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Penfold J, Thomas RK. Neutron reflection and the thermodynamics of the air-water interface. Phys Chem Chem Phys 2022; 24:8553-8577. [PMID: 35352746 DOI: 10.1039/d2cp00053a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
By means of isotopic substitution, measurements of the neutron reflectivity (NR) from a flat water surface generally give model independent measurements of the amount of a chosen solute at the surface irrespective of whether the layer is a mixture or whether there is any aggregation in the bulk solution. Previously, adsorption at air-water interfaces has been determined by applying the Gibbs equation to surface tension (ST) measurements, which requires assumptions about the composition of the surface and about the activity of the solute in the bulk, which, in turn, means that in practice the surface is assumed to consist of the pure solute or of a mixture of pure solutes, and that the activity of the solute in the bulk solution is known. The use of NR in combination with ST-Gibbs measurements makes it possible to (i) avoid these assumptions and hence understand several patterns of ST behaviour previously considered to be anomalous and (ii) to start to analyse quantitatively the behaviour of mixed surfactants both below and above the critical micelle concentration. These two developments in our understanding of the thermodynamics of the air-water interface are described with recent examples.
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Affiliation(s)
- Jeffrey Penfold
- ISIS Facility, Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxon, UK. .,Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, UK
| | - Robert K Thomas
- Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, UK
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2
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Tran E, Carpenter AP, Richmond GL. Probing the Molecular Structure of Coadsorbed Polyethylenimine and Charged Surfactants at the Nanoemulsion Droplet Surface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:9081-9089. [PMID: 32668900 DOI: 10.1021/acs.langmuir.0c01095] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Nanoemulsions, nanoscale oil droplets dispersed in an aqueous medium, can be stabilized by polymer-surfactant (PS) mixtures, making them ubiquitous in commercial, industrial, and pharmaceutical applications. It is well-known that the presence of PS layers coadsorbed at the droplet surface plays a significant role in droplet stability and functionality; however, little is understood about the molecular nature of this coadsorption. Such insights are especially important for application in drug delivery where physiological conditions can vary the environmental pH and significantly impact stabilization. Hence, the focus of this study examines the surface properties of ∼300 nm nanoemulsions stabilized by the coadsorption of polyethylenimine (PEI) and charged alkyl surfactants sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB). PEI is a common charge-tunable polymer used in nanocarrier templates. This study employs vibrational sum frequency scattering spectroscopy, coupled with ζ-potential and surface pressure measurements performed as a function of varying concentrations and pH. The surface specific spectroscopic results reported herein reveal that PEI adsorption and molecular ordering is influenced by both electrostatic and hydrophobic interactions. While the degree of PEI adsorption is stronger in the presence of anionic SDS than cationic DTAB, for both surfactants, PEI is molecularly disordered in acidic conditions and adopts a persistent net ordering as the solution pH becomes more basic. Both surfactants also display degrees of interfacial conformational ordering that is altered by the presence of the coadsorbed polymer. These results demonstrate the molecular-level diversity in PEI behavior at the droplet interface and provide insight into how such behavior can be controlled to yield nanocarrier technology with specific functions and enhanced efficacy.
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Affiliation(s)
- Emma Tran
- Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403, United States
| | - Andrew P Carpenter
- Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403, United States
| | - Geraldine L Richmond
- Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403, United States
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3
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Li P, Penfold J, Thomas RK, Xu H. Multilayers formed by polyelectrolyte-surfactant and related mixtures at the air-water interface. Adv Colloid Interface Sci 2019; 269:43-86. [PMID: 31029983 DOI: 10.1016/j.cis.2019.04.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 04/13/2019] [Accepted: 04/13/2019] [Indexed: 01/01/2023]
Abstract
The structure and occurrence of multilayered adsorption at the air-water interface of surfactants in combination with other oppositely charged species is reviewed. The main species that trigger multilayer formation are multiply charged metal, oligo- and polyions. The structures vary from the attachment of one or two more or less complete surfactant bilayers to the initial surfactant monolayer at the air-water interface to the attachment of a greater number of bilayers with a more defective structure. The majority of the wide range of observations of such structures have been made using neutron reflectometry. The possible mechanisms for the attraction of surfactant bilayers to an air-water interface are discussed and particular attention is given to the question of whether these structures are true equilibrium structures.
