Electrorheological Operation of Low-/High-Permittivity Core/Shell SiO2/Au Nanoparticle Microspheres for Display Media

Abstract

In this study, we synthesized core/shell structures comprising monodisperse 3-mu m SiO2 microspheres and gold nanoparticles (AuNPs, ca. 6.7 nm) as the core and shell components, respectively. Using a layer-by-layer cross-linking process with a dithiol cross-linking agent, we prepared low-permittivity AuNP-encapsulated higa-permittivity SiO2 core/shell microspheres with variable AuNP shell thicknesses. The dispersivity of the microspheres in solution was enhanced after grafting poly(ethylene glycol) monomethyl ether thiol (PEG-SH) onto the AuNP layer on the SiO2 microspheres. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images revealed sesame ball-like structures for these SiO2@AuNP@PEG microspheres. We encapsulated aqueous dispersions of these SiO2@AuNP microspheres into sandwich structured displays (SSDs) to investigate their electrorheological properties, observing reversibly electroresponsive transmittance that is ideally suited for display applications. Increasing the thickness of the AuNP layer dramatically enhanced the stringing behavior of the SiO2 microspheres, resulting in increased transmittance of the SSD. The response time of the electroresponsive electrorheological fluids also decreased significantly after modifying the SiO2 with the AuNP layers. The effective permittivities of these composites could be predicted from the real (epsilon) and imaginary (epsilon) parts of the Clausius-Mossotti formalism.