Electrohydrodynamic instabilities of polymer thin films: Filler effect

The influence of various nanoparticles with different dimension, density, dielectric constant, and surface property on electrohydrodynamic (EHD) instabilities of polymer/nanoparticle nanocomposite thin films was examined as a function of nanoparticle concentration. Transmission electron microscopy (TEM) images of polystyrene (PS)/nanoparticles (NPs) thin films demonstrated that all the nanoparticles were uniformly distributed in polymer matrix and the homogeneous dispersions of nanoparticles were not affected by thermal annealing above glass transition temperature. Optical microscopy (OM) observations indicated that thin films of polystyrene containing silica (SiO2), gold (Au), cadmium selenide (CdSe), and titania (TiO2) nanoparticles showed electrohydrodynamic instability patterns similar to those seen in pure polystyrene, up to 3 vol% nanoparticles. The presence of nanoparticles changed the dielectric constant of the thin films, which led to systematic variations in the wavelengths of the surface instabilities, which were consistent with calculated values. Cross-sectional transmission electron microscopy (TEM) images showed that migration or aggregation of the nanoparticles occurred only for silica contrary to other nanoparticles. This work points to a simple route to reduce the scale of final well-ordered columnar structures.