A New Imaginary Term in the 2nd Order Nonlinear Susceptibility from Charged Interfaces

Ma, Emily; Kim, Jeongmin; Liu, Yangdongling; Lozier, Emilie; Miller, Thomas A.; Wang, Hongfei; Geiger, Franz M.; ohno, Paul

doi:10.26434/chemrxiv.14378810.v1

Cited by 3 publications

(9 citation statements)

References 17 publications

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“…43,62 This procedure yields a calibration and referencing ratio, C/R, of 3.6 × 10 −22 m 2 V −1 in our spectrometer. 9 The results are shown in Figure 2A−C. In the first 5 min, the 0.1 M to 10 μM jump results in a continuous change in the surface potential to increasingly negative values, as one would expect.…”

Section: ■ Resultsmentioning

confidence: 73%

“…Hysteresis is not observed in any of the three ionic strength cycling experiments, for a given experiment; that is, the starting and final χ (2) and Φ(0) tot point estimates obtained upon completion of the return jump are comparable to one another within error (5%). 9 We find that the χ (2) and Φ(0) tot values determined for the 1 mM condition depend on whether we start the experiment at 1 mM or whether we jump to it from 0.1 M or from 10 μM. Figure 3 summarizes the results from the two experiments that begin at 0.1 M NaCl in a χ (2) :Φ(0) tot correlation plot (Figure 3A; see Figure S7A for a plot of all three experiments shown in Figure 1).…”

Section: ■ Resultsmentioning

confidence: 99%

“…41 At low ionic strength, λ D ≈ 1 × 10 −7 m and φ → π DC,EDL 2 , whereas at high ionic strength, φ DC,EDL → 0. 41 We recently reported a newly identified term, χ X (3) , which is ∼1.5 × χ water (3) , 9 where for offresonant SHG, χ water (3) = (9.6 ± 1.9) × 10 −22 m 2 V −2 from experiments 65 and 10.3 × 10 −22 m 2 V −2 from quantum mechanical calculations. 73 Our current HD-SHG spectrometer records the SHG amplitude and phase every 12 s, which is a reasonable compromise given the maximum speed of our 100 mm delay stage motor and acceptable signal-to-noise levels.…”

Section: ■ Methodsmentioning

confidence: 98%

“…In the experiments (also see the Supporting Information sections S1−S4), we apply heterodyne-detected second harmonic generation (HD-SHG) 9,41,42,71 to evaluate the following relationship describing the second-and third-order mixing with the interfacial potential:…”

Section: ■ Methodsmentioning

confidence: 99%

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Stern and Diffuse Layer Interactions during Ionic Strength Cycling

Kim

Chang

et al. 2021

J. Phys. Chem. C

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Second harmonic generation amplitude and phase measurements are acquired in real time from fused silica:water interfaces that are subjected to ionic strength transitions conducted at pH 5.8. In conjunction with atomistic modeling, we identify correlations between structure in the Stern layer, encoded in the total second-order nonlinear susceptibility, 𝜒 !"! ($) , and in the diffuse layer, encoded in the product of 𝜒 !"! ($) and the total interfacial potential, 𝛷(0) !"! .𝜒 !"! ($) : 𝛷(0) !"! correlation plots indicate that the dynamics in the Stern and diffuse layers are decoupled from one another under some conditions (large change in ionic strength), while they change in lockstep under others (smaller change in ionic strength) as the ionic strength in the aqueous bulk solution varies. The quantitative structural and electrostatic information obtained also informs on the molecular origin of hysteresis in ionic strength cycling over fused silica.Atomistic simulations suggest a prominent role of contact ion pairs (as opposed to solventseparated ion pairs) in the Stern layer. Those simulations also indicate that net water alignment is limited to the first 2 nm from the interface, even at 0 M ionic strength, highlighting water's polarization as an important contributor to nonlinear optical signal generation.

