Effect of the Modifier Structure on the Performance of Barium Titanate/Poly(vinylidene fluoride) Nanocomposites for Energy Storage Applications

Fluorinated Polydopamine Shell Decorated Fillers in Polytetrafluoroethylene Composite for Achieving Highly Reduced Coefficient of Thermal Expansion

The noticeable difference in the coefficient of thermal expansion (CTE) for polytetrafluoroethylene (PTFE) coatings and copper substrates is a major challenge for thermal debonding of the copper-clad laminate (CCL) in high-frequency communications. Theoretically, ceramic fillers with low CTEs in the coating can effectively reduce the gap, and there remains a trade-off between the dispersibility of fillers and the interfacial interactions with the polymeric matrix. Here, we propose a novel approach to prepare a pentafluorobenzoyl chloride (PFBC)-modified polydopamine (PDA) shell on silica particles by using amidation. Such modified particles perform excellent dispersion and exhibit diminished interfacial gaps in the PTFE matrix, which highly reduces CTE to 77 ppm/°C, accounting for only 48.1% of the neat coating. Moreover, the composite exhibits enhanced mechanical strength and toughness, and consequently suppresses thermal debonding in CCL under high-temperature conditions. Therefore, results present a promising potential for its use in the next-generation CCL of high-frequency communication devices.

Energy Storage Performance of Polymer-Based Dielectric Composites with Two-Dimensional Fillers

Dielectric capacitors have garnered significant attention in recent decades for their wide range of uses in contemporary electronic and electrical power systems. The integration of a high breakdown field polymer matrix with various types of fillers in dielectric polymer nanocomposites has attracted significant attention from both academic and commercial sectors. The energy storage performance is influenced by various essential factors, such as the choice of the polymer matrix, the filler type, the filler morphologies, the interfacial engineering, and the composite structure. However, their application is limited by their large amount of filler content, low energy densities, and low-temperature tolerance. Very recently, the utilization of two-dimensional (2D) materials has become prevalent across several disciplines due to their exceptional thermal, electrical, and mechanical characteristics. Compared with zero-dimensional (0D) and one-dimensional (1D) fillers, two-dimensional fillers are more effective in enhancing the dielectric and energy storage properties of polymer-based composites. The present review provides a comprehensive overview of 2D filler-based composites, encompassing a wide range of materials such as ceramics, metal oxides, carbon compounds, MXenes, clays, boron nitride, and others. In a general sense, the incorporation of 2D fillers into polymer nanocomposite dielectrics can result in a significant enhancement in the energy storage capability, even at low filler concentrations. The current challenges and future perspectives are also discussed.

Dielectric and Structural Properties of the Hybrid Material Polyvinylidene Fluoride-Bacterial Nanocellulose-Based Composite

In the search for environmentally friendly materials with a wide range of properties, polymer composites have emerged as a promising alternative due to their multifunctional properties. This study focuses on the synthesis of composite materials consisting of four components: bacterial nanocellulose (BNC) modified with magnetic Fe3O4, and a mixture of BaTiO3 (BT) and polyvinylidene fluoride (PVDF). The BT powder was mechanically activated prior to mixing with PVDF. The influence of BT mechanical activation and BNC with magnetic particles on the PVDF matrix was investigated. The obtained composite films' structural characteristics, morphology, and dielectric properties are presented. This research provides insights into the relationship between mechanical activation of the filler and structural and dielectric properties in the PVDF/BT/BNC/Fe3O4 system, creating the way for the development of materials with a wide range of diverse properties that support the concept of green technologies.

Dielectric and energy storage properties of surface-modified BaTi0.89Sn0.11O3@polydopamine nanoparticles embedded in a PVDF-HFP matrix

In the most recent electronic and electric sectors, ceramic-polymer nanocomposites with high dielectric permittivity and energy density are gaining popularity. However, the main obstacle to improving the energy density in flexible nanocomposites, besides the size and morphology of the ceramic filler, is the low interfacial compatibility between the ceramic and the polymer. This paper presents an alternative solution to improve the dielectric permittivity and energy storage properties for electronic applications. Here, the poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) matrix is filled with surface-modified BaTi0.89Sn0.11O3/polydopamine nanoparticles (BTS11) nanoparticles, which is known for exhibiting multiphase transitions and reaching a maximum dielectric permittivity at room temperature. BTS11 nanoparticles were synthesized by a sol-gel/hydrothermal method at 180 °C and then functionalized by polydopamine (PDA). As a result, the nanocomposites exhibit dielectric permittivity (εr) of 46 and a low loss tangent (tan δ) of 0.017 at 1 kHz at a relatively low weight fraction of 20 wt% of BTS11@PDA. This is approximately 5 times higher than the pure PVDF-HFP polymer and advantageous for energy storage density in nanocomposites. The recovered energy storage for our composites reaches 134 mJ cm-3 at an electric field of 450 kV cm-1 with a high efficiency of 73%. Incorporating PDA-modified BTS11 particles into the PVDF-HFP matrix demonstrates highly piezo-active regions associated with BTS11 particles, significantly enhancing functional properties in the polymer nanocomposites.

