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Surface forces and friction between Langmuir-Blodgett polymer layers in a nonpolar solvent
Univ Bristol, Sch Chem, Bristol BS8 1TS, England.;Syngenta, Jealotts Hill Int Res Ctr, Bracknell RG42 6EY, England..ORCID iD: 0000-0002-2599-9979
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. Univ Bristol, Sch Chem, Bristol BS8 1TS, England.ORCID iD: 0000-0002-9815-8329
Univ Bristol, Sch Chem, Bristol BS8 1TS, England.;Diamond Light Source, Harwell Sci & Innovat Campus, Didcot OX11 0DE, Oxon, England..
Infineum UK Ltd, Milton Hill Business & Technol Ctr, Abingdon OX13 6BB, Oxon, England..
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2024 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 653, p. 1432-1443Article in journal (Refereed) Published
Abstract [en]

Optimization of boundary lubrication by tuning the confined molecular structures formed by surface-active additives such as surfactants and polymers is of key importance to improving energy efficiency in mechanical processes. Here, using the surface forces apparatus (SFA), we have directly measured the normal and shear forces between surface layers of a functionalised olefin copolymer (FOCP) in n-dodecane, deposited onto mica using the Langmuir-Blodgett (LB) technique. The FOCP has an olefin backbone decorated with a statistical distribution of polar-aromatic groups, with a structure that we term as "centipede". The effect of lateral confinement, characterised by the surface pressure, Pi(dep), at the air-water interface at which the LB films are transferred, was examined. Normal force profiles revealed that the thickness of the LB films increased significantly with Pi(dep), with the film thickness (t > 20 nm) inferring a multi-layered film structure, consistent with the interfacial characterisation results from synchrotron X-ray reflectivity (XRR) measurements. The coefficient of friction, mu, between the LB films spanned two orders of magnitude from superlubricity (mu similar to 0.002) to much higher friction (mu > 0.1) depending nonlinearly on Pi(dep), with the lowest friction observed at the intermediate Pi(dep). Molecular arrangement upon LB compression leads to the multilayer film with a structure akin to an interfacial gel, with transient crosslinking facilitated by the intra- and inter-molecular interactions between the functional groups. We attribute the differences in frictional behaviour to the different prevalence of the FOCP functional groups at the lubricating interface, which depends sensitively on the degree of compression at the air-water interface prior to the LB deposition. The LB films remain intact after repeated compression (up to pressures of 10 MPa) and shear cycles, indicating strong surface anchorage and structural robustness as a load-bearing and shear-mediating boundary layer. These unprecedented results from the friction measurements between LB films of a statistical copolymer in oil point towards new strategies for tailoring macromolecular architecture for mediating efficient energy dissipation in oil-based tribological applications.

Place, publisher, year, edition, pages
Elsevier BV , 2024. Vol. 653, p. 1432-1443
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-339890DOI: 10.1016/j.jcis.2023.09.146ISI: 001092436600001PubMedID: 37804612Scopus ID: 2-s2.0-85173245880OAI: oai:DiVA.org:kth-339890DiVA, id: diva2:1815127
Note

QC 20231128

Available from: 2023-11-28 Created: 2023-11-28 Last updated: 2023-11-28Bibliographically approved

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Pilkington, Georgia

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