Molecules at Liquid and Solid Surfaces

Wang, H.; Borguet, Eric; Yan, Elsa C. Y.; Zhang, D.; Gutow, J. H.; Eisenthal, Kenneth B.

doi:10.1021/la9707179

Cited by 35 publications

(55 citation statements)

References 16 publications

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“…The surface charge density and the electrostatic surface potential of colloidal nanoparticles can be obtained by fitting experimental SHG measurements as a function of added electrolyte concentrations to theoretical models, such as the Gouy-Chapman model. [33][34][35][36] Several different colloidal nanoparticle samples have been investigated using this SHG ߯ (ଷ) method, also called the electric field induced second harmonic (EFISH) technique, including polystyrene nanoparticles, 32,34,37,38 clay nanodisks, 23,39 liposomes, 40 and biologically conjugated nanoparticles. 41 Additional ߯ (ଷ) studies have been conducted on planar interfaces including electrolytes near solid/water interfaces, 33,42,43 DNA at surfaces in solution [44][45][46] and hot electron transfer dynamics from colloidal lead selenide nanocrystals to a titanium oxide surface.…”

Section: Introductionmentioning

confidence: 99%

Determination of the Surface Charge Density of Colloidal Gold Nanoparticles Using Second Harmonic Generation

2015

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Second harmonic generation is used to investigate the surface charge density of 50 nm colloidal gold nanoparticles in water. The gold nanoparticles are thiolated with mercaptosuccinic acid and are dialyzed in ultrapure water to remove excess salts and reactants. The second harmonic generation signal from the nanoparticle sample is measured as a function of added sodium chloride and magnesium chloride salt concentrations using the χ (3) technique. The experimental results are fit to the Gouy-Chapman model and to numerical solutions to the spherical PoissonBoltzmann equation that account for the nanoparticle surface curvature, the different salt valences, and ion adsorption to the Stern layer interface. The best fits use the numerical solutions including ion adsorption and determine the initial surface charge density to be −2.0 ± 0.1 x 10 −3 C/m 2 at the gold nanoparticle surface, in agreement with electrophoretic mobility measurements.In addition, the sodium ion is observed to adsorb with a higher surface charge density than the magnesium ion. These results demonstrate the important effects of surface curvature and ion adsorption in describing the surface chemistry and surface charge density of colloidal gold nanoparticles in water.

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Section: Introductionmentioning

confidence: 99%

Determination of the Surface Charge Density of Colloidal Gold Nanoparticles Using Second Harmonic Generation

2015

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“…24,[34][35][36][37][38][39][40]44 Furthermore, at sufficiently low bulk-solution concentrations, x CH 3 CN < 0.07 (3.45 M CH 3 CN), interfacial CH 3 CN molecules are argued to be hydrogenbonded to water molecules through their nitrogen atom; 36 CH 3 CN molecules are oriented with the methyl group pointing toward vacuum. Near x CH 3 CN = 0.2, approximately when the CH 3 CN surface monolayer is completed, 37 the cyano groups of the topmost CH 3 CN molecules were suggested to break hydrogen bonds with water molecules. 35,36 Loss of hydrogen bonding at higher concentration was argued to lead to less upright orientation of CH 3 CN molecules at the solution surface.…”

Section: ■ Introductionmentioning

confidence: 99%

Characterization of the Acetonitrile Aqueous Solution/Vapor Interface by Liquid-Jet X-ray Photoelectron Spectroscopy

