Preparation,Characterization,Mechanical And Electrical Mechanism Of Magnetorheological Gel Based On Polyurethane

Magnetorheological gel(MRG)is a new type of magneto-sensitive,which is developed for improving the settling stability of particles in magnetorheological fluid.It is a kind of colloidal material between the liquid magnetorheological fluid and solid magnetorheological elastomer.The matrix of the MRG is a gel-like polymer material which improves the yield stress of the MRG,and the viscosity of it can be adjusted in zero field.Due to the constraints of the gel-like matrix,the magnetic particles are evenly dispersed in the matrix in the absence of external magnetic field conditions.When the MRG subjected to a magnetic field,the magnetic particles in the matrix are magnetized.The magnetic interaction forces generated between these particles can cause the particles to move against the constraints of the matrix and accumulate along the direction of the magnetic field to form a chain-like structure.Therefore,with the changes in the particle structure,the macro-mechanical,electrical,thermal,acoustic and other properties would change with the magnetic field.These excellent magnetic-control properties make MRG great potential applications in the high power dampers,actuators,sensors,and in artificial muscle,self-healing structures and biomedical engineering.At present,as a new member of large family of magnetorheological materials,MRG is in the stage of rich material selection,optimization of preparation process and characterization of physical properties.At present,the research on MRG is mainly aimed at its mechanical properties and its related mechanism,and the researches forimproving the magneto-control properties of MRG is relative rare.In addition,in order to broaden the application of MRG in electrical field,it is urgent to characterize the magnetoelectric behavior and explore the corresponding micro-mechanism.In view of this,this paper mainly to study the development of high-performance MRG as the object of study,and to further study its magneto-mechanical properties.To establish a coupling model for the microstructure and macroscopic mechanical properties of MRG.On the other hand,in order to broaden the application of MRG in sensors and electromagnetic shielding,this paper will comprehensively study the electrical characteristics of MRG and improve its magnetoelectric properties by material preparation The relevant mechanism has been proposed to describe it.The main contents of this paper and related conclusions are as follows:Firstly,the effects of matrix,magnetic particles and additives on the magnetorhelogical behavior were studied.The polyurethane-based MRG with magnetorheological effect of up to 8500% was prepared.In addition,the addition of nickel-coated carbon nanotubes improves the performance of the MRG.The results show that the nickel-carbon nanotubes can improve the bonding between the carbonyl iron powder and the matrix,and enhance the strength of the chain structure formed under the magnetic field.The results show that the addition of a certain amount of nickel-coated carbon nanotubes is an effective measures to improve the magneto-induced modulus of MRG by about 127.3%.In order to study the effect of the shape of magnetic particles on the properties of MRG,magnetic rheological gels containing spherical and dendritic carbonyl iron powders were prepared.The results show that the preparation of magnetic particles containing two different shapes can improve the magnetorheological properties of magnetorheological fluids.In addition,for the magnetic rheological properties of the MRG,the damping properties of the MRG were analyzed in detail.The influence of viscosities,particle contents,additives on the damping characteristics of MRG have been studied,and the relevant mechanism has also been established.Finally,in order to deepen the understanding of the mechanism of MRG and to broaden the engineering application of MRG in the field of sensing,this paper comprehensively studies the electrical characteristics of MRG.The influence of magnetic field strength,the magnetic particles,the viscosity of the matrix,the additives and other factors on the magneto-induced resistivity of the MRG were studied.It has been found that the magneto-induced resistivity of MRG can be improved by adding conductive particles such as iron nanowires,carbon black and graphite.In this paper,the mechanism of magneto-induced resistivity of MRG is studied,and the theoretical model based on chain structure is proposed,and the model is tested and verified by experiments.