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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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Wierenga PA, Basheva ES, Delahaije RJBM. Variations in foam collapse and thin film stability with constant interfacial and bulk properties. Adv Colloid Interface Sci 2023; 312:102845. [PMID: 36709573 DOI: 10.1016/j.cis.2023.102845] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Revised: 01/20/2023] [Accepted: 01/20/2023] [Indexed: 01/24/2023]
Abstract
The stability of foams is commonly linked to the interfacial properties of the proteins and other surfactants used. This study aimed to use these relationships to explain differences in foam stability observed among similar beer samples from different breweries. The foam stability was different for each sample (Nibem foam stability ranged from 206 to 300 s), but ranking was similar for all three foaming methods used, thus independent of the method, gas, etc. Differences in foam stability were dominated by differences in coalescence, as illustrated by the correlation with the stability of single bubbles and thin liquid films. The differences in coalescence stability could not be explained by the measured interfacial properties (e.g. surface pressure, adsorption rate, dilatational modulus and surface shear viscosity), or the bulk properties (concentration, pH, ionic strength, viscosity), since they were similar for all samples. The drainage rates and disjoining pressure isotherms measured in thin liquid films were also similar for all samples, further limiting the options to explain the differences in foam stability using known arguments. The differences in coalescence stability of the thin films was shown to depend on the liquid in between the adsorbed layers of the thin film, using a modified capillary cell to exchange this liquid (to a buffer, or one of the other samples). This illustrates the need to review our current understanding and to develop new methods both for experimental study and theoretical description, to better understand foam stability in the future.
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Affiliation(s)
- Peter Alexander Wierenga
- Laboratory of Food Chemistry, Wageningen UR, Bornse Weilanden 9, Wageningen 6708, WG, the Netherlands.
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3
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Leister N, Götz V, Jan Bachmann S, Nachtigall S, Hosseinpour S, Peukert W, Karbstein H. A comprehensive methodology to study double emulsion stability. J Colloid Interface Sci 2023; 630:534-548. [DOI: 10.1016/j.jcis.2022.10.119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Revised: 10/15/2022] [Accepted: 10/22/2022] [Indexed: 11/05/2022]
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4
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Mikhailovskaya A, Chatzigiannakis E, Renggli D, Vermant J, Monteux C. From Individual Liquid Films to Macroscopic Foam Dynamics: A Comparison between Polymers and a Nonionic Surfactant. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:10768-10780. [PMID: 35998760 PMCID: PMC9454262 DOI: 10.1021/acs.langmuir.2c00900] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Revised: 08/12/2022] [Indexed: 06/15/2023]
Abstract
Foams can resist destabilizaton in ways that appear similar on a macroscopic scale, but the microscopic origins of the stability and the loss thereof can be quite diverse. Here, we compare both the macroscopic drainage and ultimate collapse of aqueous foams stabilized by either a partially hydrolyzed poly(vinyl alcohol) (PVA) or a nonionic low-molecular-weight surfactant (BrijO10) with the dynamics of individual thin films at the microscale. From this comparison, we gain significant insight regarding the effect of both surface stresses and intermolecular forces on macroscopic foam stability. Distinct regimes in the lifetime of the foams were observed. Drainage at early stages is controlled by the different stress-boundary conditions at the surfaces of the bubbles between the polymer and the surfactant. The stress-carrying capacity of PVA-stabilized interfaces is a result of the mutual contribution of Marangoni stresses and surface shear viscosity. In contrast, surface shear inviscidity and much weaker Marangoni stresses were observed for the nonionic surfactant surfaces, resulting in faster drainage times, both at the level of the single film and the macroscopic foam. At longer times, the PVA foams present a regime of homogeneous coalescence where isolated coalescence events are observed. This regime, which is observed only for PVA foams, occurs when the capillary pressure reaches the maximum disjoining pressure. A final regime is then observed for both systems where a fast coalescence front propagates from the top to the bottom of the foams. The critical liquid fractions and capillary pressures at which this regime is obtained are similar for both PVA and BrijO10 foams, which most likely indicates that collapse is related to a universal mechanism that seems unrelated to the stabilizer interfacial dynamics.
