The conductive, dielectric, and surface properties of several water-free polymer or inorganic material based ER fluids, as well as their response times, are investigated to elucidate the physical ground of the electrorheological (ER) effect. It is found that the slow polarization, especially the interfacial polarization rather than the Debye polarization, might be responsible for the observed phenomena. A possible ER mechanism is proposed as follows: a large interfacial polarization would facilitate the particle to attain a large amount of charges on the surface, then leading to the turn of particle along the direction of an electric field to form a fibrillation structure; the strength of fibrillation chains is thus determined by the particle polarization force, i.e., the particle dielectric constant. The rationality that the marked interfacial polarization would likely drive the particles to turn is theoretically addressed on the basis of experimental results.

No abstract

The effect of the dielectric properties of electrorheological fluids on electrorheology was investigated in DC electric fields by using both hydrous and anhydrous electrorheological fluids. The relaxation frequency, which is defined by a local maximum of the dielectric loss factor of an electrorheological fluid, was in the range from 100- whenever the electrorheological fluid had a large electrorheological effect. This effect increased with increasing difference between the dielectric constants below and above the relaxation frequency both for hydrous and anhydrous electrorheological fluids, when the relaxation frequency was in the range 100-. For the electrorheological fluid containing microcrystalline cellulose, the change of the rheology curve, namely the shear rate versus shear stress ( versus ) curve, with increasing adsorbed water content could be interpreted in terms of the relation between the shear rate and the polarization rate. The mechanism of electrorheology could also explain the effect of the current density on the ER effect.

Information on the solubility of OH-carbonated hydroxyapatite, Ca10(PO4)6(CO3)x(OH)2-2x, previously has not been available. In the present study the solubility product (Ksp) of OH-carbonated hydroxyapatite was measured in a 0.1 M acetic acid and sodium acetate buffer solution in a pH range of 4.0-5.8 at a CO2 partial pressure of 10(-3.52) atm. The equilibrium solubility increased with the increase of carbonate content. The Ksp values decreased with the decrease of pH. For example, Ksps were 10(-119), 10(-123), and 10(-130) for pure hydroxyapatite at pH 4.9, 4.5, and 4.1, respectively. The decrease of Ksp was not accounted for by calcium-carbonate complexation. Ksp measured at isoelectric points (L) was expressed as pL = 118.65 - 0.47316 x (CO2 wt%)2.4176. From this formula, the L values were calculated for pure and fully carbonated hydroxyapatite as 10(-118.7) and 10(102.8), respectively. The L value for pure hydroxyapatite agreed with values measured under carbonate-free conditions. Therefore, the L values were regarded as the Ksp for OH-carbonated hydroxyapatite excluding errors arising from carbonate contamination in the solution.