Fabrication of Polyaniline Coated Snowman-like Pmma Microparticle and Its Electrorheology

Monodisperse anisotropic particles have tremendous potentials in materials science and engineering (Hosein et al., 2010). As one of this kind of materials, snowman-like particles have drawn a special attention in the aspects of both their synthesis mechanism and applications. In this study, we synthesized micron-sized snowman-like poly(methyl methacrylate) (PMMA) particles via a seed emulsion polymerization method, in which the cross-linked PMMA seed was swollen by methyl methacrylate monomer solutions and then polymerized. To induce semiconducting properties to the particles, they were coated with polyaniline (PANI) similar to core/shell structured PANI/PMMA microbead (Cho et al., 2003). The morphologies of the PMMA seeds, snowman like particles with and without coating are shown in Fig. 1. When the semiconducting anisotropic particles are dispersed in silicone oil, they exhibit electrorheological (ER) properties of yield stress and dramatically increased shear viscosity under an electric field (Choi & Jhon, 2009, Zhao & Yin, 2002). This ER behaviour is said to stem from the polarization of the particles, resulting in the structural change (Zhang et al, 2010). We analyzed these anisotropic particle based ER fluid using a rheometer. A flow curve of shear stress vs. shear rate was fitted using a rheological equation of state as shown in Fig. 2. The dielectric spectra, as supporting data for the ER effect, were also measured using a LCR meter. It was further found that the relaxation time of this ER fluid was relatively shorter than typical ER fluid, explaining their relation to the ER characteristics (Liu et al., 2010, Liu et al., 2011). The novelty of this work is noted that compared to our previous work of core-shell structured PANI/PMMA microbeads, snowman-like microparticles in this study exhibit a very short polarization relaxation time in dielectric analysis which induce faster chain formation due to its anisotropic shape.