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Affiliation(s)
- Alesya Mikhailovskaya
- Soft
Matter Science and Engineering, ESPCI Paris, CNRS, PSL University, Sorbonne University, 75005 Paris, Franceand
- Institut
de Chimie et des Matériaux Paris-Est, CNRS UMR 7182, 2-8 rue Henri Dunant, 94320 Thiais, France
| | - Emmanouil Chatzigiannakis
- Department
of Materials, ETH Zürich, Vladimir Prelog Weg 5, 8032 Zürich, Switzerland and
- Polymer
Technology Group, Eindhoven University of
Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands
| | - Damian Renggli
- Department
of Materials, ETH Zürich, Vladimir Prelog Weg 5, 8032 Zürich, Switzerland and
| | - Jan Vermant
- Department
of Materials, ETH Zürich, Vladimir Prelog Weg 5, 8032 Zürich, Switzerland and
| | - Cécile Monteux
- Soft Matter
Science and Engineering, ESPCI Paris, CNRS,
PSL University, Sorbonne University, 75005 Paris, France
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5
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Rafe A, Selahbarzin S, Kulozik U, Hesarinejad MA. Dilatational rheology-property relationships of β-lactoglobulin /high methoxyl pectin mixtures in aqueous foams. Food Hydrocoll 2022. [DOI: 10.1016/j.foodhyd.2022.107683] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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6
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Zhou H, Vu G, McClements DJ. Formulation and characterization of plant-based egg white analogs using RuBisCO protein. Food Chem 2022; 397:133808. [PMID: 35914453 DOI: 10.1016/j.foodchem.2022.133808] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 07/16/2022] [Accepted: 07/25/2022] [Indexed: 11/04/2022]
Abstract
RuBisCO protein, which can be isolated from abundant and sustainable plant sources, can mimic some of the desirable functional attributes of egg white proteins. In this study, plant-based egg white analogs were successfully produced using 10 w% RuBisCO solutions (pH 8). These protein solutions had similar apparent viscosity-shear rate profiles, shear modulus-temperature profiles, gelling temperatures, and final gel strengths as egg white. However, there were some differences. RuBisCO protein gels were slightly darker than egg white, which was attributed to the presence of phenolic impurities. Moreover, RuBisCo proteins exhibited a single thermal transition temperature (∼66 °C) whereas egg white proteins exhibited two (∼66 and ∼81 °C). RuBisCO gels were more brittle but less chewy and resilient than egg white gels. This study provides valuable insights into the potential of RuBisCO protein for formulating plant-based egg white analogs.
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Affiliation(s)
- Hualu Zhou
- Biopolymers and Colloids Laboratory, Department of Food Science, University of Massachusetts, Amherst, MA 01003, USA
| | - Giang Vu
- Biopolymers and Colloids Laboratory, Department of Food Science, University of Massachusetts, Amherst, MA 01003, USA
| | - David Julian McClements
- Biopolymers and Colloids Laboratory, Department of Food Science, University of Massachusetts, Amherst, MA 01003, USA.
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7
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Adsorption, Surface Viscoelasticity, and Foaming Properties of Silk Fibroin at the Air/Water Interface. COLLOIDS AND INTERFACES 2022. [DOI: 10.3390/colloids6030040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Like other proteins, the natural silk fibroin (SF) extracted from domesticated silkworms can adsorb at the air/water interface and stabilize foam due to its amphiphilic character and surface activity. At the interface, the adsorbed SF molecules experience structural reorganization and form water-insoluble viscoelastic films, which protect foam bubbles from coalescence and rupture. The solution conditions, such as protein concentration, pH, and additives, have significant influences on the molecular adsorption, layer thickness, interfacial mechanical strength, and, thus, on the foaming properties of SF. The understanding of the relationship between the interfacial adsorption, surface viscoelasticity, and foaming properties of SF is very important for the design, preparation, and application of SF foams in different fields.
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8
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Rafe A, Glikman D, Rey NG, Haller N, Kulozik U, Braunschweig B. Structure-property relations of β-lactoglobulin/κ-carrageenan mixtures in aqueous foam. Colloids Surf A Physicochem Eng Asp 2022. [DOI: 10.1016/j.colsurfa.2022.128267] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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9
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Interfacial properties of milk proteins: A review. Adv Colloid Interface Sci 2021; 295:102347. [PMID: 33541692 DOI: 10.1016/j.cis.2020.102347] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 12/14/2020] [Accepted: 12/14/2020] [Indexed: 12/22/2022]
Abstract
The interfacial properties of dairy proteins are of great interest to the food industry. Food manufacturing involves various environmental conditions and multiple processes that significantly alter the structure and colloidal stability of food materials. The effects of concentration, pH, heat treatment, addition of salts etc., have considerable influence on the surface activity of proteins and the mechanical properties of the interfacial protein films. Studies to date have established some understanding of the links between environmental and processing related parameters and their impacts on interfacial behavior. Improvement in knowledge may allow better design of interfacial protein structures for different food applications. This review examines the effects of environmental and processing conditions on the interfacial properties of dairy proteins with emphasis on interfacial tension dynamics, dilatational and surface shear rheological properties. The most commonly used surface analytical techniques along with relevant methods are also addressed.
