ISBN 978-3-8439-5489-1

978-3-8439-5489-1, Reihe Mikrosystemtechnik

Renato Maraula
Friction, Mechanical Stability and Super-lubricating Properties of Surface-Attached Hydrogels

203 Seiten, Dissertation Albert-Ludwigs-Universität Freiburg im Breisgau (2024), Softcover, B5

Zusammenfassung / Abstract

Every year, high friction and wear consume up to 100 TJ of energy and contribute to 8120 Mt of carbon dioxide emissions. Although lubricants can reduce friction, most are oil-based and only partially recyclable. In addition, oil spills pose serious environmental risks, highlighting the need for environmentally friendly alternatives.

Inspired by the lubrication system of synovial joints, this research investigates surface-attached hydrogels that store and release water under pressure to form a lubricating film. Specifically, surface-attached hydrogels of P(DMAA-co-MABP) crosslinked via the CHic reaction (C-H insertion crosslinking) will be investigated.

A major challenge for hydrogels is their limited mechanical strength, which requires the investigation of their load bearing limits. This research presents a model for predicting the maximum contact pressure leading to hydrogel rupture under different indenter geometries. Different results from pyramidal and spherical indenters provide insight into the effective use of hydrogels as oil-free lubricants. In relation to the indentation mechanism of surface-attached hydrogels, this work also considers the influence of surface tension and scenarios involving extreme stretching of the polymer chains, ultimately leading to rupture.

Strategies to achieve superlubricity (coefficient of friction μ < 0.01) are explored, including patterned hydrogels, the addition of styrene sodium sulfonate (SSNa) for charge introduction, and water-based lubricants like polyethylene glycol (PEG) and polyacrylamide (PAM), mimicking synovial joint biomechanics.