On the impact of functionalization and thermal treatment on dielectric behavior of low content TiO2 PVDF nanocomposites (original) (raw)
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Owing to the high surface to volume ratio of nanoparticles, nanoparticle-modified polymers promise to exhibit properties exceeding bounds predicted by effective media approaches, where the effective response is not solely dependent on inherent nanoparticle properties but rather dominated by nature and volume content of interface. This study is focused on 1) investigating impact of surface treatment and thermal processing of nanoTiO2-modified-PVDF on dielectric and mechanical properties of resulting nanocomposites, and 2) highlighting a unique dielectric behavior of nanoparticle-reinforced polymers where an initial increase in dielectric permittivity is seen at very low content followed by a decrease resulting from nanoparticle-polymer interaction. X-Ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared spectroscopy (FT-IR) confirm efficient particle surface modification by showing the presence of atoms from coupling agent molecules on the particle's surface. Scanning Electron Microscopy (SEM) of TiO2/PVDF nanocomposites verifies that surface porosity was removed by a post annealing process. Dynamic Mechanical Analysis (DMA) results demonstrate an increase in storage modulus in the glassy region from 67 to 108% as compared to the pristine PVDF for TiO2 contents varying from 5 to 20 wt% (2.3 to 10 vol%) as a result of adding functionalization and thermal treatment. Based on Dielectric Spectroscopy measurements, a 74% increase in permittivity is observed at 0.1 Hz and a 30% increase at 1 kHz, both at relatively low volume content (2.3 vol%), owing to the good dispersion, high interfacial volume content and strong interaction. A further increase of TiO2 content decreases the dielectric permittivity as a result of dipolar confinement. Contributions of the study are two-fold: firstly, compared to the current literature, this increase in the value of dielectric permittivity at such a low volume content using TiO2 nanoparticles is unprecedented and has not been reported so far; and secondly, the study brings to light a unique nanodielectric behavior where the initial increase in permittivity is followed by a decrease owing to dipolar confinement resulting from particle/polymer interaction
Preparation of TiO2 Polymer Nanodielectrics via a Solvent-Based Technique
The effect of adding surface-functionally treated TiO 2 nanoparticles on dielectric properties of PVDF matrix was investigated. Porosity of the nanocomposite films showed to have an impact on dielectric permittivity results. Thermal annealing was proposed as an effective way to overcome the porosity problem. By combination of surface treatment of particles and thermal annealing of nanocomposite films, considerable enhancement in dielectric permittivity of TiO 2 -PVDF nanocomposites was achieved. The experimental results were far higher than theoretical values based on Maxwell model, indicating the presence of an active interphase with high dielectric constant in the system.
PREPARATION OF TIO2 POLYMER NANODIELECTRICS VIA A SOLVENT-BASED
The effect of adding surface-functionally treated TiO 2 nanoparticles on dielectric properties of PVDF matrix was investigated. Porosity of the nanocomposite films showed to have an impact on dielectric permittivity results. Thermal annealing was proposed as an effective way to overcome the porosity problem. By combination of surface treatment of particles and thermal annealing of nanocomposite films, considerable enhancement in dielectric permittivity of TiO 2 -PVDF nanocomposites was achieved. The experimental results were far higher than theoretical values based on Maxwell model, indicating the presence of an active interphase with high dielectric constant in the system.
