Direct differentiation of the types of polarization responsible for the electrorheological effect by a dielectric method

Debye polarization, ionic displacement polarization, and Maxwell-Wagner (in terfacial) polarization are discussed in this paper, because they would mos t likely take place in an electrorheological (ER) suspension. The temperatu re dependences of the dielectric loss tangent maximums governed by these th ree types of polarization are theoretically found to be quite different. Gi ven this fact, a method that can directly distinguish the polarization type and clarify which polarization would be mainly responsible for the ER effe ct is proposed. Two kinds of typical ER suspensions, heterogeneous particle type and homogeneous liquid crystalline polymer type, are studied using ou r method. It is found that Maxwell-Wagner polarization would be responsible for the ER effect both in a heterogeneous and in a homogeneous ER system. These findings present direct experimental evidence for the previous assump tion that the Maxwell-Wagner polarization would dominate in the heterogeneo us ER system and also shed light on the ER mechanism in a liquid crystallin e polymer-type ER system. (C) 2001 Academic Press.