Intermolecular interactions between bottlebrush polymers boost the protection of surfaces against frictional wear

Abstract

Polymers exhibiting the bottlebrush (BB) architecture have excellent lubricating properties. However, to motivate their use in real life systems, they must also protect surfaces against frictional damage. In this article, we synthesized a library of polyzwiterrionic bottlebrush polymers of different architectures to explore the effect of intermolecular interactions on their conformation at interfaces and their tribological properties. Using the surface forces apparatus, we show that increasing the number of adhesive blocks on the BB polymers does not impact the friction coefficient on mica surfaces, μ, which remained close to μ = 0.02 but drastically increased the threshold pressure, P∗, at which wear initiates from P∗ = 0.4 ± 0.1 up to 8.0 ± 0.8 MPa. In mixtures of high molecular weight hyaluronic acid and BB polymers, a synergistic interaction between polymers occurred, leading to a significant increase in P∗, independently of the BB polymer tested and even reaching superprotection for strongly interacting polymers (up to P∗ > 14 MPa). Overall, these results show that strong intermolecular interaction between BB polymers and high molecular weight linear polymers is a promising strategy to create highly protective lubricants.