Abstract
A facile in situ synthesis approach and a size control strategy were established to obtain Ag2S nanoparticles in polyimide (PI) composite coatings. Such Ag2S nanoparticles in the composite coatings were characterized, and the effects of the as-obtained Ag2S nanoparticles of different sizes on the mechanical and tribological properties of the nanocomposite coatings were investigated. Results indicate that the in situ synthesized Ag2S nanoparticles exhibited good dispersibility and bimodal and multimodal size distribution in the nanocomposite coatings. The size of the Ag2S nanoparticles can be effectively controlled by adjusting the substituent alkyl chain length of single-source precursor, and these Ag2S nanoparticles exhibited superior improvement to mechanical and tribological properties of the nanocomposite coatings. More importantly, the Ag2S nanoparticles with the proper grain size and bimodal size distribution provided the optimal mechanical and tribological properties for the nanocomposite coatings, and the excellent tribological properties were attributed to their outstanding mechanical properties and strong ability to form a homogenous and stable protective tribofilm.
Highlights
As functionalizing and reinforcing additives, nanoparticles have exerted a tremendous fascination in composite materials, due to their small size effect and strong interfacial activity with the reinforced matrices [1,2,3,4,5]
The Ag2S nanoparticles obtained from the precursors with different substituent alkyl chain length in nanocomposite coatings showed diffraction peaks of (−111), (111), (−112), (−121), (121), (−103), (031), (200), (−123), (014), and (−213) crystalline planes, and these diffraction peaks matched well with the characteristic peaks of monoclinic Ag2S phase with good crystallinity [30,31]
Several diffraction peaks of crystal plane for sample of S-C6, such as (111), (−121), (121), (−103), were slightly broadened compared to the sample S-C4. This indicates that the substituent alkyl chain length of the precursors had a great influence on the grain size of the in situ synthesized Ag2S nanoparticles
Summary
As functionalizing and reinforcing additives, nanoparticles have exerted a tremendous fascination in composite materials, due to their small size effect and strong interfacial activity with the reinforced matrices [1,2,3,4,5]. Nanoparticles with a high surface energy usually tend to agglomerate, which is hurtful to their dispersion in polymer matrices and to their reinforcing efficacy as well [6,7]. To overcome this drawback, researchers have attempted to improve the dispersibility of nanoparticles through mechanical grinding [8], ultrasonic dispersing [9,10], chemical modification [11,12], and the like. The influence of nanoparticle size and size distribution on their comprehensive properties still waits to be revealed at depth
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