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10
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Kubbutat P, Leitão L, Kulozik U. Stability of Foams in Vacuum Drying Processes. Effects of Interactions between Sugars, Proteins, and Surfactants on Foam Stability and Dried Foam Properties. Foods 2021; 10:foods10081876. [PMID: 34441652 PMCID: PMC8392398 DOI: 10.3390/foods10081876] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 08/05/2021] [Accepted: 08/11/2021] [Indexed: 01/16/2023] Open
Abstract
The hypothesis was that saccharides mediate interactions between surface-active components and that this will have an impact on foam decay during the drying process. Static light scattering was performed to determine changes in interactions between the foam stabilizer on a molecular level. Furthermore, pendant drop and oscillating drop measurements were performed to examine the surface tension and surface rheology. Foams were dried in conventional dryers as well as microwave-supported vacuum dryers. Final foam properties were determined. It was shown that the addition of sugars, often added as protective substances for sensitive organic molecules, resulted in lower repulsion between different types of surface-active components, namely polysorbate 80 and β-lactoglobulin (β-lg). Differences in impact of the types of sugars and between different types of surfactant, protein, and small molecules were observed influencing the foam decay behavior. The interfacial properties of polysorbate 80 and β-lg were influenced by the type of the used sugars. The surface elasticity of protein stabilized surfaces was higher compared to that of polysorbate stabilized systems. Protein stabilized systems remained more stable compared to polysorbate systems, which was also affected by the used saccharide. Overall, a correlation between molecular interactions and foam decay behavior was found.
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11
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Lautenbach V, Hosseinpour S, Peukert W. Isoelectric Point of Proteins at Hydrophobic Interfaces. Front Chem 2021; 9:712978. [PMID: 34395381 PMCID: PMC8360839 DOI: 10.3389/fchem.2021.712978] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Accepted: 07/19/2021] [Indexed: 12/02/2022] Open
Abstract
Structural and colloidal stability of proteins at different surfaces and interfaces is of great importance in many fields including medical, pharmaceutical, or material science. Due to their flexibility, proteins tend to respond to their environmental conditions and can undergo structural and conformational changes. For instance, alterations in physiological factors such as temperature, ions concentration, or pH as well as the adsorption to an interface can initiate protein aggregation. Therefore, at different surfaces and interfaces the characterization of the structural and colloidal stability of proteins, which is mainly influenced by their electrostatic and hydrophobic interactions, is of fundamental importance. In this study, we utilized sum frequency generation (SFG) spectroscopy to assess the role of solution pH on the polarity and magnitude of the electric field within the hydration shell of selected model proteins adsorbed to a hydrophobic surface. We used polystyrene (PS) as a model hydrophobic surface and determined the isoelectric point (IEP) of four structurally different model proteins. Comparing the measured IEP of proteins at the PS/solution or air/solution interface with that determined in the bulk solution via zeta potential measurement, we found significant similarities between the IEP of surface adsorbed proteins and those in the bulk aqueous phase. The pH dependence behavior of proteins was correlated to their amino acid composition and degree of hydrophobicity.