Electrical Heaters for Anti/De-Icing of Polymer Structures

The problem of icing for surfaces of engineering structures requires attention more and more every year. Active industrialization in permafrost zones is currently underway; marine transport in Arctic areas targets new goals; the requirements for aerodynamically critical surfaces of wind generators and aerospace products, serving at low temperatures, are increasing; and fiber-reinforced polymer composites find wide applicability in these structural applications demanding the problem of anti/de-icing to be addressed. The traditional manufacturing approaches are superimposed with the new technologies, such as 3D printers and robotics for laying heat wires or cheap and high-performance Thermal Sprayed methods for metallic cover manufacturing. Another next step in developing heaters for polymer structures is nano and micro additives to create electrically conductive heating networks within. In our study, we review and comparatively analyze the modern technologies of structure heating, based on resistive heating composites.

A Comprehensive Review on Barium Titanate Nanoparticles as a Persuasive Piezoelectric Material for Biomedical Applications: Prospects and Challenges

Stimulation of cells with electrical cues is an imperative approach to interact with biological systems and has been exploited in clinical practices over a wide range of pathological ailments. This bioelectric interface has been extensively explored with the help of piezoelectric materials, leading to remarkable advancement in the past two decades. Among other members of this fraternity, colloidal perovskite barium titanate (BaTiO₃ ) has gained substantial interest due to its noteworthy properties which includes high dielectric constant and excellent ferroelectric properties along with acceptable biocompatibility. Significant progression is witnessed for BaTiO₃ nanoparticles (BaTiO₃ NPs) as potent candidates for biomedical applications and in wearable bioelectronics, making them a promising personal healthcare platform. The current review highlights the nanostructured piezoelectric bio interface of BaTiO₃ NPs in applications comprising drug delivery, tissue engineering, bioimaging, bioelectronics, and wearable devices. Particular attention has been dedicated toward the fabrication routes of BaTiO₃ NPs along with different approaches for its surface modifications. This review offers a comprehensive discussion on the utility of BaTiO₃ NPs as active devices rather than passive structural unit behaving as carriers for biomolecules. The employment of BaTiO₃ NPs presents new scenarios and opportunity in the vast field of nanomedicines for biomedical applications.

Electrospun Co Nanoparticles@PVDF-HFP Nanofibers as Efficient Catalyst for Dehydrogenation of Sodium Borohydride

Metallic Co NPs@poly(vinylidene fluoride-co- hexafluoropropylene) nanofibers (PVFH NFs) were successfully synthesized with the help of electrospinning and in situ reduction of Co²⁺ ions onto the surface of PVFH membrane. Synthesis of PVFH NFs containing 10, 20, 30, and 40 wt% of cobalt acetate tetrahydrate was achieved. Physiochemical techniques were used to confirm the formation of metallic Co@PVFH NFs. High catalytic activity of Co@PVFH NFs in the dehydrogenation sodium borohydride (SBH) was demonstrated. The formulation with 40 wt% Co proved to have the greatest performance in comparison to the others. Using 1 mmol of SBH and 100 mg of Co@PVFH NFs, 110 mL of H₂ was produced in 19 min at a temperature of 25 °C, but only 56, 73, and 89 mL were produced using 10, 20, and 30 wt% Co, respectively. With the rise of catalyst concentration and reaction temperature, the amount of hydrogen generated increased. By raising the temperature from 25 to 55 °C, the activation energy was lowered to be 35.21 kJ mol^-1 and the yield of H₂ generation was raised to 100% in only 6 min. The kinetic study demonstrated that the reaction was pseudo-first order in terms of the amount of catalyst utilized and pseudo-zero order in terms of the SBH concentration. In addition, after six cycles of hydrolysis, the catalyst showed outstanding stability. The suggested catalyst has potential applications in H₂ generation through hydrolysis of sodium borohydride due to its high catalytic activity and flexibility of recycling.