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Affiliation(s)
- Peixun Li
- STFC, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0RA, United Kingdom
| | - Jeffery Penfold
- STFC, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0RA, United Kingdom
| | - Robert K Thomas
- Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford, OX1 3QZ, United Kingdom.
| | - Hui Xu
- KLK OLEO, Room 1603, 16th Floor, LZY Tower, 4711 Jiao Tong Road, Putuo District, Shanghai 200331, China
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Mansour OT, Cattoz B, Beaube M, Heenan RK, Schweins R, Hurcom J, Griffiths PC. Segregation versus Interdigitation in Highly Dynamic Polymer/Surfactant Layers. Polymers (Basel) 2019; 11:polym11010109. [PMID: 30960093 PMCID: PMC6402036 DOI: 10.3390/polym11010109] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2018] [Revised: 12/23/2018] [Accepted: 12/28/2018] [Indexed: 11/29/2022] Open
Abstract
Many polymer/surfactant formulations involve a trapped kinetic state that provides some beneficial character to the formulation. However, the vast majority of studies on formulations focus on equilibrium states. Here, nanoscale structures present at dynamic interfaces in the form of air-in-water foams are explored, stabilised by mixtures of commonly used non-ionic, surface active block copolymers (Pluronic®) and small molecule ionic surfactants (sodium dodecylsulfate, SDS, and dodecyltrimethylammonium bromide, C12TAB). Transient foams formed from binary mixtures of these surfactants shows considerable changes in stability which correlate with the strength of the solution interaction which delineate the interfacial structures. Weak solution interactions reflective of distinct coexisting micellar structures in solution lead to segregated layers at the foam interface, whereas strong solution interactions lead to mixed structures both in bulk solution, forming interdigitated layers at the interface.
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Affiliation(s)
- Omar T Mansour
- Faculty of Engineering and Science, University of Greenwich, Medway Campus, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK.
| | - Beatrice Cattoz
- Faculty of Engineering and Science, University of Greenwich, Medway Campus, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK.
| | - Manon Beaube
- Faculty of Engineering and Science, University of Greenwich, Medway Campus, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK.
| | - Richard K Heenan
- Science and Technology Facilities Council, ISIS Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, UK.
| | - Ralf Schweins
- Institut Laue Langevin ILL, 6 rue Jules Horowitz, 38000 Grenoble, France.
| | - Jamie Hurcom
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3TB, UK.
| | - Peter C Griffiths
- Faculty of Engineering and Science, University of Greenwich, Medway Campus, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK.
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Mansour OT, Cattoz B, Beaube M, Montagnon M, Heenan RK, Schweins R, Appavou MS, Griffiths PC. Assembly of small molecule surfactants at highly dynamic air-water interfaces. SOFT MATTER 2017; 13:8807-8815. [PMID: 29139528 DOI: 10.1039/c7sm01914a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Small-angle neutron scattering has been used to probe the interfacial structure of foams stabilised by small molecule surfactants at concentrations well below their critical micelle concentration. The data for wet foams showed a pronounced Q-4 dependence at low Q and noticeable inflexions over the mid Q range. These features were found to be dependent on the surfactant structure (mainly the alkyl chain length) with various inflexions across the measured Q range as a function of the chain length but independent of factors such as concentration and foam age/height. By contrast, foam stability (for C < CMC) was significantly different at this experimental range. Drained foams showed different yet equally characteristic features, including additional peaks attributed to the formation of classical micellar structures. Together, these features suggest the dynamic air-water interface is not as simple as often depicted, indeed the data have been successfully described by a model consisting paracrystalline stacks (multilayer) of adsorbed surfactant layers; a structure that we believe is induced by the dynamic nature of the air-water interface in a foam.
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Affiliation(s)
- Omar T Mansour
- Faculty of Engineering and Science, University of Greenwich, Medway Campus, Central Avenue, Chatham Maritime, Kent, ME4 4TB, UK.
