Carboxylic acid functionalized MWNT coated poly(methyl methacrylate) microspheres and their electroresponse

The effect of solvent on adsorption of the multi-walled carbon nanotube (MWNT) onto poly(methyl methacrylate) (PMMA) microspheres is examined and then their electrorheological (ER) behavior under an applied electric field when dispersed in a silicone oil is observed, using the MWNT which was initially modified with carboxylic acid functional groups on its outside wall through an oxidation treatment (c-MWNT). The c-MWNT was successfully incorporated onto the PMMA microsphere surface in either Di-water or methanol, while the adsorption state of the c-MWNT is strongly dependent on the solvent used. The dense and well dispersed c-MWNT is found to be more strongly attached onto the surface of PMMA microspheres when prepared in Di-water than in methanol. It is believed that hydrogen bonding component in the Hansen solubility parameter is a principal factor determining dispersion state of the c-MWNT in the solvent, because the nanotubes used have carboxylic acid functional groups on their surface forming hydrogen bonding between c-MWNT and the solvent. Moreover, c-MWNT/PMMA microsphere as an ER material dispersed in a silicone oil is observed to exhibit typical ER characteristics of fibril structure under an applied electric field, and the ER characteristics are found to be influenced by the conductivity of c-MWNT/PMMA microspheres.