Macromolecules
Macromolecules
5 years ago

Cross-Linking Highly Lubricious Phosphocholinated Polymer Brushes: Effect on Surface Interactions and Frictional Behavior

Cross-Linking Highly Lubricious Phosphocholinated Polymer Brushes: Effect on Surface Interactions and Frictional Behavior
Steven P. Armes, Jacob Klein, Michael J. Driver, Odeya Tairy, Noa Iuster
Poly[2-(methacryloyloxy)ethylphosphorylcholine] (pMPC) brushes provide extremely low friction coefficients up to high compressions, but their use as boundary lubricating layers is limited by the challenge of surface grafting of the chains. Coating by thin layers of cross-linked pMPC hydrogels may provide an attractive alternative. Here we use a surface force balance (SFB) and other techniques to examine the effect of light cross-linking (0.1% cross-linker) on the surface interactions and frictional behavior of grafted-from pMPC brushes on mica, up to physiologically high contact pressures. Atomic force microscopy, X-ray photoelectron spectroscopy, and interferometric surface-excess measurements show little difference between the non-cross-linked (linear) pMPC brushes and the cross-linked brushes prepared under otherwise identical conditions. Normal force–distance profiles between the polymer-bearing surfaces, however, reveal a marked compaction of the unperturbed thickness of the cross-linked brushes relative to linear ones, attributed to the cross-linking which limits chain swelling. The cross-linked pMPC layers exhibit very low friction (friction coefficients of order 10–3–10–4, depending on sliding velocities), similar to the corresponding linear brushes and due to hydration lubrication by the highly hydrated phosphocholine monomer structure. Within the range of our parameters, however, there is a marked qualitative difference in the dependence of friction on sliding velocity vs. While for the linear brushes friction is only very weakly vs-dependent (over 3 orders of magnitude in vs), due to a self-regulating brush interpenetration, for the cross-linked brushes friction increases markedly with vs (∼vs1/2), an effect attributed to suppression of interpenetration by the cross-links.

Publisher URL: http://dx.doi.org/10.1021/acs.macromol.7b01423

DOI: 10.1021/acs.macromol.7b01423

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.