Orientational fluctuations and phase transitions of long chain molecules at the air/water interface

Zhao, Xiaolin; Subrahmanyan, Suchitra; Eisenthal, Kenneth B.

doi:10.1103/physrevlett.67.2025

Cited by 17 publications

(18 citation statements)

References 31 publications

(12 reference statements)

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“…Only the species in the basic solutions were reported to exhibit an “unexpected” orientational fluctuation. In light of the findings with respect to halide ions presented in this work, it is reasonable to surmise that OH – ion is the species that is interacting with p -NP – and phenolic monolayers , observed in the earlier study. This of course assumes that OH – ions are adsorbed at the air–aqueous interface, which is a subject of vibrant debate .…”

Section: Discussionsupporting

confidence: 53%

Variation in Average Molecular Orientation of an Organic Anion at the Air–Aqueous Interface: Influence of Halide Ions

et al. 2018

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Molecular adsorption and orientation of an organic anion, p-nitrophenolate (p-NP–), at the air–aqueous interface have been studied using second harmonic generation techniques and surface tensiometry. It is shown that p-NP– not only adsorbs to the neat air–aqueous interface but also exhibits an orientational rearrangement at the surface. The average p-NP– orientation with respect to the surface normal is found to increase from ∼36 to ∼52° with increasing p-NP– surface coverage. Dipole–dipole and electrostatic interactions between p-NP– adsorbates are not the source of this orientation change. Exploration of this intriguing behavior in the presence of electrolytes revealed that interaction between inorganic ions and p-NP– augments its binding affinity and the observed orientation fluctuation. This study provides a critical understanding of the role halide, and plausibly hydroxide ions, play in influencing adsorbate orientation at an interface and thus paves the way to better elucidate chemical reactivity in sea salt aerosols and related environmental surfaces.

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Section: Discussionsupporting

confidence: 53%

Variation in Average Molecular Orientation of an Organic Anion at the Air–Aqueous Interface: Influence of Halide Ions

et al. 2018

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“…͑21͒ and ͑22͔͒, were measured as a function of time using a synchronously pumped picosecond dye laser and a single photon counting detection system. 9 To simultaneously measure the p and s polarized components of the SH signal, the collected SH light was first collimated and passed through a pair of polarizer cubes. The first cube passes the E p component of the SH light and reflects the E s component out the side window.…”

Section: Methodsmentioning

confidence: 99%

“…A range of techniques including surface pressure, interface electric potential, 1 light scattering, 2 ellipsometry, 3 fluorescence microscopy, 4 x-ray and neutron diffraction and reflection 5 have been used to study the various equilibrium phases and phase transitions of these quasi-two-dimensional systems. In a number of these experimental and theoretical studies, it has been proposed that the phase structure and phase transitions in an amphilphile monolayer could involve quantities such as density, 1 molecular configuration, 6 and orientation, [7][8][9] etc. as order parameters.…”

Section: Introductionmentioning

confidence: 99%

Monolayer orientational fluctuations and a new phase transition at the air water interface detected by second harmonic generation

Zhao

Eisenthal

1995

The Journal of Chemical Physics

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Articles you may be interested inSecond-harmonic generation and Maxwell displacement current spectroscopy of chiral organic monolayers at the air-water interface Detection of phase transition of monolayers at the air-water interface by compression using Maxwell displacement current and optical second harmonic generation Orientational order study of monolayers at the air-water interface by Maxwell-displacement current and optical second harmonic generation Fluctuations in the second harmonic intensity were observed in a number of insoluble amphilphiles spread at an air/aqueous interface. The fluctuations, which depend on the polarization of both the incident light and the second harmonic light generated, indicate a new phase transition for which the orientation of the head group is the order parameter. It is found that the phase transition occurs in certain long chain aromatic species but not in others of the same chain length with different head groups. The phase transition is identified as a weak first order transition. Agreement is obtained with a modified Landau-Ginzburg equation in which the chain-chain interactions provide a friction for the motions of the head groups.