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Affiliation(s)
- Vanessa Lautenbach
- Institute of Particle Technology (LFG), Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Saman Hosseinpour
- Institute of Particle Technology (LFG), Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Wolfgang Peukert
- Institute of Particle Technology (LFG), Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
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12
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Guckeisen T, Hosseinpour S, Peukert W. Effect of pH and urea on the proteins secondary structure at the water/air interface and in solution. J Colloid Interface Sci 2021; 590:38-49. [PMID: 33524719 DOI: 10.1016/j.jcis.2021.01.015] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 01/05/2021] [Accepted: 01/06/2021] [Indexed: 01/09/2023]
Abstract
HYPOTHESIS The secondary structure of proteins affects their functionality and performance in physiological environments or industrial applications. Change of the solution pH or the presence of protein denaturants are the main chemical means that can alter the secondary structure of proteins or lead to protein denaturation. Since proteins in the bulk solution and those residing at the solution/air interface experience different local environments, their response to chemical denaturation can be different. EXPERIMENTS We utilize circular dichroism and chiral/achiral sum frequency generation spectroscopy to study the secondary structure of selected proteins as a function of the solution pH or in the presence of 8 M urea in the bulk solution and at the solution/air interface, respectively. FINDINGS The liquid/air interface can enhance or decrease protein conformation stability. The change in the secondary structure of the surface adsorbed proteins in alkaline solutions occurs at pH values lower than those denaturing the studied proteins in the bulk solution. In contrast, while 8 M urea completely denatures the studied proteins in the bulk solution, the liquid/air interface prevents the urea-induced denaturation of the surface adsorbed proteins by limiting the access of urea to the hydrophobic side chains of proteins protruding to air.
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Affiliation(s)
- Tobias Guckeisen
- Institute of Particle Technology (LFG), Friedrich-Alexander-Universität-Erlangen-Nürnberg (FAU), Cauerstraße 4, 91058 Erlangen, Germany.
| | - Saman Hosseinpour
- Institute of Particle Technology (LFG), Friedrich-Alexander-Universität-Erlangen-Nürnberg (FAU), Cauerstraße 4, 91058 Erlangen, Germany.
| | - Wolfgang Peukert
- Institute of Particle Technology (LFG), Friedrich-Alexander-Universität-Erlangen-Nürnberg (FAU), Cauerstraße 4, 91058 Erlangen, Germany.
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13
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Influence of salt addition on the surface and foaming properties of silk fibroin. Colloids Surf A Physicochem Eng Asp 2021. [DOI: 10.1016/j.colsurfa.2020.125621] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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14
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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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15
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β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 4. Impact on the Stability of Foam Films and Foams. MINERALS 2020. [DOI: 10.3390/min10070636] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The complexity and high sensitivity of proteins to environmental factors give rise to a multitude of variables, which affect the stabilization mechanisms in protein foams. Interfacial and foaming properties of proteins have been widely studied, but the reported unique effect of pH, which can be of great interest to applications, has been investigated to a lesser extent. In this paper, we focus on the impact of pH on the stability of black foam films and corresponding foams obtained from solutions of a model globular protein—the whey β-lactoglobulin (BLG). Foam stability was analyzed utilizing three characteristic parameters (deviation time, transition time and half-lifetime) for monitoring the foam decay, while foam film stability was measured in terms of the critical disjoining pressure of film rupture. We attempt to explain correlations between the macroscopic properties of a foam system and those of its major building blocks (foam films and interfaces), and thus, to identify structure-property relationships in foam. Good correlations were found between the stabilities of black foam films and foams, while relations to the properties of adsorption layers appeared to be intricate. That is because pH-dependent interfacial properties of proteins usually exhibit an extremum around the isoelectric point (pI), but the stability of BLG foam films increases with increasing pH (3–7), which is well reflected in the foam stability. We discuss the possible reasons behind these intriguingly different behaviors on the basis of pH-induced changes in the molecular properties of BLG, which seem to be determining the mechanism of film rupture at the critical disjoining pressure.