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Braun L, Uhlig M, von Klitzing R, Campbell RA. Polymers and surfactants at fluid interfaces studied with specular neutron reflectometry. Adv Colloid Interface Sci 2017; 247:130-148. [PMID: 28822539 DOI: 10.1016/j.cis.2017.07.005] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Accepted: 07/08/2017] [Indexed: 01/18/2023]
Abstract
This review addresses the advances made with specular neutron reflectometry in studies of aqueous mixtures of polymers and surfactants at fluid interfaces during the last decade (or so). The increase in neutron flux due to improvements in instrumentation has led to routine measurements at the air/water interface that are faster and involve samples with lower isotopic contrast than in previous experiments. One can now resolve the surface excess of a single deuterated component on the second time scale and the composition of a mixture on the minute time scale, and information about adsorption processes and dynamic rheology can also be accessed. Research areas addressed include the types of formed equilibrium surface structures, the link to foam film stability and the range of non-equilibrium effects that dominate the behavior of oppositely charged polyelectrolyte/surfactant mixtures, macroscopic film formation in like-charged polymer/surfactant mixtures, and the properties of mixtures of bio-polymers with surfactants and lipids.
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Anionic surfactant – Biogenic amine interactions: The role of surfactant headgroup geometry. J Colloid Interface Sci 2016; 466:213-9. [DOI: 10.1016/j.jcis.2015.12.030] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2015] [Revised: 12/14/2015] [Accepted: 12/17/2015] [Indexed: 12/11/2022]
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Penfold J, Thomas RK, Li P. Impact of biogenic amine molecular weight and structure on surfactant adsorption at the air–water interface. J Colloid Interface Sci 2016; 463:199-206. [DOI: 10.1016/j.jcis.2015.10.058] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 10/22/2015] [Accepted: 10/23/2015] [Indexed: 10/22/2022]
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Thomas RK, Penfold J. Multilayering of Surfactant Systems at the Air-Dilute Aqueous Solution Interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:7440-7456. [PMID: 25684058 DOI: 10.1021/la504952k] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
In the last 15 years there have been a number of observations of surfactants adsorbed at the air-water interface with structures more complicated than the expected single monolayer. These observations, mostly made by neutron or X-ray reflectivity, show structures varying from the usual monolayer to monolayer plus one or two additional bilayers to multilayer adsorption at the surface. These observations have been assembled in this article with a view to finding some common features between the very different systems and to relating them to aspects of the bulk solution phase behavior. It is argued that multilayering is primarily associated with wetting or prewetting of the air-water interface by phases in the bulk system, whose structures depend on an overall attractive force between the constituent units. Two such phases, whose formation is assumed to be partially driven by strong specific ion binding, are a concentrated lamellar phase that forms at low concentrations and a swollen lamellar phase that is not space-filling. Multilayering phenomena at the air-water interface then offer a delicate and easy means of studying the finer details of the incompletely understood attraction that leads to these two phases, as well as an interesting new means of self-assembling surface structures. In addition, multilayering is often associated with unusual wetting characteristics. Examples of systems discussed, and in some cases their bulk phase behavior, include surfactants with multivalent metal counterions, surfactants with oligomers and polymers, surfactant with hydrophobin, dichain surfactants, lung surfactant, and the unusual system of ethanolamine and stearic acid. Two situations where the air-water surface is deliberately held out of equilibrium are also assessed for features in common with the steady-state/equilibrium observations.
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Affiliation(s)
- Robert K Thomas
- †Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QZ, United Kingdom
| | - Jeffrey Penfold
- †Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QZ, United Kingdom
- ‡STFC, Rutherford-Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0RA, United Kingdom
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Penfold J, Thomas R, Li P. Biogenic amine – Surfactant interactions at the air–water interface. J Colloid Interface Sci 2015; 449:167-74. [DOI: 10.1016/j.jcis.2014.11.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 11/04/2014] [Accepted: 11/05/2014] [Indexed: 11/16/2022]
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Yanez Arteta M, Campbell RA, Watkins EB, Obiols-Rabasa M, Schillén K, Nylander T. Interactions of Small Dendrimers with Sodium Dodecyl Sulfate at the Air–Water Interface. J Phys Chem B 2014; 118:11835-48. [DOI: 10.1021/jp507230m] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Marianna Yanez Arteta
- Division
of Physical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
| | - Richard A. Campbell
- Institut Laue-Langevin, 71 avenue
des Martyrs - CS 20156, 38042 Grenoble Cedex 9, France
| | - Erik B. Watkins
- Lujan
Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| | - Marc Obiols-Rabasa
- Division
of Physical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
| | - Karin Schillén
- Division
of Physical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
| | - Tommy Nylander
- Division
of Physical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
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