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Gochev GG, Campbell RA, Schneck E, Zawala J, Warszynski P. Exploring proteins at soft interfaces and in thin liquid films - From classical methods to advanced applications of reflectometry. Adv Colloid Interface Sci 2024; 329:103187. [PMID: 38788307 DOI: 10.1016/j.cis.2024.103187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2024] [Revised: 05/12/2024] [Accepted: 05/12/2024] [Indexed: 05/26/2024]
Abstract
The history of the topic of proteins at soft interfaces dates back to the 19th century, and until the present day, it has continuously attracted great scientific interest. A multitude of experimental methods and theoretical approaches have been developed to serve the research progress in this large domain of colloid and interface science, including the area of soft colloids such as foams and emulsions. From classical methods like surface tension adsorption isotherms, surface pressure-area measurements for spread layers, and surface rheology probing the dynamics of adsorption, nowadays, advanced surface-sensitive techniques based on spectroscopy, microscopy, and the reflection of light, X-rays and neutrons at liquid/fluid interfaces offers important complementary sources of information. Apart from the fundamental characteristics of protein adsorption layers, i.e., surface tension and surface excess, the nanoscale structure of such layers and the interfacial protein conformations and morphologies are of pivotal importance for extending the depth of understanding on the topic. In this review article, we provide an extensive overview of the application of three methods, namely, ellipsometry, X-ray reflectometry and neutron reflectometry, for adsorption and structural studies on proteins at water/air and water/oil interfaces. The main attention is placed on the development of experimental approaches and on a discussion of the relevant achievements in terms of notable experimental results. We have attempted to cover the whole history of protein studies with these techniques, and thus, we believe the review should serve as a valuable reference to fuel ideas for a wide spectrum of researchers in different scientific fields where proteins at soft interface may be of relevance.
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Affiliation(s)
- Georgi G Gochev
- Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, 30239 Krakow, Poland; Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
| | - Richard A Campbell
- Division of Pharmacy and Optometry, University of Manchester, M13 9PT Manchester, UK
| | - Emanuel Schneck
- Physics Department, Technical University Darmstadt, 64289 Darmstadt, Germany
| | - Jan Zawala
- Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, 30239 Krakow, Poland
| | - Piotr Warszynski
- Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, 30239 Krakow, Poland
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2
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Tadmor R, Multanen V, Stern Y, Yakir YB. Drops retracting while forming a rim. J Colloid Interface Sci 2021; 581:496-503. [DOI: 10.1016/j.jcis.2020.07.109] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 07/21/2020] [Accepted: 07/22/2020] [Indexed: 01/31/2023]
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3
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Pullanchery S, Kulik S, Okur HI, de Aguiar HB, Roke S. On the stability and necessary electrophoretic mobility of bare oil nanodroplets in water. J Chem Phys 2020; 152:241104. [DOI: 10.1063/5.0009640] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Affiliation(s)
- S. Pullanchery
- Laboratory for Fundamental BioPhotonics, Institute of Bioengineering (IBI), Institute of Materials Science (IMX) and Engineering, School of Engineering (STI), and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - S. Kulik
- Laboratory for Fundamental BioPhotonics, Institute of Bioengineering (IBI), Institute of Materials Science (IMX) and Engineering, School of Engineering (STI), and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - H. I. Okur
- Laboratory for Fundamental BioPhotonics, Institute of Bioengineering (IBI), Institute of Materials Science (IMX) and Engineering, School of Engineering (STI), and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
- Department of Chemistry and National Nanotechnology Research Center (UNAM), Bilkent University, 06800 Ankara, Turkey
| | - H. B. de Aguiar
- Laboratoire Kastler Brossel, ENS-Université PSL, CNRS, Sorbonne Université, Collège de France, 24 rue Lhomond, 75005 Paris, France
| | - S. Roke
- Laboratory for Fundamental BioPhotonics, Institute of Bioengineering (IBI), Institute of Materials Science (IMX) and Engineering, School of Engineering (STI), and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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Zdrali E, Etienne G, Smolentsev N, Amstad E, Roke S. The interfacial structure of nano- and micron-sized oil and water droplets stabilized with SDS and Span80. J Chem Phys 2019; 150:204704. [PMID: 31153210 DOI: 10.1063/1.5083844] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
