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Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers
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. SP Technical Research Institute of Sweden.ORCID iD: 0000-0002-2288-819X
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2017 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 487, 88-96 p.Article in journal (Refereed) Published
Abstract [en]

Equilibration in adsorbing polymer systems can be very slow, leading to different physical properties at a given condition depending on the pathway that was used to reach this state. Here we explore this phenomenon using a diblock copolymer consisting of a cationic anchor block and a thermoresponsive block of poly(2-isopropyl-2-oxazoline), PIPOZ. We find that at a given temperature different polymer chain densities at the silica surface are achieved depending on the previous temperature history. We explore how this affects surface and friction forces between such layers using the atomic force microscope colloidal probe technique. The surface forces are purely repulsive at temperatures <40 degrees C. A local force minimum at short separation develops at 40 degrees C and a strong attraction due to capillary condensation of a polymer-rich phase is observed close to the bulk phase separation temperature. The friction forces decrease in the cooling stage due to rehydration of the PIPOZ chain. A consequence of the adsorption hysteresis is that the friction forces measured at 25 degrees C are significantly lower after exposure to a temperature of 40 degrees C than prior to heating, which is due to higher polymer chain density on the surface after heating.

Place, publisher, year, edition, pages
Academic Press, 2017. Vol. 487, 88-96 p.
Keyword [en]
Surface forces, Friction, Boundary lubrication, PIPOZ, Poly(2-isopropyl-2-oxazoline), Thermoresponsive polymer, Adsorption hysteresis
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-198864DOI: 10.1016/j.jcis.2016.10.021ISI: 000388550600011PubMedID: 27756003Scopus ID: 2-s2.0-84992378692OAI: oai:DiVA.org:kth-198864DiVA: diva2:1061725
Funder
Swedish Research Council
Note

QC 20170103

Available from: 2017-01-03 Created: 2016-12-22 Last updated: 2017-04-04Bibliographically 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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Supervisors
Note

QC 20170407

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

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