A phosphonic acid is used as a surface initiator for the growth of polystyrene and polymethylmethacrylate (PMMA) from barium titanate (BTO) nanoparticles through atom transfer radical polymerization with activators regenerated by electron transfer. This results in the barium titanate cores embedded in the grafted polymer. The one-component system, PMMA-grafted-BTO, achieves a maximum extractable energy density of 2 J/cm(3) at a field strength of ∼220 V/μm, which exhibits a 2-fold increase compared to that of the composite without covalent attachment or the neat polymer. Such materials have potential applications in hybrid capacitors due to the high permittivity of the nanoparticles and the high breakdown strength, mechanical flexibility, and ease of processability due to the organic polymer. The synthesis, processing, characterization, and testing of the materials in capacitors are discussed.
Polymer materials with large dielectric constants are desirable for the development of high energy density capacitors. We show that the dielectric properties of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] can be improved by the use of processing conditions that favor formation of a highly crystalline morphology of the nonpolar α-phase. Through the use of spin coating, thermal treatment above the melting temperature, and quenching, we were able to attain a highly crystalline, α-phase rich morphology that has a quite large dielectric constant of 77 ± 10 at 1 kHz. The final morphology and phase composition of the terpolymer films depend strongly on the postprocessing thermal treatment and the quality of the solvent. Evaluation of the polarization behavior of the terpolymer films as a function of electric field reveal that the polymer exhibits a relaxor-ferroelectric behavior and has a substantial energy density of 9.7 J/cm(3) at fields of up to approximately 470 V/μm. Under millisecond pulsed charge-discharge measurements a 3-fold increase in energy density (27 J/cm(3)) is obtained at high fields (∼600 V/μm). Our study demonstrates that the processing conditions and morphology of fluorinated terpolymer films are controlling factors for achievement of high dielectric permittivity and energy density that are critical for high performance capacitors.
Abstract:We report the preparation of lignin-based rigid polyurethane (RPU) foams from surface functionalized kraft lignin via a simple and environmentally benign process. Lignin was functionalized with polyisocyanate at 80 • C for 1 h, the resulting lignin-polyisocyanate prepolymer was confirmed by increased viscosity and Fourier-transform infrared spectroscopy (FTIR). The RPU foams containing up to 30% surface functionalized lignin as a substitute for petroleum-based polyols exhibited comparable thermal and mechanical properties to conventional RPU foams. The lignin-based RPU foams prepared from surface functionalization outperformed RPU foams without the surface functionalization, showing up to 47% and 45% higher specific compressive strength and modulus, respectively, with a 40% lignin substitution ratio. Thermal insulation and temperature-stability of the two types of the foams were comparable. The results indicate that the surface functionalization of lignin increases reactivity and homogeneity of the lignin as a building block in RPU foams. The life cycle assessment for the lignin-based RPU foams shows that the surface functionalization process would have overall lesser environmental impacts when compared with the traditional manufacturing of RPU foams with synthetic polyols. These findings suggest the potential use of surface functionalized lignin as a sustainable core material replacement for synthetic polyols in building materials.
materials are largely characterized by increasing relative permittivity, [5][6][7][8] and breakdown strength, [9][10][11][12] pursued primarily by incorporating highk nanosize-fi llers into a normal or a relaxor ferroelectric polymer matrix. Recently, greater attention has been given to the improvement of energy extraction efficiency by modifying the crystalline phase and cross-linking of polymers, [13][14][15] particularly transforming normal ferroelectric polymers into relaxor ferroelectrics that feature narrow polarization hysteresis and decreased loss upon discharge. [ 16,17 ] Hybrid sol-gels, a relatively new class of materials for dielectric energy storage, have also shown potential for high-energy dielectrics with the covalent incorporation of dipolar moieties capable of reorientational polarization in the sol-gel matrix. [ 18,19 ] In particular, silica-based hybrid sol-gels bearing compact cyanoethyl groups that can undergo orientational polarization under electric fi elds have exhibited a relative permittivity of ≈20 and an energy storage density of 7 J cm −3 with an energy extraction effi ciency of 90% at ≈300 V µm −1 . [ 3 ] Although high extraction effi ciency was achieved at moderate fi eld strength due to a linear-like polarization response, charge carrier injection and associated electrical conduction substantially compromised the energy-storage capability of this sol-gel material for fi eld values above 300 V µm −1 . Here, we present an all-solution-processed hybrid sol-gel bilayer capacitors based on 2-cyanoethyltrimethoxysilane (CNETMS) in which an n-alkylphosphonic acid (PA-SAM) is formed between the sol-gel fi lm and the metal electrode. The PA-SAM is incorporated to serve as a charge-blocking layer, to suppress carrier injection from an aluminum metal electrode into the sol-gel fi lm and mitigate associated electrical conduction in sol-gel fi lms at high electric fi elds. The CNETMS/PA-SAM bilayer structure shows outstanding improvements in electrical failure reliability, energy extraction effi ciency, and energy storage density, as compared with previously reported capacitor devices. [ 4,20 ] An illustration of the CNETMS/PA-SAM bilayer device structure employed in this work is shown in Figure 1 a. PA-SAMs with varying length of the alkyl chains (propyl: PPA, octyl: OPA, and octadecyl: ODPA) were self-assembled on top of CNETMS sol-gel fi lms. As a representative example, the chemical structure of n -octylphosphonic acid is shown in Figure 1 b. PA-SAMs were chosen because of: (1) the facile chemisorption of the phosphonic acid group on metal oxide surfaces, [ 21,22 ] (2) the simple deposition process for the formation of an SAM via dipping of the sol-gel fi lm into the solution of PA, and (3) the utilization of a densely packed SAM as a charge-blocking layer, [23][24][25] providing a potential energy barrier at the metal-dielectric junction. The PA-SAMs on the CNETMS sol-gel fi lms were The development of effi cient, high-performance materials for electrical energy storage is essential to me...
Sustainable textile dyeing technology using nanofibrillated cellulose is developed that would significantly reduce wastewater and potential environmental costs.
Hybrid organic-inorganic sol-gel dielectric thin films from a neat 2-cyanoethyltrimethoxysilane (CNETMS) precursor have been fabricated and their permittivity, dielectric strength, and energy density characterized. CNETMS sol-gel films possess compact, polar cyanoethyl groups and exhibit a relative permittivity of 20 at 1 kHz and breakdown strengths ranging from 650 V/μm to 250 V/μm for film thicknesses of 1.3 to 3.5 μm. Capacitors based on CNETMS films exhibit extractable energy densities of 7 J/cm(3) at 300 V/μm, as determined by charge-discharge and polarization-electric field measurements, as well as an energy extraction efficiency of ~91%. The large extractable energy resulting from the linear dielectric polarization behavior suggests that CNETMS films are promising sol-gel materials for pulsed power applications.
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