In this work, we provide a comparison between the stability and the interfacial structure of micrometer-sized and nanometer-sized droplets by employing a multi-instrumental approach comprised of the surface-sensitive technique of sum frequency scattering as well as dynamic light scattering and microscopy. We monitor the stability of oil-in-water and water-in-oil emulsions and the structure of surfactants at the oil/water nano-interface, when stabilized with an oil-soluble neutral surfactant (Span80), a water-soluble anionic surfactant (sodium dodecyl sulfate, SDS), or with a combination of the two. Micron-sized droplets are found to be stabilized only when a surfactant soluble in the continuous phase is present in the system, in agreement with what is traditionally observed empirically. Surprisingly, the nanodroplets behave differently. Both oil and water nanodroplets can be stabilized by the same (neutral Span80) surfactant but with different surface structures. A combination of SDS and Span80 also suffices, but for the case of water droplets, the strongly amphiphilic SDS molecules are not detected at the interface. For the case of oil droplets, both surfactants are at the interface but do not structurally affect one another. Thus, it appears that, in this study, empirical rules such as the Bancroft rule, the hydrophile-lipophile-balance scale, and the surfactant affinity difference predict the stability of the micrometer-sized droplets better than the nanometer-sized ones, probably due to a different balance of interactions on different length scales.
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Affiliation(s)
- Evangelia Zdrali
- Laboratory for Fundamental BioPhotonics, Institutes of Bioengineering and Materials, School of Engineering, and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Gianluca Etienne
- Soft Materials Laboratory, Institute of Materials, School of Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Nikolay Smolentsev
- Laboratory for Fundamental BioPhotonics, Institutes of Bioengineering and Materials, School of Engineering, and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Esther Amstad
- Soft Materials Laboratory, Institute of Materials, School of Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Sylvie Roke
- Laboratory for Fundamental BioPhotonics, Institutes of Bioengineering and Materials, School of Engineering, and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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Smolentsev N, Smit WJ, Bakker HJ, Roke S. The interfacial structure of water droplets in a hydrophobic liquid. Nat Commun 2017; 8:15548. [PMID: 28537259 PMCID: PMC5458086 DOI: 10.1038/ncomms15548] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Accepted: 04/05/2017] [Indexed: 12/21/2022] Open
Abstract
Nanoscopic and microscopic water droplets and ice crystals embedded in liquid hydrophobic surroundings are key components of aerosols, rocks, oil fields and the human body. The chemical properties of such droplets critically depend on the interfacial structure of the water droplet. Here we report the surface structure of 200 nm-sized water droplets in mixtures of hydrophobic oils and surfactants as obtained from vibrational sum frequency scattering measurements. The interface of a water droplet shows significantly stronger hydrogen bonds than the air/water or hexane/water interface and previously reported planar liquid hydrophobic/water interfaces at room temperature. The observed spectral difference is similar to that of a planar air/water surface at a temperature that is ∼50 K lower. Supercooling the droplets to 263 K does not change the surface structure. Below the homogeneous ice nucleation temperature, a single vibrational mode is present with a similar mean hydrogen-bond strength as for a planar ice/air interface.
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Affiliation(s)
- Nikolay Smolentsev
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), and Institute of Materials Science (IMX), School of Engineering (STI), and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | | | - Huib J. Bakker
- AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Sylvie Roke
- Laboratory for Fundamental BioPhotonics (LBP), Institute of Bioengineering (IBI), and Institute of Materials Science (IMX), School of Engineering (STI), and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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Boubekri R, Gross M, In M, Diat O, Nobili M, Möhwald H, Stocco A. MHz Ultrasound Induced Roughness of Fluid Interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:10177-10183. [PMID: 27635785 DOI: 10.1021/acs.langmuir.6b02167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The interface between two fluids is never flat at the nanoscale, and this is important for transport across interfaces. In the absence of any external field, the surface roughness is due to thermally excited capillary waves possessing subnanometric amplitudes in the case of simple liquids. Here, we investigate the effect of ultrasound on the surface roughness of liquid-gas and liquid-liquid interfaces. Megahertz (MHz) frequency ultrasound was applied normal to the interface at relatively low ultrasonic pressures (<0.6 MPa), and the amplitudes of surface fluctuations have been measured by light reflectivity and ellipsometry. We found a dramatic enhancement of surface roughness, roughly linear with intensity, with vertical displacements of the interface as high as 50-100 nm. As a consequence, the effective contact area between two fluids can be increased by ultrasound. This result has a clear impact for enhancing interface based processes such as mass or heat transfer.
