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Poly(Ethylene Oxide) Based Bottle-Brush Polymers and their Interaction with the Anionic Surfactant Sodium Dodecyl Sulphate: Solution and Interfacial Properties
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of this thesis work is to study the physico-chemical properties of poly(ethylene oxide), PEO, based brush polymers both in solution and at solid/aqueous interfaces. The importance of studying the surface properties of brush polymers can be related to a broad spectrum of interfacial-related applications such as colloidal stability, lubrication, detergency, protein repellency to name a few. In many applications it is desirable to form brush-like structures through simple physisorption. In this context the surface properties of PEO based brush polymers differing in molecular architecture were studied, using ellipsometry and surface force apparatus (SFA), to gain some understanding regarding the effect of molecular architecture on the formation of brush structures. The molecular architecture was varied by varying the charge/PEO ratio along the backbone. This study demonstrates that the formation of a brush structure at solid/aqueous interface is due to interplay between the attraction of the backbone to the surface and the repulsions between the PEO side chains. An optimal balance between the two antagonistic factors is required if one aims to build a well-defined brush structure at the interface. In this study the brush-like structures are formed when 25-50% of the backbone segments carry poly(ethylene oxide) side chains. Scattering techniques such as light and neutron reveal that these brush polymers are stiff-rods up to a charge to PEO ratio of 75:25. These stiff PEO brush polymer easily replace the more flexible linear PEO at the silica/water interface, the reason being that the entropy loss on adsorption is smaller for the brush polymer due to its stiff nature.  Polymer-surfactant systems play a ubiquitous role in many technical formulations. It is well known that linear PEO, which adopts random coil conformation in aqueous solution, interact strongly with the anionic surfactant, Sodium Dodecyl Sulphate (SDS). It is of interest to study the interaction between SDS and brush PEO owing to the fact that the PEO side chains have limited flexibility as compared to the linear PEO.  The interaction between brush PEO and the anionic surfactant SDS in solution are studied using different techniques such as NMR, tensiometry, SANS and light scattering. The main finding of this study is that the interaction is weaker compared to the linear PEO-SDS interactions which poses an interesting question regarding the role of chain flexibility in polymer-surfactant interactions.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , x, 68 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:17
Keyword [en]
PEO brush polymers, brush polymers, PEO, poly(ethylene oxide), polymer-surfactant, sodium dodecyl sulphate (SDS), Ellipsomtery, PEO-SDS interactions
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4680ISBN: 978-91-7178-900-6 (print)OAI: oai:DiVA.org:kth-4680DiVA: diva2:13392
Public defence
2008-04-11, E2, KTH, Lindstedtsvägen 26, Stockholm, 09:00
Opponent
Supervisors
Note
QC 20100813Available from: 2008-03-27 Created: 2008-03-27 Last updated: 2010-08-13Bibliographically approved
List of papers
1. Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR
Open this publication in new window or tab >>Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR
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2007 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 312, no 1, 21-33 p.Article in journal (Refereed) Published
Abstract [en]

A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO(45)MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 A. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PE045MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements.

Keyword
comb polymer; comb polyelectrolyte; polymer-surfactant association; polyelectrolyte-surfactant aggregate; small-angle neutron scattering; light scattering; NMR; surface tension; polyelectrolyte; surfactant; SDS
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-6677 (URN)10.1016/j.jcis.2006.09.004 (DOI)000247286100004 ()2-s2.0-34249817580 (Scopus ID)
Note
QC 20100813. Uppdaterad från submitted till published (20100813).Available from: 2005-09-22 Created: 2005-09-22 Last updated: 2017-12-14Bibliographically approved
2. Surface Properties of Bottle-Brush Polyelectrolytes on Mica: Effects of Side Chain and Charge Densities
Open this publication in new window or tab >>Surface Properties of Bottle-Brush Polyelectrolytes on Mica: Effects of Side Chain and Charge Densities
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2007 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 24, 12222-12232 p.Article in journal (Refereed) Published
Abstract [en]

