Chayan Dutta | University of Southern California (original) (raw)

Chayan Dutta

Address: Los Angeles, California, United States

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Papers by Chayan Dutta

Research paper thumbnail of Plasmonically Enhanced Spectral Upconversion for Improved Performance of GaAs Solar Cells under Nonconcentrated Solar Illumination

Research paper thumbnail of Insight Into Water Structure at the Surfactant Surfaces and in Micro-Emulsion Confinement

Interactions with surfactant molecules can significantly alter the structure of interfacial water... more Interactions with surfactant molecules can significantly alter the structure of interfacial water. We present a comparative study of water/surfactant interactions using two different spectroscopic approaches: water at planar surfactant monolayers by sum frequency generation (SFG) spectroscopy, and interfacial water confined in reverse micelles formed by the same surfactants using infrared (IR) absorption spectroscopy. We report spectral features in the OH stretching region (3200-3700 cm-1) that are observed in both IR and SFG spectra, albeit with different relative amplitudes, for ionic surfactant sodium 1,4 bis 2 ethylhexylsulfosuccinate (AOT) and nonionic surfactant polyoxyethylene 4-lauryl ether (Brij L-4) reverse micelles in hexane and corresponding monolayers at the air/water interface. A prominent feature in the SFG spectra of the OH-stretch at 3560 cm-1 is attributed to water molecules that have a weak donor hydrogen bond to the surfactant head group. The same feature is observed in IR spectra of reverse micelles after deconvoluting the interfacial vs. bulk spectral contributions. We performed orientational analysis on these water molecules utilizing the polarization dependent SFG, which shows the average tilt angle of the OH-stretch of surfactant bound water molecules ~ 155˚ with respect to the surface normal.

Research paper thumbnail of On the Assignment of the Vibrational Spectrum of the Water Bend at the Air/Water Interface

We previously reported the spectrum of the water bend vibrational mode (ν 2) at the air/water int... more We previously reported the spectrum of the water bend vibrational mode (ν 2) at the air/water interface measured using sum-frequency generation (SFG). Here, we present experimental evidence to aid the assignment of the ν 2 spectral features to H-bonded classes of interfacial water, which is in general agreement with two recent independently published theoretical studies. The dispersive line shape shows an apparent frequency shift between SSP and PPP polarization combinations (SFG−visible−infrared). This is naturally explained as an interference effect between the negative (1630 cm −1) and positive (1662 cm −1) peaks corresponding to " free−OH " and " H-bonded " species, respectively, which have different orientations and thus different amplitudes in SSP and PPP spectra. A surfactant monolayer of sodium dodecyl sulfate (SDS) was used to suppress the free OH species at the surface, and the corresponding SFG spectral changes indicate that these water molecules with one of the hydrogens pointing up into the air phase contribute to the negative peak at 1630 cm −1 .

Research paper thumbnail of Plasmonically Enhanced Spectral Upconversion for Improved Performance of GaAs Solar Cells under Nonconcentrated Solar Illumination

Research paper thumbnail of Insight Into Water Structure at the Surfactant Surfaces and in Micro-Emulsion Confinement

Interactions with surfactant molecules can significantly alter the structure of interfacial water... more Interactions with surfactant molecules can significantly alter the structure of interfacial water. We present a comparative study of water/surfactant interactions using two different spectroscopic approaches: water at planar surfactant monolayers by sum frequency generation (SFG) spectroscopy, and interfacial water confined in reverse micelles formed by the same surfactants using infrared (IR) absorption spectroscopy. We report spectral features in the OH stretching region (3200-3700 cm-1) that are observed in both IR and SFG spectra, albeit with different relative amplitudes, for ionic surfactant sodium 1,4 bis 2 ethylhexylsulfosuccinate (AOT) and nonionic surfactant polyoxyethylene 4-lauryl ether (Brij L-4) reverse micelles in hexane and corresponding monolayers at the air/water interface. A prominent feature in the SFG spectra of the OH-stretch at 3560 cm-1 is attributed to water molecules that have a weak donor hydrogen bond to the surfactant head group. The same feature is observed in IR spectra of reverse micelles after deconvoluting the interfacial vs. bulk spectral contributions. We performed orientational analysis on these water molecules utilizing the polarization dependent SFG, which shows the average tilt angle of the OH-stretch of surfactant bound water molecules ~ 155˚ with respect to the surface normal.

Research paper thumbnail of On the Assignment of the Vibrational Spectrum of the Water Bend at the Air/Water Interface

We previously reported the spectrum of the water bend vibrational mode (ν 2) at the air/water int... more We previously reported the spectrum of the water bend vibrational mode (ν 2) at the air/water interface measured using sum-frequency generation (SFG). Here, we present experimental evidence to aid the assignment of the ν 2 spectral features to H-bonded classes of interfacial water, which is in general agreement with two recent independently published theoretical studies. The dispersive line shape shows an apparent frequency shift between SSP and PPP polarization combinations (SFG−visible−infrared). This is naturally explained as an interference effect between the negative (1630 cm −1) and positive (1662 cm −1) peaks corresponding to " free−OH " and " H-bonded " species, respectively, which have different orientations and thus different amplitudes in SSP and PPP spectra. A surfactant monolayer of sodium dodecyl sulfate (SDS) was used to suppress the free OH species at the surface, and the corresponding SFG spectral changes indicate that these water molecules with one of the hydrogens pointing up into the air phase contribute to the negative peak at 1630 cm −1 .

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