7 research outputs found
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 (BaTiO<sub>3</sub>, 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,
BaTiO<sub>3</sub> 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