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Section: ■ Resultsmentioning

confidence: 73%

Section: ■ Resultsmentioning

confidence: 99%

Section: ■ Methodsmentioning

confidence: 98%

Section: ■ Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Stern and Diffuse Layer Interactions during Ionic Strength Cycling

Kim

Chang

et al. 2021

J. Phys. Chem. C

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“…Additional work will be required to address the role of contact ion pairs and solvent-separated ion pairs in such systems. 62,63 EXPERIMENTAL SECTION…”

Section: Discussionmentioning

confidence: 99%

The electrical‐double layer revisited

et al. 2022

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The electrical-double layer (EDL) model is fundamental to our understanding of interactions in ionic solutions, and is widely used in chemical, biological, and technological contexts, particularly in the description of aqueous electrolyte solutions. However, recent experiments have raised questions regarding the validity of this model in polar, aprotic solvents; some observations, such as a surface potential that changes sign with increasing salt concentration, are not consistent with the EDL picture. We demonstrate in a model system, acetonitrile at a silica interface, that solvent organization dictates the ionic distributions. Ion-transport measurements in nanopores, surface-selective spectroscopy, and molecular dynamics simulations reveal that the distribution of ions in acetonitrile at a silica interface is determined by the lipid-bilayer-like organization that the interface imposes upon the liquid, which accounts for the change in sign of the potential. Our findings emphasize the importance of including solvent molecules and ions explicitly in descriptions of solid/liquid interfaces.

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Quantification of Stern Layer Water Molecules, Total Potentials, and Energy Densities at Fused Silica:Water Interfaces for Adsorbed Alkali Chlorides, CTAB, PFOA, and PFAS

Chang,

Lozier,

et al. 2023

J. Phys. Chem. A

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We have employed amplitude- and phase-resolved second-harmonic generation spectroscopy to investigate ion-specific effects of monovalent cations at the fused silica:water interface maintained under acidic, neutral, and alkaline conditions. We find a negligible dependence of the total potential (as negative as −400 mV at pH 14), the second-order nonlinear susceptibility (as large as 1.5 × 10–21 m2 V–1 at pH 14), the number of Stern layer water molecules (1 × 1015 cm–2 at pH 5.8), and the energy associated with water alignment upon going from neutral to high pH (ca. −24 kJ mol–1 to −48 kJ mol–1 at pH 13 and 14, close to the cohesive energy of liquid water but smaller than that of ice) on chlorides of the alkali series (M+ = Li+, Na+, K+, Rb+, and Cs+). Attempts are presented to provide estimates for the molecular hyperpolarizability of the cations and anions in the Stern layer at high pH, which arrive at ca. 20-fold larger values for α total ions (2) = α M + (2) + α OH – (2) + α Cl – (2) when compared to water’s molecular hyperpolarizability estimate from theory and point to a sizable contribution of deprotonated silanol groups at high pH. In contrast to the alkali series, a pronounced dependence of the total potential and the second-order nonlinear susceptibility on monovalent cationic (cetrimonium bromide, CTAB) and anionic (perfluorooctanoic and perfluorooctanesulfonic acid, PFOA and PFOS) surfactants was quantifiable. Our findings are consistent with a low surface coverage of the alkali cations and a high surface coverage of the surfactants. Moreover, they underscore the important contribution of Stern layer water molecules to the total potential and second-order nonlinear susceptibility. Finally, they demonstrate the applicability of heterodyne-detected second-harmonic generation spectroscopy for identifying perfluorinated acids at mineral:water interfaces.

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A New Imaginary Term in the 2nd Order Nonlinear Susceptibility from Charged Interfaces

Cited by 3 publications

References 17 publications

Stern and Diffuse Layer Interactions during Ionic Strength Cycling

Stern and Diffuse Layer Interactions during Ionic Strength Cycling

The electrical‐double layer revisited

Quantification of Stern Layer Water Molecules, Total Potentials, and Energy Densities at Fused Silica:Water Interfaces for Adsorbed Alkali Chlorides, CTAB, PFOA, and PFAS

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