Room Temperature Ionic Liquids (RTIL) form micro-structures both in the bulk and near charged surfaces that are still not well understood. Continuum theories, including mean-field (Poisson-Boltzmann) and integral equations techniques (Mean Spherical approximation), predict that electrostatic interactions do not affect the density-density correlation function. This suggests a useful decoupling of the ionic positions and their charge. Given information about the location of the ions, electrostatic interactions give rise to a “spin-glass” Hamiltonian, where the valence of the charges plays the role of spins. In absence of solvent, the large electrostatic energy (compared with thermal fluctuations) drives the spin-glass to its ground state. We apply the spin-glass model to Molecular Dynamics (MD) simulations of RTILs in the bulk and near charged surfaces, and find exceptional agreement between the predicted ground state and the simulations. We are able to recover not only the correct charge distributions and double layer structure, but also the exact charges of nearly all of the ions. This suggests a hidden long-range order in ionic liquids, that carries information about the charges. We further explore how this long range order disappears with increased solvent content, by studying Solvent-in-Salt MD simulations and random geometric graphs.<br/>

Room temperature ionic liquids as spin glasses

256th National Meeting (2018)

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