Tribological Properties of Polydimethylsiloxane Grafted with Poly(Ethylene Glycol) Methyl Ether Methacrylate Under Water Lubrication

Abstract

Polydimethylsiloxane (PDMS) is a polymer material characterized by its flexibility, biocompatibility, non-toxicity, excellent stability, and high transparency. It is also easy to process and allows for control over its physical properties. However, its inherent hydrophobicity limits its application in certain fields. To address this limitation, research is being conducted to modify the surface properties of PDMS through polymer grafting. In this work, poly(ethylene glycol) methyl ether methacrylate (mPEG-MA) was grafted onto the PDMS surface to convert its hydrophobic characteristics to hydrophilicity. The tribological properties of the modified PDMS were then evaluated under conditions of hydrophilicity and water lubrication. Polymer grafting was performed by generating radicals on the surface of PDMS through ultraviolet (UV) irradiation using a photoinitiator, followed by grafting with mPEG-MA. The water contact angle, which serves as an indicator of hydrophilicity, was measured and revealed a decrease in the contact angle as the conditions for mPEG-MA grafting were intensified, signifying an increase in hydrophilicity. Additionally, the tribological properties under water lubrication improved with a higher degree of mPEG-MA grafting. Notably, PDMS grafted with a 20 wt.% mPEG-MA aqueous solution via UV irradiation for 12 h consistently maintained a coefficient of friction (COF) of less than 0.02 under water lubrication. Surface damage was observed locally in the dimples only under a load of 3 N.