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.
