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Title: Molecular characterization of water and surfactant AOT at nanoemulsion surfaces

Abstract

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. Our work 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 counterionsmore » (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.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Univ. of Oregon, Eugene, OR (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1373424
Alternate Identifier(s):
OSTI ID: 1540261
Grant/Contract Number:  
SC0014278
Resource Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 114 Journal Issue: 51; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; science & technology; nanoemulsions; oil-water interfaces; vibrational sum-frequency scattering spectroscopy; surface spectroscopy; surfactants

Citation Formats

Hensel, Jennifer K., Carpenter, Andrew P., Ciszewski, Regina K., Schabes, Brandon K., Kittredge, Clive T., Moore, Fred G., and Richmond, Geraldine L. Molecular characterization of water and surfactant AOT at nanoemulsion surfaces. United States: N. p., 2017. Web. doi:10.1073/pnas.1700099114.
Hensel, Jennifer K., Carpenter, Andrew P., Ciszewski, Regina K., Schabes, Brandon K., Kittredge, Clive T., Moore, Fred G., & Richmond, Geraldine L. Molecular characterization of water and surfactant AOT at nanoemulsion surfaces. United States. doi:10.1073/pnas.1700099114.
Hensel, Jennifer K., Carpenter, Andrew P., Ciszewski, Regina K., Schabes, Brandon K., Kittredge, Clive T., Moore, Fred G., and Richmond, Geraldine L. Mon . "Molecular characterization of water and surfactant AOT at nanoemulsion surfaces". United States. doi:10.1073/pnas.1700099114.
@article{osti_1373424,
title = {Molecular characterization of water and surfactant AOT at nanoemulsion surfaces},
author = {Hensel, Jennifer K. and Carpenter, Andrew P. and Ciszewski, Regina K. and Schabes, Brandon K. and Kittredge, Clive T. and Moore, Fred G. and Richmond, Geraldine L.},
abstractNote = {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. Our work 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.},
doi = {10.1073/pnas.1700099114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 51,
volume = 114,
place = {United States},
year = {2017},
month = {7}
}

Journal Article:
Free Publicly Available Full Text
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DOI: 10.1073/pnas.1700099114

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