Abstract
Abstract
Electrorheological fluids (ERFs) are materials with high potential for many electromechanical devices thanks to their ability to couple electronics with mechanical components rapidly. However, employment in such devices demands compliance with several fundamental requirements, such as high static yield stresses, low off-field viscosities, fast response times, and reversible behavior when the electric field is switched on and off. In this paper, a series of six simple electrorheological tests are suggested as guidelines to determine the main performance parameters of ERFs with the aim of enhancing their design and characterization. Tests for the measurement of static and dynamic yield stresses, as well as for the evaluation of the response times and reversibility after switching the electric field on and off (at constant shear stress), are proposed. In addition, relevant parameters such as the minimum shear stress required to maintain fluid flow under a given electric field (“hold stress”), or the maximum electric field at which the fluid can still be maintained in motion at a fixed shear stress (“hold field”), can be determined. Silicone oil-based suspensions of synthesized calcium titanyl oxalate (CTO) powders were selected as test suspensions. In this regard, the present study also highlighted how differences in the physicochemical properties of CTO powders can strongly affect the electrorheological behavior, pointing out the need to identify and better control the key parameters governing the synthesis of the powders. An empirical relationship between the yield stresses and the physical properties of the powders (size and specific surface area) is proposed.