Electrical energy storage plays a key role in mobile electronic devices, stationary power systems, and hybrid electric vehicles. There is a great need for development of new materials with superior electrical energy density since current ceramics and polymers fall significantly short of rising demands in advanced applications. The introduction of inorganic nanoparticles into polymer matrices to form dielectric polymer nanocomposites represents one of the most promising and exciting avenues to this end. This approach is motivated by the idea that the combination of ceramic materials of large permittivity with polymers of high breakdown strength could lead to a large energy storage capacity, as energy density is proportional to the product of permittivity and the square of the applied electric field. Moreover, large interfacial areas in the composites containing nanometer scale fillers promote the exchange coupling effect through a dipolar interface layer and result in higher polarization levels and dielectric responses. Compared to conventional ceramic materials, polymer-based dielectric materials also offer processing advantages including mechanical flexibility and the ability to be molded into intricate configurations for electronic and electric devices with reduced volume and weight. While most of the current studies on dielectric nanocomposites are focused on the enhancement of dielectric permittivity, few examples have investigated dielectric properties and associated energy densities at high electric fields. Ferroelectric metal oxides such as Pb(Zr,Ti)O 3 (PZT), Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMNT), and BaTiO 3 have been popular choices as filler materials in dielectric nanocomposites because of their high permittivities. However, from the energy storage point of view, inclusion of nanoparticles with permittivities on the order of hundreds and even thousands into polymers, which generally possess a permittivity less than 10, might not be desirable for an appreciable increase in energy density. As the filler has a much greater permittivity than the polymer matrix, most of the increase in effective dielectric permittivity comes though an increase in the average field in the polymer matrix with very little of the energy being stored in the high permittivity filler phase. Furthermore, the presence of a large contrast in permittivity between two phases gives rise to a highly inhomogeneous electric field and thus a significantly reduced effective breakdown strength of the composite. In this communication, we report high-energy-density polymer nanocomposites based on surface-functionalized TiO 2 nanocrystals as dopants in a ferroelectric poly(vinylidene fluoride-tertrifluoroethylene-ter-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)). In this approach, the polymer matrix and TiO 2 filler possess comparable dielectric permittivities of 42 and 47, respectively, measured using an inductance, capacitance, resistance (LCR) meter at room temperature and 1 kHz. High dielectric performance in the nanocomposites is realized via the large enhancement in polarization response at high electric fields and changes in polymer microstructure induced by the nanofillers.
Dielectric response and energy storage efficiency of low content TiO2-polymer matrix nanocomposites
Composites Part A: Applied Science and Manufacturing, 2015
TiO 2 /epoxy nanocomposites were prepared at different filler concentrations varying from 3 to 12 phr (parts per hundred resin per weight). The dispersion of TiO 2 was examined by Scanning Electron Microscopy and proved to be adequate. Differential Scanning Calorimetry was implemented to determine the glass to rubber transition temperature of the polymer matrix. The dielectric analysis was performed via Broadband Dielectric Spectroscopy in a wide frequency and temperature range. Five different mechanisms were observed in the spectra of the examined composites which are identified, in terms of increasing temperature at constant frequency, as c, b, Intermediate Dipolar Effect (IDE), a and Interfacial Polarization (IP) relaxation modes. The activation energies of all relaxation modes were calculated. Finally, the dielectric response of the TiO 2 nanocomposites compared to that of the TiO 2 microcomposites reveals that the former exhibit significantly higher energy storage efficiency even at lower TiO 2 concentration than the corresponding of the microcomposites.
Dielectric properties of polymer nanoparticle composites
Polymer, 2007
Well-dispersed high dielectric permittivity titanium dioxide (TiO 2 ) nanoparticles were synthesized utilizing a block copolymer as a template. The nanoparticles were confined within microphase separated domains of sulfonated styrene-b-(ethylene-ran-butylene)-b-styrene (S-SEBS) block copolymers. A crosslinker (vinyltrimethoxysilane) was incorporated into the block copolymer matrices in order to decrease the dielectric loss from the free sulfonic acid groups. Dynamic mechanical analysis experiments confirmed that nanoparticles and crosslinker were confined within the crosslinked sulfonated styrene blocks and had no effect on the chain relaxation behavior of [ethylene-ran-butylene] blocks. Dielectric experiments showed that higher permittivity composites can thus be obtained with a significant decrease in loss tan d (<0.01) when crosslinked with vinyltrimethoxysilane.
