The interplay of massively collective non-covalent interactions can give rise to surprising bulk material properties. I will describe a new type of solid material that simultaneously possesses a high mechanical stiffness and yet free (liquid-like) ion motions inside. We build this material from a rigid-rod ionic polymer (essentially sulfonated Kevlar) and a strongly correlated liquid (an ionic liquid). We call this new class of materials “molecular ionic composites” (MICs).<br/>By contemplating the non-covalent forces and anisotropy present in these systems, we can understand the correlated “electrostatic network” that arises in MICs. The figure shows an MD simulated view of a MIC, looking down the polyanion rod axes (yellow sulfonates and turquoise polymer backbones), which are surrounded by correlated clouds of ionic liquid cations (blue) and anions (red). The sulfonated rigid-rod polymer forms a helical dimer that helps provide a rigidity persistence length of ~ 100 nanometers along the rod axis. The high stiffness (E’ up to 3 GPa), high thermal stability (up to 300 deg. C), high conductivity (up to 8 mS/cm), and anisotropic properties of MICs show promise for enabling safe and higher density rechargeable batteries as well as other electrochemical devices. This talk will overview our attempts to understand and design the behaviors of MICs from atomic to bulk length scales by combining NMR spectroscopy and diffusometry, MD simulations, dielectric spectroscopy, shear rheology, tensile testing, X-ray diffraction, and a host of other characterization techniques.

Molecular ionic composites: Stiff solids with liquid-like ions inside

255th National Meeting (2018)

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