Synthesis and properties of a solvent-free MWCNT-based nanofluid

Carboxylic-acid functionalized multiwall carbon nanotubes (MWCNT-COOH) were first modified by (CH3O)3Si(CH2)3SO3H by an esterification reaction of the carboxylic-acid group with a methoxy group, then by hydrolyzing N,N-di(2-hydroxyethoxy)ethyl octadecylamine by an ion exchange reaction to form a quaternary ammonium salt as a soft shell of the MWCNTs. The modified MWCNTs had a larger diameter than the original MWCNTs and their MWCNT content was up to 16.03 wt.%. The loss modulus of the modified MWCNTs is bigger than the storage modulus, which is a characteristic of a solvent-free nanofluid. The modified MWNTs can be well dispersed in deionized water and the resulting dispersion is stable. Their seepage threshold value in water is about 5 mg/g. arbon Materials 2014, 29(3): 203–208]