Suspensions of Hollow Polydivinylbenzene Nanoparticles Decorated with Fe3O4 Nanoparticles as Magnetorheological Fluids for Microfluidics Applications

Hollow polydivinylbenzene@Fe3O4 (h-PDVB@Fe3O4) nanoparticles with a relatively narrow size distribution were prepared by depositing Fe3O4 nanoparticles on h-PDVB. Because of the cavity in the hollow structure, the density of h-PDVB@Fe3O4 (rho = 1.83 g/cm(3)) was significantly reduced from that of Fe3O4 (4.52 g/cm(3)). Deposition of Fe3O4 particles of 10-20 nm size (average particle size similar or equal to 14.3 +/- 2.5 nm) on the h-PDVB made the h-PDVB@ Fe3O4 particle surface quite rough while preserving the spherical shape. The MR suspensions were prepared by dispersing h-PDVB@Fe3O4 in silicone oil medium, and their magnetorheological properties were investigated. The dynamic modulus and the yield stress under magnetic field decreased compared to those of pure Fe3O4 suspension, but the MR behavior of h-PDVB @ Fe3O4 suspension was well preserved. Interestingly, contrasting MR performance of two suspensions (h-PDVB@Fe3O4 (Fe3O4 nanoparticle size L-214.3 +/- 2.5 nm) and foamed PS/Fe3O4 (Fe3O4 nanoparticle size similar or equal to 50-100 nm)) with similar densities was observed at high and low magnetic field strength regions due to the particle size difference. The long-term sedimentation stability of the suspensions was investigated with a Turbiscan apparatus. Because of reduced density mismatch between particles and silicon oil medium, the h-PDVB@Fe3O4 suspension exhibited a significantly improved stability compared to that of the pure Fe3O4 suspension, with only 13% of light transmission after 24 h. The MR performance and enhanced longterm sedimentation stability represent a viable application of h-PDVB@Fe3O4 suspensions to microfluidic devices.