New Insights into the Quantitative Relationship between Surface Chemistry of Fullerene (C60) and Solubility Parameters and Compatibility with Polymers.

The quantitative relationship between the surface chemistry of carbon materials and the compatibility with polymers is a fundamental and vital physical chemistry problem in the field of polymer nanocomposites. Traditional experimental methods are difficult to solve this problem, so no theory has been formed to guide the functionalization of carbon materials. In this work, the quantitative relationship between functional groups and Hildebrand (δ) and transformed Hansen (δ and δ) solubility parameters of fullerene (C60) was determined by molecular dynamics simulation. Besides, which solubility parameter can more accurately predict the compatibility between C60 and three typical polymers with different polarity as a function of grafting ratio is investigated. Very interestingly, no matter which group is grafted, δ and δ of C60 show a slight increase first and then a decrease with the grafting ratio, whereas δ first increases abruptly and then decreases slightly. The introduction of polar groups (-OH, -COOH, and -NH) is conducive to improving the compatibility between C60 and polymers, whereas the introduction of the nonpolar group (-CH) is not. In terms of predicting compatibility, the Hildebrand solubility parameter is better than the Hansen solubility parameter due to the nonpolar nature of the polymers, even for nitrile butadiene rubber. Finally, the optimum grafting ratios corresponding to the maximum binding energies of C60/polymers mixtures were obtained. This study provides a new understanding of the functionalization of C60 at the molecular level and promotes the development of the theory of the thermodynamics of mixing.