Abstract
The magnetorheological (MR) fluid is a kind of smart material, whose shear yield stress can be adjusted through changing the strength of the external magnetic field, and this kind of changing only takes a few milliseconds. The MR fluid is composed of micro/nanometer ferromagnetic particles, carrier fluids and some additives. Among them, the performance of ferromagnetic particles will mainly affect the sedimentation stability and the magnetic saturation of the MR fluid. Therefore, they are expected to have characteristics of both low density and high magnetism. In this paper, the multi-walled carbon nanotubes (MWNTs) were adopted to coat on the carbonyl iron (CI) particles with grafting technology using ultrasonication and mechanical stirring. The coated CI particles with perfect core-shell structure were prepared and the influence of the dosages of grafting agent and MWNTs were tested. And then, MR fluids with CI particles coated with MWNTs were prepared and the coating effect was studied through surface topography analysis, particle density, and magnetic properties of composite magnetic particles and stability tests of the prepared MR fluids. The results showed that although the magnetic saturation of the prepared MR fluids with CI particles coated with MWNTs would reduce slightly, the particles density and the adsorption force between the particles were decreased effectively, which are both advantageous to the improvement of the sedimentation stability of MR fluids.
Highlights
MR fluids with carbonyl iron (CI) particles coated with multi-walled carbon nanotubes (MWNTs) were prepared and the coating effect was studied through surface topography analysis, particle density, and magnetic properties of composite magnetic particles
MR fluids with CI particles coated with MWNTs were developed and the coating effect was studied through surface topography particle density, and magnetic properties of composite magnetic particles and stability tests of the prepared MR fluids
The influence of the dosages of grafting agent and MWNTs on the coating effect were analyzed to verify the effect of CI particles coated with MWNTs on the improvement of the sedimentation stability
Summary
Magnetorheological (MR) fluid is a kind of typical smart material with unique magnetic rheological properties characterized by a reversible change in viscosity and yield stress under magnetic field (Kim et al, 2013), which has been widely applied in many fields, such as sealing (Mitamura et al, 2008), target drug delivery (Kim and Kim, 2003; Oh and Park, 2011), lubrication (Arruebo et al, 2007), removal of water pollutants (Goldowsky, 1980), dampers (Olabi and Grunwald, 2007; Ferroudj et al, 2013; Zong et al, 2013; Zhu et al, 2018), brakes (Mangal and Kumar, 2015) etc. Rabinow (1948) prepared the original MR fluid consisting of magnetic particles and carrier liquid in 1948. Xu et al (2003) reported that MR fluids can transform between solid and liquid due to the existence of the magnetic particles; the iron particles are magnetized and MR fluids can be changed rapidly from liquid to solid in the presence of a magnetic field, while. Kim and Choi (2011) prepared the polymeric solution by solving PEO in distilled water and acquired an MR fluid from the distribution of carbonyl iron in a polymeric solution, the mismatching of magnetic particles and the carrier liquid still remained to be overcome in order to make considerable breakthroughs in improving the sedimentation stability of MR fluids. Jiang et al (2010) adopted coated poly (methyl methacrylate) (PMMA) to coat on the surface of CI particles in order to obtain composite CIPMMA particles and discovered the prepared MR fluid based on CI-PMMA particles exhibited better sedimentation stability. Mrlik et al (2013) adopted cholesteryl chloroformate to coat on the surface of CI particles and discovered that the sedimentation rate of MR fluids based on the prepared composite particles has greatly decreased due to better compatibility between the particles and silicon oil. Every 2 h different kinds of additives including dispersant, lubricant, and anti-sedimentation agent are added quantitatively in sequence, at the same time, make the liquid keep continuous stirring
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