Nano-Sized Calcium Copper Titanate for the Fabrication of High Dielectric Constant Functional Ceramic-Polymer Composites

A novel calcium copper titanate (CaCu₃Ti₄O₁₂)–polyvinylidene fluoride composite (CCTO@PVDF) with Cu-deficiency was successfully prepared through the molten salt-assisted method. The morphology and structure of polymer composites uniformly incorporated with CCTO nanocrystals were characterized. At the same volume fraction, the CCTOs with Cu-deficiency displayed higher dielectric constants than those without post-treatment. A relatively high dielectric constant of 939 was obtained at 64% vol% CCTO@PVDF content, 78 times that of pure PVDF. The high dielectric constants of these composites were attributed to the homogeneous dispersion and interfacial polarization of the CCTO into the PVDF matrix. These composites also have prospective applications in high-frequency regions (10⁶ Hz). The enhancement of the dielectric constant was predicted in several theoretical models, among which the EMT and Yamada models agreed well with the experimental results, indicating the excellent distribution in the polymer matrix.

High-energy-density polymer dielectrics via compositional and structural tailoring for electrical energy storage

Dielectric capacitors with higher working voltage and power density are favorable candidates for renewable energy systems and pulsed power applications. A polymer with high breakdown strength, low dielectric loss, great scalability, and reliability is a preferred dielectric material for dielectric capacitors. However, their low dielectric constant limits the polymer to achieve satisfying energy density. Therefore, great efforts have been made to get high-energy-density polymer dielectrics. By compositional and structural tailoring, the synergic integrations of the multiple components and optimized structural design effectively improved the energy storage properties. This review presents an overview of recent advancements in the field of high-energy-density polymer dielectrics via compositional and structural tailoring. The surface/interfacial engineering conducted on both microscale and macroscale for polymer dielectrics is the focus of this review. Challenges and the promising opportunities for the development of polymer dielectrics for capacitive energy storage applications are presented at the end of this review.

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A detailed summary of the state-of-the-art polymer dielectrics

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The comparison of polymer nanocomposites with 0D, 1D, and 2D nanofillers

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Analyzing high U_e polymer dielectrics via compositional and structural tailoring

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Summary of micro- or macro-surface and interface engineering

Research Advances in Hierarchically Structured PVDF-BasedAll-Organic Composites for High-Energy Density Capacitors

Polymer film capacitors have been widely applied in many pulsed power fields owing to their fastest energy-released rates. The development of ferroelectric polyvinylidene fluoride (PVDF)-based composites has become one of the hot research directions in the field of high-energy storage capacitors. Recently, hierarchically-structured all-organic composites have been shown to possess excellent comprehensive energy storage performance and great potential for application. In this review, most research advances of hierarchically-structured all-organic composites for the energy storage application are systematically classified and summarized. The regulating strategies of hierarchically structured all-organic composites are highlighted from the perspective of preparation approaches, tailored material choices, layer thicknesses, and interfaces. Systematic comparisons of energy storage abilities are presented, including electric displacement, breakdown strength, energy storage density, and efficiency. Finally, we present the remaining problems of hierarchically structured all-organic composites and provide an outlook for future energy storage applications.

Surface-initiated reversible addition fragmentation chain transfer of fluoromonomers: an efficient tool to improve interfacial adhesion in piezoelectric composites

Baryum titanate/P(VDF-co-TrFE) piezoelectric composites with sturdy interfaces thanks to surface-initiated RAFT polymerization prepared fluoropolymer brushes.

Interfacial Effect on Dielectric Properties of Self-Assembled Polythiourea-Based Copolymers for Ultrahigh Energy Storage

Polymer dielectrics are highly desirable in capacitor applications due to their low cost, high stability, and reliability. However, there still remains a lack of feasible methods to prepare polymer dielectrics with high energy density and low dielectric loss, which severely hampers the development of compact and efficient power electronics. Here, an amphiphilic block copolymer, polythiourea-b-polydimethylsiloxane (PTU-b-PDMS), with an extraordinarily high energy density of 29.8 J cm^-3 and a low loss is synthesized via polyaddition polymerization. This is highly relevant to the block molecule conformation in the interfacial region of the self-assembled PTU-b-PDMS. The block molecule in the interface adopts an extended conformation when the PTU forms nanodots, whereas the block molecule adopts a coiled conformation when the PTU forms nanostrands. The observation and characterization have proved that the coiled block molecule in the interfacial region can simultaneously induce extra strong charge trapping sites and dipolar polarization. It substantially improves the breakdown strength from 652 to 1166 MV m^-1 , while maintaining a high dielectric constant of 5 and a low loss of <0.01. This work offers unprecedented structural insights into the conformation-induced interfacial effect and enables rational design of self-assembled copolymers to boost their dielectric properties and energy density.

