Bottlebrush block copolymers in nonpolar media
: self-assembly, surface forces, and lubrication

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Bottlebrush copolymers (BBPs) are ubiquitous in nature, found in the form of glycoproteins with a large variety of molecular architectures and compositions. They are known to mediate lubrication in mammalian joints through synergistic self-assembly with other biomolecules and biomacromolecules to produce boundary films that are super lubricating at high pressures. Despite thorough investigations in aqueous conditions, their mediation of surface forces in oils is relatively unexplored. Here, three BBPs with different molecular architectures of
copolymerised poly(acrylate)s consisting of hydrophobic ethylhexyl acrylate and polar oligoethylene glycol acrylate monomers have been investigated. Small-angle neutron scattering (SANS) measurements revealed that they self-assembled to form structures (i.e. core-shell cylinders, spherical micelles and nano-clusters) in n-dodecane (a model oil), and the polymer-solvent interactions underpinning the self-assembly behaviour were discussed. The dry polymer films on mica via dip-coating was characterised using X-ray reflectivity (XRR) and the surface forces between polymer-bearing mica were directly measured using the surface force apparatus (SFA). Normal force measurements indicated aggregate adsorption for all polymer architectures, and the forces were modelled with the Alexander-de Gennes (AdG) theory. The friction forces mediated by the polymer films were also measured to evaluate their efficacy in mediating lubrication in a nonpolar medium. These results help elucidate the structure-function relationship of BBPs at the solid-liquid interface and will aid in the future
rational design of bottlebrush polymer friction modifying additives in oil.
Date of Award3 Oct 2023
Original languageEnglish
Awarding Institution
  • University of Bristol
SponsorsInfineum UK Ltd & Engineering and Physical Sciences Research Council
SupervisorBrian Vincent (Supervisor) & Wuge H Briscoe (Supervisor)

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