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Effects of adsorption of low-molecular-weight triblock copolymers on interactions between hydrophobic surfaces in water
YKI – Ytkemiska institutet.
1999 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, 3242-3249 p.Article in journal (Refereed)
Abstract [en]

In this work, we report on the interaction forces between hydrophobized silica surfaces immersed in polymer solutions. The polymers studied were a series of polyethylene oxide-polytetrahydrofuran-polyethylene oxide (PEO-PTHF-PEO) triblock copolymers and a polyethylene oxide homopolymer. The interaction forces were measured by the interfacial gauge technique. We show how the interactions depend on the adsorbed state of the copolymers, which in turn depends both on the copolymer concentration and the adsorption time. Above a critical surface coverage, the interaction between approaching surfaces was found to begin with a steric repulsion due to overlap of the adsorbed polymer layers. This repulsion increases as the distance between the surfaces was decreased. The energy-distance curve could, in this regime, be accounted for by the theory of grafted polymer brushes by Alexander-de Gennes. However, the interaction curves did not follow this prediction for small surface-to-surface distances. Instead, the repulsion stabilised at a more or less constant level with decreasing inter-surface separation. Finally, however, hard wall contact was established between the two surfaces. We infer that adsorbed copolymers to a large extent are expelled from the gap between the surfaces in this surface-to-surface distance range. The force needed to expel copolymers from the inter-surface gap was shown to be equal to the surface pressure at the solid-liquid interface. We also studied the influence of the rate of approach and separation of the surfaces on the energy-distance curves. The process of expelling polymers from the surface-to-surface gap was shown to depend on the velocity of the approaching surfaces and the surface coverage. For high approach rates and/or large surface coverage's, the lateral mobility of the polymers was generally observed to restrict the expulsion process of polymers from the gap. However, rapidly repeated force curves measured at constant rate in succession were found to be perfectly reproducible.

Place, publisher, year, edition, pages
1999. Vol. 15, 3242-3249 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-27235OAI: oai:DiVA.org:ri-27235DiVA: diva2:1054239
Note
A1241Available from: 2016-12-08 Created: 2016-12-08Bibliographically approved

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