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Affiliation(s)
- Rym Boubekri
- Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France
- Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA, CNRS, UM, ENSCM), BP 17171, 30207 Cedex Bagnols-sur-Cèze, France
| | - Michel Gross
- Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France
| | - Martin In
- Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France
| | - Olivier Diat
- Institut de Chimie Séparative de Marcoule, UMR 5257 (CEA, CNRS, UM, ENSCM), BP 17171, 30207 Cedex Bagnols-sur-Cèze, France
| | - Maurizio Nobili
- Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France
| | - Helmuth Möhwald
- Max-Planck-Institute of Colloids and Interfaces , Am Mühlenberg, 14476 Potsdam, Germany
| | - Antonio Stocco
- Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Montpellier F-34095, France
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7
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David R. A density depletion model for the interfacial tension between immiscible liquids. Colloids Surf A Physicochem Eng Asp 2016. [DOI: 10.1016/j.colsurfa.2016.03.055] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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8
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Björneholm O, Hansen MH, Hodgson A, Liu LM, Limmer DT, Michaelides A, Pedevilla P, Rossmeisl J, Shen H, Tocci G, Tyrode E, Walz MM, Werner J, Bluhm H. Water at Interfaces. Chem Rev 2016; 116:7698-726. [PMID: 27232062 DOI: 10.1021/acs.chemrev.6b00045] [Citation(s) in RCA: 358] [Impact Index Per Article: 44.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The interfaces of neat water and aqueous solutions play a prominent role in many technological processes and in the environment. Examples of aqueous interfaces are ultrathin water films that cover most hydrophilic surfaces under ambient relative humidities, the liquid/solid interface which drives many electrochemical reactions, and the liquid/vapor interface, which governs the uptake and release of trace gases by the oceans and cloud droplets. In this article we review some of the recent experimental and theoretical advances in our knowledge of the properties of aqueous interfaces and discuss open questions and gaps in our understanding.
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Affiliation(s)
- Olle Björneholm
- Department of Physics and Astronomy, Uppsala University , Box 516, 751 20 Uppsala, Sweden
| | - Martin H Hansen
- Technical University of Denmark , 2800 Kongens Lyngby, Denmark.,Department of Chemistry, University of Copenhagen , Universitetsparken 5, 2100 Copenhagen, Denmark
| | - Andrew Hodgson
- Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, United Kingdom
| | - Li-Min Liu
- Thomas Young Centre, London Centre for Nanotechnology, Department of Physics and Astronomy, and Department of Chemistry, University College London , London WC1E 6BT, United Kingdom.,Beijing Computational Science Research Center , Beijing, 100193, China
| | - David T Limmer
- Princeton Center for Theoretical Science, Princeton University , Princeton, New Jersey 08544, United States
| | - Angelos Michaelides
- Thomas Young Centre, London Centre for Nanotechnology, Department of Physics and Astronomy, and Department of Chemistry, University College London , London WC1E 6BT, United Kingdom
| | - Philipp Pedevilla
- Thomas Young Centre, London Centre for Nanotechnology, Department of Physics and Astronomy, and Department of Chemistry, University College London , London WC1E 6BT, United Kingdom
| | - Jan Rossmeisl
- Department of Chemistry, University of Copenhagen , Universitetsparken 5, 2100 Copenhagen, Denmark
| | - Huaze Shen
- International Center for Quantum Materials and School of Physics, Peking University , Beijing 100871, China
| | - Gabriele Tocci
- Thomas Young Centre, London Centre for Nanotechnology, Department of Physics and Astronomy, and Department of Chemistry, University College London , London WC1E 6BT, United Kingdom.,Laboratory for fundamental BioPhotonics, Laboratory of Computational Science and Modeling, Institutes of Bioengineering and Materials Science and Engineering, School of Engineering, and Lausanne Centre for Ultrafast Science, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland
| | - Eric Tyrode
- Department of Chemistry, KTH Royal Institute of Technology , 10044 Stockholm, Sweden
| | - Marie-Madeleine Walz
- Department of Physics and Astronomy, Uppsala University , Box 516, 751 20 Uppsala, Sweden
| | - Josephina Werner
- Department of Physics and Astronomy, Uppsala University , Box 516, 751 20 Uppsala, Sweden.,Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences , Box 7015, 750 07 Uppsala, Sweden
