Specifics about Specific Ion Adsorption from Heterodyne-Detected Second Harmonic Generation

Abstract

Ion specific outcomes at aqueous interfaces remain among the most enigmatic phenomena in interfacial chemistry. Here, charged fused silica/water interfaces have been probed by homodyne-and heterodyne-detected (HD) second harmonic generation (SHG) spectroscopy at pH 7 and pH 5.8 and for concentrations of LiCl, NaCl, NaBr, NaI, KCl, RbCl, and CsCl ranging from 10 M to several 100 mM. For ionic strengths around 0.1 mM to 1 mM,

Probing the Mineral–Water Interface with Nonlinear Optical Spectroscopy

“…Hence, the surface potential and the zeta potential are related to one another and cannot be treated separately. Although the Gouy–Chapman model has been shown to provide a good qualitative prediction of the ionic strength dependence of the NL response, [14e] it does not yield a satisfying description over the entire concentration range. For the model to work, dramatic changes in the screening properties need to be invoked by, for example, changes in the interfacial dielectric permittivity [15, 24] . This implies that some information is contained in the NL response that has so far not been considered.…”

“…Additionally, further changes in the surface charge and/or Stern layer charge were also necessary. A follow‐up study from 2019 showed that the level of the plateau at high concentration depends on the size of both the cation and anion [24] . This was interpreted as ion‐specific Stern‐layer properties among the investigated alkali halides.…”

A New Imaginary Term in the Second-Order Nonlinear Susceptibility from Charged Interfaces

“…2 Interference fringes are recorded using a second piece of z-cut a-quartz as a local oscillator on a 100 mm long translational stage, with each measurement taking about four minutes, as described previously. [1][2][3] Each mm distance equals 3.158° in phase space, allowing us to map out close to 90 percent of a given fringe. Fig.…”

Untersuchung der Mineral‐Wasser‐Grenzschicht mit nicht‐linearer optischer Spektroskopie

“…Außerdem mussten weitere Änderungen in der Oberflächenladung und/oder der Sternschichtladung vorgenommen werden. Eine Nachfolgestudie von 2019 zeigte, dass das Niveau des Plateaus bei einer hohen Konzentration sowohl von der Kationen‐ als auch von der Anionengröße abhängt [24] . Dies wurde als ionenspezifische Sternschichteigenschaft der untersuchten Alkalimetallhalogenide interpretiert.…”

“…Damit das Modell funktioniert, müssen drastische Änderungen der Abschirmungseigenschaften z. B. durch die Änderungen in der grenzflächenaktiven dielektrischen Permittivität [15, 24] angeführt werden. Dies impliziert, dass die NL‐Intensität einige Informationen enthält, welche bisher noch nicht einbezogen wurden.…”