Hindered cracking in colloidal suspension coatings via evaporation-driven lyotropic liquid crystals

Abstract

We demonstrate that lyotropic liquid crystalline (LC) phases, formed by the molecular interactions between 1-glyceryl monooleyl ether (GME) and water, offer new pathways for producing crack-free particulate films from colloidal suspensions. Drying experiments on titanium dioxide-ethanol-water-GME suspension systems revealed a 15-fold increase in the critical cracking thickness, above which cracks spontaneously evolve, compared to suspensions without additives. Contrary to previous theoretical predictions based on capillary forces, the critical thicknesses ethanol-lean suspensions increased with higher particle packing volume fractions in the dried films. We developed a new phenomenological model that incorporates the formation of viscoelastic LC phases and found it to be in quantitative agreement with measurements. This suggests a versatile route for delaying cracking by introducing thermodynamically metastable phases of amphiphilic molecules. The evaporation-induced isotropic-LC transition was further verified by numerical predictions of the compositional trajectories on the phase diagram.