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Tethered Poly(2-isopropyl-2-oxazoline) Chains: Temperature Effects on Layer Structure and Interactions Probed by AFM Experiments and Modeling
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. SP Technical Research Institute of Sweden, Sweden .ORCID iD: 0000-0002-2288-819X
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2015 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 10, 3039-3048 p.Article in journal (Refereed) Published
Abstract [en]

Thermoresponsive polymer layers on silica surfaces have been obtained by utilizing electrostatically driven adsorption of a cationic-nonionic diblock copolymer. The cationic block provides strong anchoring to the surface for the nonionic block of poly(2-isopropyl-2-oxazoline), referred to as PIPOZ. The PIPOZ chain interacts favorably with water at low temperatures, but above 46 degrees C aqueous solutions of PIPOZ phase separate as water becomes a poor solvent for the polymer. We explore how a change in solvent condition affects interactions between such adsorbed layers and report temperature effects on both normal forces and friction forces. To gain further insight, we utilize self-consistent lattice mean-field theory to follow how changes in temperature affect the polymer segment density distributions and to calculate surface force curves. We find that with worsening of the solvent condition an attraction develops between the adsorbed PIPOZ layers, and this observation is in good agreement with predictions of the mean-field theory. The modeling also demonstrates that the segment density profile and the degree of chain interpenetration under a given load between two PIPOZ-coated surfaces rise significantly with increasing temperature.

Place, publisher, year, edition, pages
2015. Vol. 31, no 10, 3039-3048 p.
National Category
Chemical Sciences Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-165219DOI: 10.1021/la504653wISI: 000351327300013PubMedID: 25686020Scopus ID: 2-s2.0-84925004133OAI: oai:DiVA.org:kth-165219DiVA: diva2:810152
Note

QC 20150506

Available from: 2015-05-06 Created: 2015-04-24 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Polymers in Aqueous Lubrication
Open this publication in new window or tab >>Polymers in Aqueous Lubrication
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main objective of this thesis work was to gain understanding of the layer properties and polymer structures that were able to aid lubrication in aqueous media. To this end, three types of polyelectrolytes: a diblock copolymer, a train-of-brushes and two brush-with-anchor mucins have been utilized. Their lubrication ability in the boundary lubrication regime has been examined by Atomic Force Microscopy with colloidal probe.

The interfacial behavior of the thermoresponsive diblock copolymer, PIPOZ60-b-PAMPTAM17,on silica was studied in the temperature interval 25-50 ˚C. The main finding is that adsorption hysteresis, due to the presence of trapped states, is important when the adsorbed layers are in contact with a dilute polymer solution. The importance of trapped states was also demonstrated in the measured friction forces, where significantly lower friction forces, at a given temperature, were encountered on cooling than on the preceding heating stage, which was attributed to increased adsorbed amount. On the heating stage the friction force decreased with increasing temperature despite the worsening of the solvent condition, and the opposite trend was observed when using pre-adsorbed layers (constant adsorbed amount) as a consequence of increased segment-segment attraction.

The second part of the studies was devoted to the interfacial properties of mucins on PMMA. The strong affinity provided by the anchoring group of C-PSLex and C-P55 together with their more extended layer structure contribute to the superior lubrication of PMMA compared to BSM up to pressures of 8-9 MPa. This is a result of minor bridging and lateral motion of molecules along the surface during shearing. We further studied the influence of glycosylation on interfacial properties of mucin by utilizing the highly purified mucins, C-P55 and C-PSLex. Our data suggest that the longer and more branched carbohydrate side chains on C-PSLex provide lower interpenetration and better hydration lubrication at low loads compared to the shorter carbohydrate chains on C-P55. However, the longer carbohydrates appear to counteract disentanglement less efficiently, giving rise to a higher friction force at high loads.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 66 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:15
Keyword
Lubrication, boundary lubrication, friction, surface forces, adsorption, adsorption hysteresis, non-equilibrium state, diblock copolymer, polyelectrolyte, thermoresponsive, mucin, QCM-D, ellipsometry, AFM
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-204931 (URN)978-91-7729-305-7 (ISBN)
Public defence
2017-03-31, Kollegiesalen, Brinellvägen 8, KTH-campus, Stockholm, 10:00 (English)
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Note

QC 20170407

Available from: 2017-04-07 Created: 2017-04-04 Last updated: 2017-04-07Bibliographically approved

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