Sum-frequency vibrational spectroscopy of soluble surfactants at the air/water interface

Bell, Graham R.; Bain, Colin D.; Ward, Robert N.

doi:10.1039/ft9969200515

Cited by 177 publications

(308 citation statements)

References 40 publications

Supporting

Mentioning

291

Contrasting

Unclassified

Order By: Relevance

“…2) that occupy different chemical environments and orientations. These spectral assignments are consistent with vibrational sum-frequency literature in the C-H region (19,32,40).…”

Section: Hydrophobic Chain Ordering Of Aot At Planar and Curved Surfacessupporting

confidence: 77%

“…In all cases, spectra were taken of the C-H and S-O vibrational stretching modes of AOT and the O-H stretching modes of water. In selected C-H studies, D 2 O was chosen to replace H 2 O to remove the spectral interference of overlapping H 2 O modes with the blue side of the C-H stretching modes (27,32,33). Likewise, hexadecane-d 34 and CCl 4 were chosen as the oil phases for regular and reverse nanoemulsion systems, respectively, because of their optical transparencies.…”

Section: Experimental Approachmentioning

confidence: 99%

See 1 more Smart Citation

Molecular characterization of water and surfactant AOT at nanoemulsion surfaces

Hensel

Carpenter

Ciszewski

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Nanoemulsions and microemulsions are environments where oil and water can be solubilized in one another to provide a unique platform for many different biological and industrial applications. Nanoemulsions, unlike microemulsions, have seen little work done to characterize molecular interactions at their surfaces. This study provides a detailed investigation of the near-surface molecular structure of regular (oil in water) and reverse (water in oil) nanoemulsions stabilized with the surfactant dioctyl sodium sulfosuccinate (AOT). Vibrational sum-frequency scattering spectroscopy (VSFSS) is used to measure the vibrational spectroscopy of these AOT stabilized regular and reverse nanoemulsions. Complementary studies of AOT adsorbed at the planar oil-water interface are conducted with vibrational sum-frequency spectroscopy (VSFS). Jointly, these give comparative insights into the orientation of interfacial water and the molecular characterization of the hydrophobic and hydrophilic regions of AOT at the different oil-water interfaces. Whereas the polar region of AOT and surrounding interfacial water molecules display nearly identical behavior at both the planar and droplet interface, there is a clear difference in hydrophobic chain ordering even when possible surface concentration differences are taken into account. This chain ordering is found to be invariant as the nanodroplets grow by Ostwald ripening and also with substitution of different counterions (Na:AOT, K:AOT, and Mg:AOT) that consequently also result in different sized nanoparticles. The results paint a compelling picture of surfactant assembly at these relatively large nanoemulsion surfaces and allow for an important comparison of AOT at smaller micellar (curved) and planar oil-water interfaces.nanoemulsions | oil-water interfaces | vibrational sum-frequency scattering spectroscopy | surface spectroscopy | surfactants W e are all familiar with the adage that "oil and water do not mix," but of course, it depends upon the definition of "mix." Emulsions are an important special case, where the oil is dispersed as tiny droplets in the aqueous phase, taxonomically called a regular emulsion, or where the water is dispersed as tiny droplets throughout the oil phase, called a reverse emulsion. Because both emulsions are thermodynamically unstable, overcoming this requires an emulsifying agent such as a surfactant. Recently, there has been interest in surfactant-stabilized emulsions with droplet diameters in the nanoscale range for unique applications in drug delivery (1, 2) and oil recovery (3, 4) and as nanoreactors to produce materials ranging from polymers to quantum dots (5). Regular or reverse emulsions with droplet diameters in the range of 10-1,000 nm are called nanoemulsions. Little is known about the processes or molecular structures that result in their stability via surfactants. Even less is known about the structure-function relationship, which is crucial to determine the best surfactant for a given nanoemulsion application. Their utility hinges on a ...

show abstract

“…2) that occupy different chemical environments and orientations. These spectral assignments are consistent with vibrational sum-frequency literature in the C-H region (19,32,40).…”

Section: Hydrophobic Chain Ordering Of Aot At Planar and Curved Surfacessupporting

confidence: 77%

Section: Experimental Approachmentioning

confidence: 99%

Molecular characterization of water and surfactant AOT at nanoemulsion surfaces

Hensel

Carpenter

Ciszewski

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…The theory behind SFG as a surface-sensitive spectroscopic technique and the analysis to obtain orientation of methyl and methylene groups has been discussed previously. [12][13][14][15][16][17][18][19] Here we summarize the main points to understand the work reported in this paper. The second-order nonlinear susceptibility can be expressed using a Lorentzian function with a resonance peak at ω q and width Γ q corresponding to a resonance mode q.…”

mentioning

confidence: 99%

“…The second-order nonlinear susceptibility can be expressed using a Lorentzian function with a resonance peak at ω q and width Γ q corresponding to a resonance mode q. 19 The first term in eq 1, eff,NR , corresponds to the nonresonance contribution that is wavelength-independent and the second term to the resonance contribution. For a monochromatic source, the SFG intensity is proportional to ( tot ) 2 .…”

mentioning

confidence: 99%

Molecular Structure of Hydrophobic Alkyl Side Chains at Comb Polymer-Air Interface

