| 초록 |
Electrorheological (ER) fluids are generally colloidal suspensions whose rheological properties depend strongly and reversibly on applied electric fields. The ER behaviors are attributed to the structural change of the dispersed particles, consequently increasing or decreasing the apparent viscosity of the fluids. In most cases, it is a common practice that particles of the same size purposely selected for use in ER fluids. Therefore, multi-dispersity in particle size is avoided partly due to factors whose effects are not well understood. In this study, monodisperse poly(styrene-co-acrylonitrile)(SAN) microspheres were prepared by two-step seeded polymerization method, and their electrorheological characterizations were performed. Because SAN microspheres alone cannot give enhanced ER property, ER fluids were obtained by hydrolysis of cyano groups of primary non-hydrolyzed SAN particles. In addition, in order to investigate the effect of bimodal size distribution on ER behavior, ER suspensions of hydrolyzed SAN particles with three different sizes (5, 10, 15㎛) were used. Bi-dispersed ER fluids were prepared by mixing the different two particles at various volume fractions. The bi-dispersed ER fluids showed drastic enhancement peaks of the dynamic yield stress at a certain small particle/large particle ratio for fixed solid/liquid volume fractions.
|
