Mechanism Study On Effect Of Particle Surface Morphology On Properties Of Electrorheological Fluids

As a kind of smart soft materials, electrorheological fluids (ERFs) are smart fluids of polarized dielectric micro/nano-particles dispersed in insulating oil. Under an applied field, it is obvious for the structure and properties of ER fluids to change, so ER fluids as smart materials have a wide application prospect. Throughout years of research process of ER fluids, it can be found that most studies have focused on the dielectric particles. At present, researchers mainly concerned with improving the shear stress and stability of ER fluids by adding polar molecules or other ways, but surface morphology of particles influence on ER fluids properties and the related mechanism analysis are less researched. Therefore, we used solvothermal method to synthesize rough surface flower-like particles. Compared flower-like particles-based ER fluid with spherical particles-based ER fluid, we analyze the influences between the morphology of particles and ER effect, such as shear stress, sedimentation stability and so on. At the same time, the inter-particle friction model is used to theoretically analyze the contribution of inter-particle friction to ER properties. The main points of the research are as follows:(1) To combine the nanoscale structure and morphology into microscale structure, we fabricated rough surface flower-like particles and smooth spherical particles with solvothermal method. The morphology and structure of the particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and infrared spectroscopy (FT-IR), the results showed that flower-like particles and spherical particles are amorphous. Based on the characterization of two kinds of particles, the formation process of flower-like particles has been further studied.(2) Under quasi-static test mode, compared the properties of two ER fluids with each other, it has been found that flower-like particles-based ER fluid presents a better ER effect than spherical particles-based ER fluid. The thorn structure on the surface of flower-like particles is helpful to improve the wettability between flower-like particles and silicon oil and the friction between particles, which makes flower-like particles ER fluid has a stronger ER properties. Besides, dependence of the sedimentation stability of two ER fluids on time was tested. After 1 days’ setting without disturb, the sedimentation ratio of flower-like particles ER fluid was 91.60%, but the sedimentation ratio of spherical particles ER fluid was quickly dropped to 8.49%. Because of the thorn structure on the surface of flower-like particles, particles dispersed in silicon is difficult to agglomeration and is also able to gain greater buoyancy, so the sedimentation stability of the flower-like particles-based ER fluid was much better than that of the smooth spherical particles-based material.(3) Under dynamic oscillatory test mode, using the friction model analyzed the effect of inter-particle friction stress on ER effect. The relationship between strain and modulus showed that two ER fluids were in their linear viscoelastic regions at 0.1% stain amplitude, and the subsequent dynamic oscillatory was tested at 0.1% stain amplitude. The calculation results indicated that, under a lower electric field, the inter-particle friction stress τf plays a dominant role in ER effects; under a higher electric field, the field-induced stress re has a dominant influence on ER activities. Owing to the thorn structure, flower-like particles obtain greater inter-particle friction stress, so the flower-like particles-based ER fluid has better ER effects. Thereby, the inter-particle friction stress is a significant influence factor for ER properties.