Sessile droplet templating of miniature porous hemispheres from colloid crystals

A process for efficient and reproducible preparation of assemblies with a controlled hemispherical shape 10-100 μm in diameter was investigated. The use of hydrophobized substrates and higher volume fractions allowed for overriding of the coffee ring effect that commonly distorts the spherical surface of droplets drying on surfaces. The particles were concentrated and confined in the thin film that formed and were transported to the periphery by the flux of liquid, compensating for evaporation near the three phase contact line. The evaporating dynamics of the drying colloidal suspension drops were monitored using a CCD camera affixed to a microscope, and the resulting crystalline structure was observed with scanning electron microscopy (SEM). It was observed that the structures are stable in water and can readily withstand the level of mechanical loading.