Velocity Weakening in Anisotropic Friction on a Tilted Titania Nanorod Forest

TL;DR

This study reveals that anisotropic titania nanorod surfaces exhibit velocity-dependent friction that weakens with increased sliding speed, influenced by nanorod viscoelasticity, with potential applications in microscale sensors.

Contribution

It demonstrates velocity weakening in anisotropic nanorod friction and models it using viscoelastic creep, advancing understanding of nanoscale directional friction behavior.

Findings

Friction decreases logarithmically with speed

Velocity weakening is more pronounced perpendicular to tilt

Creep measurements align with the SLS viscoelastic model

Abstract

In this study, we demonstrate velocity-dependent directional friction on a surface structured with tilted (~57{\deg}) titania nanorods using standard and colloidal probe force microscopy. Friction is measured at four different sliding speeds in two configurations, along and opposite to the tilt and perpendicular to the tilt direction, exhibiting anisotropic friction. Furthermore, friction decreases logarithmically with increasing sliding speed, which is attributed to the viscoelastic bending of the nanorods caused by stress-induced defect migration. The velocity weakening is more pronounced in the direction perpendicular to the tilt than along and opposite to it. The experimental findings are corroborated by creep measurements, which are well-reproduced by the Standard Linear Solid (SLS) model of viscoelasticity. Our results may be applied to the development of direction- and velocity-dependent sensors for microscale sliding motion as a robust alternative to structured interfaces based on polymeric materials.