Establishing the principles and demonstrating the unique properties of novel reconfigurable nano- and microparticle structures bound by liquid bridges

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CBET - 1604116PI: Velev, Orlin D.Many technologically important materials are made by assembling colloidal particles into structures that often start with simple chains or filaments. A variety of techniques are available to assemble particles into chains, but so far it has proven challenging to make permanent chains that are flexible. This project will explore a new method for making highly flexible particle chains based on capillary attractions between particles coated with liquid lipids, which is broadly similar to the way sandcastles are bound by small volumes of liquid. The particles assemble due to liquid bridges that form between them when they are aligned by a magnetic field. Because the bridges are fluid, the resulting filaments are extremely flexible. The goal of the project is to characterize the capillary binding between colloidal particles and demonstrate that it can be used to make new classes of nanoparticle assemblies in the form of filaments, networks, and gels. Results of the project will provide new opportunities for assembling soft multifunctional materials whose properties can be dynamically controlled, such as temperature-responsive and self-repairing gels and novel 3D printing inks. The unusual characteristics of the materials that will be made in the project will provide a unique opportunity for science demonstrations to high-school students how nanoscale structures affect macroscopic properties. The project will provide training grounds for students to participate in hands-on research in nanoscale engineeringSuper-paramagnetic nanoparticles will be dispersed into aqueous solutions of fatty acid salts, which completely wet the particle's surface. Fatty acid molecules condense onto the surface to form liquid-like shells. The liquid-coated nanoparticles are assembled by applying an external magnetic field to align the particles into filaments, which remain intact after the external field is removed. The physical properties of filaments and other structures formed by the nanocapillary binding of isotropic and patchy particles will be investigated as a function of bridge fluidity, type and composition of the surface-condensed lipid. The project will focus on understanding the fundamental origins and measuring the magnitude of the capillary bridging force, on characterizing and modeling the properties of the assembled filaments, on using the assembly method to make hierarchical nano-microstructures, and on developing novel thixotropic gels. Such gels, based on silicone beads capillary bound by a liquid silicone precursor, will be tested as new material for 3D printing of flexible, porous and biologically compatible structures.