Surface properties of a series of cationic bottle-brush polyelectrolytes with 45-unit-long poly(ethylene oxide) side chains were investigated by phase modulated ellipsometry and surface force measurements. The evaluation of the adsorbed mass of polymer on mica by means of ellipsometry is complex due to the transparency of mica and its birefringence and low dielectric constant. We therefore employed a new method to overcome these difficulties. The charge and the poly(ethylene oxide) side chain density of the bottle-brush polymers were varied from zero charge density and one side chain per segment to one charge per segment and no side chains, thus spanning the realm from a neutral bottle-brush polymer, via a partly charged brush polyelectrolyte, to a linear fully charged polyelectrolyte. The adsorption properties depend crucially on the polymer architecture. A minimum charge density of the polymer is required to facilitate adsorption to the oppositely charged surface. The maximum adsorbed amount and the maximum side chain density at the surface are obtained for the polymer with 50% charged segments and the remaining 50% of the segments carrying poly(ethylene oxide) side chains. It is found that brushlike layers are formed when 25-50% of the segments carry poly(ethylene oxide) side chains. In this paper, we argue that the repulsion between the side chains results in an adsorbed layer that is non-homogeneous on the molecular level. As a result, not all side chains will contribute equally to the steric repulsion but some will be stretched along the surface rather than perpendicular to it. By comparison with linear polyelectrolytes, it will be shown that the presence of the side chains counteracts adsorption. This is due to the entropic penalty of confining the side chains to the surface region.

Keyword
Birefringence; Charge density; Ellipsometry; Mica; Permittivity; Polyethylene oxides; Polymers; Bottle-brush polyelectrolytes; Linear polyelectrolytes; Steric repulsion
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-8142 (URN)10.1021/la701716t (DOI)000250976700048 ()2-s2.0-36649038755 (Scopus ID)
Note
QC 20100813Available from: 2008-03-27 Created: 2008-03-27 Last updated: 2017-12-14Bibliographically approved
3. Adsorption of Low charge Density Polyelectrolyte Containing Poly(ethylene oxide) Side chains on Silica: Effects of Ionic strength and pH
Open this publication in new window or tab >>Adsorption of Low charge Density Polyelectrolyte Containing Poly(ethylene oxide) Side chains on Silica: Effects of Ionic strength and pH
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2005 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 38, no 14, 6152-6160 p.Article in journal (Refereed) Published
Abstract [en]

Adsorption characteristics of a random copolymer of poly(ethylene oxide) monomethyl ether methacrylate and methacryloxyethyl trimethylammonium chloride (PEOMENIA:METAC) on silica were studied using stagnation point adsorption reflectometry (SPAR), quartz crystal microbalance with dissipation (QCM-D), and contact angle techniques. The PEOMEMA:METAC copolymer used in this study is a low charge density polyelectrolyte, with 2% of the monomer units carrying permanent positive charges and 98% containing poly(ethylene oxide) side chains that are approximately 45 repeating units long. The surface excess was determined as a function of pH and concentration of indifferent electrolyte. It was found that the presence of a small amount of 1: 1 electrolyte decreases the adsorbed amount significantly. Further, increasing the pH at a constant ionic strength, 10 mM, results in decreasing surface excess. It is suggested that the adsorption is realized via a combination of non-Coulomb interactions between the poly(ethylene oxide), PEO, grafts and protonated silanol groups at the silica-solution interface and an electrostatic interaction between the charged segments and the oppositely charged surface. Increasing pH and/or salt concentration results in progressive charging of the silica surface with the consequent decrease in affinity between silica and PEO, explaining the decrease in the adsorbed amount of the polymer.

Keyword
Adsorption; Ammonium compounds; Contact angle; Copolymers; Electric charge; Ionic strength; pH effects; Polyethylene oxides; Quartz; Reflectometers; Silica; Charge density; Low charge density polyelectrolytes; Quartz crystal microbalance with dissipation (QCM-D); Stagnation point adsorption reflectometry (SPAR)
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-8143 (URN)10.1021/ma050851x (DOI)000230376400041 ()2-s2.0-22944446391 (Scopus ID)
Note
QC 20100813Available from: 2008-03-27 Created: 2008-03-27 Last updated: 2017-12-14Bibliographically approved
4. Adsorption characteristics of bottle-brush polymers on silica: Effect of side chain and charge density
Open this publication in new window or tab >>Adsorption characteristics of bottle-brush polymers on silica: Effect of side chain and charge density
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2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 10, 5341-5349 p.Article in journal (Refereed) Published
Abstract [en]

The adsorption behavior of bottle-brush polymers with different charge/PEO ratio on silica was studied using optical reflectometry and QCM-D. The results obtained under different solution conditions clearly demonstrate the existence of two distinct adsorption mechanisms depending on the ratio of charge/PEO. In the case of low-charge density brush polymers (0- 10 mol %), the adsorption occurs predominantly through the PEO side chains. However, the presence of a small amount of charge along the backbone (as low as 2 mol %) increases the adsorption significantly above that of the uncharged bottle-brush polymer in pure water. As the charge density of the brush polymers is increased to 25 mol % or larger the adsorption occurs predominantly through electrostatic interactions. The adsorbed layer structure was studied by measuring the layer dissipation using QCM-D. The adsorbed layer formed by the uncharged brush polymer dissipates only a small amount of energy that indicates that the brush lie along the surface, the scenario in which the maximum number of PEO side chains interact with the surface. The adsorbed layers formed by the low-charge density brush polymers (2- 10 mol %) in water are more extended, which results in large energy dissipation, whereas those formed by the high-charge density brush polymers (50- 100 mol _%) have their backbone relatively flat on the surface and the energy dissipation is again low.

