Abstract
In this study, a verified process of the “grafting from” approach using surface initiated atom transfer radical polymerization was applied for the modification of a graphene oxide (GO) surface. This approach provides simultaneous grafting of poly(2-(trimethylsilyloxy)ethyl methacrylate) (PHEMATMS) chains and a controllable reduction of the GO surface. This allows the fine tuning of its electrical conductivity, which is a crucial parameter for applications of such hybrid composite particles in electrorheological (ER) suspensions. The successful coating was confirmed by transmission electron microscopy and Fourier-transform infrared spectroscopy. The molecular characteristics of PHEMATMS were characterized by gel permeation chromatography. ER performance was elucidated using a rotational rheometer under various electric field strengths and a dielectric spectroscopy to demonstrate the direct impact of both the relaxation time and dielectric relaxation strength on the ER effectivity. Enhanced compatibility between the silicone oil and polymer-modified GO particles was investigated using contact angle measurements and visual sedimentation stability determination. It was clearly proven that the modification of the GO surface improved the ER capability of the system due to the tunable conductivity during the surface-initiated atom transfer radical polymerization (SI-ATRP) process and the enhanced compatibility of the GO particles, modified by polymer containing silyl structures, with silicone oil. These unique ER properties of this system appear very promising for future applications in the design of ER suspensions.
Highlights
Electrorheological (ER) fluids are smart materials that can change their mechanical properties upon the application of an external electric field
A simultaneous reduction and coating process of graphene oxide (GO) led to both an increase of its conductivity, and a significant improvement of the sedimentation stability and ER performance thanks to its substantial shell, enhancing compatibility [3,9,15,21]
Fourier transform infrared (FTIR) spectra were recorded on a Nicolet 6700 (Nicolet, USA) using an attenuated total reflectance (ATR) technique with Ge crystal and 64 scans with a resolution of 4 cm–1 within a GO sheets with an attached ATRP initiator (1 g) were put into a Schlenk flask and the flask was evacuated and backfilled with argon three times
Summary
Electrorheological (ER) fluids are smart materials that can change their mechanical properties upon the application of an external electric field. Chemical and physical functionalization of the graphene surface is necessary to achieve compatibility with its surroundings and several methods have been developed to improve the process of stabilization and the modification of the graphene [9,11,12]. For the ER application, the graphene needs to be oxidized to decrease its high conductivity, which, from the application point of view, is not desirable, as there is a risk of creating a short circuit [14,15,16] These drawbacks of GO can be overcome by an additional reduction of GO, which is usually performed before or after a suitable surface modification. According to our knowledge, such a modification is a pioneer study, with regards to both the GO modification with silyl-based polymer grafting using the SI-ATPR approach, and its impact on the ER performance
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