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Friction in aqueous media tuned by temperature-responsive polymer layers
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-2288-819X
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
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2010 (English)In: SOFT MATTER, ISSN 1744-683X, Vol. 6, no 11, 2489-2498 p.Article in journal (Refereed) Published
Abstract [en]

An atomic force microscope colloidal probe technique has been employed to probe normal and friction forces between silica surfaces coated with adsorbed layers of a diblock copolymer of the composition poly(N-isopropylacrylamide)(48)-block-poly(3-acrylamidopropyl)trimethyla mmonium chloride)(20), abbreviated PNIPAAM(48)-b-PAMPTMA(+)(20). The interactions between the PNIPAAM(48)-b-PAMPTMA(+)(20)-coated surfaces across a 0.1 mM NaCl (pH 6) solution at 25 degrees C are purely repulsive, due to a combination of steric and electrostatic double-layer forces. However, when the temperature is increased to 35 degrees C, and subsequently to 45 degrees C, an attractive force develops at short separations due to the unfavourable PNIPAAM-water interaction at these temperatures. The temperature-dependent polymer-water interaction has implications for the friction force between the layers. At 25 degrees C a frictional force that increases linearly with increasing load is observed once the surfaces are brought into close contact. At higher temperatures significantly higher friction forces appear as a consequence of attractive segment-segment interactions. Further, a clearly expressed hysteresis between friction forces encountered on loading and unloading is detected. Our results demonstrate that both normal and friction forces between surfaces can be controlled by temperature changes when temperature-responsive polymers are employed, and friction forces can be adjusted as required from low to high.

Place, publisher, year, edition, pages
2010. Vol. 6, no 11, 2489-2498 p.
Keyword [en]
URN: urn:nbn:se:kth:diva-13999DOI: 10.1039/c003320kISI: 000278046300019ScopusID: 2-s2.0-77952833269OAI: diva2:328969
QC20100707Available from: 2010-07-07 Created: 2010-07-07 Last updated: 2010-07-07Bibliographically 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.
Trita-CHE-Report, ISSN 1654-1081 ; 2010:22
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
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)
QC 20100707Available from: 2010-06-04 Created: 2010-06-04 Last updated: 2011-02-04Bibliographically approved

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