Crack formation in wet colloidal pillars

TL;DR

This paper studies crack formation in wet colloidal pillars, revealing how wetting energy balances influence crack initiation and providing guidelines to prevent cracks during fabrication.

Contribution

It introduces a simple relationship between particle size and pillar dimensions based on wetting energy, aiding in crack prevention in colloidal structures.

Findings

Cracks form during drying at the free end of the pillar.

A balance of wetting energy terms explains crack formation.

A practical guideline for crack-free fabrication is derived.

Abstract

We investigate the initiation of cracks in vertically freestanding water-saturated colloidal pillars constructed using a direct-write technique. Paradoxically, the cracks form during drying at the free end, far from the substrate, where the particle network is unconstrained in contracting its volume as it bears compression by a uniform capillary pressure acting at its outer surface. This is explained by a dominant balance of wetting energy terms, from which follows a simple relationship between the particle size and pillar dimensions that captures the presence or absence of cracks. This relationship provides a practical guideline for fabricating crack-free colloidal structures.