Novel, cylindrical, ribbon-like membranes are formed when colloidal particles adsorb at the air-water interfaces of droplets confined between two glass plates (Fig. a). We have found that the ease with which such ribbon membranes bend depends on particle shape. Ellipsoidal particles on the interface locally deform the interface and thereby introduce strong capillary forces into the membrane that couple the particles into networks. The resultant membrane scaffolding can resist bending by as much as one hundred times more than similar membranes formed by spherical particles at the air-water interface [Phys. Rev. Lett. 108, 2012]. This increased bending rigidity makes interface buckling (Fig. b) harder, which in turn, reduces the effects of interface pinning and leads to uniform deposition of anisotropic particles from the evaporating drop (Fig. c). This deposition during evaporation is in stark contrast to that of similar drops containing spherical particles (Fig. d). The mechanisms for evaporation for the confined drops are also demonstrably different that for sessile drops which produce the famous coffee ring effect [Nature 476, 2011]. Besides their fundamental interest, these discoveries provide insight about how to control thin film uniformity and quality in applications such as arise in printing, painting and even genotyping.
