Effect of a non-volatile cosolvent on crack pattern induced by desiccation of a colloidal gel

TL;DR

This study demonstrates that adding a non-volatile cosolvent like glycerol to colloidal gels reduces crack formation during drying by flattening pressure gradients, leading to crack-free coatings at sufficient glycerol concentrations.

Contribution

It reveals how glycerol addition influences crack patterns in drying colloidal gels by modifying pressure gradients and mechanical properties, a novel insight into crack prevention mechanisms.

Findings

Glycerol inhibits crack formation in colloidal gels.

Addition of >10% glycerol results in crack-free coatings.

Glycerol reduces the elastic modulus of the gel.

Abstract

Consolidation of colloidal gels results in enormous stresses that are usually released in the formation of undesirable cracks. The capacity of a gel network to crack during drying depends on the existence and significance of a pressure gradient in the pore liquid; in addition it depends on the way the gel relaxes the resulting drying stresses. In this paper the effect of a binary mixture of solvents saturating the gel network on the crack patterns formation is investigated. Indeed, incorporation of a small quantity of non-volatile cosolvent, i.e. glycerol, inhibits drying-induced cracks; moreover addition of a concentration greater than 10% to a colloidal dispersion leads to a crack free coating in room conditions. Mass variation with time reveals that both evaporation rate and cracking time are not affected by glycerol, in the range of added glycerol contents studied. In addition measurements of mechanical properties show that the elastic modulus is reduced with glycerol content. The decrease of the number of cracks with the glycerol content is related to the flattening of the pressure gradient in the pore liquid. The mechanism is shown to be due to the combination of two processes: flow driven by the pressure gradient and diffusion mechanisms in accordance with Scherer work (1989).