The interplay of collective intermolecular interactions and molecular orientation can give rise to surprising bulk material properties. I will describe a new type of oriented solid that simultaneously possesses a high mechanical stiffness and yet free (liquid-like) ion motions inside. We build this material from a strongly correlated liquid (an ionic liquid) and an oriented liquid consisting of a rigid-rod ionic polymer (essentially sulfonated Kevlar) in solution. We call this an “electrostatic network ion gel” (ENIG) and we might also consider this solid to be a “1D reinforced liquid”.<br/>     I will begin this talk by discussing phenomena in and parallels between correlated (ionic) liquids and oriented liquids. By contemplating the non-covalent forces and anisotropy present in these systems, we can understand the massively collective network that arises in an ENIG. The figure below shows an MD simulated view of an ENIG, looking down the polymer 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 is not only rigid in the single-molecule sense, but forms a helical dimer that helps provide a rigidity persistence length of at least tens of nanometers along the rod axis. In water solution, these extremely high aspect ratio rods form a highly aligned (S = 0.8) liquid at &gt; 1 wt%, which, along with the correlated ions, appear to be key to forming the rigid ENIG matrix. 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 ENIGs show promise for enabling high density and safe Li batteries as well as other electrochemical devices such as mechanical actuators.

Correlated liquid + oriented liquid = reinforced liquid: Conduction, alignment, and stiffness in a soft material

254th National Meeting (2017)

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