抄録
In this work a fundamental investigation is performed on the subject of colloidal dampers rendered controllable under electric and magnetic fields. In order to adjust the damping and elastic characteristics of a colloidal damper, the pressurization level inside the cylinder can be dynamically changed by using a pressure controlling device. Correlation between the desired change of damping ratio and the necessary pressure fluctuation is firstly clarified. Then, one evaluates if such task can be accomplished by adjusting the capillary pressure through a surface tension controlling device, to control the surface tension of the working liquid under electric and magnetic fields. Theoretical model is based on the Laplace-Washburn equation for capillary pressure, on the Young's equation for contact angle, and on the Neumann's relationship between the solid, liquid, and solid-liquid surface tensions. Semi-empirical equations to take into account the influence of electromagnetic field on the liquid surface tension were obtained based on several wetting experiments. Thus, using micro- pipettes, liquid drops of pure water and water based ferrofluid, with the volume in the range of 0.1-100 μL, were deposed on an acrylic plate inside the uniform electric field created between the plates of a condenser of variable capacitance, or inside the uniform magnetic field created between the disks of an electromagnet of variable intensity. Following main conclusions were inferred from the results obtained: 1) under a fluctuation of 266 % (-102 %) for the dynamic advancing (receding) pressure, a controllable colloidal damper with practical applications can be achieved; 2) in order to obtain such fluctuation for the advancing (receding) pressure, it is necessary to produce a fluctuation of 88 % (-12.5 %) for the water's surface tension; 3) desired change for the liquid surface tension can be achieved under electric or magnetic fields, if the applied voltage is at least of 8.6kV (for water), or the applied magnetic flux density is at least of 31.5mT (for MSG W10).
