Water Density in the Electric Double Layer at the Insulator/Electrolyte Solution Interface

Abstract

I studied the spatial structure of the thick transition region between n-hexane and a colloidal solution of 7-nm silica particles by X-ray reflectivity and grazing incidence small-angle scattering. The interfacial structure is discussed in terms of a semiquantitative interface model wherein the potential gradient at the n-hexane/sol interface reflects the difference in the potentials of "image forces" between the cationic Na + and anions (nanoparticles) and the specific adsorption of surface charge at the interface between the adsorbed layer and the solution, as well as at the interface between the adsorbed layer and n-hexane. The X-ray scattering data revealed that the average density of water in the field ∼10 9 -10 10 V/m of the electrical double layer at the hexane/silica sol interface is the same as, or only few percent higher (1-7%) than, its density under normal conditions.

Model-Independent X-Ray Scattering Study of a Silica Sol Surface

“…Finally, the thickness of layer 4 coincides with the diameter of colloidal nanoparticles in the solution and their surface density is much higher than their density in the bulk of the solution. This model is in agreement with small-angle grazing scattering and diffraction data [1,13].…”

Ion-size effect at the surface of a silica hydrosol

“…A field of such strength, which is impossible to obtain in an electrolytic capacitor, is common at the surface of a silica hydrosol that is strongly polarized by the forces of electrical imaging. 32,33 Previous x-ray reflectivity and grazing-incidence diffraction data for NaOH-stabilized and Csenriched suspensions with monodispersed 5-, 7-and 22-nm silica particles suggest that a four-layer model can describe the structure of the hydrosol's surface (see Fig. 2).…”

“…2). [32][33][34][35] The top two layers in Fig. 2 reflect the adsorption of alkali ions, i.e., a low-density layer 1 of suspended (elevated) ions, and a layer 2 of space charge with the surface density of Na with an NaOH-stabilized sol of 22 nm silica particles (~ 30% of SiO 2 by weight).…”

Электростатические И Структурные Эффекты При Адсорбции Полилизина На Поверхности Монослоя DMPS

“…Интенсивность сфокусированного монохроматического луча фотонов с длиной волны λ ≈ 0.18Å (энергия E кванта ∼ 70 кэВ, ∆E/E = 0.4 %) составляла ∼ 10 10 ф/с при размерах сечения пучка ∼ 6 мкм по высоте и ∼ 150 мкм в горизонтальной плоскости. Методика проведения измерений R описана в работах [18][19][20][21]. Образцы монослоев фосфолипида DMPS приготавливались в условиях, аналогичных приведенным выше при измерениях диаграмм сжатия, но в ванне-тарелке из тетрафторэтилена круглой формы (диаметром 10 см).…”