| | - Hendrik Bluhm
- Chemical Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
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Stocco A, Su G, Nobili M, In M, Wang D. In situ assessment of the contact angles of nanoparticles adsorbed at fluid interfaces by multiple angle of incidence ellipsometry. SOFT MATTER 2014; 10:6999-7007. [PMID: 24910076 DOI: 10.1039/c4sm00482e] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Here multiple angle of incidence ellipsometry was successfully applied to in situ assess the contact angle and surface coverage of gold nanoparticles as small as 18 nm, coated with stimuli-responsive polymers, at water-oil and water-air interfaces in the presence of NaCl and NaOH, respectively. The interfacial adsorption of the nanoparticles was found to be very slow and took days to reach a fairly low surface coverage. For water-oil interfaces, in situ nanoparticle contact angles agree with the macroscopic equilibrium contact angles of planar gold surfaces with the same polymer coatings, whilst for water-air interfaces, significant differences have been observed.
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Affiliation(s)
- Antonio Stocco
- Université Montpellier 2, Laboratoire Charles Coulomb UMR 5221, F-34095, Montpellier, France.
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Ramírez P, Stocco A, Muñoz J, Miller R. Interfacial rheology and conformations of triblock copolymers adsorbed onto the water-oil interface. J Colloid Interface Sci 2012; 378:135-43. [PMID: 22575779 DOI: 10.1016/j.jcis.2012.04.033] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2012] [Revised: 04/11/2012] [Accepted: 04/12/2012] [Indexed: 01/03/2023]
Abstract
The conformation and the dilatational properties of three non-ionic triblock PEO-PPO-PEO (where PEO is polyethyleneoxide and PPO is polypropyleneoxide) copolymers of different hydrophobicity and molecular weight were investigated at the water-hexane interface. The interfacial behavior of the copolymers was studied by combining dilatational rheology using the oscillating drop method and ellipsometry. From the dilatational rheology measurements the limiting elasticity values, E(0), of the Pluronics as function of surface pressure, Π, and adsorption time were obtained, i.e. E(0)(t) and E(0)(Π). Here, it is shown that E(0)(t) depends on the number of PEO units and on the bulk concentration, showing maximum and minimum surface elasticity values which indicate conformational changes in the interfacial layer. Furthermore, in the framework of the polymer scaling law theory, conformational transitions were discussed in E(0) vs. Π plots. In a dilute regime (Π<14 mN m(-1)) at the water-hexane interface, E(0)=2Π fits well all the data, which indicates a two-dimensional "stretched chain" conformation. Increasing Π, two other interfacial transitions could take place. The different behavior of Pluronic copolymers could be also described by the local minima of E(0), which depends on the hydrophobicity of the copolymers. Conformational transitions observed by interfacial rheology were compared to ellipsometric data. Experimental results were discussed and explained on the basis of two- and three-dimensional copolymer structure taking into account that PPO chains could be partially immersed in hexane and water.
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Affiliation(s)
- Pablo Ramírez
- Departamento de Ingeniería Química, Facultad de Química, Universidad de Sevilla, Sevilla, Spain.
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Day JPR, Pudney PDA, Bain CD. Ellipsometric study of the displacement of milk proteins from the oil–water interface by the non-ionic surfactant C10E8. Phys Chem Chem Phys 2010; 12:4590-9. [DOI: 10.1039/b921887d] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Stocco A, Tauer K. High-resolution ellipsometric studies on fluid interfaces. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2009; 30:431-438. [PMID: 20012666 DOI: 10.1140/epje/i2009-10544-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Accepted: 11/13/2009] [Indexed: 05/28/2023]
Abstract
In this article, highly accurate experimental results reveal the interfacial profile between different macroscopic fluid phases. The deviation from a step profile, quantified by the ellipsometric quantity J(1), shows a strong correlation with the cohesive energy quantified by the Gordon parameter G . Surprisingly, at high values of G , J (1)( < 0) deviates significantly from any predictions. Findings for water and water-like interfaces can be interpreted in terms of the strength of hydrogen bonding at the surface.
