Graphene oxide modified by betaine moieties for improvement of electrorheological performance†
Novel graphene oxide bearing betaine moieties as sulfobetaine (GO-SB), carboxybetaine (GO-CB) and carboxybetaine ester (GO-CBE) moieties were prepared in two simple fabrication processes based on silanization and a thiol–ene click-reaction. Betaine modified particles showed appropriate electrical conductivity for electrorheological applications and the electrorheological behavior was confirmed by on-line microscopic observation. Analysis of the dielectric data using the Havriliak–Negami model showed that the suspension bearing the carboxybetaine ester moiety (GO-CBE) in silicone oil had the highest dielectric relaxation strength and fastest relaxation time due to enhanced charge transfer caused by a specific carboxybetaine ester feature. Analysis of the rheological data of the prepared suspensions at various external fields by the power-law model revealed that the conductivity mechanism is responsible for the electrorheological effect. Development of the internal structures was considerably improved for the GO-CBE sample with a yield stress up to 97 Pa at 5 wt% GO-CBE particles in suspension.