Abstract
A colloidal membrane is a one rod-length thick monolayer of aligned rods which spontaneously assembles in a mixture of rod-like viruses and non-adsorbing polymer. The complex structure of the monolayer edge modifies its fluctuations, effectively smoothing out the interface. We demonstrate that long filaments such as F-actin or flagella preferentially dissolve in the membrane's edge and can be used to control its interfacial properties. This effect is not driven by energetic interactions, but is rather a direct consequence of the intrinsic geometry of the constituent particles; hence we call such filaments geometrical edgeactants. Using optical manipulation techniques we adsorb individual filaments onto the edge of the colloidal membrane and measure their influence on the edge fluctuations. Edgeactants stiffen the interface, increasing its bending rigidity by up to an order of magnitude. Furthermore, they also locally suppress a polymorphic transition into twisted ribbons inherent to colloidal membranes. These results demonstrate new ways to control soft materials in which the final structure is only determined by the geometry of the constituent objects.