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Temperature-Dependent Adsorption and Adsorption Hysteresis of a Thermoresponsive Diblock Copolymer
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.ORCID iD: 0000-0002-2288-819X
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2014 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 15, 4333-4341 p.Article in journal (Refereed) Published
Abstract [en]

A nonionic-cationic diblock copolymer, poly(2-isopropyl-2-oxazoline)(60)-b-poly((3-acrylamidopropyl)- trimethylammonium chloride)(17), (PIPOZ(60)-b-PAMPTMA(17)), was utilized to electrostatically tether temperature-responsive PIPOZ chains to silica surfaces by physisorption. The effects of polymer concentration, pH, and temperature on adsorption were investigated using quartz crystal microbalance with dissipation monitoring and ellipsometry. The combination of these two techniques allows thorough characterization of the adsorbed layer in terms of surface excess, thickness, and water content. The high affinity of the cationic PAMPTMA(17) block to the negatively charged silica surface gives rise to a high affinity adsorption isotherm, leading to (nearly) irreversible adsorption with respect to dilution. An increase in solution pH lowers the affinity of PIPOZ to silica but enhances the adsorption of the cationic block due to increasing silica surface charge density, which leads to higher adsorption of the cationic diblock copolymer. Higher surface excess is also achieved at higher temperatures due to the worsening of the solvent quality of water for the PIPOZ block. Interestingly, a large hysteresis in adsorbed mass and other layer properties was observed when the temperature was cycled from 25 to 45 degrees C and then back to 25 degrees C. Possible causes for this temperature hysteresis are discussed.

Place, publisher, year, edition, pages
2014. Vol. 30, no 15, 4333-4341 p.
Keyword [en]
Irreversible adsorption, Negatively charged, Polymer concentrations, Quartz crystal microbalance with dissipation monitoring, Temperature hysteresis, Temperature-dependent adsorption, Temperature-responsive, Thermo-responsive
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-145826DOI: 10.1021/la500377wISI: 000334991400017Scopus ID: 2-s2.0-84899408073OAI: oai:DiVA.org:kth-145826DiVA: diva2:721381
Funder
Swedish Research CouncilVinnova
Note

QC 20140604

Available from: 2014-06-04 Created: 2014-06-02 Last updated: 2017-12-05Bibliographically 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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Supervisors
Note

QC 20170407

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

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