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Sara RJ, Coers D, Behrman C, Bobay J, Subir M. Molecular Adsorption and Physicochemical Properties at Liquid/Liquid Nanoemulsion Soft Interfaces: Effect of Charge and Hydrophobicity. J Phys Chem B 2024. [PMID: 38498699 DOI: 10.1021/acs.jpcb.3c07907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/20/2024]
Abstract
Contrary to the popular adage, "Oil and water do not mix", evidence of mixtures comprising the two "immiscible" liquids is universal. In the presence of an emulsifier, oil and water mix to form a colloidal suspension known as emulsion. Their utility in many areas such as food chemistry, biomedical health sectors, catalysis, and the petroleum industry is well recognized. While their application in our society is pervasive, tantalizing fundamental questions regarding the chemistry that takes place at the oil/water soft interface still linger. For instance, do organic compounds show proclivity for this molecularly thin boundary and, if so, what forces, hydrophobic or pure electrostatic among others, drive the molecular interactions? The focus of this Article is on molecular adsorption at the interface of oil-in-water (O/W) nanoemulsion (NE) droplets. The effect of the interfacial surfactant charge (positive, negative, zwitterionic, and neutral) on the affinity of aromatic organic compounds on the O/W NEs has been studied. Using a second harmonic generation (SHG), a nonlinear light scattering technique, we have explored the adsorption equilibrium of charged and neutral organic dyes. By variation of the surfactant functional group and thereby the interfacial charge properties, the source of the adsorption interaction, if any, has been deduced. The population of surfactants containing a charged functional group at the O/W interface is found to be sparse, yet adsorption at some of these interfaces has been observed. A purely electrostatic Coulomb interaction plays a key role, but the presence of a charged interface does not necessitate molecular adsorption. Hydrophobic interactions are not a major driving force of adsorption for the SHG dyes studied. However, a possible pi-interaction is likely in explaining the accumulation of neutral aromatic compounds at the O/W NE interface. These intricate adsorption features are discussed in the context of NE interfacial charge properties and their stability upon molecular adsorption.
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Affiliation(s)
- Rubyat J Sara
- Department of Chemistry, Ball State University, Muncie, Indiana 47306, United States
| | - Derek Coers
- Department of Chemistry, Ball State University, Muncie, Indiana 47306, United States
| | - Charles Behrman
- Department of Chemistry, Ball State University, Muncie, Indiana 47306, United States
| | - Jaron Bobay
- Department of Chemistry, Ball State University, Muncie, Indiana 47306, United States
| | - Mahamud Subir
- Department of Chemistry, Ball State University, Muncie, Indiana 47306, United States
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Lin L, Liu Z, Premadasa UI, Li T, Ma YZ, Sacci RL, Katsaras J, Hong K, Collier CP, Carrillo JMY, Doughty B. The Unexpected Role of Cations in the Self-Assembly of Positively Charged Amphiphiles at Liquid/Liquid Interfaces. J Phys Chem Lett 2022; 13:10889-10896. [PMID: 36394318 DOI: 10.1021/acs.jpclett.2c02921] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Conventional wisdom suggests that cations play a minimal role in the assembly of cationic amphiphiles. Here, we show that at liquid/liquid (L/L) interfaces, specific cation effects can modulate the assemblies of hydrophobic tails in an oil phase despite being attached to cationic headgroups in the aqueous phase. We used oligo-dimethylsiloxane (ODMS) methyl imidazolium amphiphiles to identify these specific interactions at hexadecane/aqueous interfaces. Small cations, such as Li+, bind to the O atoms in the ODMS tail and pin it to the interface, thereby imposing a kinked conformation─as evidenced by vibrational sum frequency generation spectroscopy and molecular dynamics simulations. While larger Cs+ ions more readily partition to the interface, they do not form analogous complexes. Our data not only point to ways for controlling amphiphile structure at L/L interfaces but also suggest a means for the separation of Li+, or related applications, in soft-matter electronics.
