This project focuses on basic science and technological applications of organic-inorganic hybrid materials created by attaching short polymer chains (corona) to hard, inorganic nanostructures. Termed Nanoscale Organic Hybrid Materials (NOHMs), they are the first example of an organic-inorganic hybrid material in which each nanoscale building block is itself a hybrid. This design provides opportunities for scientific exploration and for engineering new materials with unusual combinations of properties that take advantage of the large library of available nanostructures and polymers for manipulating physical properties and function. Research in this study considers a particular family of NOHMs in which the corona is comprised of lithium-ion conducting polymers. This focus is motivated by the potential such materials hold for creating battery electrolytes with high, liquid-like ionic conductivity, tunable mechanical properties, and non-flammability under normal operating conditions for batteries. The work is important because it will enable batteries to safely utilize energetic metals as their anodes and to offer substantial increases in the amount of energy stored. Aspects of this promise have already been realized with the creation of a technology start-up company, NOHMs Technologies, which currently employs 14 persons. It is expected that further technological development may occur over the four-year performance period of this NSF award as fundamental understanding of the materials grow and as this understanding leads to new non-flammable electrolyte designs that can be used as drop-in replacements for currently used flammable battery electrolytes. The flexible design of NOHMs in multiple, easy-to-appreciate applications of broad-based societal interest (including batteries, 3D printing, and advanced lubricants) also provides important opportunities for introducing younger students (K-12) to nanotechnology. The project will engage these students and their teachers through demonstrations based on batteries. These demonstrations will be designed to teach students to think about batteries as chemical reactors that produce electrical energy as the principal product, and about the relationship between applications-oriented properties and the basic chemical and physical processes that must be understood and controlled to achieve them.
This project focuses on structure, component dynamics, and ion transport in Nanoscale Organic Hybrid Materials (NOHMs) created by densely tethering short polymer chains to inorganic nanostructures. A consequence of the design of NOHMs is that grafted polymer (corona) segments experience an entropic attractive force created by the constraint that segments must homogeneously fill the space between nanoparticle cores. This entropic force is currently believed to be responsible for at least three effects: (i) strong correlations of the cores, (ii) physical constraints analogous to cross-links on the corona, and (iii) suppressed density fluctuations on large length-scales, which causes the materials to exhibit low-wave vector structure distinct from conventional hard-sphere suspensions, but analogous to incompressible molecular fluids. On continuum length-scales the materials behave as soft glassy complex fluids in which each suspended particle carries around a share of the suspending medium at all times. In contrast, on nanometer length scales, they are granular. By isolating and studying contributions to NOHMs physical properties from surface crowding of corona chains, geometric confinement of corona chains between neighboring particles, entropy-mediated temporary cross-links between corona, and slow translation and reorientation dynamics of correlated cores, the proposed study will determine how interactions between corona polymer chains influence structure, rheology, and ion transport properties of the materials. The work will also explore phase stability, dynamics and ion transport in NOHMs, NOHMs/NOHMs blends, and NOHMs polymer blends. The proposed study aims to construct a physical model framework for understanding NOHMs transport behaviors and rheology.
