Structure And Properties Study Of Titanium Dioxide-Based Electrorheological Fluids

Electrorheological fluid is a two-phase suspension system,which is typically composed of polarized particles dispersed in an insulating medium.The ER effect,instantaneous and reversible changing in rheological properties of the fluids under the applied electric field,arises from the formation of chain-like or column-like structures between neighboring polarized particles along the direction of electric field.Due to the advantages of controllable rheological properties in response to an external electric field,the ER fluid promises wide range applications in electrically controllable devices,such as clutches,brakes and shock absorbers.Various conducting materials have been employed to disperse in silicone oil to fabricate ER fluids,ranging from conducting polymers to inorganic semiconductor.Among them,TiO₂ is considered as a suitable candidate due to its relatively high permittivity,non-toxic,chemical stability.However,the practical applications of ER fluids is still limited by low conductivity,weak interfacial polarization,narrow operation temperature,particles sedimentation,insufficient yield stress.On the other hand,TiO₂nanoparticles with special morphologies were designed with facial strategies improve the ER effect,such as core@shell structure,hollow structure,nanocomposite and 2D materials.Moreover,the as-synthesized TiO₂ nanoparticles were characterized by using XRD,SEM,TEM,XPS,FT-IR and TG.The morphological effect on ER properties was also investigated and the corresponding polarization method was discussed.The main contents and major results are given as follows:?1?Ethanol and isopropanol were used as the cosolvent to synthesize bowl shape TiO₂ particles by solvothermal method.We propose the formation mechanism of bowl shape TiO₂ was Ostwald ripening effect.Moreover,SEM,TEM and XRD were employed to confirm the morphological and crystalline structure of bowl shape TiO₂.At last,the bowl shape TiO₂ was dispersed into silicone oil to form a uniform ER fluid.The ER fluid exhibited an outstanding ER effect under the action of applied electric field.?2?The anatase TiO₂ enclosed with?100?facets was prepared with a hydrothermal method using titanium nanofibers as precursor,in which the precursor was firstly synthesized by a hydrothermal reaction in alkali solution.It was found that the selective adsorption of OH^-on the?100?facets of anatase TiO₂ was mainly responsible for the exposure of?100?facets.The large surface area resulted from the anisotropy of the special morphology leaded to an improvement of ER activity.In addition,the morphology influence on the dielectric property was confirmed by measurement of broadband dielectric spectroscopy.?3?A simple method for synthesis of porous TiO₂ was developed via a two-step route using titanium-MOF as a precursor,in which MOFs were firstly prepared by a cetyltrimethyl ammonium bromide?CTAB?assisted solvothermal method and then calcined in air at 500°C.After pyrolysis of precursor MOFs,the anatase TiO₂inherited the porosity of precursor and processed a large surface area and uniform pore distribution,which was then utilized as an electrorheological?ER?material by dispersing in silicone oil.The ER activities of MOF and porous TiO₂ based suspensions under applied electric fields were investigated in a controlled shear rate?CSR?mode.In contrast of MOFs based ER fluid,the suspension of porous TiO₂exhibited a higher ER efficiency and lower leakage current.Furthermore,the improvement of dielectric properties was found to be responsible for the enhanced ER effect through the investigation of dielectric spectrum.?4?Flower-like TiO₂@MoS₂ nanocomposite with a hierarchical and core@shell structure was synthesized using a two-step hydrothermal method,in which the flower-like Ti-containing precursor backbone was initially prepared to provide a large surface to enable the MoS₂ sheets to coat on TiO₂ uniformly.The glucose and acetate ion were found to play a crucial role in the formation of the intimate interface between TiO₂ and MoS₂.The hierarchical composite was dispersed in silicone oil as ER fluids,which exhibited a high ER efficiency by combining the advantages of TiO₂hierarchical structures and suitable conductivity of MoS₂ sheets.The high polarization strength and suitable dielectric relaxation of ER fluid was obtained under electric fields,which leaded to the improvement of interfacial polarization and ER activity.