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Affiliation(s)
- Lu Lin
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Zening Liu
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Uvinduni I Premadasa
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Tianyu Li
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee37996, United States
| | - Ying-Zhong Ma
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Robert L Sacci
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - John Katsaras
- Laboratories and Soft Matter Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
- Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Kunlun Hong
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - C Patrick Collier
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Jan-Michael Y Carrillo
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | - Benjamin Doughty
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
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Schnurbus M, Hardt M, Steinforth P, Carrascosa-Tejedor J, Winnall S, Gutfreund P, Schönhoff M, Campbell RA, Braunschweig B. Responsive Material and Interfacial Properties through Remote Control of Polyelectrolyte-Surfactant Mixtures. ACS APPLIED MATERIALS & INTERFACES 2022; 14:4656-4667. [PMID: 35029383 DOI: 10.1021/acsami.1c18934] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Polyelectrolyte/surfactant (P/S) mixtures find many applications but are static in nature and cannot be reversibly reconfigured through the application of external stimuli. Using a new type of photoswitchable surfactants, we use light to trigger property changes in mixtures of an anionic polyelectrolyte with a cationic photoswitch such as electrophoretic mobilities, particle size, as well as their interfacial structure and their ability to stabilize aqueous foam. For that, we show that prevailing hydrophobic intermolecular interactions can be remotely controlled between poly(sodium styrene sulfonate) (PSS) and arylazopyrazole tetraethylammonium bromide (AAP-TB). Shifting the chemical potential for P/S binding with E/Z photoisomerization of the surfactants can reversibly disintegrate even large aggregates (>4 μm) and is accompanied by a substantial change in the net charging state of PSS/AAP-TB complexes, e.g., from negative to positive excess charges upon light irradiation. In addition to the drastic changes in the bulk solution, also at air-water interfaces, the interfacial stoichiometry and structure change drastically on the molecular level with E/Z photoisomerization, which can also drive the stability of aqueous foam on a macroscopic level.
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Affiliation(s)
- Marco Schnurbus
- Institute of Physical Chemistry and Center of Soft Nanoscience, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Michael Hardt
- Institute of Physical Chemistry and Center of Soft Nanoscience, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Pascal Steinforth
- Institute of Physical Chemistry and Center of Soft Nanoscience, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Javier Carrascosa-Tejedor
- Institut Laue-Langevin, 71 Avenue des Martyrs, CS 20156, 38042 Grenoble Cedex 9, France
- Division of Pharmacy & Optometry, University of Manchester, M13 9PT Manchester, United Kingdom
| | - Samuel Winnall
- Institut Laue-Langevin, 71 Avenue des Martyrs, CS 20156, 38042 Grenoble Cedex 9, France
- Division of Pharmacy & Optometry, University of Manchester, M13 9PT Manchester, United Kingdom
| | - Philipp Gutfreund
- Institut Laue-Langevin, 71 Avenue des Martyrs, CS 20156, 38042 Grenoble Cedex 9, France
| | - Monika Schönhoff
- Institute of Physical Chemistry and Center of Soft Nanoscience, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Richard A Campbell
- Division of Pharmacy & Optometry, University of Manchester, M13 9PT Manchester, United Kingdom
| | - Björn Braunschweig
- Institute of Physical Chemistry and Center of Soft Nanoscience, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
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Tsuei M, Sun H, Kim YK, Wang X, Gianneschi NC, Abbott NL. Interfacial Polyelectrolyte-Surfactant Complexes Regulate Escape of Microdroplets Elastically Trapped in Thermotropic Liquid Crystals. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:332-342. [PMID: 34967209 DOI: 10.1021/acs.langmuir.1c02580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Polyelectrolytes adsorbed at soft interfaces are used in contexts such as materials synthesis, stabilization of emulsions, and control of rheology. Here, we explore how polyelectrolyte adsorption to aqueous interfaces of thermotropic liquid crystals (LCs) influences surfactant-stabilized aqueous microdroplets that are elastically trapped within the LCs. We find that adsorption of poly(diallyldimethylammonium chloride) (PDDA) to the interface of a nematic phase of 4-cyano-4'-pentylbiphenyl (5CB) triggers the ejection of microdroplets decorated with sodium dodecylsulfate (SDS), consistent with an attractive electrical double layer interaction