Cluster synthesis of monodisperse rutile-TiO2 nanoparticlesand dielectric TiO2–vinylidene fluoride oligomer nanocomposites

Abstract

The embedding of oxide nanoparticles in polymer matrices produces a greatly enhanceddielectric response by combining the high dielectric strength and low loss of suitable hostpolymers with the high electric polarizability of nanoparticles. The fabrication ofoxide–polymer nanocomposites with well-controlled distributions of nanoparticles is,however, challenging due to the thermodynamic and kinetic barriers betweenthe polymer matrix and nanoparticle fillers. In the present study, monodisperseTiO2 nanoparticles having an average particle size of 14.4 nm and predominant rutile phase wereproduced using a cluster-deposition technique without high-temperature thermalannealing and subsequently coated with uniform vinylidene fluoride oligomer(VDFO) molecules using a thermal evaporation source, prior to deposition asTiO2–VDFO nanocomposite films on suitable substrates. The molecular coatings onTiO2 nanoparticles serve two purposes, namely to prevent theTiO2 nanoparticles from contacting each other and to couple the nanoparticlepolarization to the matrix. Parallel-plate capacitors made ofTiO2–VDFO nanocomposite film as the dielectric exhibit minimum dielectric dispersion and lowdielectric loss. Dielectric measurements also show an enhanced effective dielectric constant inTiO2–VDFO nanocomposites as compared to that of pure VDFO. This study demonstrates forthe first time a unique electroactive particle coating in the form of a ferroelectric VDFOthat has high-temperature stability as compared to conventionally used polymers forfabricating dielectric oxide–polymer nanocomposites.