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“…6 The translational and rotational motions of long chain molecules at the planar air/water interface have been studied also by SHG measurements. [7][8][9] SHG is sensitive to both the interface molecular density and molecular orientation. As the molecules rotate and diffuse at the interface, fluctuations in the SHG were observed.…”

Section: Introductionmentioning

confidence: 99%

“…A translational diffusion constant for the motion of interfacial clusters was found, 9 and a new orientational phase transition of a monolayer at the air-water interface was observed. 7,8 The anisotropic particles used in the present study are diskshaped montmorillonite particles. A montmorillonite particle is centrosymmetric, and therefore does not give an SHG signal from the bulk.…”

Section: Introductionmentioning

confidence: 99%

Rotational Dynamics of Anisotropic Microscopic Particles Studied by Second Harmonic Generation

and

Eisenthal

2000

J. Phys. Chem. B

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This letter reports the application of second harmonic generation (SHG) to study the rotational dynamics of anisotropic microparticles. In this study, disk-shaped clay particles of montmorillonites with a diameter of 0.5 µm and a thickness of 0.01 µm suspended in liquid media were studied. Fluctuations in the SH signal observed upon irradiating the samples with the fundamental light are attributed to the rotational motion of the particles. The relaxation times obtained from the autocorrelation of the fluctuations are 0.024 ( 0.04 s for water, 0.25 ( 0.01 for glycerol/water (74:26 w/w), and 0.63 ( 0.01 s for glycerol/water (80:20 w/w). These values are of the same order of magnitudes for the relaxation times calculated using the StokesEinstein model for rotation of an oblate particle. IntroductionSecond harmonic generation (SHG) was applied to study the rotational dynamics of anisotropic microparticles. Since SHG from a microscopic centrosymmetric particle is the result of the coherent addition of the second harmonic fields from the particle surface, 2 the SHG intensity depends on the shape as well as the orientation of the particle with respect to the incident and detected direction. Fluctuations in the SHG intensity were observed from anisotropic disk-shaped clay particles suspended in liquid media, which is attributed to the rotation of the anisotropic particles in the liquid media. These fluctuations were not observed for the spherical microscopic particles: polystyrene beads and oil droplets in an oil/water emulsion. The rotational relaxation time of anisotropic particles can be obtained from an analysis of the fluctuations. In these studies, disk-shaped clay particles are montmorillonites with a diameter of 0.5 µm and a thickness of 0.01 µm and were suspended in water or in a mixture of glycerol and water. The size distribution of the clay particles is 0.5 ( 0.15 µm. We have found that the relaxation time depends on the viscosity of the media, 0.024 ( 0.04 s for water, 0.25 ( 0.01 for glycerol/water (76:24 w/w), and 0.63 ( 0.01 s for glycerol/water (80:20 w/w). These values are consistent with the rotational relaxation times calculated by approximating the clay particles by an oblate structure of the same dimensions.Surface specific second harmonic generation (SHG) is a second-order spectroscopic technique, which involves conversion of incident light at a fundamental frequency ω to light at twice the frequency 2ω via a nonlinear interaction with the medium. 1 Under the dipole approximation, SHG is forbidden in centrosymmetric media, e.g., in bulk solution. Since surfaces are intrinsically noncentrosymmetric, SHG becomes dipoleallowed, and thus is surface specific. This surface selectivity has made SHG a powerful method for probing dynamic and equilibrium processes at interfaces. 1 SHG has recently been shown to be a new way to study microparticle surfaces. 2 Since the local regions of the surfaces of microparticles can be noncentrosymmetric even when the particle, e.g., a sphere, is centrosymmetric, the sec...

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Orientational fluctuations and phase transitions of long chain molecules at the air/water interface

Cited by 17 publications

References 31 publications

Variation in Average Molecular Orientation of an Organic Anion at the Air–Aqueous Interface: Influence of Halide Ions

Variation in Average Molecular Orientation of an Organic Anion at the Air–Aqueous Interface: Influence of Halide Ions

Monolayer orientational fluctuations and a new phase transition at the air water interface detected by second harmonic generation

Rotational Dynamics of Anisotropic Microscopic Particles Studied by Second Harmonic Generation

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