Free volume dependence of dielectric behaviour in sandwich-structured high dielectric performances of poly(vinylidene fluoride) composite films

A dielectric film with a trilayer structure is fabricated to obtain both a high dielectric constant and superior electrical breakdown strength simultaneously. The outer layers of the trilayered composite film are composed of barium titanate (BTO) particles dispersed in poly(vinylidene fluoride) (PVDF) to ensure a relatively high dielectric constant, while the central layer of the composite film consists of exfoliated hexagonal boron nitride nanosheets (BNNS) dispersed in PVDF to provide high electrical breakdown strength. Compared with pristine PVDF, the dielectric constant and breakdown strength are simultaneously enhanced due to the sandwich structure, and the dielectric loss is maintained at a low level. Most important of all, positron annihilation lifetime spectroscopy (PALS) is applied to study the atomic-scale free volume holes of PVDF composite films and the effect of free volume holes on the dielectric constant and breakdown strength. Results show that the size of free volume holes of PVDF increased with the addition of BTO, but it decreased firstly and then increased with the BNNS loading. The correlation between dielectric properties and the size of free volume holes of the PVDF matrix was discussed in each layer. It is illustrated that the experimental dielectric constant of the PVDF/BTO single-layered film is consistent with the theoretical value at a lower BTO loading but smaller than the theoretical value at a higher BTO loading, which is probably ascribed to the increased size of free volume holes. The breakdown strength of the PVDF/BNNS film increased with the introduction of BNNS and the reduced size of free volume holes, which is ascribed to the reduced partial discharge phenomenon. The atomic-scale microstructure analysis based on free volume holes provides valuable ideas and new understanding for the study of the mechanism of the dielectric behaviour of polymer composites.

Interface-Strengthened Polymer Nanocomposites with Reduced Dielectric Relaxation Exhibit High Energy Density at Elevated Temperatures Utilizing a Facile Dual Crosslinked Network

High-temperature ceramic/polymer nanocomposites with large energy density as the reinforcement exhibit great potential for energy storage applications in modern electronic and electrical power systems. Yet, a general drawback is that the increased dielectric constant is usually achieved at the cost of decreased breakdown strength, thus leading to moderate improvement of energy density and even displaying a marked deterioration under high temperatures and high electric fields. Herein, a new strategy is reported to simultaneously improve breakdown strength and discharged energy density by a step-by-step, controllable dual crosslinking process, which constructs a strengthened interface as well as reduces molecular chains relaxation under elevated temperatures. Great breakdown strength and discharged energy density is achieved in the dual crosslinked network BT-BCB@DPAES nanocomposites at elevated temperatures when compared to noninterfacial-strengthened, BT/DPAES composites, i.e., an enhanced breakdown strength and a discharged energy density of 442 MV m^-1 and 3.1 J cm^-3 , increasing by 66% and 162%, and a stable cyclic performance over 10 000 cycles is demonstrated at 150 °C. Moreover, the enhancement through the synergy of two crosslinked networks is rationalized via a comprehensive phase-field model for the composites. This work offers a strategy to enhance the electric storage performances of composites at high temperatures.

The role of interfacial H-bonding on the electrical properties of UV-cured resin filled with hydroxylated Al2O3 nanoparticles

Surface hydroxylation of crude Al₂O₃ (c-Al₂O₃) nanoparticles by H₂O₂ was conducted to tailor the electrical properties of UV-cured resin. The hydroxyl groups on Al₂O₃ particles were designed to establish hydrogen bonding between the hydroxyl and carboxyl groups, which favors the enhancement of interfacial strength between fillers and UV-cured resin matrix. The effect of interfacial strength on the electrical properties was investigated. Owing to the improved interfacial strength, it can be conjectured that a larger volume of the interaction zone exists in UV-cured resin/hydroxylated Al₂O₃ (UV/h-Al₂O₃) composites. As a consequence, the number of deeper traps is increased, restraining the charge migration and raising the charge injection barrier. Thus, UV/h-Al₂O₃ composites exhibit remarkably enhanced breakdown strength, improved volume resistivity and suppressed space charge accumulation in comparison with that of UV/c-Al₂O₃ composites at the same filler content. It was found that the addition of 0.5 wt% h-Al₂O₃ increases the AC breakdown strength and volume resistivity by 15.5% and 367.9%, respectively. Our results suggest that hydroxylation is an efficient way to improve the electrical properties of UV-cured resin nanocomposites, thus promoting stereolithography 3D printing in the application of electrical and electronic fields.

