Liquid crystallinity and magnetorheological performance of polymeric liquid crystal magnetic composites

Magnetorheological fluids (MRF) are regarded as a novel 'intelligent' material because they show the ability to respond to external stimuli. However, with the extension of working time, the agglomeration and sedimentation of magnetic particles become a serious problem, which has a great impact on the magnetorheological performance. Many methods have been proposed to overcome the particle settling problem, including magnetic particle modification and carrier liquid modification, but they all show negative effects on the magnetorheological performance of MRF. A new method to prepare the magnetic liquid crystal (LC) composites [PEA-COOH]SO3H@Fe3O4 series, with Fe3O4 nanoparticles as core and side-chain supramolecular LC polymers with different mesogen contents as coating, were reported. The chemical structure, magnetic property and LC properties were investigated by a variety of techniques. In order to study the effects of the mesogen content and LC phase state of magnetic LC composites on magnetorheological performance and sedimentation stability, MRF based on silicone oil carrier liquid and [PEA-COOH]SO3H@Fe3O4 dispersed phase were prepared. It was found that dynamic yield stress, plastic viscosity and the sedimentation ratio increased slightly with increasing mesogen content in the magnetic LC composites. What's more, MRF prepared by magnetic LC composites annealed in LC state exhibited better magnetorheological performance and sedimentation stability than those in glassy state and isotropic state. These results indicated that the synergetic effects of LC orientation and magnetic field-induced arrangement of Fe3O4 magnetic particles can improve the magnetorheological performance and sedimentation stability of MRF.