Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers
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
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.
Surface forces, Friction, Boundary lubrication, PIPOZ, Poly(2-isopropyl-2-oxazoline), Thermoresponsive polymer, Adsorption hysteresis
IdentifiersURN: urn:nbn:se:kth:diva-198864DOI: 10.1016/j.jcis.2016.10.021ISI: 000388550600011PubMedID: 27756003ScopusID: 2-s2.0-84992378692OAI: oai:DiVA.org:kth-198864DiVA: diva2:1061725
FunderSwedish Research Council
QC 201701032017-01-032016-12-222017-01-03Bibliographically approved