Evaporation-driven colloidal cluster assembly using droplets on superhydrophobic fractal-like structures

• Published in: Soft matter Vol. 17; no. 3; pp. 506 - 515
• Main Authors: Seyfert, Carola, Berenschot, Erwin J W, Tas, Niels R, Susarrey-Arce, Arturo, Marin, Alvaro
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 21.01.2021
• Subjects: Assembly; Clusters; Droplets; Evaporation; Evaporation rate; Fractals; Hydrophobic surfaces; Hydrophobicity; Microparticles; Spheroids; Substrates; Wetting
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/d0sm01346c

Microparticles can be considered building units for functional systems, but their assembly into larger structures typically involves complex methods. In this work, we show that a large variety of macro-agglomerate clusters ("supra-particles") can be obtained, by systematically varying the initial particle concentration in an evaporating droplet, spanning more than 3 decades. The key is the use of robust superhydrophobic substrates: in this study we make use of a recently discovered kind of patterned surface with fractal-like microstructures which dramatically reduce the contact of the droplet with the solid substrate. Our results show a clear transition from quasi-2D to 3D clusters as a function of the initial particle concentration, and a clear transition from unstable to stable 3D spheroids as a function of the evaporation rate. The origin of such shape transitions can respectively be found in the dynamic wetting of the fractal-like structure, but also in the enhanced mechanical stability of the particle agglomerate as its particle packing fraction increases.