High-dielectric-constant self-assembled nodular structures in polymer/gold nanoparticle films

We utilize spin-casting and ultraviolet (UV) light-induced polymerization to make organic-inorganic nanocomposite thin films. The initial mixture consists of polycaprolactone (PCL) stabilized gold nanoparticles, reactive monomer alkoxytitanium triacrylate, and photoinitiator benzophenone, dissolved in n-butyl acetate (BuAc) solvent. Upon spin-casting and under UV light, solvent evaporates and triacrylate monomer undergoes polymerization, forming a hybrid film exhibiting complex morphologies on several length scales. In particular, we observe a controlled core-shell microdomain assembly of metal nanoparticles, compatibilizer, and metal-infused photo-cross-linkable acrylate polymer host. The composite film also exhibits high electrical capacitance due to the large effective dielectric constant of the metal nanoparticle-rich nodules. We characterize the morphology of the film using both polarized light optical, transmission electron (TEM), and atomic force (AFM) microscopy and propose a theoretical model explaining the formation of macro- and microphase-separated structures. Our results demonstrate a route to engage molecular self-assembly in an organometallic hybrid composite which achieves unexpected and unusual material properties that could be used in the electronics industry.