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16
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Buszewski B, Rodzik A, Railean-Plugaru V, Sprynskyy M, Pomastowski P. A study of zinc ions immobilization by β-lactoglobulin. Colloids Surf A Physicochem Eng Asp 2020. [DOI: 10.1016/j.colsurfa.2020.124443] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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17
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Imani IM, Noei N, Azizian S. Foam analysis of aqueous solution containing ion pair of methyl violet and SDS. Colloids Surf A Physicochem Eng Asp 2020. [DOI: 10.1016/j.colsurfa.2019.124338] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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18
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Gochev GG, Scoppola E, Campbell RA, Noskov BA, Miller R, Schneck E. β-Lactoglobulin Adsorption Layers at the Water/Air Surface: 3. Neutron Reflectometry Study on the Effect of pH. J Phys Chem B 2019; 123:10877-10889. [PMID: 31725291 DOI: 10.1021/acs.jpcb.9b07733] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Several characteristics of β-lactoglobulin (BLG) layers adsorbed at the air/water interface exhibit a strong pH dependence, but our knowledge on the underlying structure-property relations is still fragmental. Here, we therefore extend our recent studies by neutron reflectometry (NR) and provide a comprehensive overview through direct measurements of the surface excess Γ and the layers' molecular structure. This enables comparison with available literature data to draw general conclusions. The NR experiments were performed at various pH values and within a wide range of protein concentrations, CBLG. Adsorption kinetics measurements in air-contrast-matched-water and over a narrow Qz range enabled direct quantification of the dynamic surface excess Γ(t) and are found to be consistent with ellipsometry data. Near the isoelectric point, pI, the rates of adsorption and Γ are maximal but only at sufficiently high CBLG. NR data collected over a wider Qz range and in two aqueous isotopic contrasts revealed the structure of adsorbed BLG layers at a steady state close to equilibrium. Independent of the pH, BLG was found to form dense monolayers with average thicknesses of 1.1 nm, suggesting flattening of the BLG globules upon adsorption as compared with their bulk dimensions (≈3.5 nm). Near pI and at sufficiently high CBLG, a thick (≈5.5 nm) but looser secondary sublayer is additionally formed adjacent to the dense primary monolayer. The thickness of this sublayer can be interpreted in terms of disordered BLG dimers. The results obtained and notably the specific interfacial structuring of BLG near pI complement previous observations relating the impact of solution pH and CBLG on other interfacial characteristics such as surface pressure and surface dilational viscoelasticity modulus.
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Affiliation(s)
- Georgi G Gochev
- Max Planck Institute of Colloids and Interfaces , 14476 Potsdam , Germany.,Institute of Physical Chemistry , Bulgarian Academy of Sciences , 1113 Sofia , Bulgaria
| | - Ernesto Scoppola
- Max Planck Institute of Colloids and Interfaces , 14476 Potsdam , Germany
| | - Richard A Campbell
- Institut Laue-Langevin , 71 Avenue des Martyrs, CS20156 , 38042 Grenoble , France.,Division of Pharmacy and Optometry , University of Manchester , M13 9PT Manchester , U.K
| | - Boris A Noskov
- Institute of Chemistry , St. Petersburg State University , 198504 Saint-Petersburg , Russia
| | - Reinhard Miller
- Max Planck Institute of Colloids and Interfaces , 14476 Potsdam , Germany
| | - Emanuel Schneck
- Max Planck Institute of Colloids and Interfaces , 14476 Potsdam , Germany
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19
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Richert ME, Gochev GG, Braunschweig B. Specific Ion Effects of Trivalent Cations on the Structure and Charging State of β-Lactoglobulin Adsorption Layers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:11299-11307. [PMID: 31398284 DOI: 10.1021/acs.langmuir.9b01803] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The properties of proteins at interfaces are important to many processes as well as in soft matter materials such as aqueous foam. Particularly, the protein interfacial behavior is strongly linked to different factors like the solution pH or the presence of electrolytes. Here, the nature of the electrolyte ions can significantly modify the interfacial properties of proteins. Therefore, molecular level studies on interfacial structures and charging states are needed. In this work, we addressed the effects of Y3+ and Nd3+ cations on the adsorption of the whey protein β-lactoglobulin (BLG) at air-water interfaces as the function of electrolyte concentration. Both cations caused very similar but dramatic changes at the interface and in the bulk solution. Here, measurements of the electrophoretic mobility and with vibrational sum-frequency generation (SFG) spectroscopy were applied and consistently showed a reversal of the BLG net charge at remarkably low ion concentrations of 30 (bulk) and 40 (interface) μM of Y3+ or Nd3+ for a BLG concentration of 15 μM. SFG spectra of carboxylate stretching vibrations from Asp or Glu residues of interfacial BLG showed significant changes in the resonance frequency, which we associate to specific and efficient binding of Y3+ or Nd3+ ions to the proteins carboxylate groups. Characteristic reentrant condensation for BLG moieties with bound trivalent ions was found in a broad concentration range around the point of zero net charge. The highest colloidal stability of BLG was found for ion concentrations <20 μM and >50 μM. Investigations on macroscopic foams from BLG solutions revealed the existence of structure-property relations between the interfacial charging state and the foam stability. In fact, a minimum in foam stability at 20 μM ion concentration was found when the interfacial net charge was negligible. At this concentration, we propose that the persistent BLG molecules and weakly charged BLG aggregates drive foam stability, while outside the bulk reentrant zone the electrostatic disjoining pressure inside foam lamellae dominates foam stability. Our results provide new information on the charge reversal at the liquid-gas interface of protein/ion dispersions. Therefore, we see our findings as an important step in the clarification of reentrant condensation effects at interfaces and their relevance to foam stability.
