R&D Profile: Assemblies of hybrid nanoparticles for energy storage applications - Air Force Research Laboratory, WPAFB, OH, USA
Scientists at the Air Force Research Laboratory are going beyond traditional polymeric composites, creating dielectric materials by direct assembly of the core-shell hybrid nanoparticles.
R&D Profile Courtesy of: Maxim N. Tchoul, Scott P. Fillery, Hilmar Koerner, Lawrence F. Drummy, Folusho T. Oyerokun, Peter A. Mirau, Michael F. Durstock, and Richard A. Vaia, Materials and Manufacturing Directorate, Air Force Research Laboratory, WPAFB, OH, USA
Future electronically-intensive technologies need novel solutions for on-demand, rapid power storage and delivery, including ultra-high energy density capacitors. One nanomaterial concept with promise to address the myriad of processing-performance challenges underlying these power technologies is single-component hybrid nanoparticles. Consisting of a high dielectric constant core, such as titanium dioxide (TiO2) or barium titanate (BaTiO3), the single-component hybrid nanoparticles are formed by grafting polystyrene to the nanoparticle surface via a combination of phosphate coupling and “click” chemistry.
Despite the high inorganic loading (60 % by weight for TiO2, or 27% by vol.), judicious design of the polymeric corona results in a neat (i.e. absence of matrix) hybrid nanoparticle assembly that exhibits physical properties typical of a thermoplastic polymer (Fig A). The material exhibits a glass transition at 110 oC, softens upon heating and undergoes drawing into a fiber, indicating prospective large scale processing by sheet extrusion or compression molding. Additionally, the material maintains solubility and can form films via solution casting.
Electron microscopy and X-Ray scattering have confirmed the highly uniform distribution of nanoparticles within the material, which is consistent with the excellent optical transparency [Figure A]. Dielectric spectroscopy of 100 nm spin-coated films of a TiO2(27 vol%)-polystyrene hybrid material have a dielectric constant of 12 at 1 kHz [Figure B]. Synthesis of hybrid nanoparticles with a BaTiO3 core along with detailed dielectric breakdown studies are currently underway with the expectation to obtain materials with even larger dielectric storage characteristics.
Potential application of these materials for capacitors has been demonstrated. Through continually fundamental studies, the Air Force Research Laboratory’s scientists hope to establish the criteria relating the structure of the polymeric corona to the processability and dielectric characteristics of the hybrid nanoparticle assembly.
Figure A. The 2 mm thick film of TiO2-polystyrene assembly of hybrid nanoparticles containing 60 % of TiO2 by weight (left), and the fibers produced by drawing this film over the hot surface (right)
Figure A. Dielectric spectroscopy of the 100 nm thick film of the TiO2-polystyrene, 60% TiO2 by weight.
