Surface modifications for the effective dispersion of carbon nanotubes in solvents and polymers

Abstract

The preparation of effective dispersions of carbon nanotubes (CNTs) presents a major impediment to the extension and utilization of CNTs. CNTs intrinsically tend to bundle and/or aggregate. The prevention of such behavior has been explored by testing various surface modification techniques to improve the dispersibility of CNTs in a variety of solvents and polymer matrices. General guidelines for the design of end-use tailor-fit surface modifications to achieve a particular CNT dispersibility have not thus far been articulated. This review aims to identify such guidelines by providing a perspective of the state of the art in surface modifications and the resultant dispersibility of CNTs. Surface modifications and dispersion properties must first be defined by agreeing upon a few new terms, such as the degree of surface modification, degree of substitution, and degree of dispersion, to determine the possible relationship(s) that may exist between surface characteristics and the dispersibility of CNTs. Furthermore, several critical issues that require concerted in-depth studies are discussed with particular emphasis on the quantitative characterization of CNT surface modifications and dispersions. This discussion describes the Flory–Huggins interaction parameter based on the solubility parameter for CNTs, which is correlated with the dispersibility in the surrounding media.