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Affiliation(s)
- Manuela E Richert
- Institute of Physical Chemistry and Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster Corrensstraße 28/30 , 48149 Münster , Germany
| | - Georgi G Gochev
- 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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20
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Guckeisen T, Hosseinpour S, Peukert W. Isoelectric Points of Proteins at the Air/Liquid Interface and in Solution. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:5004-5012. [PMID: 30892047 DOI: 10.1021/acs.langmuir.9b00311] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Electrostatic interactions play essential roles in determining the function, colloidal stability, and adsorption of proteins on different surfaces and interfaces. Therefore, a molecular-level understanding of the charge state of the proteins under different conditions is required to explain their macroscopic properties. In this study, we have employed an inherently surface-sensitive spectroscopic tool, sum frequency generation spectroscopy, to determine the charge state of a wide range of proteins as a function of pH at the air/liquid interface via measurement of the degree of orientation of water molecules. We compared the isoelectric point (IEP) of the 12 investigated proteins at the air/liquid interface with that in the bulk solution obtained through zeta potential measurements. Ellipsometry is performed to determine the film thickness at the air/liquid interface at different charge states. In particular, protein aggregation at the IEP is reflected by increased film thickness. For all proteins, the interfacial point of zero charge is close (with less than 1 pH unit variation) to that in the bulk solution.
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Affiliation(s)
- Tobias Guckeisen
- Institute of Particle Technology (LFG) , Friedrich-Alexander-Universität-Erlangen-Nürnberg (FAU) , Cauerstraße 4 , 91058 Erlangen , Germany
| | - Saman Hosseinpour
- Institute of Particle Technology (LFG) , Friedrich-Alexander-Universität-Erlangen-Nürnberg (FAU) , Cauerstraße 4 , 91058 Erlangen , Germany
| | - Wolfgang Peukert
- Institute of Particle Technology (LFG) , Friedrich-Alexander-Universität-Erlangen-Nürnberg (FAU) , Cauerstraße 4 , 91058 Erlangen , Germany
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García Rey N, Weißenborn E, Schulze-Zachau F, Gochev G, Braunschweig B. Quantifying Double-Layer Potentials at Liquid-Gas Interfaces from Vibrational Sum-Frequency Generation. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2019; 123:1279-1286. [PMID: 30713590 PMCID: PMC6354727 DOI: 10.1021/acs.jpcc.8b10097] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 12/13/2018] [Indexed: 05/31/2023]
Abstract
Vibrational sum-frequency generation (SFG) spectroscopy is demonstrated as a fast method to quantify variations of the electric double-layer potential ϕ0 at liquid-gas interfaces. For this, mixed solutions of nonionic tetraethyleneglycol-monodecylether (C10E4) and cationic hexadecyltrimethylammonium bromide (C16TAB) surfactants were investigated using SFG spectroscopy and a thin-film pressure balance (TFPB). Derjaguin-Landau-Verwey-Overbeek analysis of disjoining pressure isotherms obtained with the TFPB technique provides complementary information on ϕ0, which we apply to validate the results from SFG spectroscopy. By using a single ϕ0 value, we can disentangle χ(2) and χ(3) contributions to the O-H stretching modes of interfacial water molecules in the SFG spectra. Having established the latter, we show that unknown double-layer potentials at the liquid-gas interface from solutions with different C16TAB/C10E4 mixing ratios can be obtained from an analysis of SFG spectra and are in excellent agreement with the complementary results from the TFPB technique.
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22
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Salt-dependent interaction behavior of β-Lactoglobulin molecules in relation to their surface and foaming properties. Colloids Surf A Physicochem Eng Asp 2018. [DOI: 10.1016/j.colsurfa.2018.09.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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23
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Richert ME, García Rey N, Braunschweig B. Charge-Controlled Surface Properties of Native and Fluorophore-Labeled Bovine Serum Albumin at the Air-Water Interface. J Phys Chem B 2018; 122:10377-10383. [PMID: 30339752 PMCID: PMC6245422 DOI: 10.1021/acs.jpcb.8b06481] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
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Proteins
at interfaces are important for protein formulations and
in soft materials such as foam. Here, interfacial stability and physicochemical
properties are key elements, which drive macroscopic foam properties
through structure–property relations. Native and fluorescein
isothiocyanate-labeled bovine serum albumin (BSA) were used to modify
air–water interfaces as a function of pH. Characterizations
were performed with tensiometry and sum-frequency generation (SFG).
