Electrorheological (ER) fluids are fascinating materials with a wide range of potential applications. However, low performance in electric field and poor sedimentation stability are the most serious limitations for these applications. To reduce the mentioned drawbacks various materials such as graphene were explored. Recent efforts to improve performance of the ER fluids led to the modification of the graphene with polymer substances. Herein, the proposed ER structures are based on the graphene oxide (GO) sheets controllably grafted with poly(methyl methacrylate) (PMMA). The oxygen-containing functional groups introduced by modified Hummers method enabled the immobilization of 2-Bromoisobutyryl bromide onto the GO. The controlled PMMA chain growth was performed by atom transfer radical polymerization resulting in the GO-g-PMMA entities. The reaction process was monitored via nuclear magnetic resonance spectroscopy and gel permeation chromatography. The successful grafting process was confirmed via infrared spectroscopy. Conductivity of the neat GO as well as the fabricated GO-g-PMMA structures was investigated using four-point method, while their reduction was examined via Raman spectroscopy. Such particles were further thoroughly dispersed in silicone oil (SO) and the ER performance of as-prepared ER fluids was investigated. The system containing the GO-g-PMMA exhibited superior dynamic yield stress and higher ER effects as the modified particles were able to develop more rigid field-induced internal structures, due to the enhanced particle conductivity and thus better response to external electric field. The results also showed that the presence of PMMA grafts enhanced the compatibility with SO, which was reflected in substantially improved stability against sedimentation.Keywords: electrorheology, steady shear, graphene oxide, surface modification, atom transfer radical polymerization
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