Annular cracks in thin films of nanoparticle suspensions drying on a fiber

TL;DR

This study investigates the formation of annular crack patterns in drying nanoparticle suspension films on fibers, linking crack spacing to film thickness and substrate friction through experiments and modeling.

Contribution

It provides a quantitative analysis of crack spacing dependence on film thickness and substrate friction in nanoparticle suspension drying on fibers.

Findings

Crack spacing varies linearly with film thickness.

Friction force influences the critical stress for cracking.

Experimental data aligns with Kitsunezaki's model.

Abstract

We report an experimental study of the crack pattern formed during the drying of a colloidal suspension. A horizontal fiber, which provides a one dimensional, boundary-free substrate, is coated by a film of micronic thickness. The geometry imposes a remarkable annular crack pattern and allowing precise measurements of the crack spacing over a short range of film thickness (between 2 and 10 $\mu$m) which varies linearly with the film height. We compare our experimental data with a model proposed by Kitsunezaki which suggests that the variation of the crack spacing with the film thickness depends on the ratio between a critical stress at cracking and a critical stress for slipping on the substrate. By measuring the friction force of the colloidal gels on a hydrophobic surface through a cantilever technique, we can deduce the critical crack stress for these colloidal gels simply by measuring the crack spacing of the pattern.