SFG spectra of O–H stretching vibrations reveal a phase reversal
and a pronounced minimum in O–H intensity at pH values of 5.3
and 4.7 for native and labeled BSA, respectively. This minimum is
attributed to the interfacial isoelectric point (IEP) and is accompanied
by a minimum in surface tension and negligible ζ-potentials
in the bulk. Interfacial proteins at pH values close to the IEP can
promote macroscopic foam stability and are predominately located in
the lamellae between individual gas bubbles as evidenced by confocal
fluorescence microscopy. Different from the classical stabilization
mechanisms, for example, via the electrostatic disjoining pressure,
we propose that the presence of more close-packed BSA, because of
negligible net charges, inside the foam lamellae is more effective
in reducing foam drainage as compared to a situation with strong repulsive
electrostatic interactions.
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Affiliation(s)
- Manuela E Richert
- Institute of Physical Chemistry , Westfälische Wilhelms-Universität Münster , Corrensstraße 28/30 , 48149 Münster , Germany
| | - Natalia García Rey
- Institute of Physical Chemistry , Westfälische Wilhelms-Universität Münster , Corrensstraße 28/30 , 48149 Münster , Germany.,Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster , Busso-Peus-Straße 10 , 48149 Münster , Germany
| | - Björn Braunschweig
- Institute of Physical Chemistry , Westfälische Wilhelms-Universität Münster , Corrensstraße 28/30 , 48149 Münster , Germany.,Center for Soft Nanoscience , Westfälische Wilhelms-Universität Münster , Busso-Peus-Straße 10 , 48149 Münster , Germany
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Sung W, Krem S, Kim D. Binding of trivalent ions on fatty acid Langmuir monolayer: Fe3+ versus La3+. J Chem Phys 2018; 149:163304. [DOI: 10.1063/1.5028296] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Affiliation(s)
- Woongmo Sung
- Department of Physics, Sogang University, Seoul 121-742, South Korea
| | - Sona Krem
- Department of Physics, Sogang University, Seoul 121-742, South Korea
| | - Doseok Kim
- Department of Physics, Sogang University, Seoul 121-742, South Korea
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25
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Schulze-Zachau F, Bachmann S, Braunschweig B. Effects of Ca 2+ Ion Condensation on the Molecular Structure of Polystyrene Sulfonate at Air-Water Interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:11714-11722. [PMID: 30188134 PMCID: PMC6170951 DOI: 10.1021/acs.langmuir.8b02631] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 09/05/2018] [Indexed: 06/02/2023]
Abstract
The structure of poly(sodium 4-styrenesulfonate) (NaPSS) polyelectrolytes at air-water interfaces was investigated with tensiometry, ellipsometry, and vibrational sum-frequency generation (SFG) in the presence of low and high CaCl2 concentrations. In addition, we have studied the foaming behavior of 20 mM NaPSS solutions to relate the PSS molecular structure at air-water interfaces to foam properties. PSS polyelectrolytes without additional salt exhibited significant surface activity, which can be tuned further by additions of CaCl2. The hydrophobicity of the backbone due to incomplete sulfonation during synthesis is one origin, whereas the effective charge of the polyelectrolyte chain is shown to play another major role. At low salt concentrations, we propose that the polyelectrolyte is forming a layered structure. The hydrophobic parts are likely to be located directly at the interface in loops, whereas the hydrophilic parts are at low concentrations stretched out into near-interface regions in tails. Increasing the Ca2+ concentration leads to ion condensation, a collapse of the tails, and likely to Ca2+ intra- and intermolecular bridges between polyelectrolytes at the interface. The increase in both surface excess and foam stability originates from changes in the polyelectrolyte's hydrophobicity due to Ca2+ condensation onto the PSS polyanions. Consequently, charge screening at the interface is enhanced and repulsive electrostatic interactions are reduced. Furthermore, SFG spectra of O-H stretching bands reveal a decrease in intensity of the low-frequency branch when c(Ca2+) is increased whereas the high-frequency branch of O-H stretching modes persists even for 1 M CaCl2. This originates from the remaining net charge of the PSS polyanions at the air-water interface that is not fully compensated by condensation of Ca2+ ions and leads to electric-field-induced contributions to the SFG spectra of interfacial H2O. A charge reversal of the PSS net charge at the air-water interface is not observed and is consistent with bulk electrophoretic mobility measurements.