Induced Hydrophilicity and In Vitro Preliminary Osteoblast Response of Polyvinylidene Fluoride (PVDF) Coatings Obtained via MAPLE Deposition and Subsequent Thermal Treatment

Recent advancements in biomedicine have focused on designing novel and stable interfaces that can drive a specific cellular response toward the requirements of medical devices or implants. Among these, in recent years, electroactive polymers (i.e., polyvinylidene fluoride or PVDF) have caught the attention within the biomedical applications sector, due to their insolubility, stability in biological media, in vitro and in vivo non-toxicity, or even piezoelectric properties. However, the main disadvantage of PVDF-based bio-interfaces is related to the absence of the functional groups on the fluoropolymer and their hydrophobic character leading to a deficiency of cell adhesion and proliferation. This work was aimed at obtaining hydrophilic functional PVDF polymer coatings by using, for the first time, the one-step, matrix-assisted pulsed evaporation (MAPLE) method, testing the need of a post-deposition thermal treatment and analyzing their preliminary capacity to support MC3T3-E1 pre-osteoblast cell survival. As osteoblast cells are known to prefer rough surfaces, MAPLE deposition parameters were studied for obtaining coatings with roughness of tens to hundreds of nm, while maintaining the chemical properties similar to those of the pristine material. The in vitro studies indicated that all surfaces supported the survival of viable osteoblasts with active metabolisms, similar to the “control” sample, with no major differences regarding the thermally treated materials; this eliminates the need to use a secondary step for obtaining hydrophilic PVDF coatings. The physical-chemical characteristics of the thin films, along with the in vitro analyses, suggest that MAPLE is an adequate technique for fabricating PVDF thin films for further bio-applications.

Achieving Secondary Dispersion of Modified Nanoparticles by Hot-Stretching to Enhance Dielectric and Mechanical Properties of Polyarylene Ether Nitrile Composites

Enhanced dielectric and mechanical properties of polyarylene ether nitrile (PEN) are obtained through secondary dispersion of polyaniline functionalized barium titanate (PANI-f-BT) by hot-stretching. PANI-f-BT nanoparticles with different PANI content are successfully prepared via in-situ aniline polymerization technology. The transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopic instrument (XPS) and Thermogravimetric analysis (TGA) results confirm that the PANI layers uniformly enclose on the surface of BaTiO₃ nanoparticles. These nanoparticles are used as functional fillers to compound with PEN (PEN/PANI-f-BT) for studying its effect on the mechanical and dielectric performance of the obtained composites. In addition, the nanocomposites are uniaxial hot-stretched by 50% and 100% at 280 °C to obtain the oriented nanocomposite films. The results exhibit that the PANI-f-BT nanoparticles present good compatibility and dispersion in the PEN matrix, and the hot-stretching endows the second dispersion of PANI-f-BT in PEN resulting in enhanced mechanical properties, crystallinity and permittivity-temperature stability of the nanocomposites. The excellent performances of the nanocomposites indicate that a new approach for preparing high-temperature-resistant dielectric films is provided.

Interface design for high energy density polymer nanocomposites

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area.

Significantly Enhanced Energy Density by Tailoring the Interface in Hierarchically Structured TiO2-BaTiO3-TiO2 Nanofillers in PVDF-Based Thin-Film Polymer Nanocomposites

Dielectric polymer nanocomposites with a high breakdown field and high dielectric constant have drawn significant attention in modern electrical and electronic industries due to their potential applications in dielectric and energy storage systems. The interfaces of the nanomaterials play a significant role in improving the dielectric performance of polymer nanocomposites. In this work, polydopamine (dopa)-functionalized TiO₂-BaTiO₃-TiO₂ (TiO₂-BT-TiO₂@dopa) core@double-shell nanoparticles have been developed as novel nanofillers for high-energy-density capacitor applications. The hierarchically designed nanofillers help in tailoring the interfaces surrounding the polymer matrix as well as act as individual capacitors in which the core and outer TiO₂ shell function as a capacitor plate because of their high electrical conductivity while the middle BT layer functions as a dielectric medium due to high dielectric constant. Detailed electrical characterizations have revealed that TiO₂-BT-TiO₂@dopa/poly(vinylidene fluoride) (PVDF) possesses a higher relative dielectric permittivity (ε_r), breakdown strength ( E_b), and energy density as compared to those of PVDF, TiO₂/PVDF, TiO₂@dopa/PVDF, and TiO₂-BT@dopa/PVDF polymer nanocomposites. The ε_r and energy density of TiO₂-BT-TiO₂@dopa/PVDF were 12.6 at 1 kHz and 4.4 J cm^-3 at 3128 kV cm^-1, respectively, which were comparatively much higher than those of commercially available biaxially oriented polypropylene having ε_r of 2.2 and the energy density of 1.2 J cm^-3 at a much higher electric field of 6400 kV cm^-1. It is expected that these results will further open new avenues for the design of novel architecture for high-performance polymer nanocomposite-based capacitors having core@multishell nanofillers with tailored interfaces.

