(637a) Capillary Bridging of Particles As a Tool for Supracolloidal Assembly

Authors: 
Bharti, B., North Carolina State University
Rubinstein, M., University of North Carolina at Chapel Hill
Velev, O. D., North Carolina State University

The capillary forces on the macro- and nanoscale are emerging as a research theme of interest, because of the very unusual characteristics of the attraction potential induced by liquid bridging as compared to the traditional surface interactions. Capillary attraction between particles can lead to their assembly into complex architectures at sub-micron length-scale. However, the presence of capillary forces at the nanoscale has not been reported or used as a tool for nanoparticle binding in liquid media. Recently we demonstrated that these nanocapillary forces can be used for making new classes of nanoparticle assemblies in the form of ultraflexible filaments and self-healing 2D gels. We showed that maghemite nanoparticles wetted with lipids can be assembled into mocrofilaments upon the application of external magnetic field. The lipid capillary bridges formed between the particles enable their permanent binding and sustain the flexible microfilament structure. The universality of this fluid induced particle binding approach has now been demonstrated by extending it to lipid mediated capillary bridging to microscale. Here we direct the assembly of metallo-dielectric patchy microparticles into well-defined colloidal clusters bound by fluid induced capillary interactions. Polystyrene microspheres can be designed to have discrete iron oxide surface patch(es) of controllable size and shape. The strong affinity of n-alkanoic fatty acids for iron oxide can be used for its selective condensation on the oxidized metal patch. The condensed fluid fatty acid patch makes the particle stereoselectively sticky and leads to their self‑assembly into discrete clusters of well-defined morphology. This lipid based capillary binding is an unconventional way of assembling structures at meso-, micro and nanoscale. The ordered structures can be further used to organize materials that can self-reconfigure by changing the phase of capillary binding fluid.