Frequency-dependent response of confined electrolytes Minh-Thê Hoang Ngoc 1 , Benjamin Rotenberg 1 , Gabriel Stoltz 2 1 CNRS, Sorbonne Université, France 2 CERMICS, Ecole des Ponts, Marne-la-Vallée, France
Experimentally, the ionic current of confined electrolytes exhibits generic low-frequency fluctuations, yet a full explanation of the microscopic origins of this “1/f” noise remains elusive [1-2] . Understanding the underlying dynamics remains a crucial step to control the transport of water and ions at the nanoscale [3] , and the frequency- dependent conductivity of electrolytes reflects the various timescales governing microscopic dynamics [4] . Using Brownian particles simulations [5] and continuous modeling, we investigate the effects of confinement, adsorption on surfaces and ion-ion interactions on the response of confined electrolyte solutions to oscillating electric fields. Making use of appropriate Green–Kubo relation [6-7] for the electrical conductivity, we highlight the contributions of the underlying thermal fluctuations and of the interactions of the particles between themselves and with external potentials. The frequency-dependent conductivity always decays from a bulk-like behavior at high frequency to a vanishing conductivity at low frequency due to the confinement of the charge carriers by the walls. We discuss the characteristic features of this crossover, and most importantly how the transition frequency depends on the confining distance and the salt concentration, and the fact that adsorption on the walls may lead to significant changes both at high- and low-frequencies. Conversely, our results illustrate the possibility to obtain information on diffusion between walls, charge relaxation and adsorption by analyzing the frequency-dependent conductivity [8] . This work is part of the ERC project SENSES (grant No. 863473). Project website: https://benrotenberg.github.io/erc-senses/ References 1. S.J. Heerema, G.F. Schneider, M. Rozemuller, L. Vicarelli, H.W. Zandbergen, C. Dekker, “1/f noise in graphene nanopores”, Nanotechnology 26 074001 (2015) 2. D.P. Hoogerheide, S. Garaj, J.A. Golovchenko, “Probing Surface Charge Fluctuations with Solid-State Nanopores”, Physical Review Letter 102, 256804 (2009) 3. N. Kavokine, R. R. Netz, L. Bocquet, “Fluids at the Nanoscale: from continuum to sub-continuum transport”, Annual Review of Fluid Mechanics Vol. 53:377-410 (2021) 4. A. Chandra, B. Bagchi, “Frequency dependence of ionic conductivity of electrolyte solutions”,The Journal of chemical physics 112, 1876 (2000) 5. M. Jardat, O. Bernard, P. Turq, G. R. Kneller, “Transport coefficients of electrolyte solutions from Smart Brownian dynamics simulations”, The Journal of chemical physics 110, 7993 (1999) 6. B. Felderhof and R. Jones, “Linear response theory of the viscosity of suspensions of spherical brownian particles”, Physica A: Statistical Mechanics and its Applications 146, 417–432 (1987). 7. R. Joubaud, G. Pavliotis, and G. Stoltz, “Langevin dynamics with space-time periodic nonequilibrium forcing”,Journal of Statistical Physics 158, 1–36 (2014) 8. T. Hoang Ngoc Minh, G. Stoltz, B. Rotenberg “Frequency and field-dependent response of confined electrolytes from Brownian dynamics simulations”, The Journal of chemical physics 158, 104103 (2023)
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