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Affiliation(s)
- A Stocco
- Max Planck Institute of Colloids and Interfaces, 14476, Golm, Germany.
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Stocco A, Tauer K, Pispas S, Sigel R. Dynamics at the air-water interface revealed by evanescent wave light scattering. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2009; 29:95-105. [PMID: 19430825 DOI: 10.1140/epje/i2009-10455-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2008] [Revised: 12/23/2008] [Accepted: 03/25/2009] [Indexed: 05/27/2023]
Abstract
A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle illumination. Peak width and height are affected by the interfacial profile and the focusing of the beam. In addition, the propagation of capillary waves was studied at the surface of pure water and in the presence of latex particles and amphiphilic diblock copolymers. The range of the scattering vectors where propagating surface waves were detected is by far wider than standard surface quasi-elastic light scattering (SQELS) and comparable with those of X-ray photon correlation spectroscopy (XPCS).
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Affiliation(s)
- A Stocco
- Max Planck Institute of Colloids and Interfaces, 14476, Golm, Germany.
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Abstract
Hydrophobicity manifests itself differently on large and small length scales. This review focuses on large-length-scale hydrophobicity, particularly on dewetting at single hydrophobic surfaces and drying in regions bounded on two or more sides by hydrophobic surfaces. We review applicable theories, simulations, and experiments pertaining to large-scale hydrophobicity in physical and biomolecular systems and clarify some of the critical issues pertaining to this subject. Given space constraints, we cannot review all the significant and interesting work in this active field.
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Affiliation(s)
- Bruce J Berne
- Department of Chemistry, Columbia University, New York, New York 10027, USA.
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Kashimoto K, Yoon J, Hou B, Chen CH, Lin B, Aratono M, Takiue T, Schlossman ML. Structure and depletion at fluorocarbon and hydrocarbon/water liquid/liquid interfaces. PHYSICAL REVIEW LETTERS 2008; 101:076102. [PMID: 18764557 DOI: 10.1103/physrevlett.101.076102] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2008] [Indexed: 05/26/2023]
Abstract
The results of x-ray reflectivity studies of two oil/water (liquid/liquid) interfaces are inconsistent with recent predictions of the presence of a vaporlike depletion region at hydrophobic/aqueous interfaces. One of the oils, perfluorohexane, is a fluorocarbon whose superhydrophobic interface with water provides a stringent test for the presence of a depletion layer. The other oil, heptane, is a hydrocarbon and, therefore, is more relevant to the study of biomolecular hydrophobicity. These results are consistent with the subangstrom proximity of water to soft hydrophobic materials.
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Affiliation(s)
- Kaoru Kashimoto
- Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
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Bresme F, Chacón E, Tarazona P, Tay K. Intrinsic structure of hydrophobic surfaces: the oil-water interface. PHYSICAL REVIEW LETTERS 2008; 101:056102. [PMID: 18764409 DOI: 10.1103/physrevlett.101.056102] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2007] [Indexed: 05/26/2023]
Abstract
We investigate the water-oil interface using molecular dynamics simulations of realistic models of alkanes and water. The intrinsic density profiles are computed using a methodology that removes the smoothing effect of the capillary waves. We show that at 300 K the intrinsic width of the gap separating the oil and water phases spans little more than one water molecule diameter, and undergoes very weak short-ranged fluctuations, indicating that the water-oil interface is a rigid molecular structure at ambient temperature. Only near the drying transition (above 500 K for dodecane), the gap features uncoupled fluctuations of the oil and water surfaces, as expected in a typical drying structure. We find that the intrinsic structure of water next to the oil phase is remarkably similar to the bare water-vapor interface.
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Affiliation(s)
- Fernando Bresme
- Department of Chemistry, Imperial College London, London, United Kingdom.
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