Nanoscale Structure of the Oil-Water Interface

Fukuto, Masa; Ocko, B. M.; Bonthuis, Douwe Jan; Netz, Roland R.; Steinrück, Hans‐Georg; Pontoni, Diego; Kuzmenko, Ivan; Haddad, Julia; Deutsch, Moshe

doi:10.1103/physrevlett.117.256102

Cited by 30 publications

(40 citation statements)

References 28 publications

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“…Thus, the nearly flat spectral response found in the SSP spectra, and minimal response in PPP polarization combination, indicate the interfacial hexadecane lies relatively parallel to the interface. This is consistent with X-ray reflectivity measurements and molecular dynamics simulations (28). Furthermore, the presence of a minimal CH stretching response for bare hexadecane droplets supports computational work concluding there must exist a rough alkane surface necessary to provide space for a free OD to exist (12).…”

Section: Water Bonding and Hydrophobic Structuring At The Lcne Surfacesupporting

confidence: 85%

Formation and surface-stabilizing contributions to bare nanoemulsions created with negligible surface charge

Carpenter

Tran

Altman

et al. 2019

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

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The stabilization of nanoemulsions, nanosized oil droplets dispersed in water, is commonly achieved through the addition of surfactants and polymers. However, nanoemulsions in the absence of emulsifiers have been observed to acquire a significant negative charge at their surface, which ultimately contributes to their stability. While the source of this negative charge is disputed to this day, its presence is taken as an inherent property of the aqueous–hydrophobic interface. This report provides a look at the molecular structure and bonding characteristics of bare aqueous–hydrophobic nanoemulsion interfaces. We report the creation of bare nanoemulsions with near zero surface charge, which are marginally stable for several days. The process of creating these low-charge nanoemulsions (LCNEs) required rigorous cleaning procedures and proper solvent storage conditions. Using vibrational sum-frequency scattering spectroscopy, we measure the structure and bonding of the interfacial aqueous and hydrophobic phases. The surfaces of these LCNE samples possess a measurable free OH vibration, not found in previous studies and indicative of a clean interface. Tuning the nanoemulsion charge through addition of anionic surfactants, modeling potential surface-active contaminants, we observe the free OH to disappear and a reorientation of the interfacial hydrophobic molecules at micromolar surfactant concentrations. Notably, the free OH vibration provides evidence for stronger dispersion interactions between water molecules and the hydrophobic phase at the LCNE surface compared with similar planar water–alkane interfaces. We propose the stronger bonding interactions, in addition to an ordered interfacial aqueous layer, contribute to the delayed droplet coalescence and subsequent phase separation.

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Section: Water Bonding and Hydrophobic Structuring At The Lcne Surfacesupporting

confidence: 85%

Formation and surface-stabilizing contributions to bare nanoemulsions created with negligible surface charge

Carpenter

Tran

Altman

et al. 2019

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

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“…On a molecular level, the mechanism for this trend might lie in the structure of the alkane/water interface. It has been observed that an interfacial electron depletion layer with a thickness δ exists between water and hydrophobic alkane chains by both X-ray reflectivity (XR) measurements 39 – 41 and atomistic molecular dynamics (MD) simulations 42 , 43 . The few water molecules in the depletion layer (electron density < 40% that of bulk water 44 ) can buckle in the intermolecular space near the ends of alkane molecules (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…3b ), and create a template for the formation of an ice nucleus 29 . The alkane chains adjacent to the water molecules preferentially have their longest axis parallel to the water interface with a tilt angle β 39 . This tilt angle increases with m and l , resulting in a more parallel orientation for longer alkanes 39 .…”

Section: Resultsmentioning

confidence: 99%

“…The alkane chains adjacent to the water molecules preferentially have their longest axis parallel to the water interface with a tilt angle β 39 . This tilt angle increases with m and l , resulting in a more parallel orientation for longer alkanes 39 . Accordingly, longer alkane chains are expected to reduce the corrugation and roughness of the interface on the side of alkanes.…”

Section: Resultsmentioning

confidence: 99%

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Long-term deep-supercooling of large-volume water and red cell suspensions via surface sealing with immiscible liquids

2018

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Supercooling of aqueous solutions is a fundamentally and practically important physical phenomenon with numerous applications in biopreservation and beyond. Under normal conditions, heterogeneous nucleation mechanisms critically prohibit the simultaneous long-term (> 1 week), large volume (> 1 ml), and low temperatures (< −10 °C) supercooling of aqueous solutions. Here, we report on the use of surface sealing of water by an oil phase to significantly diminish the primary heterogeneous nucleation at the water/air interface. We achieve deep supercooling (down to −20 °C) of large volumes of water (up to 100 ml) for long periods (up to 100 days) simultaneously via this approach. Since oils are mixtures of various hydrocarbons we also report on the use of pure alkanes and primary alcohols of various lengths to achieve the same. Furthermore, we demonstrate the utility of deep supercooling via preliminary studies on extended (100 days) preservation of human red blood cells.

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“…While the effect of an external field on fluids is fundamentally important, theoretical treatment of interfaces in a field have received only limited attention with almost no work on capillary waves [9][10][11][12][13]. This is despite the importance of capillary waves in the nanoscale structure of interfaces [14][15][16][17]. A relation between the amplitude of the capillary waves, the field strength, and surface stiffness is lacking and measuring these quantities experimentally is difficult, which makes developing an empirical relation among these quantities a challenge.…”

Section: Introductionmentioning

confidence: 99%

Effect of an external field on capillary waves in a dipolar fluid

et al. 2017

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The role of an external field on capillary waves at the liquid-vapor interface of a dipolar fluid is investigated using molecular dynamics simulations. For fields parallel to the interface, the interfacial width squared increases linearly with respect to the logarithm of the size of the interface across all field strengths tested. The value of the slope decreases with increasing field strength, indicating that the field dampens the capillary waves. With the inclusion of the parallel field, the surface stiffness increases with increasing field strength faster than the surface tension. For fields perpendicular to the interface, the interfacial width squared is linear with respect to the logarithm of the size of the interface for small field strengths, and the surface stiffness is less than the surface tension. Above a critical field strength that decreases as the size of the interface increases, the interface becomes unstable due to the increased amplitude of the capillary waves.

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Nanoscale Structure of the Oil-Water Interface

Cited by 30 publications

References 28 publications

Formation and surface-stabilizing contributions to bare nanoemulsions created with negligible surface charge

Formation and surface-stabilizing contributions to bare nanoemulsions created with negligible surface charge

Long-term deep-supercooling of large-volume water and red cell suspensions via surface sealing with immiscible liquids

Effect of an external field on capillary waves in a dipolar fluid

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