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Electrolyte-filled subnanometre pores exhibit exciting physics and play an increasingly important role in science and technology. In supercapacitors, for instance, ultranarrow pores provide excellent capacitive characteristics. However, ions experience difficulties in entering and leaving such pores, which slows down charging and discharging processes. In an earlier work we showed for a simple model that a slow voltage sweep charges ultranarrow pores quicker than an abrupt voltage step. A slowly applied voltage avoids ionic clogging and co-ion trapping—a problem known to occur when the applied potential is varied too quickly—causing sluggish dynamics. Herein, we verify this finding experimentally. Guided by theoretical considerations, we also develop a non-linear voltage sweep and demonstrate, with molecular dynamics simulations, that it can charge a nanopore even faster than the corresponding optimized linear sweep. For discharging we find, with simulations and in experiments, that if we reverse the applied potential and then sweep it to zero, the pores lose their charge much quicker than they do for a short-circuited discharge over their internal resistance. Our findings open up opportunities to greatly accelerate charging and discharging of subnanometre pores without compromising the capacitive characteristics, improving their importance for energy storage, capacitive deionization, and electrochemical heat harvesting. Narrowing pores filled with an electrolyte usually slows down their charge-discharge dynamics. Here the authors demonstrate through molecular dynamics simulations and experiments with novolac-derived carbon electrodes how non-linear voltage sweeps can accelerate charging and discharging of subnanometer pores.

I discuss the strong link between the transmission line (TL) equation and the TL circuit model for the charging of an electrolyte-filled pore of finite length. In particular, I show how Robin and Neumann boundary conditions to the TL equation, proposed by others on physical grounds, also emerge in the TL circuit subject to a stepwise potential. The pore relaxes with a timescale \\(\\), an expression for which consistently follows from the TL circuit, TL equation, and from the pore's known impedance. An approximation to \\(\\) explains the numerically determined relaxation time of the stack-electrode model of Lian et al. [Phys. Rev. Lett. 124, 076001 (2020), arXiv:1911.09924].

Most self-reported diagnoses of gout will originate from a diagnosis made by a family physician as most patients presenting with acute gout are managed by them. 2 5 This makes the primary care setting particularly relevant to test the ACR criteria.

With two minimal models, I study how electrode curvature affects the response of electrolytes to applied electrostatic potentials. For flat electrodes, Bazant et al. [Phys. Rev. E. 70, 021506 (2004)] popularized the \"RC\" timescale \\(_D L/D\\), with \\(_D\\) being the Debye length, \\(2L\\) the electrode separation, and \\(D\\) the ionic diffusivity. For thin electric double layers near concentric spherical and coaxial cylindrical electrodes, I show here that equivalent circuit models again predict the correct ionic relaxation timescales. Importantly, these timescales explicitly depend on both electrode radii, not simply on their difference.

Electric double layer (EDL) formation underlies the functioning of supercapacitors and several other electrochemical technologies. Here, we study how the EDL formation near two flat blocking electrodes separated by \\(2L\\) is affected by beyond-mean-field Coulombic interactions, which can be substantial for electrolytes of high salt concentration or with multivalent ions. Our model combines the Nernst-Planck and Bazant-Storey-Kornyshev (BSK) equations; the latter is a modified Poisson equation with a correlation length \\(_c\\). In response to a voltage step, the system charges exponentially with a characteristic timescale \\(\\) that depends nonmonotonically on \\(_c\\). For small \\(_c\\), \\(\\) is given by the BSK capacitance times a dilute electrolyte's resistance, in line with [Zhao, Phys. Rev. E 84, 051504 (2011)]; here, \\(\\) decreases with increasing \\(_c\\). Increasing the correlation length beyond \\(_c L^2/3_D^1/3\\), with \\(_D\\) the Debye length, \\(\\) reaches a minimum, rises as \\( _D_c/D\\), and plateaus at \\(=4L^2/(^2 D)\\). Our results imply that strongly correlated, strongly confined electrolytes - ionic liquids in the surface force balance apparatus, say - move slower than predicted so far.

Batteries, supercapacitors, and several other electrochemical devices charge by accumulating ions in the pores of electrolyte-immersed porous electrodes. The charging of such devices has long been interpreted using equivalent circuits and the partial differential equations these give rise to. Here, we discuss the validity of the transmission line (TL) circuit and equation for modeling a single electrolyte-filled pore in contact with a reservoir of resistance \\(R_r\\). The textbook derivation of the pore-reservoir impedance \\(R_r+Z_p\\) from the TL equation does not correctly account for ionic current conservation at the pore-reservoir interface. However, correcting this shortcoming leads to the same impedance. We also show that the pore impedance \\(Z_p\\) can be derived directly from the TL circuit, bypassing the TL equation completely. The TL circuit assumes equipotential lines in an electrolyte-filled pore to be straight, which is not the case near the pore entrance and end. To determine the importance of these regions, we numerically simulated the charging of pores of different lengths \\(_p\\) and radii \\(_p\\) through the Poisson-Nernst-Planck equations. We find that pores with aspect ratios beyond \\(_p/_p5\\) have impedances in good agreement with \\(Z_p\\).

