Comment on 'Development of a Measurement Technique for Ion Distribution in an Extended Nanochannel by Super-Resolution-Laser-Induced Fluorescence'

摘要

The electrical double layer (EDL) is an important concept for understanding electrostatic force acting between changed entities and describing the ionic distribution in the vicinity of a charged surface. According to the theories and relevant experiments, the thickness of the EDL depends on the ionic strength of a solution in contact with a charged surface. When the solution contains an appreciably high concentration of an electrolyte, i.e., millimolar or higher, the thickness of the EDL becomes as thin as a few nanometers. Difficulty in direct measurements of such a thin layer has facilitated theoretical work rather than experimental approaches. The Gouy-Chapman (GC) model derived from the Poisson-Boltzmann (PB) theory, which is one of the simple and intuitively understandable theories, basically well interprets a number of experimental facts, including the behavior of an electroactive solute at an electrode interface, the zeta potential of colloidal particles and charged surfaces, and even the separation behavior of ions in ion-exchange chromatography. However, there are some criticisms against the PB theory because it deals with ions as point charges and, therefore, the characters of ions are ignored. Theoretical simulations have been extensively attempted to reveal the distribution of ions and electrostatic potential in the EDL. Some results have suggested more complex distributions than that predicted by the GC model, while a number of studies still support this classical model particularly in the region apart from the charged surface.