Investigation of Tribological Behavior in DLC-Coated Thermosensitive Polymers Using Atomic Force Microscopy

This study explores the mechanical and tribological behaviors of poly(ethylene terephthalate) (PET) substrates at the nanoscale with and without a 75 nm diamond-like carbon (DLC) coating, addressing the limitations of polymer-based nanoimprint lithography (NIL) in extreme environmental conditions. Adhesion, friction, nanoindentation, and wear characteristics were thoroughly studied with atomic force microscopy (AFM) in the temperature range of 20-80 °C and relative humidity of 30-70% RH while controlling for temperature and humidity in the AFM. The uncoated PET exhibited increased adhesion force, friction coefficient, and wear rate with an increase in temperature, particularly at temperatures that approached its glass transition temperature. The DLC-coated PET, on the other hand, preserved its low adhesion (≤87 nN), friction coefficient (≈0.08-0.10), and wear depth (∼3 nm), demonstrating excellent stability in extreme environmental conditions. Nanoindentation measurements demonstrated that the DLC coating had increased hardness and elastic modulus approximately by 900 and 180 times, respectively, and maintained its mechanical stability at 80 °C. Overall, these results affirm that DLC is an excellent candidate for a protective coating on thermosensitive polymers in NIL applications, while also providing a solid basis for increasing mold durability, pattern fidelity, and process stability in high-temperature and high-humidity environments.