Sum-frequency vibrational spectroscopy of the solid/liquid interface

Bain, Colin D.

doi:10.1039/ft9959101281

Cited by 629 publications

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“…The methylene contribution indicates that the Comb alkyl side chains are more disordered and suggests a larger population of gauche defects than observed at the air/Comb interface. 10 Further, the Fermi resonance peak at 2935 cm -1 is larger than that observed at the air/Comb interface in comparison to the methyl symmetric peak at 2875 cm -1 . Our earlier results have shown that the magnitude of the Fermi peak with respect to methyl symmetric peak is sensitive to the crystallinity of the Comb alkyl side chains at the surface.…”

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confidence: 92%

“…5,6 Further details of SFG theory and the details of SFG spectrometers have been discussed previously. 9,10 Samples for SFG were prepared by spin coating a film ∼300-nm thick from a 5 wt % solution of hPS (M w ) 108 kg/mol, M w / M n ≈ 1.06 or deuterated PS, M w ) 125 kg/mol M w /M n ≈ 1.13) in toluene onto the surface of a sapphire prism and annealing the film at 110°C under vacuum for 3 h. A second film ∼200 nm thick was then spin-cast on top of the first from a warm 6 wt % solution of Comb (M w ) 70 kg/mol M w /M n ≈ 3.0) in 50/50 mixture of octanol and butanol (both nonsolvents for PS), and the bilayer sample ( Figure 1) was annealed again for 3 h at 110°C under vacuum. For comparison in separate experiments a film ∼200 nm thick was spin-cast from 6 wt % solution of Comb in toluene onto the surface of a sapphire prism and annealed at 110°C under vacuum for 3 h. The details of our SFG spectrometer and the internal reflection geometry have been described previously.…”

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confidence: 99%

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Probing Polymer/Polymer Interfaces

2002

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When two immiscible polymer surfaces are contacted, it is expected that their surface functionality will arrange or structure to minimize free energy. Understanding the structure of polymer/ polymer interfaces is important in areas of adhesion, polymer blends, and nanocomposites. The current understanding of polymer/ polymer interface structure is based on interfacial energies, either measured or calculated on the basis of the Flory-Huggins parameter, which accounts for unfavorable interaction of the different monomer repeat units. 1,2 However, directly probing the structure and orientation at polymer/polymer interfaces has not been possible due to insufficient contrast between the bulk and the interface. In this work we have taken advantage of recent developments in infrared-visible sum frequency spectroscopy (SFG) to study polymer/polymer interfaces. This technique has been recently used to study a variety of polymer interfaces including polymer/ air, polymer/liquid, and polymer/solid interfaces. [3][4][5][6] Here we report the first SFG measurement of molecular structure at poly(vinyl-N-octadecylcarbamate-co-vinyl acetate)/poly(styrene) (Comb/PS) polymer/polymer interface. The carbamate Comb polymers are widely used as release coatings for pressure sensitive adhesives, and their low adhesion at polymer/polymer interfaces with adhesives is attributed to their interfacial structure. 7 SFG involves mixing a visible high-intensity laser beam of frequency ω 1 , with a tunable infrared wavelength source of frequency ω 2 . According to the dipole approximation, generation of a SFG photon (at ω 3 ) ω 1 + ω 2 ) is forbidden in the centrosymmetric bulk and is nonzero at interfaces where inversion symmetry is broken. The SFG is resonantly enhanced when ω 2 overlaps with the resonant frequency of a molecular vibrational mode that is both infrared and Raman active. The SFG output is also enhanced by 1 to 2 orders of magnitude when the incidence angle of the input beams is close to the critical angle for total internal reflection (explained by higher Fresnel coefficients of the reflected SFG signal near critical angles). The enhancement in SFG signal near critical angles has been used recently to study liquid/ liquid 8 and polymer/solid interfaces. 5,6 Further details of SFG theory and the details of SFG spectrometers have been discussed previously. 9,10 Samples for SFG were prepared by spin coating a film ∼300-nm thick from a 5 wt % solution of hPS (M w ) 108 kg/mol, M w / M n ≈ 1.06 or deuterated PS, M w ) 125 kg/mol M w /M n ≈ 1.13) in toluene onto the surface of a sapphire prism and annealing the film at 110°C under vacuum for 3 h. A second film ∼200 nm thick was then spin-cast on top of the first from a warm 6 wt % solution of Comb (M w ) 70 kg/mol M w /M n ≈ 3.0) in 50/50 mixture of octanol and butanol (both nonsolvents for PS), and the bilayer sample (Figure 1) was annealed again for 3 h at 110°C under vacuum. For comparison in separate experiments a film ∼200 nm thick was spin-cast from 6 wt % solution of Comb in t...

