Xuezhao Wang

TIO2 BASED ELECTRORHEOLOGICAL FLUID WITH HIGH YIELD STRESS

We have fabricated several TiO2 based ER fluids with doping and without designed doping, which exhibit the high yield stress up to more than 100kPa. The titanium oxide nanoparticles were synthesized by using wet chemical method. The ER effect of those materials is dominated by the special additives, such as amide or its ramification, as well as the remained molecules or ions in the sample preparation. It is found that the yield stress is also strongly dependent on the viscosity of the oil. The prepared ER fluids possess other attractive characters, for instance the current density is low and against sedimentation.

The electrorheological fluids with high shear stress

A series of high performance ER fluids newly manufactured in our laboratory are presented. The yield stress of those ER fluids can reach several tens of kPa, 100 kPa and even 200 kPa, respectively. For understanding the high shear stress effect a model is proposed base on the electric field induced molecular bounding effect. The main effective factors in fabricating the high performance ER are discussed.

HIGH PERFORMANCE CALCIUM TITANATE NANOPARTICLE ER FLUIDS

A type of calcium titanate (CTO) nanoparticles was synthesized by means of wet chemical method [1] without coating on the particles. The CTO/silicone oil ER fluid exhibits excellent electrorheological properties: high shear stress (~50-100 kPa) under dc electric field, a low current density (less than 2μA/cm2 at 5kV/mm), and long term stability against sedimentation. Although there are not special additives in the ER fluids, it is found from the chemical analysis that a trace of alkyl group, hydroxyl group, carbonyl group and some ions is remained in the particles which may dominate the ER response.

The synthesis and electrorheological effect of a strontium titanyl oxalate suspension

Strontium titanyl oxalate (STO) particles were synthesized with the co-precipitation method. Suspensions made by dispersing the STO particles in silicone oil exhibit an excellent electrorheological (ER) effect with high yield stress, high shear stress at higher shear rate, and low current density. By analyzing the Fourier transform infrared spectra of STO particles heated at different temperatures and measuring the yield stresses of the corresponding ER fluids, it is confirmed that the polar molecules absorbed on the particles play a crucial role in the giant ER effect. The phenomena observed in STO ER fluids can be explained by using the model of a polar molecule dominated electrorheological (PM-ER) effect.

Polar molecule type electrorheological fluids

The static and dynamic shear stress of newly developed electrorheological (ER) fluids can reach more than 100 kPa and over 60 kPa at 3 kV/mm, respectively. The high yield stress of those ER fluids and its near linear dependence on the electric field are different from the conventional ER fluids and can not be explained with traditional dielectric theory. Experiment demonstrates that the polar molecules adsorbed on the particles play crucial role in those ER fluids, which can be named as polar molecule type electrorheological (PM-ER) fluids. To explain PM-ER effect a model is proposed based on the interaction of polar molecule-charge in between the particles, where the local electric field is much higher than the external one and can cause the polar molecules aligning. The main effective factors for achieving high-performance PM-ER fluids are discussed.

The methods for measuring shear stress of polar molecule dominated electrorheological fluids

Recently, a series of electrorheological (ER) fluids with high yield stress up to hundreds of kilopascals, which is named as polar molecule dominated electrorheological (PM-ER) fluids, has been developed. The mechanism of PM-ER fluids is quite different from that of conventional ER fluids. The normal rheometer cannot be used anymore to measure the shear stress of PM-ER fluid because a slide occurs at the interface between PM-ER fluids and metallic electrodes. In this paper, a proper technique for measuring the yield stress of PM-ER fluids is presented. By using this method, the intrinsic yield stress and the shear modulus of PM-ER fluids can be obtained conveniently, and the boundary effect at electrodes can be eliminated.

The methods for measuring shear stress of polar molecule dominated ER fluids

A series of ER fluids materials with high shear stress have been developed recently, which named as polar molecule dominated electrorheological (PM-ER) fluids. Difficulties have been met in shear stress measurement process due to the slide of PM-ER fluids on the surface of metallic electrodes. In this paper, two shearing configurations have been developed to remove the interface effect. The intrinsic shear stress of ER fluids can be obtained by using the devices.

POLAR-MOLECULE-DOMINATED ELECTRORHEOLOGICAL (PM-ER) FLUIDS: THE PROPERTIES AND EVALUATIONS

In recent years, a new type ER fluids named as polar-molecule-dominated electrorheological (PM-ER) fluids have been developed, of which the yield stress can reach more than 100 kPa and behaves a linear dependence on the electric field. A brief description on the composition and synthesizing method for the materials is given. The main merits of PM-ER fluid are as follows: high yield stress, the shear stress increasing with shear rate up to more than 103s-1, low current density, rapid electric response and anti-sedimentation. Some perspectives on PM-ER fluid and its applications are presented.

ELECTRIC FIELD-INDUCED INTERACTION FORCE BETWEEN TWO SPHERES

An apparatus is developed to study field-induced forces between two spheres. The mutual forces of a couple of identical spheres made of different materials in various media have been measured precisely as the function of inter-spherical spacing, field strength and field frequency. The respective dependences of the forces on inter-spherical spacing, field strength, field frequency and sphere size are obtained. By comparing the measured results with available theoretical calculations we conclude that a further improvement on the theoretical model should be carried out for explaining the most experimental results when the particle nearly contact.