et al. 2014

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We report photoelectron spectroscopy measurements from binary acetonitrile−water solutions, for a wide range of acetonitrile mole fractions (x CH 3 CN = 0.011−0.90) using a liquid microjet. By detecting the nitrogen and carbon 1s photoelectron signal of CH 3 CN from aqueous surface and bulk solution, we quantify CH 3 CN's larger propensity for the solution surface as compared to bulk solution. Quantification of the strong surface adsorption is through determination of the surface mole fraction as a function of bulk solution, x CH 3 CN , from which we estimate the adsorption free energy using the Langmuir adsorption isotherm model. We also discuss alternative approaches to determine the CH 3 CN surface concentration, based on analysis of the relative amount of gas-versus liquid-phase CH 3 CN, obtained from the respective photoelectron signal intensities. Another approach is based on the core-level binding energy shifts between liquid-and gas-phase CH 3 CN, which is sensitive to the change in solution surface potential and thus sensitive to the surface concentration of CH 3 CN. Gibbs free energy of adsorption values are compared with previous literature estimates, and we consider the possibility of CH 3 CN bilayer formation. In addition, we use the observed changes in N 1s and C 1s peak positions to estimate the net molecular surface dipole associated with a complete CH 3 CN surface monolayer, and discuss the implications for orientation of CH 3 CN molecules relative to the solution surface. ■ INTRODUCTIONExperimental molecular-level investigations of the electronic structure of aqueous solutions have recently become possible by using photoelectron (PE) spectroscopy in combination with a liquid microjet either in vacuum 1−3 or at near ambient pressure conditions. 4−6 Studies reported to date are largely comprised of neat liquid water, aqueous solutions of common electrolytes, and low-concentration solutions containing common organic and inorganic solute molecules and ions. 7−21 Typically, PE spectroscopy accesses solute electron binding energies, both lowest ionization energies and core-level energies, the latter being most suited for interpreting differences in solvation configuration at the solution surface or in the bulk of solution. PE spectroscopy can also provide a quantitative measure of solute concentrations across the solution interface, or it can be used to characterize, for instance, chemical equilibria as a function of concentration or pH, both near the top surface region and more deeply into the solution. The possibility to make such a direct comparison between surface and bulk-solution properties is indeed a rather unique feature of PE spectroscopy. The method's variable information depth is due to the strongly energy-dependent electron mean free path, which can be adjusted experimentally by a suitable choice of applied ionization photon energies. 1,22,23 To our knowledge, the present work reports the first PE spectroscopy study of a binary highly volatile solution studied over a wide range of concent...

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“…BBSFG) has application to the molecular level understanding of time-resolved interfacial processes. 1 SFG is becoming widely used as an analytical technique to understand a variety of interfaces [2][3][4][5][6][7][8][9][10] since it is surface-selective, provides spectroscopic data, i.e. molecular level information, and it can be utilized in most pressure regimes, e.g.…”

Section: Introductionmentioning

confidence: 99%

Broadband Sum Frequency Generation with Two Regenerative Amplifiers: Temporal Overlap of Femtosecond and Picosecond Light Pulses

Hommel

Allen

2001

ANAL. SCI.

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Sum frequency generation (SFG) spectroscopy is a valuable tool for studying interfaces such that the boundary between two adjoining phases can be probed with minimal interference from the adjacent bulk material. More recently, broadbandwidth sum frequency generation (BBSFG) techniques are being explored. This technique using IR broad-bandwidth fs pulses overlapped with narrow-bandwidth ps pulses to obtain BBSFG spectra is described. In the BBSFG system design presented here, the fs pulse and the ps pulse that are generated in separate regenerative amplifiers are overlapped temporally. This temporal overlap process is discussed. In addition, images of the sum frequency response demonstrate its viability. The new approach in experimental design described here for this emerging technology, BBSFG, has application for studying time-dependent processes at interfaces that inherently produce low SFG signal levels such as airaqueous interfaces.

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Molecules at Liquid and Solid Surfaces

Cited by 35 publications

References 16 publications

Determination of the Surface Charge Density of Colloidal Gold Nanoparticles Using Second Harmonic Generation

Determination of the Surface Charge Density of Colloidal Gold Nanoparticles Using Second Harmonic Generation

Characterization of the Acetonitrile Aqueous Solution/Vapor Interface by Liquid-Jet X-ray Photoelectron Spectroscopy

Broadband Sum Frequency Generation with Two Regenerative Amplifiers: Temporal Overlap of Femtosecond and Picosecond Light Pulses

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