Keyword
QUARTZ-CRYSTAL MICROBALANCE, POLY(ETHYLENE OXIDE), POLYETHYLENE OXIDE, COMPETITIVE ADSORPTION, PROTEIN ADSORPTION, AQUEOUS-SOLUTIONS, SURFACE-CHARGE, POLYELECTROLYTE, WATER, KINETICS
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-14002 (URN)10.1021/la703739v (DOI)000255856100026 ()2-s2.0-44649139286 (Scopus ID)
Note
QC 20100707Available from: 2010-07-07 Created: 2010-07-07 Last updated: 2017-12-12Bibliographically approved
5. Interfacial Properties of Chitosan-PEO graft Oligomers: Surface Competition with Unmodified Chitosan Oligomers
Open this publication in new window or tab >>Interfacial Properties of Chitosan-PEO graft Oligomers: Surface Competition with Unmodified Chitosan Oligomers
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2006 (English)In: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 132, 124-130 p.Article in journal (Refereed) Published
Abstract [en]

Oligomers of chitosan carrying 45 units long poly(ethylene oxide), PEO, chains grafted to the C-6 position of the sugar units were prepared using a novel synthesis route. The graft density was high, close to one poly(ethylene oxide) chain grafted to each sugar unit of the chitosan oligomer but a small fraction of unreacted chitosan remained in the sample. The molecular weight distribution of the sample was determined using GPC. The interfacial properties of the chitosan-PEO graft oligomers were evaluated using X-ray photoelectron spectroscopy and surface force measurements. It was found that the small fraction of unreacted chitosan was significantly enriched at the solid-solution interface on negatively charged muscovite mica surfaces. The interactions between chitosan-PEO oligomer coated surfaces were found to be dominated by the extended PEO chains, and at high coverage the measured forces were consistent with those expected for polymer brushes. Addition of salt up to 10 mM did not result in any significant desorption of preadsorbed oligomer layers.

Keyword
chitosan; graft copolymers; poly(ethylene oxide); polymer brushes; surface forces
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-8145 (URN)10.1007/2882_027 (DOI)000238029200016 ()2-s2.0-33750941158 (Scopus ID)
Note
QC 20100813Available from: 2008-03-27 Created: 2008-03-27 Last updated: 2017-12-14Bibliographically approved
6. Viscoelastic properties of adsorbed bottle-brush polymer layers studied by quartz crystal microbalance: Dissipation measurements
Open this publication in new window or tab >>Viscoelastic properties of adsorbed bottle-brush polymer layers studied by quartz crystal microbalance: Dissipation measurements
2008 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 38, 15028-15036 p.Article in journal (Refereed) Published
Abstract [en]

Adsorbed layers of a series of bottle-brush polyelectrolytes with 45 units long poly(ethylene oxide) [PEO], side chains have been investigated by the quartz crystal microbalance technique with dissipation monitoring. The data have been evaluated with three different models, the Sauerbrey model, the Johannsmann model, and the Voigt model. It is found that all three models predict the same trend in the variations of sensed mass and hydrodynamic layer thickness with polymer architecture, that is, with the backbone charge to side chain density ratio. However, the simple Sauerbrey model underestimates the sensed mass by a factor of 1.15-1.45 compared to the more accurate Voigt model. By following the evolution of the layer dissipation, elasticity, and viscosity with increasing surface coverage it was concluded that the layers formed by brush polymers with intermediate charge densities undergo a structural change as the coverage is increased. Initially, the polymers are anchored to the surface via the PEO side chains. However, as the adsorption proceeds a structural change that brings the backbone to the surface and forces the side chains to extend from it is observed. The layer elasticity and viscosity as a function of surface coverage go through a maximum in this transition region.

Keyword
CHARGE-DENSITY, SIDE-CHAIN, THIN-FILMS, ADSORPTION, SILICA
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-14000 (URN)10.1021/jp804395f (DOI)000259342400049 ()2-s2.0-53849094458 (Scopus ID)
Note
QC 20100707Available from: 2010-07-07 Created: 2010-07-07 Last updated: 2017-12-12Bibliographically approved

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