Numerical Simulation of Proton Distribution with Electric Double Layer in Extended Nanospaces

Abstract

Understanding the properties of liquid confined in extended nanospaces (10-1000 nm) is crucial for nanofluidics. Because of the confinement and surface effects, water may have specific structures and reveals unique physicochemical properties. Recently, our group has developed a super resolution laser-induced fluorescence (LIF) technique to visualize proton distribution with the electrical double layer (EDL) in a fused-silica extended nanochannel (Kazoe, Y.; Mawatari, K.; Sugii, Y.; Kitamori, T. Anal. Chem.2011, 83, 8152). In this study, based on the coupling of the Poisson-Boltzmann theory and site-dissociation model, the effect of specific water properties in an extended nanochannel on formation of EDL was investigated by comparison of numerical results with our previous experimental results. The numerical results of the proton distribution with a lower dielectric constant of approximately 17 were shown to be in good agreement with our experimental results, which confirms our previous observation showing a lower water permittivity in an extended nanochannel. In addition, the higher silanol deprotonation rate in extended nanochannels was also demonstrated, which is supported by our previous results of NMR and streaming current measurements. The present results will be beneficial for a further understanding of interfacial chemistry, fluid physics, and electrokinetics in extended nanochannels.

Energy Conversion From Salinity Gradient Using Microchip With Nafion Membrane

“…When the electrolyte was at higher pH value, the additional OH -were repelled by the cation-selective membrane, but might associate with H 2 O to form H 3 O 2 -28,29 . According to previously studies [30][31][32][33] , results indicated the spatial variation of surface charge density strongly depends on bulk concentration and pH value. The surface charge density increases with increasing the pH value due to the H + ion concentration is high in the Nafion membrane.…”

Investigation of Unique Protonic and Hydrodynamic Behavior of Aqueous Solutions Confined in Extended Nanospaces

“…The distribution of the proton concentrations of aqueous solutions in extended nanospaces was calculated, using numerical simulation, as a function of the effective dielectric constant (e) of the solution, and compared with the experimental data obtained using STED microscopy. [41] As shown in Figure 9, when the e value of 17 was assumed in a 410 nm-sized space, the experimental and theoretical profiles of proton concentrations were found to have similarities with each other. The e reduction to about 1/5 of that of the bulk (e = 79) for the extended nanospace was in good agreement with the value obtained by our streaming potential measurement.…”

Fundamentals and Modeling of Electrokinetic Transport in Nanochannels

“…When an aqueous solution is in contact with the substrate material of a solid‐state nanochannel, such as silicone dioxide (SiO 2 ), it reveals a charge‐regulated nature due to the protonation/deprotonation surface reaction. This implies that the surface charge property of the nanochannel depends strongly on the local concentration of the hydrogen ions (i.e., a pH value effect) on its surface 28–30. These surface charges attract the counter‐ions within the aqueous solution while simultaneously repulsing the co‐ions.…”