Modulating interfacial charge distribution and compatibility boosts high energy density and discharge efficiency of polymer nanocomposites

Polymer nanocomposite dielectrics, composed of polymer matrices with high breakdown strength and nanofillers with high dielectric constant, can achieve outstanding energy density. However, the great difference of intrinsic surface properties between the polymer and nanofillers will lead to poor compatibility and thus damage the dielectric properties of the composites. Introducing a transition layer to the filler surface can effectively reduce the degree of mismatch. In this work, we use a “direct in situ polymerization” method to synthesize core–shell BaTiO₃ nanoparticles (BTO_nps) with three types of stable and dense fluoro-polymer shells, e.g., poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), poly(2,2,3,4,4,4-hexafluorobutyl methacrylate) (PHFBMA), and poly(1H,1H,7H-dodecafluoroheptyl methacrylate) (PDFHMA), and individually disperse them into the poly(vinylidene fluoride-co-hexafluoro propylene) (P(VDF-HFP)) matrix. Benefitting from the good interaction between the fluorine-containing segments in the shell polymer and the matrix segments, the dispersion of core–shell BTO_nps and their compatibility with P(VDF-HFP) are improved, which leads to a significant improvement in the dielectric properties of the nanocomposites. The results show that BTO@PDFHMA/P(VDF-HFP) composite exhibits an ultrahigh energy density of 16.8 J cm⁻³ at 609 MV m⁻¹ with particle loading amount of 15 wt%, compared to 11.5 J cm⁻³ at 492 MV m⁻¹ for a conventional solution blended BTO/P(VDF-HFP) composite. Meanwhile, the discharge efficiency is enhanced from ∼62 to ∼78%. It is elucidated that the core–shell strategy can achieve improved particle dispersion and dielectric properties. We consider that this simple method can well achieve the preparation of core–shell structures in dielectric nanocomposites.

Fluoro-polymer shells concomitantly enhance the energy density and discharge efficiency by active interactions with BTO cores and P(VDF-HFP).

Core–shell structured poly(vinylidene fluoride)-grafted-BaTiO3 nanocomposites prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization of VDF for high energy storage capacitors

Core–shell structured PVDF-g-BaTiO₃ nanocomposites were prepared by surface-initiated RAFT of VDF from BaTiO₃ nanoparticles.

Interface Modulation of Core-Shell Structured BaTiO₃@polyaniline for Novel Dielectric Materials from Its Nanocomposite with Polyarylene Ether Nitrile

The core-shell structured polyaniline-functionalized-BaTiO₃ (BT@PANI) nanoparticles with controllable shell layer thicknesses are developed via in-situ aniline polymerization technology and characterized in detail. The results prove that the PANI shell layer with the adjustable and controllable thicknesses of 3⁻10 nm are completely stabilized on the surface of the BaTiO₃ core. In addition, the BT@PANI nanoparticles are regarded as the hybrid nanofillers to prepare PEN/BT@PANI nanocomposite films with a PEN matrix. The research results indicate that the surface functionalized nanoparticles facilitate the compatibility and dispersibility of them in the PEN matrix, which improves the properties of the PEN/BT@PANI nanocomposites. Specifically, the PEN/BT@PANI nanocomposites exhibit thermal stability, excellent permittivity-frequency, and dielectric properties-temperature stability. Most importantly, the energy density of nanocomposites is maintained at over 70% at 180 °C compared with that at 25 °C. All these results reveal that a new way to prepare the high-performance PEN-based nanocomposites is established to fabricate an energy storage component in a high temperature environment.

Interfacial engineering tailoring the dielectric behavior and energy density of BaTiO3/P(VDF-TrFE-CTFE) nanocomposites by regulating a liquid-crystalline polymer modifier structure

