Abstract
A drop of an aqueous suspension of nanoparticles placed on a substrate forms a solid deposit as it dries. For dilute suspensions, particles accumulate within a narrow ring at the drop edge, whereas a uniform coating covering the entire wetted area forms for concentrated suspensions. In between these extremes, we report two additional regimes characterized by non-uniform deposit thicknesses and by distinct crack morphologies. We show that both the deposit shape and the number of cracks are controlled exclusively by the initial particle volume fraction. The different regimes share a common avalanche-like crack propagation dynamics, as a result of the delamination of the deposit from the substrate.
Highlights
Thin films of colloidal suspensions in contact with a substrate are prone to failure upon drying.[1,2,3,4] As the solvent evaporates, the particles are deposited on the substrate and form a closepacked coating.[5]
Coffee rings occurring in dilute suspensions and crack patterns occurring in concentrated suspensions illustrate two major limitations for using colloidal suspensions in coating applications: deposit heterogeneity and fragility
Our results reveal the rich variety of crack morphologies that can develop in drying drops of colloidal suspensions
Summary
Thin films of colloidal suspensions in contact with a substrate are prone to failure upon drying.[1,2,3,4] As the solvent evaporates, the particles are deposited on the substrate and form a closepacked coating.[5]. In the double-crack regime the width of the outer ring does not increase beyond 40% of the drop radius: the cracks stop branching into secondary cracks at a critical volume fraction f* = 6.3% Æ 0.4%, denoting the transition between the doublecrack and the single-crack regime.
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