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Affiliation(s)
- Felix Schulze-Zachau
- Institute
of Physical Chemistry and Center for Soft Nanoscience, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
| | - Silvia Bachmann
- Institute
of Particle Technology (LFG), Friedrich-Alexander-Universität
Erlangen-Nürnberg (FAU), Cauerstraße 4, 91058 Erlangen, 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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Metal Ion Interactions with Crude Oil Components: Specificity of Ca2+ Binding to Naphthenic Acid at an Oil/Water Interface. COLLOIDS AND INTERFACES 2018. [DOI: 10.3390/colloids2030040] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
On the basis of dynamic interfacial tension measurements, Ca2+ has been shown specifically to interact with naphthenic acid (NA) at the n-heptane/water interface, consistent with NA adsorption followed by interfacial complexation and formation of a more ordered interfacial film. Optimum concentrations of Ca2+ and NA have been found to yield lower, time-dependent interfacial tensions, not evident for Mg2+ and Sr2+ or for several alkali metal ions studied. The results reflect the specific hydration and coordination chemistry of Ca2+ seen in biology. Owing to the ubiquitous presence of Ca2+ in oilfield waters, this finding has potential relevance to the surface chemistry underlying crude oil recovery. For example, “locking” acidic components at water/oil interfaces may be important for crude oil emulsion stability, or in bonding bulk oil to mineral surfaces through an aqueous phase, potentially relevant for carbonate reservoirs. The relevance of the present results to low salinity waterflooding as an enhanced crude oil recovery technique is also discussed.
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Streubel S, Schulze-Zachau F, Weißenborn E, Braunschweig B. Ion Pairing and Adsorption of Azo Dye/C 16TAB Surfactants at the Air-Water Interface. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2017; 121:27992-28000. [PMID: 29285205 PMCID: PMC5742476 DOI: 10.1021/acs.jpcc.7b08924] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2017] [Revised: 10/29/2017] [Indexed: 06/01/2023]
Abstract
Mixed layers of 6-hydroxy-5-[(4-sulfophenyl)azo]-2-naphthalenesulfonate (Sunset Yellow, SSY) and cetyltrimethylammonium bromide (C16TAB) at the air-water interface were studied using vibrational sum-frequency generation (SFG) and dynamic surface tension measurements. In the bulk, addition of C16TAB to SSY aqueous solution causes substantial changes in UV/vis absorption spectra, which originate from strong electrostatic interactions between the anionic SSY azo dye with the cationic C16TAB surfactant. These interactions are a driving force for the formation of SSY/C16TAB ion pairs. The latter are found to be highly surface active while free SSY molecules show no surface activity. Dynamic SFG as well as surface tension measurements at low SSY concentrations reveal that free C16TAB surfactants adsorb at the air-water interface on time scales <1 s where they initially form the dominating surface species, but on longer time scales free C16TAB is exchanged by SSY/C16TAB ion pairs. This causes a dramatic reduction of the surface tension to 35 mN/m but also in foam stability. These changes are accompanied by a substantial loss in SFG intensity from O-H stretching bands around 3200 and 3450 cm-1, which we relate to a decrease in surface charging due to adsorption of ion pairs with no or negligible net charges. For SSY/C16TAB molar ratios >0.5, the O-H bands in SFG spectra are reduced to very low intensities and are indicative to electrically neutral SSY/C16TAB ion pairs. This conclusion is corroborated by an analysis of macroscopic foams, which become highly instable in the presence of neutral SSY/C16TAB ion pairs. From an analysis of SFG spectra of air-water interfaces, we show that the electrostatic repulsion forces inside the ubiquitous foam films are reduced and thus remove the major stabilization mechanism within macroscopic foam.
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Affiliation(s)
- Saskia Streubel
- Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany
| | - Felix Schulze-Zachau
- Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany
| | - Eric Weißenborn
- Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany
| | - Björn Braunschweig
- Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany
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