Gautam

Dhinojwala

2001

Macromolecules

View full text Add to dashboard Cite

Introduction. Polymers with long side chains (comb polymers) provide unique opportunities to tailor surface properties of polymer films for applications in the areas of adhesion, friction, membrane transport, and biocompatibility. [1][2][3][4][5][6][7][8] In particular, polymers containing long alkyl or fluorinated alkyl side chains have been used to generate hydrophobic surfaces with surface energies that are comparable to those created by well-ordered self-assembled monolayers (SAM). 1-2,9-10 Comb copolymers with alkyl side chains typically show two thermal transitions: one associated with smectic liquid crystalline order where the d spacing is proportional to the length of the side groups 1,2 and the other associated with crystallization of the alkyl side chains. The surface energy of alkyl side chain comb polymers decreases with increase in the length of the alkyl side groups until a certain critical chain length, after which it asymptotes to a constant value. 1 These observations are reminiscent of results for SAM's where the length of the alkyl chains, packing, and mobility of the chains control the surface energies. 9,10 Although, considerable work has been done in the past in understanding the molecular ordering of SAM, very little is known about the molecular structure of alkyl chains at the comb polymer-air interface. 11 In this Communication, we report the first spectroscopic measurement of the molecular structure of octadecyl alkyl side chains at poly(vinyl octadecyl carbamatesco-vinyl acetate)-air interface (the polymer will be referred to as octadecyl polymer for simplicity) using the surface sensitive sum-frequency generation (SFG) technique. 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 1 + ω 2 ) is forbidden in the centrosymmetric bulk and is nonzero at interfaces where the inversion symmetry is broken. 12-16 SFG intensities are resonantly enhanced when ω 2 overlaps with the resonant frequency of a molecular vibrational mode that is both infrared and Raman active. The intensity, polarization, and resonance frequency of the SFG signal yield chemical and orientational information on molecules at interfaces. [12][13][14][15][16][17][18] Here, we compare the differences in the surface structure of 65 nm thick octadecyl polymer films prepared by spin-coating to a 7 nm polymer layer prepared by solution dipping on a mica substrate. In both cases, the SFG signals show strong methyl asymmetric and symmetric stretching vibrations indicating ordered methyl terminal groups. For the adsorbed octadecyl films, the SFG signal associated with methylene vibrations is higher indicating increased gauche defects in

show abstract

“…is often not necessary to analyze the polarization dependence of these antisymmetric modes by simply assuming the methyl group is freely rotating [114,115,116,117]. However, as will be shown later, for molecules like leucine with two methyl groups, an analysis on the antisymmetric modes is essential in determining the molecular orientation.…”

Section: Methodsmentioning

confidence: 99%

Sum-Frequency Generation from Chiral Media and Interfaces

2006

View full text Add to dashboard Cite

Professor Yuen-Ron Shen, Co-chair Professor Richard J. Saykally, Co-chair Sum frequency generation (SFG), a second-order nonlinear optical process, is electric-dipole forbidden in systems with inversion symmetry. As a result, it has been used to study chiral media and interfaces, systems intrinsically lacking inversion symmetry.This thesis describes recent progresses in the applications of and new insights into SFG from chiral media and interfaces.SFG from solutions of chiral amino acids is investigated, and a theoretical model explaining the origin and the strength of the chiral signal in electronic-resonance SFG spectroscopy is discussed. An interference scheme that allows us to distinguish enantiomers by measuring both the magnitude and the phase of the chiral SFG response is described, as well as a chiral SFG microscope producing chirality-sensitive images with sub-micron 2 resolution. Exploiting atomic and molecular parity nonconservation, the SFG process is also used to solve the Ozma problems.Sum frequency vibrational spectroscopy is used to obtain the adsorption behavior of leucine molecules at air-water interfaces. With poly(tetrafluoroethylene) as a model system, we extend the application of this surface-sensitive vibrational spectroscopy to fluorinecontaining polymers.

show abstract

Sum-frequency vibrational spectroscopy of soluble surfactants at the air/water interface

Cited by 177 publications

References 40 publications

Molecular characterization of water and surfactant AOT at nanoemulsion surfaces

Molecular characterization of water and surfactant AOT at nanoemulsion surfaces

Molecular Structure of Hydrophobic Alkyl Side Chains at Comb Polymer-Air Interface

Sum-Frequency Generation from Chiral Media and Interfaces

Contact Info

Product

Resources

About