Dielectric polymer-based nanocomposites have attracted significant attention in recent years for energy storage applications because of their potential high permittivity and breakdown strength. The coupling effect of a nanofiller/matrix interface plays a crucial role in the dielectric and electric properties of polymer-based nanocomposites. In this paper, three kinds of side-chain liquid crystalline fluoric-polymers, denoted as P-nF (n = 3, 5 or 7, which is the number of terminal fluoric groups), were grafted on the surface of BaTiO3 nanoparticles by a surface-initiated reversible-addition-fragmentation chain transfer polymerization method. The nanocomposite films were prepared via core-shell BaTiO3 nanoparticles dispersed in a poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) P(VDF-TrFE-CTFE) polymer matrix. The frequency dependent dielectric properties and energy storage capability of the polymer nanocomposites were studied. The results showed that the permittivity and energy densities of the polymer nanocomposites depended on the molecular structure of the modifier, especially the number of electron-rich fluoric groups. Firstly, all modified BaTiO3 nanoparticles were homogeneously dispersed in the polymer matrix, resulting in the polymer nanocomposites presenting a higher breakdown strength compared with the unmodified BaTiO3 nanoparticles. Secondly, the changes in the nanocomposites' permittivity exhibited diversity for three modifiers due to many influential factors. Thirdly, compared with neat P(VDF-TrFE-CTFE), the discharge energy densities of the polymer nanocomposites are all significantly improved. The highest discharge energy densities of nanocomposites with 5 vol% P-3F@BT reached 14.5 J cm-3. These findings suggest that the optimal interfacial modifier should be carefully decided by combining various properties of the nanocomposites for energy storage.

High Permittivity Nanocomposites Embedded with Ag/TiO₂ Core⁻Shell Nanoparticles Modified by Phosphonic Acid

In this paper, nanocomposites that contain core-shell Ag/TiO₂ particles as the filler and polytetrafluoroethylene (PTFE) as the matrix were investigated. Two surfactants, namely octyl phosphonic acid (OPA) and pentafluorobenzyl phosphonic acid (PFBPA), were applied to modify Ag/TiO₂ fillers for uniform dispersion in the matrix. Fourier transform infrared spectroscopy analysis of bonds between the TiO₂ shells and the phosphonic modifiers shows Ti⁻O⁻P chemical bonding between the Ag/TiO₂ fillers and the modifiers. Thermogravimetric analysis results show a superior adsorption effect of PFBPA over OPA on the Ag/TiO₂ filler surface at the same weight percentage. For nanocomposites that contain modified Ag/TiO₂ nanoparticles, the loss was reduced despite the high permittivity at the same loading. The permittivity of the nanocomposites by PFBPA is larger than that of OPA, because the more uniform dispersion of inorganic particles in the PTFE matrix enhances the interfacial polarization effect. The mechanism of enhanced dielectric performance was studied and discussed.

Interfacial Coupling Effect in Organic/Inorganic Nanocomposites with High Energy Density

Organic/inorganic nanocomposites (OINs) can be potentially used as high-performance capacitors due to their rapid charge-discharge capability along with respectable power density. The coupling effect of the filler/matrix interface plays a prominent role in the dielectric and electric properties of OINs. Along with a review of contemporary theoretical models, recent advances in interfacial optimization to improve energy density through careful interface control and design are also presented. Possible mechanisms that may improve energy density and potential applications for high-energy-density capacitors are also highlighted.

High energy density in PVDF nanocomposites using an optimized nanowire array

Introducing PZT as the coating layer of TiO₂ nanowire arrays, the obtained TiO₂-P/PVDF nanocomposite achieved a high permittivity and breakdown electric field of 53 at 1 kHz and 550 kV mm⁻¹, respectively, resulting in a higher discharged energy density of 12.4 J cm⁻³.

Significantly improved energy density of BaTiO3 nanocomposites by accurate interfacial tailoring using a novel rigid-fluoro-polymer

This work presents a novel approach to precisely tailor the interfacial layer thicknesses of BaTiO₃ by modulating the polymerization degree of a rigid liquid-crystalline fluoro-polymer to investigate the interfacial thickness effect on the dielectric behavior of polymer nanocomposites.

Effect of the coverage level of carboxylic acids as a modifier for barium titanate nanoparticles on the performance of poly(vinylidene fluoride)-based nanocomposites for energy storage applications

Changes in the breakdown strength of nanocomposites show diversity as the modifier content increases for different modifiers.

Single Molecule Study on Polymer-Nanoparticle Interactions: The Particle Shape Matters

The study on the nanoparticle-polymer interactions is very important for the design/preparation of high performance polymer nanocomposite. Here we present a method to quantify the polymer-particle interaction at single molecule level by using AFM-based single molecule force spectroscopy (SMFS). As a proof-of-concept study, we choose poly-l-lysine (PLL) as the polymer and several different types of polyoxometalates (POM) as the model particles to construct several different polymer nanocomposites and to reveal the binding mode and quantify the binding strength in these systems. Our results reveal that the shape of the nanoparticle and the binding geometry in the composite have significantly influenced the binding strength of the PLL/POM complexes. Our dynamic force spectroscopy studies indicate that the disk-like geometry facilitate the unbinding of PLL/AlMo₆ complexes in shearing mode, while the unzipping mode becomes dominate in spherical PLL-P₈W₄₈ system. We have also systematically investigated the effects of charge numbers, particle size, and ionic strength on the binding strength and binding mode of PLL/POM, respectively. Our results show that electrostatic interactions dominate the stability of PLL/POM complexes. These findings provide a way for tuning the mechanical properties of polyelectrolyte-nanoparticle composites.

