Liquid flow retardation in nanospaces due to electroviscosity: Electrical double layer overlap, hydrodynamic slippage, and ambient atmospheric CO2 dissolution

Abstract

A theoretical investigation is performed into the electroviscous-induced retardation of liquid flows through finitely long nanochannels or nanotubes with large wells at either end. Given the assumption of equilibrium conditions between the ionic solution in the wells and that within the nanochannel or nanotube, an exact solution is derived for the overlapped electrical double layer (EDL) for the case where the concentrations of the positive and negative ions in the wells may be unequal. The ion concentrations in the wells are determined by the conditions of global electroneutrality and mass conservation. It is shown that the overlapped EDL model proposed by Baldessari and Santiago [J. Colloid Interface Sci. 325, 526 (2008)10.1016/j.jcis.2008.06.007] is in fact the same as the “thick EDL model” (i.e., the traditional Poisson-Boltzmann model) when the positive and negative ion concentrations in the large enough wells are both equal to the bulk concentration of the salt solution. Utilizing the proposed overlapped EDL analytical model, an investigation is performed to evaluate the effects of hydrodynamic slippage on the flow retardation caused by electroviscosity in nanochannels or nanotubes. Furthermore, exact and approximate solutions are derived for the electroviscosity in ion-selective nanochannels and nanotubes. It is shown that in the absence of slip, the maximum electroviscosity in nanochannels and nanotubes containing a unipolar solution of simple monovalent counter-ions occurs at surface charge densities of h|σ| = 0.32 nm × C/m2 and a|σ| ≈ 0.4 nm × C/m2, respectively. In addition, it is shown that the electroviscosity in a nanotube is smaller than that in a nanochannel. For example, given a LiCl solution, the maximum electroviscosites in a non-slip nanochannel and non-slip nanotube are ηa/η ≈ 1.6 and 1.47, respectively. For both nanospaces, the electroviscosity is greatly increased when the liquid slip effect is taken into account. Significantly, under slip conditions, the electroviscosity in the nanotube is greater than that in the nanochannel. Finally, an investigation is performed into the effects of ambient atmospheric CO2 dissolution on the electroviscosities of salt/buffer solution and deionized (DI) water in silica nanochannels. The results show that the electroviscosity of CO2-saturated DI water (pH = 5.6) can be reasonably neglected in silica nanochannels with a height of less than 100 nm.

Self‐Powered Wearable Electronics Based on Moisture Enabled Electricity Generation

“…The above results clearly show that the electrical generating capacity of TDNN MEEGs arises from the diffusion of water molecules along the many nanochannels that exist in the nanowire network. The streaming potential,a classic electrokinetic phenomenon induced by driving ionic solutions through narrow channels under a pressure gradient, is likely the source of the voltage measured across the electrodes. As synthesized, TiO 2 nanowires are negative charged in neutral water and have a zeta potential of ≈−20 mV (Figure S20, Supporting Information).…”

Fundamentals and Modeling of Electrokinetic Transport in Nanochannels

“…Significantly, the electroviscosity in the nanotube is greater than that in the nanochannel under slip conditions, as shown in Figure 6. When the slip length is comparable with the nanochannel half‐height or nanotube radius, the electroviscous effect increases the intrinsic viscosity by more than 100 % 48…”

“…Moreover, the lines with circle symbols represent the results obtained for a nanotube. The numerical results were obtained using the full PB model and given Cl − co‐ions, a low salt concentration of ${c{{\infty \hfill \atop i\hfill}}}$ =0.1 mM, and a specific surface charge density of σ =−10 mC/m 2 48…”

“…The numerical results were obtained using the full PB model and given Cl − co‐ions, a low salt concentration of ${c{{\infty \hfill \atop i\hfill}}}$ =0.1 mM, and a specific surface charge density of σ =−10 mC/m 2 . The numbers in the figure represent the value of the slip ratio, i.e., b / h or b / a 48…”

A Self-Powered Nanogenerator for the Electrical Protection of Integrated Circuits from Trace Amounts of Liquid

“…Waterproofing technologies such as specialized packaging and the typical application of glue/rubber sealants have been utilized to protect laptops and other electronic devices from water and other liquids, but the packaging and sealing of PCBs are expensive and can decrease the dissipation of excess heat [1]. Recent research on water-induced power generators shows that the electrical output of these units can be sufficient to power external circuits [2][3][4][5][6][7][8][9][10][11], suggesting an alternative to solve this problem. This new methodology would involve using the electrical output of an onboard water-induced power generator to trigger the cutoff of power to the PCB prior to the formation of a short circuit induced by the ingress of liquid.…”