Comparative investigation of different silane surface functionalizations of fullerene-like WS2

Inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles are useful additives for polymers and lubricating agents, in particular when their surfaces are functionalized by silane modifiers. However, both the success of such a silanization reaction and its effect on the final dispersion quality are still doubtful. In this work, IF-WS2 are functionalized using three different silane modifiers and investigated with X-ray photoelectron spectrometry, infrared spectroscopy, titration, thermogravimetric analysis, and mass spectroscopy. Eventually, they are dispersed within ethanol by sonication to compare the dispersing behavior. The combination of the different analytical techniques revealed that the IF-WS2 surfaces can be functionalized with two of the used silane modifiers, while the third one was repeatedly unsuccessful. The amount of Si on the particles seems to be a fairly clear indication for the success of the functionalization reaction. The IF-WS2 seems to oxidize during the functionalization process, probably producing acidic SO2 or SO3, which can fully acidify a basic surface modifier. The executed treatment without any added silane modifier improved the dispersibility of the IF-WS2 within ethanol to some extent, but added modifiers deteriorated it significantly. TEM images indicate that IF-WS2 particles form aggregates, which might be the reason for the limited dispersibility.