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Viscoelastic properties of adsorbed bottle-brush polymer layers studied by quartz crystal microbalance: Dissipation measurements
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
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.

Place, publisher, year, edition, pages
2008. Vol. 112, no 38, 15028-15036 p.
Keyword [en]
CHARGE-DENSITY, SIDE-CHAIN, THIN-FILMS, ADSORPTION, SILICA
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-14000DOI: 10.1021/jp804395fISI: 000259342400049Scopus ID: 2-s2.0-53849094458OAI: oai:DiVA.org:kth-14000DiVA: diva2:328966
Note
QC 20100707Available from: 2010-07-07 Created: 2010-07-07 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Adsorption behaviour of bottle-brush and block copolymers at solid-liquid interfaces
Open this publication in new window or tab >>Adsorption behaviour of bottle-brush and block copolymers at solid-liquid interfaces
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis was spurred on by needs of current scientific and technological developments in the area of surface modification by use of adsorbed polymer layers. The importance of surface properties of polymer layers can be imparted in a broad spectrum of interfacial-related applications like lubrication, colloidal stability, detergency, and protein resistant surfaces, to just mention a few. Irrespective of all areas of application an underlying factor in all is the deep implication and footprint the molecular architecture has on the interfacial properties of polymer layers. In this context this thesis has the intention of raising awareness of the importance of the polymer architecture on interfacial behavior and the stability of layers formed by bottle-brush polymers and by temperature responsive block copolymers under different conditions. The first part of this thesis work was largely devoted to the surface properties of a series of cationic bottle-brush polymers, consisting of a main chain carrying charges and poly(ethylene oxide) (PEO) side chains close to randomly distributed along the backbone. Here particular attention was devoted to varying the molecular architecture by changing the charge/PEO ratio along the backbone. The studies demonstrated that the surface excess of the polymers went through a maximum as the number of backbone charges increased. Furthermore, the bottle-brush adlayers revealed sensitivity to changes in both ionic strength and pH when the numbers of backbone charges were relatively low. Layer properties were comprehensively elucidated by determining not only the adsorbed mass, but also layer thickness, water content and layer viscoelasticity. The change in these properties during formation of the adsorption layer was found to be complex, demonstrating significant conformational changes in the layer. The studies aimed at creating surface coatings with good resistance against species of high surface affinity, with a central interest in proteins, elucidated the optimal balance of the bottle-brush structure. The results revealed two scenarios, depending on both the type of protein and the areal density (grafting density) of the PEO side chains at the silica surface, where either protein adsorption was suppressed or enhanced by the presence of adlayers of the bottle-brush polymers. Low protein adsorption was achieved when the polymers have enough electrostatic attachment points to ensure a strong binding to the surface and at the same time a sufficient amount of PEO side chains that screen the protein-surface interactions. In the second part of the thesis a combination of QCM-D, AFM and reflectometry techniques was employed to probe the interfacial characteristics of temperature responsive cationic diblock copolymers, poly(N-ivisopropylacrylamide)m-block-poly(3-acrylamidopropyl)trimethyl ammonium chloride)n. The adsorption of these polymers to silica was of a high affinity, with no dramatic structural changes occurring during the layer build-up. The temperature dependent behavior of the adlayers demonstrated that the polymer interfacial conformation could be reversibly altered merely by cycling temperature above and below the lower critical solution temperature (LCST). This was found to have significant effects on both surface forces and boundary lubrication.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xiii, 77 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2010:22
Keyword
Adsorption, Lubrication, Layer viscoelasticity, Protein repellency, Polymer architecture, Silica, Bottle-brush polymers, Poly(ethylene oxide), PEO, Block copolymer, Poly(N-isopropylacrylamide), QCM-D, AFM, Reflectometry
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-13213 (URN)978-91-7415-611-4 (ISBN)
Public defence
2010-06-14, F3, Lindstedtsvägen 26, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20100707Available from: 2010-06-04 Created: 2010-06-04 Last updated: 2011-02-04Bibliographically approved
2. Poly(Ethylene Oxide) Based Bottle-Brush Polymers and their Interaction with the Anionic Surfactant Sodium Dodecyl Sulphate: Solution and Interfacial Properties
Open this publication in new window or tab >>Poly(Ethylene Oxide) Based Bottle-Brush Polymers and their Interaction with the Anionic Surfactant Sodium Dodecyl Sulphate: Solution and Interfacial Properties
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
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:nbn:se:kth:diva-4680 (URN)978-91-7178-900-6 (ISBN)
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

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