between the microdroplets and LC interface. The concentration of PDDA that triggers release of the microdroplets (millimolar), however, is three orders of magnitude higher than that which saturates the LC interfacial charge (micromolar). Observation of a transient reorientation of the LC during escape of microdroplets leads us to conclude that complexes of PDDA and SDS form at the LC interface and thereby regulate interfacial charge and microdroplet escape. Poly(sodium 4-styrenesulfonate) (PSS) also triggers escape of dodecyltrimethylammonium bromide (DTAB)-decorated aqueous microdroplets from 5CB with dynamics consistent with the formation of interfacial polyelectrolyte-surfactant complexes. In contrast to PDDA-SDS, however, we do not observe a transient reorientation of the LC when using PSS-DTAB, reflecting weak association of DTAB and PSS and slow kinetics of formation of PSS-DTAB complexes. Our results reveal the central role of polyelectrolyte-surfactant dynamics in regulating the escape of the microdroplets and, more broadly, that LCs offer the basis of a novel probe of the structure and properties of polyelectrolyte-surfactant complexes at interfaces. We demonstrate the utility of these new insights by triggering the ejection of microdroplets from LCs using peptide-polymer amphiphiles that switch their net charge upon being processed by enzymes. Overall, our results provide fresh insight into the formation of polyelectrolyte-surfactant complexes at aqueous-LC interfaces and new principles for the design of responsive soft matter.
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Affiliation(s)
- Michael Tsuei
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
| | - Hao Sun
- Department of Chemistry, Materials Science & Engineering and Biomedical Engineering, Northwestern University, Evanston, Illinois 60208, United States
- Department of Chemistry and Chemical & Biomedical Engineering, University of New Haven, West Haven, Connecticut 06516, United States
| | - Young-Ki Kim
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
- Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, Gyengbuk 37673, Korea
| | - Xin Wang
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
| | - Nathan C Gianneschi
- Department of Chemistry, Materials Science & Engineering and Biomedical Engineering, Northwestern University, Evanston, Illinois 60208, United States
| | - Nicholas L Abbott
- Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
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Glikman D, Braunschweig B. Nanoscale Effects on the Surfactant Adsorption and Interface Charging in Hexadecane/Water Emulsions. ACS NANO 2021; 15:20136-20147. [PMID: 34898170 DOI: 10.1021/acsnano.1c08038] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Nanoscale properties at interfaces play a key role in the colloidal stability of emulsions and other soft matter materials where physical properties need to be controlled from the nano to macroscopically visible length scales. Our molecular level understanding of oil-water interfaces arises mostly from results at extended interfaces and the common view that emulsions are stabilized by a large number of surfactant molecules at the droplet's interface which, however, has been recently challenged. In this work, we show that the particle size and the curvature of oil droplets at the nanoscale is of great importance for the interface adsorption of dodecyl sulfate surfactants and possible counterion condensation at the charged hexadecane-water interface. Using second-harmonic scattering, we have studied the surface charge of oil droplets in nanoemulsions where we systematically varied the particle size R between 80 and 270 nm and demonstrate that the surface charge density σ changes drastically with size: For sizes >200 nm, σ is similar to what can be expected at flat extended interfaces, while σ is dramatically reduced by almost an order of magnitude when the particle size of the oil droplet is 80 nm. Using a theoretical approach that considers counterion condensation, we quantify the nanoscale effects on the change in surface charge with particle size and find excellent agreement with our experimental result. Modeling of the experimental results also implies that the charge per particle remains constant and depends on a critical balance of surfactant adsorption and ion condensation.
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Affiliation(s)
- Dana Glikman
- Institute of Physical Chemistry and Center for Soft Nanoscience, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Björn Braunschweig
- Institute of Physical Chemistry and Center for Soft Nanoscience, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
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Braun L, Kühnhammer M, von Klitzing R. Stability of aqueous foam films and foams containing polymers: Discrepancies between different length scales. Curr Opin Colloid Interface Sci 2020. [DOI: 10.1016/j.cocis.2020.08.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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