometer-resolution apparatus.

Findings

No-slip boundary condition on hydrophilic surfaces.

Significant slip (~100 nm) on hydrophobic surfaces.

Use of Dynamic Surface Force Apparatus for nanometer-scale measurements.

Abstract

t has been shown that the flow of a simple liquid over a solid surface can violate the so-called no-slip boundary condition. We investigate the flow of polar liquids, water and glycerol, on a hydrophilic Pyrex surface and a hydrophobic surface made of a Self-Assembled Monolayer of OTS (octadecyltrichlorosilane) on Pyrex. We use a Dynamic Surface Force Apparatus (DSFA) which allows one to study the flow of a liquid film confined between two surfaces with a nanometer resolution. No-slip boundary conditions are found for both fluids on hydrophilic surfaces only. Significant slip is found on the hydrophobic surfaces, with a typical length of one hundred nanometers.