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Lubrication Properties of Bottle-Brush Polyelectrolytes: An AFM Study on the Effect of Side Chain and Charge Density
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.ORCID iD: 0000-0002-5444-7276
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
Department of Polymer Chemistry, Vilnius University.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 7, 3336-3347 p.Article in journal (Refereed) Published
Abstract [en]

The effect of side chain to charge ratio on the frictional properties of adsorbed layers formed by bottle-brush polyelectrolytes with poly(ethylene oxide) side chains has been investigated. The brush polyelectrolytes were preadsorbed from 0.1 mM NaNO3 solutions onto mica and silica surfaces; the interfacial friction was then measured in polyelectrolyte-free solutions via AFM (with the silica surface acting as the colloidal probe). It was concluded that the decisive factor for achieving favorable lubrication properties is the concentration of nonadsorbing poly(ethylene oxide) side chains in the interfacial region. However, contrary to what may be expected, the results showed that an ideal brush layer structure with the adsorbed polymers adopting comb-like conformation is not necessary for achieving a low coefficient of friction in the asymmetric mica-silica system. In fact, the lowest coefficient of friction (< 0.01) under applied pressures as high as 30 MPa was observed for a system with a side chain to charge ratio of 9: 1, incapable of forming brush-like layers.

Place, publisher, year, edition, pages
2008. Vol. 24, no 7, 3336-3347 p.
Keyword [en]
Atomic force microscopy, Charge density, Mica, Polyethylene oxides, Silica, Asymmetric mica, Bottle-brush polyelectrolytes
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-8077DOI: 10.1021/la703229nISI: 000254480500053Scopus ID: 2-s2.0-42249112292OAI: oai:DiVA.org:kth-8077DiVA: diva2:13303
Note
QC 20100830. Uppdaterad från in press till published (20100830).Available from: 2008-03-07 Created: 2008-03-07 Last updated: 2010-08-30Bibliographically approved
In thesis
1. Lubrication and Surface Properties of Adsorbed Layers of Polyelectrolytes and Proteins
Open this publication in new window or tab >>Lubrication and Surface Properties of Adsorbed Layers of Polyelectrolytes and Proteins
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Friction forces between protein / polyelectrolyte layers, adsorption properties of proteins, and conformational changes due to variation in electrolyte concentration have been investigated. The aim was to obtain better understanding of adsorbed layer properties, with focus on the relation between layer structure and lubrication capabilities. The major techniques used were AFM (atomic force microscope) with colloidal probe for normal force and friction measurements together with QCM-D (quartz crystal microbalance with dissipation) for measurement of adsorption and conformational changes of adsorbed layers.

A comparison between some techniques for calibration of the AFM instrument for friction measurements was made to find the most suitably one for colloidal probe friction measurements in aqueous solutions. It is suggested that the normal and torsional Sader methods are preferred in combination with torsional detector sensitivity measurement, for which one new methodology has been proposed.

Adsorption was studied for bovine serum albumin, cytochrome c, myoglobin and mucin, whereas conformational changes of the adsorbed layer were monitored only for mucin. It was found that it was essential to take into account bulk density and viscosity changes for correct interpretations of QCM data when studying the effect of changes in electrolyte type and concentration on preadsorbed layers of mucin, and also when having different (high) concentrations of proteins in the measuring solution. The adsorbed amount of proteins appears to depend on the strength of the surface attachment, in such a manner that a too high affinity reduces the adsorbed amount.

Friction properties in aqueous solution have been studied for adsorbed layers of PEO45MEMA:METAC co-polyelectrolytes, with varying density of grafted PEO45 side chains and varying charge density, as well as for a naturally occurring polyelectrolyte (chitosan) and the glycoprotein mucin. These polymers were used to cover a wide range of different types of adsorbed layers and interactions to gain a better understanding of friction mechanisms and demands on layer properties for achieving favourable lubrication. It was found that the common features of low friction layers are that no attractive forces are present, and that excluded volume and / or electrostatic forces counteract chain interpenetration under load.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vii, 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:16
Keyword
biochemistry, biomedical engineering
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-4663 (URN)978-91-7178-891-7 (ISBN)
Public defence
2008-03-27, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100903Available from: 2008-03-07 Created: 2008-03-07 Last updated: 2010-09-03Bibliographically approved
2. Polyelectrolytes: Bottle-Brush Architectures and Association with Surfactants
Open this publication in new window or tab >>Polyelectrolytes: Bottle-Brush Architectures and Association with Surfactants
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis has the dual purpose of raising awareness of the importance of the mixing protocol on the end products of polyelectrolyte-oppositely charged surfactant systems, and to contribute to a better understanding of the properties of bottle-brush polyelectrolytes when adsorbed onto interfaces.

In the first part of this thesis work, the effects of the mixing protocol and the mixing procedure on formed polyelectrolyte-oppositely charged surfactant aggregates were investigated. It was shown that the initial properties of the aggregates were highly dependent on the mixing parameters, and that the difference between the resulting aggregates persisted for long periods of time.

The second part of the studies was devoted to the surface properties of a series of bottle-brush polyelectrolytes made of charged segments and segments bearing poly(ethylene oxide) side chains; particular attention was paid to the effect of side chain to charge density ratio of the polyelectrolytes. It was shown that the adsorbed mass of the polyelectrolytes, and the corresponding number of poly(ethylene oxide) bearing segments at the interface, went through a maximum as the charge density of the polyelectrolyte was increased. Also, it was found that bottle-brush polyelectrolyte layers were desorbed quite easily when subjected to salt solutions. This observation was rationalized by the unfavourable excluded volume interactions between the side chains and the entropic penalty of confining them at an interface, which weaken the strength of the binding of the polyelectrolytes to the interface. However, it was shown that the same side chains effectively protect the adsorbed layer against desorption when the layer is exposed to solutions containing an oppositely charged surfactant. Investigation of the lubrication properties of the bottle-brush polyelectrolytes in an asymmetric (mica-silica) system also related the observed favourable frictional properties to the protective nature of the side chains. The decisive factor for achieving very low coefficients of friction was found to be the concentration of the side chains in the gap between the surfaces. Interestingly, it was shown that a brush-like conformation of the bottle-brush polyelectrolyte at the interface has little effect on achieving favourable lubrication properties. However, a brush-like conformation is vital for the resilience of the adsorbed layer against the competitive adsorption of species with a higher surface affinity.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 39 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:18
Keyword
Polyelectrolyte, Surfactant, Bottle-Brush Polyelectrolyte, Comb Polyelectrolyte, Non-Equilibrium State, Polymer Architecture, Adsorption, Desorption, Association, Excluded Volume, Light Scattering, SFA, AFM, QCM-D, Turbidimeter, Mica, Silica, Surface Forces
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-4683 (URN)978-91-7178-903-7 (ISBN)
Public defence
2008-04-18, F3, Lindstedsvägen 28 100 44, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100830Available from: 2008-03-27 Created: 2008-03-27 Last updated: 2012-01-20Bibliographically approved

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