Control Of The Morphology Of Cobalt Particles And Its Effect On The Properties Of Magnetorheological Materials

Magnetorheological materials are a class of intelligent materials with magnetic field response capabilities.They are usually composed of non-magnetic matrix materials and soft magnetic micro-nano magnetic particles.They have great application value and potential in the military and civilian fields.Silicone oil-based magnetorheological fluids and rubber-based magnetorheological elastomers are the two most representative magnetorheological materials.Silicone oil-based magnetorheological fluids and rubber-based magnetorheological elastomers are the two most representative magnetorheological materials.The influences of magnetic particle type,particle size,magnetic properties,and volume fraction in magnetorheological materials on the properties of magnetorheological materials have been thoroughly studied,while the influence of the shape of magnetic particles on the properties of magnetorheological materials is rarely studied.Although some theories have pointed out that the particle morphology has a negligible effect on the properties of magnetorheological materials,the lack of relevant experimental evidence is due to the change in particle morphology usually accompanied by changes in particle size and magnetic properties.Therefore,the particle morphology cannot be analyzed as an independent influencing factor.The preparation of magnetic particles with similar particle size and magnetic properties but different morphologies is the prerequisite and key to study the effect of particle morphology.In this paper,a variety of morphology cobalt microparticles were prepared by solvothermal method.By controlling the types of reaction reagents.alkalis and surfactants in the solvothermal reaction process,the reaction temperature,etc.,to control the growth process of cobalt particles,four kinds of cobalt particles with different morphologies were prepared.According to the research purpose,spherical and flower-like cobalt particles with similar particle size and magnetic properties were finally selected as the dispersed phase of the magnetorheological material to study the rules and mechanism of the influence of the shape of the magnetic particles on its performance.First,the effect and mechanism of particle morphology on the performance of magnetorheological fluids were studied.By testing the contact angle of the two kinds of particles to the silicone oil,the wettability of the particles and the liquid silicone oil was evaluated;then the rotational rheometer was used to test the viscosity,shear properties,and magneto-rheological properties of the two magnetorheological fluids;finally The sedimentation of the two magnetorheological fluids was compared by standing test.The results show that the rough surface of the flower-like particles increases the resistance to particle movement,increases its wettability to silicone oil,and increases the viscosity of the rheological fluid.The special flower-like morphology causes a mechanical locking effect between the particles and increases its magnetic-induced shear yield strength by 13%.The special flower-like morphology reduces the agglomeration of the particles,which increases the sedimentation rate of the magnetorheological fluid by 1 50%.Secondly,the effect and mechanism of particle morphology on the properties of nagnetorheological elastomers were studied.The interfacial binding capacity of particles with different morphologies is different.In order to evaluate the influence of different interfaces,the magnetorheological elastomers using silane coupling agent modified spherical cobalt particles as the dispersed phase were prepared.Sphere cobalt particles magnetorheological elastomers were compared with flower-like cobalt particles magnetorheological elastomers and modified sphere cobalt particles magnetorheological elastomers.The results show that the flower-like morphology can improve the interface bonding between the particles and the matrix.However,there are differences in the causes and performance characteristics of modification with coupling agents to improve the interface bonding.The special flower-like morphology increases the crosslink density of the magnetorheological elastomer,increases its storage modulus and loss modulus,increases its energy dissipation density,and reduces the Payne effect.Compared with the spherical cobalt particle magnetorheological elastomer,the adjustable range of the magneto-storage modulus of the flower-shaped cobalt particle magnetorheological elastomer increased by 83%.Based on the experimental results,an internal structure model of the magnetorheological elastomer and a structural evolution model of the oscillating shear process were established.Finally,the influence mechanisn of particle morphology on the properties of magnetorheological materials was comprehensively analyzed.The flower-like particles can improve the comprehensive performance of two typical types of magnetorheological materials:magnetorheological fluid and magnetorheological elastomer.Particle morphology mainly affects magnetorheological materials through the interaction between particles and between particles and the matrix.The effects of these two aspects on the performance of different magnetorheological materials are different.By analyzing the specific laws of the influence of particle morphology on the performance of different magnetorheological materials,and determining the proportion of the effects of two aspects on different magnetorheological materials,a general mechanism model of the effect of particle morphology on the properties of magnetorheological materials can be established.