POLYMER NANO-DIELECTRICS FOR HIGH DENSITY ENERGY STORAGE

Military and commercial users require next-generation polymer dielectric materials for pulse power and power conditioning applications with rise times less than 1 ms and AC power at frequencies ranging from kHz to MHz. These power density and rate capability requirements necessitate the use of dielectric capacitors that store energy via polarization of electrons in molecular scale dipoles. Multiphase polymer composites and all-polymer dielectrics could be new kinds of materials to meet this acute need for capacitors with compact size and high rate capability. The polymer nanocomposite (PNC) approach to achieve high energy density employed a “colossal” dielectric constant material, calcium copper titanate, CaCu3Ti4O12 (CCTO) as filler, and high dielectric breakdown strength and low loss polycarbonate (PC) as the polymer matrix. This work systematically analyzes CCTO/PC composites, starting with low field dielectric properties (dielectric constant, dielectric loss) and extending to (for the first time) high field D-E polarization behavior. Our findings suggest that CCTO/PC composites are promising for applications requiring high dielectric constant at low field strength, but not as dielectrics for high density, pulse power energy storage. “Multiphase all-polymer dielectric” materials is a novel approach to meet the high rate capability demand in dielectric capacitors. Our chemistry collaborators synthesized variety of new homopolymers and copolymers that are hypothesized to form phase-separated, interfacially-dominated structures capable of storing energy through electronic conduction and interfacial polarization. The polymer architecture features a combination of conducting and insulating segments hypothesized to form phase-segregated domains with high electronic conductivity, surrounded by insulating domains that prevent percolation and inter-domain conduction. It is hoped that this method will circumvent shortcomings in existing polymeric dielectric materials for high density energy storage applications. The main result is a terthiophene-containing (PTTEMA) polymer that can store energy density up to 1.54 J/cm3, higher than commercially available biaxially oriented polypropylene (BOPP) at 200 MV/m applied electric field. In addition, different approaches, such as PTTEMA grafted onto barium titanate/PTTEMA composites and PTTEMA/PS polymer blends, have been employed to optimize PTTEMA polymers to make them suitable for pulse power applications. Finally, COMSOLTM simulations were used to understand how polymer composites microstructure affects material polarization

Graphene field effect transistors for highly sensitive and selective detection of K+ ions

Graphene-based ion sensitive field effect transistors (GISFETs) with high sensitivity and selectivity for K+ ion detection have been demonstrated utilizing valinomycin based ion selective membrane. The performance of the GISFETs for K+ ion detection was studied in various media over a concentration range of 1 μM–2 mM. The sensitivity of the sensor was found to be \u3e60 mV/decade, which is comparable to the best Si-based commercial ISFETs, with negligible interference found from Na+ and Ca2+ ions in high concentration. The sensor performance did not change significantly in Tris–HCl solution or with repeated testing over a period of two months highlighting its reliability and effectiveness for physiological monitoring. The performance of the sensor also remained unchanged when fabricated on biocompatible polyethylene terephthalate (PET) substrate, showing significant potential for developing flexible bio-implantable graphene-based ISFETs

Terthiophene-Containing Copolymers and Homopolymer Blends as High-Performance Dielectric Materials

This work explores the dielectric and polarization properties of block copolymers and homopolymer blends containing a terthiophene-rich, electronically polarized block (PTTEMA) and an insulating polystyrene block (PS). PTTEMA-<i>b</i>-PS block copolymers were synthesized by reverse addition–fragmentation chain transfer (RAFT) polymerization, and PTTEMA/PS homopolymer blends with the same PTTEMA weight percentages were produced by solution blending. DSC and XRD characterization show that crystallinity increases with PTTEMA content, indicating the presence of terthiophene-rich crystalline domains. Under an applied electric field, these domains are electronically polarized, but the insulating PS block inhibits current leakage, resulting in enhanced dielectric properties. Impedance measurements show that relative permittivity increases with PTTEMA content. The permittivity values are higher in PTTEMA-<i>b</i>-PS copolymers with moderate PTTEMA content due to the ability of the PS block to inhibit PTTEMA association, resulting in a higher density of isolated, terthiophene-rich polarizable domains. Freestanding PTTEMA/PS blend films containing up to 40 wt % PTTEMA have almost 40% greater recoverable energy density compared to pure PS films polarized to the same electric field strength

Bimodal Polymer Brush Core–Shell Barium Titanate Nanoparticles: A Strategy for High-Permittivity Polymer Nanocomposites

This paper presents a novel strategy to modify the surface chemistry of barium titanate (BaTiO₃, BT) with a bimodal population of oligothiophene polymer brushes using step-by-step reversible addition–fragmentation chain transfer (RAFT) polymerization. Compared with a previous strategy based on monomodal surface-tethered brushes, these hybrid nanoparticles, BaTiO₃ coated with bimodal oligothiophene polymer brushes, demonstrate extremely good dispersion behaviors as dielectric nanofillers in a matrix of oligothiophene polymers. These nanodielectric composites exhibit greatly improved dielectric performance and maintain linear displacement–polarization (<i>D</i>–<i>E</i>) profiles under high applied electric fields. This promising bimodal strategy could be generalized to a variety of nanoparticles for the development of novel dielectric nanocomposite systems