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Probing Polymer/Polymer Interfaces

2002

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“…2,3,[5][6][7][8] Orientation measurements of chemical groups at interfaces and surfaces were realized soon after the SFG technique was applied to the study of interfaces and surfaces. 9 Recently, the orientational angle with respect to the surface normal and the twist angle relative to the plane comprising the surface normal and the symmetry axis of the isopropyl headgroup of a leucine molecule at the air/water interface was measured.…”

Section: Introductionmentioning

confidence: 99%

Absolute Orientation of Molecules at Interfaces

2006

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A method to determine the absolute orientation of molecules at liquid interfaces by sum frequency generation (SFG) is reported. It is based on measurements of the orientations of two nonparallel vibrationally active chromophores in the molecule of interest combined with a rotation matrix formulation to obtain the absolute molecular orientation. We chose m-tolunitrile, a planar molecule adsorbed to the air/water interface, as a proof-of-method experiment. Quantitative analysis of different polarization sum frequency intensities facilitate unique peak assignments of the methyl and nitrile groups of m-tolunitrile. The SFG analysis of the measurement yields a nitrile group tilting at 53°to the surface normal, and the C 3 axis of the methyl group is almost upright at 23°with respect to the surface normal. Using a rotation matrix formulation, we found that the angle between the surface plane and the m-tolunitrile molecular plane is 70°.

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“…However, alkyl chains buried in these layers can be expected to exhibit much less overall orientational order and therefore should not yield strong SFG intensity [Bain, 1995]. For lipid bilayers, due to the intrinsic symmetry, the expected SFG intensity should be low as well.…”

Section: Surfactant Coveragementioning

confidence: 99%

Revealing structural properties of the marine nanolayer from vibrational sum frequency generation spectra

Laß¹,

Friedrichs²

2011

J. Geophys. Res.

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Natural nanolayers originating from sea surface and subsurface water samples collected in the Baltic Sea have been investigated using surface‐sensitive vibrational sum frequency generation (VSFG) spectroscopy. Distinct spectral signatures of CH and OH bond stretch vibrations have been detected at wavenumbers ranging from 2700 to 3900 cm−1. Measured water‐air interface spectra as well as observed signal intensity trends are discussed in terms of composition and structure of the natural organic nanolayer. Reasoning was based on the comparison with reference spectra, spectral trends inferred from previous VSFG studies, reported average composition of dissolved organic matter in seawater, and simplified assumption that surfactants can be classified as soluble (wet) and insoluble (dry) surfactants. Wet surfactants have been found to be dominant, and often lipid‐like compounds form a very dense surfactant nanolayer. Supported by comparison spectra of xanthan gum solutions, the observed VSFG spectral signatures were tentatively assigned to lipopolysaccharides or other lipid‐like compounds embedded in colloidal matrices of polymeric material. In addition, VSFG spectra of a polluted harbor water sample and a water sample covered with diesel oil are reported.

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Sum-frequency vibrational spectroscopy of the solid/liquid interface

Cited by 629 publications

References 36 publications

Probing Polymer/Polymer Interfaces

Probing Polymer/Polymer Interfaces

Absolute Orientation of Molecules at Interfaces

Revealing structural properties of the marine nanolayer from vibrational sum frequency generation spectra

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