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Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers
KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. SP Technical Research Institute of Sweden.ORCID-id: 0000-0002-2288-819X
Vise andre og tillknytning
2017 (engelsk)Inngår i: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 487, s. 88-96Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Academic Press, 2017. Vol. 487, s. 88-96
Emneord [en]
Surface forces, Friction, Boundary lubrication, PIPOZ, Poly(2-isopropyl-2-oxazoline), Thermoresponsive polymer, Adsorption hysteresis
HSV kategori
Identifikatorer
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, id: diva2:1061725
Forskningsfinansiär
Swedish Research Council
Merknad

QC 20170103

Tilgjengelig fra: 2017-01-03 Laget: 2016-12-22 Sist oppdatert: 2017-11-29bibliografisk kontrollert
Inngår i avhandling
1. Polymers in Aqueous Lubrication
Åpne denne publikasjonen i ny fane eller vindu >>Polymers in Aqueous Lubrication
2017 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2017. s. 66
Serie
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:15
Emneord
Lubrication, boundary lubrication, friction, surface forces, adsorption, adsorption hysteresis, non-equilibrium state, diblock copolymer, polyelectrolyte, thermoresponsive, mucin, QCM-D, ellipsometry, AFM
HSV kategori
Forskningsprogram
Kemi
Identifikatorer
urn:nbn:se:kth:diva-204931 (URN)978-91-7729-305-7 (ISBN)
Disputas
2017-03-31, Kollegiesalen, Brinellvägen 8, KTH-campus, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Merknad

QC 20170407

Tilgjengelig fra: 2017-04-07 Laget: 2017-04-04 Sist oppdatert: 2017-04-07bibliografisk kontrollert

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