Ultrafast Discharge and Enhanced Energy Density of Polymer Nanocomposites Loaded with 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3 One-Dimensional Nanofibers

One-dimensional (1D) materials as fillers introduced into polymer matrixes have shown great potential in achieving high energy storage capacity because of their large dipole moments. In this article, 1D lead-free 0.5(Ba_0.7Ca_0.3)TiO₃-0.5Ba(Zr_0.2Ti_0.8)O₃ nanofibers (BCZT NFs) were prepared via electrospinning, and their formation mechanism was systematically studied. Polypropylene acyl tetraethylene pentamine (PATP) grafted into the surface of BCZT NFs was embedded in the polymer matrixes, which effectively improved the distribution and compatibility of the fillers via chemical bonding and confined the movement of the charge carriers in the interface filler-matrix. The energy density at a relatively low electric field 380 MV m^-1 was increased to 8.23 J cm^-3 by small loading of fillers, far more than that of biaxially oriented polypropylene (BOPP) (≈ 1.2 J cm^-3 at 640 MV m^-1). Moreover, the nanocomposite loaded with 2.1 vol % BCZT@PATP NFs exhibits a superior discharge speed of ≈0.189 μs, which indicates the potential application in practice. The finite element simulation of electric potential and electric current density distribution revealed that the PATP grafted into the BCZT NFs surface could significantly improve the dielectric performances. This work could provide a new design strategy for high-performance dielectric polymer nanocomposite capacitors.

Significantly Enhanced Energy Storage Density by Modulating the Aspect Ratio of BaTiO3 Nanofibers

There is a growing need for high energy density capacitors in modern electric power supplies. The creation of nanocomposite systems based on one-dimensional nanofibers has shown great potential in achieving a high energy density since they can optimize the energy density by exploiting both the high permittivity of ceramic fillers and the high breakdown strength of the polymer matrix. In this paper, BaTiO3 nanofibers (NFs) with different aspect ratio were synthesized by a two-step hydrothermal method and the permittivity and energy storage of the P(VDF-HFP) nanocomposites were investigated. It is found that as the BaTiO3 NF aspect ratio and volume fraction increased the permittivity and maximum electric displacement of the nanocomposites increased, while the breakdown strength decreased. The nanocomposites with the highest aspect ratio BaTiO3 NFs exhibited the highest energy storage density at the same electric field. However, the nanocomposites with the lowest aspect ratio BaTiO3 NFs achieved the maximal energy storage density of 15.48 J/cm3 due to its higher breakdown strength. This contribution provides a potential route to prepare and tailor the properties of high energy density capacitor nanocomposites.

Significantly Enhanced Energy Density in Nanocomposite Capacitors Combining the TiO2 Nanorod Array with Poly(vinylidene fluoride)

A novel inorganic/polymer nanocomposite, using 1-dimensional TiO₂ nanorod array as fillers (TNA) and poly(vinylidene fluoride) (PVDF) as matrix, has been successfully synthesized for the first time. A carefully designed process sequence includes several steps with the initial epitaxial growth of highly oriented TNA on the fluorine-doped tin oxide (FTO) conductive glass. Subsequently, PVDF is embedded into the nanorods by the spin-coating method followed by annealing and quenching processes. This novel structure with dispersive fillers demonstrates a successful compromise between the electric displacement and breakdown strength, resulting in a dramatic increase in the electric polarization which leads to a significant improvement on the energy density and discharge efficiency. The nanocomposites with various height ratios of fillers between the TNA and total film thickness were investigated by us. The results show that nanocomposite with 18% height ratio fillers obtains maximum increase in the energy density (10.62 J cm^-3) at a lower applied electric field of 340 MV m^-1, and it also illustrates a higher efficiency (>85%) under the electric field less than 100 MV m^-1. Even when the electric field reached 340 MV m^-1, the efficiency of nanocomposites can still maintained at ∼70%. This energy density exceeds most of the previously reported TiO₂-based nanocomposite values at such a breakdown strength, which provides another promising design for the next generation of dielectric nanocomposite material, by using the highly oriented nanorod array as fillers for the higher energy density capacitors. Additionally, the finite element simulation has been employed to analyze the distribution of electric fields and electric flux density to explore the inherent mechanism of the higher performance of the TNA/PVDF nanocomposites.