Single-ion Soret coefficients \\(_i\\) characterize the tendency of ions in an electrolyte solution to move in a thermal gradient. When these coefficients differ between cations and anions, an electric field can be generated. For this so-called electrolyte Seebeck effect to occur, the different thermodiffusive fluxes need to be blocked by boundaries -- electrodes, for example. Local charge neutrality is then broken in the Debye-length vicinity of the electrodes. Confusingly, many authors point to these regions as the source of the thermoelectric field yet ignore them in derivations of the time-dependent Seebeck coefficient \\(S(t)\\), giving a false impression that the electrolyte Seebeck effect is purely a bulk phenomenon. Without enforcing local electroneutrality, we derive \\(S(t)\\) generated by a binary electrolyte with arbitrary ionic valencies subject to a time-dependent thermal gradient. Next, we experimentally measure \\(S(t)\\) for five acids, bases, and salts near titanium electrodes. For the steady state we find \\(S2~mV~K^-1\\) for many electrolytes, roughly one order of magnitude larger than predictions based on literature \\(_i\\). We fit our expression for \\(S(t)\\) to the experimental data, treating the \\(_i\\) as fit parameters, and also find larger-than-literature values, accordingly.

We study the transient response of an electrolytic cell subject to a small, suddenly applied temperature increase at one of its two bounding electrode surfaces. An inhomogeneous temperature profile then develops, causing, via the Soret effect, ionic rearrangements towards a state of polarized ionic charge density \\(q\\) and local salt density \\(c\\). For the case of equal cationic and anionic diffusivities, we derive analytical approximations to \\(q, c\\), and the thermovoltage \\(V_T\\) for early (\\(t_T\\)) and late (\\(t_T\\)) times as compared to the relaxation time \\(_T\\) of the temperature. We challenge the conventional wisdom that the typically large Lewis number, the ratio \\(a/D\\) of thermal to ionic diffusivities, of most liquids implies a quickly reached steady-state temperature profile onto which ions relax slowly. Though true for the evolution of \\(c\\), it turns out that \\(q\\) (and \\(V_T\\)) can respond much faster. Particularly when the cell is much bigger than the Debye length, a significant portion of the transient response of the cell falls in the \\(t_T\\) regime, for which our approximated \\(q\\) (corroborated by numerics) exhibits a density wave that has not been discussed before in this context. For electrolytes with unequal ionic diffusivities, \\(V_T\\) exhibits a two-step relaxation process, in agreement with experimental data of Bonetti et al. [J. Chem. Phys. 142, 244708 (2015)].

Macromolecular crowding affects biophysical processes as diverse as diffusion, gene expression, cell growth, and senescence. Yet, there is no comprehensive understanding of how crowding affects reactions, particularly multivalent binding. Herein, we use scaled particle theory and develop a molecular simulation method to investigate the binding of monovalent to divalent biomolecules. We find that crowding can increase or reduce cooperativity--the extent to which the binding of a second molecule is enhanced after binding a first molecule--by orders of magnitude, depending on the sizes of the involved molecular complexes. Cooperativity generally increases when a divalent molecule swells and then shrinks upon binding two ligands. Our calculations also reveal that, in some cases, crowding enables binding that does not occur otherwise. As an immunological example, we consider Immunoglobulin G-antigen binding and show that crowding enhances its cooperativity in bulk but reduces it when an Immunoglobulin G binds antigens on a surface.

At model water--vapor and water--solid interfaces, molecular ordering leads to charge oscillations and, thereby, to a spatially varying electrostatic potential. Atomistic simulations indicate that such ordering leads to an electric potential difference \\(\\), the surface potential, of about \\(-0.5\\,V\\) across the first few molecular layers. Here, we calculate surface potentials at interfaces between a simple model fluids and a solid, with Molecular Dynamics simulations. The fluids are made up of either diatomic, dipolar molecules or a single Lennard-Jones particle with a dipole moment. All fluids show some structuring near the interface, but charge oscillations and a non-zero surface potential are present only for asymmetric molecules (unequal diameters of the atoms) or molecules with an off-center dipole. We condense this finding into the criterion that the geometric and dipolar centers of a molecule must differ for the fluid to exhibit a surface potential. Remarkably, while the solid--fluid interaction strength strongly affects the magnitude of charge oscillations, it hardly affects the potential drop \\(\\). Further, our results demonstrate that changing the diameter of the smaller atom can flip the sign of the surface potential, thus highlighting the importance of steric effects.