Ionization at a solid-water interface in an applied electric field: Charge regulation

Ryuichi Okamoto, Akira Onuki

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2 Citations (Scopus)


We investigate ionization at a solid-water interface in an applied electric field. We attach an electrode to a dielectric film bearing silanol or carboxyl groups with an areal density Γ0, where the degree of dissociation α is determined by the proton density in water close to the film. We show how α depends on the density n0 of NaOH in water and the surface charge density σm on the electrode. For σm > 0, the protons are expelled away from the film, leading to an increase in α. In particular, in the range 0 < σm < eΓ0, self-regulation occurs to realize α ≅ σm/eΓ0 for n0 nc, where nc is 0.01 mol/L for silica surfaces and is 2 × 10-5 mol/L for carboxyl-bearing surfaces. We also examine the charge regulation with decreasing the cell thickness H below the Debye length κ-1, where a crossover occurs at the Gouy-Chapman length. In particular, when σm ∼ eΓ0 and H κ-1, the surface charges remain only partially screened by ions, leading to a nonvanishing electric field in the interior.

Original languageEnglish
Article number124706
JournalJournal of Chemical Physics
Issue number12
Publication statusPublished - Sept 28 2016
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry


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