Researchers at the State Key Laboratory of Solid Lubrication of the Lanzhou Institute of Chemical Physics have synthesized a novel imidazolium type of IL containing a biomimetic catecholic anchor. The catecholic ionic liquid (IL) can be successfully immobilized on a silicon surface through a catecholic anchor, allowing the tribological protection of these substrates for engineering applications.
The wettability, adhesion, and friction force for the catecholic IL SAMs were modulated by exchanging the counteranions, which all follow the trend of Cl >BF4 > NTf2. Namely, the SAMs coupled with the NTf2 anion, the most hydrophobic counteranion among the testing anions, showed the highest water contact angle value and the lowest friction and adhesive forces. DOP-IL SAMs have good tribological properties under low load, and the catecholic IL SAMs, which bind to a variety of substrate surfaces, might be developed as a potential boundary lubricating layer.
In addition, the IL spincoated films of normal ILs on DOP-IL SAMs maintain a better load-carrying capacity and antiwear ability than do pure, normal IL films on substrates. It is hypothesized that the presence of IL SAMs on surfaces can improve the wettability of the film and thus the film quality and tribological properties. Thus, IL composite films might find promising applications in the lubrication of microelectromechanical systems (MEMS).
Considering the wide substrate adaptability of catecholic attachment chemistry, this technique provides a simple and effective method of delivering IL monolayers on a variety of substrates of interest for engineering lubrication applications.