IEEE Transactions on Dielectrics and Electrical Insulation, 2017
The current study is to investigate the influence of inserting chemically modified titanium oxide (TiO2) nanoparticles on the dielectric and mechanical properties of the commercial compound Polyvinyl Chloride (PVC) used in insulating power cables. The surface modification of TiO2 nanoparticles was performed using vinyl silane coupling agent after activating their surfaces with methane-sulfonic acid. The PVC pellets were first dissolved using suitable solvent. Then, PVC/TiO2 nanocomposites, with different loadings of nanoparticles, were synthesized with the aid of ultra-sonication for better dispersion of nanoparticles. The morphology of the prepared nanocomposites was studied by field emission scanning electron microscopy (FE-SEM), and their mechanical properties were studied by performing tensile test at speed of 50 mm/min. The results showed that the insertion of functionalized nanoparticles is able to increase the tensile strength and the Young's modulus of the prepared samples, however it decreases their elongation. The dielectric properties, such as dielectric constant and dielectric loss, were also studied in a range of frequencies between 20 Hz and 1 MHz. Moreover, AC breakdown voltage of prepared samples was measured under uniform and semi-uniform field, and then, AC dielectric strength was evaluated using Finite Element Method (FEM) for semi-uniform field. For further evaluation, DC breakdown voltage was also measured under uniform field. PVC/TiO2 nanocomposites with functionalized TiO2 exhibited better dielectric properties compared to that with un-functionalized TiO2 or that of base PVC. This may be attributed to the low surface energy of the functionalized TiO2 nanoparticles that prevented the agglomeration of nanoparticles and restricted the mobility of polymeric chains.
Dielectric relaxation and AC conductivity of TiO2 nanofiller dispersed polymer nanocomposite
DAE SOLID STATE PHYSICS SYMPOSIUM 2018, 2019
The Lithium-ion conducting polymer nanocomposite (PNC) has been synthesized by the standard solution cast technique in the skeleton of PEO-PVC blend with a different content of Titanium oxide (TiO 2) as nanofiller. The lithium hexafluorophosphate (LiPF 6) was used as the salt. The dielectric strength decreases with frequency and is attributed to the dominance of the electrode polarization effect. The highest dielectric strength and lowest relaxation time (1.88 ns) were achieved for the 15 wt. % TiO 2 (PPS15T) PNCs when compared to other concentrations. The PPS15T exhibits the highest dc conductivity 2.34×10-5 S cm-1 at RT. The dielectric strength (Δɛ) and relaxation time () were in good agreement with the dc conductivity (). An interaction scheme has also been proposed to highlight the interactions between the polymer, salt and nanofiller in most visual manner.
Revue Roumaine de Chimie, 2021
In this study, a comparative study of nanocomposites with treated and untreated metal oxide nanoparticules using a plastograph was investigated. Stearic acid and co-mixing technique were chosen as a fast technique to ensure the dispersion of the filler into the polymeric matrix. Fillers were mechanically treated and co-mixed with stearic acid using kitchen coffee grinder and the mixture was then added to the polymeric matrix in a Brabender plastograph with various contents of 0.5 wt. %, 1 wt. % and 2 wt. %. The method effectiveness has been proved by AFM analysis. The results showed that the incorporation of inorganic semiconductor nanoparticles into polymeric matrix improves the dielectric properties. Results showed that with the co-mixing process and stearic acid the inorganic nanofillers have a strong influence on the permittivity of resulting nanocomposites.
Nanocomposites, 2016
Polymer nanocomposites are a promising concept to improve energy storage density of capacitors, but realizing their hypothetical gains has proved challenging. The introduction of high permittivity fillers often leads to reduction in breakdown strength due to field exclusion, which intensifies the applied electric field within the polymer matrix near nanoparticle interfaces. This has prompted research in developing new nanoparticle functionalization chemistries and processing concepts to maximize particle separation. Herein, we compare the dielectric performance of blended nanocomposites to matrix free assemblies of hairy (polymer grafted) nanoparticles (HNPs) that exhibit comparable overall morphology. The dielectric breakdown strength of polystyrene grafted BaTiO 3 (PS@BaTiO 3) systems was over 40% greater than a blended nanocomposite with similar loading (~25% v/v BaTiO 3). Hairy nanoparticles with TiO 2 cores followed similar trends in breakdown strength as a function of inorganic loading up to 40% v/v. Dielectric loss for PS@BaTiO 3 HNPs was 2-5 times lower than analogous blended films for a wide frequency spectrum (1 Hz to 100 kHz). For content above 7% v/v, grafting the polymer chains to the BaTiO 3 significantly improved energy storage efficiency. Overall this study indicates that polymer grafting improves capacitor performance relative to direct blending in likely two ways: (1) by mitigating interfacial transport to lower dielectric loss, irrespective of the dielectric contrast between matrix and nanoparticle, and (2) by restricting particle-particle hot-spots by establishing a finite minimum particle separation when the dielectric contrast between matrix and nanoparticle is large.