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Understanding the dielectric breakdown behavior of polymer nanocomposites is crucial to the design of high‐energy‐density dielectric materials with reliable performances. It is however challenging to predict the breakdown behavior due to the complicated factors involved in this highly nonequilibrium process. In this work, a comprehensive phase‐field model is developed to investigate the breakdown behavior of polymer nanocomposites under electrostatic stimuli. It is found that the breakdown strength and path significantly depend on the microstructure of the nanocomposite. The predicted breakdown strengths for polymer nanocomposites with specific microstructures agree with existing experimental measurements. Using this phase‐field model, a high throughput calculation is performed to seek the optimal microstructure. Based on the high‐throughput calculation, a sandwich microstructure for PVDF–BaTiO3 nanocomposite is designed, where the upper and lower layers are filled with parallel nanosheets and the middle layer is filled with vertical nanofibers. It has an enhanced energy density of 2.44 times that of the pure PVDF polymer. The present work provides a computational approach for understanding the electrostatic breakdown, and it is expected to stimulate future experimental efforts on synthesizing polymer nanocomposites with novel microstructures to achieve high performances.  相似文献   

3.
Investigation of the mechanics of natural materials, such as spider silk, abalone shells, and bone, has provided great insight into the design of materials that can simultaneously achieve high specific strength and toughness. Research has shown that their emergent mechanical properties are owed in part to their specific self‐organization in hierarchical molecular structures, from nanoscale to macroscale, as well as their mixing and bonding. To apply these findings to manmade materials, researchers have devoted significant efforts in developing a fundamental understanding of multiscale mechanics of materials and its application to the design of novel materials with superior mechanical performance. These efforts included the utilization of some of the most promising carbon‐based nanomaterials, such as carbon nanotubes, carbon nanofibers, and graphene, together with a variety of matrix materials. At the core of these efforts lies the need to characterize material mechanical behavior across multiple length scales starting from nanoscale characterization of constituents and their interactions to emerging micro‐ and macroscale properties. In this report, progress made in experimental tools and methods currently used for material characterization across multiple length scales is reviewed, as well as a discussion of how they have impacted our current understanding of the mechanics of hierarchical carbon‐based materials. In addition, insight is provided into strategies for bridging experiments across length scales, which are essential in establishing a multiscale characterization approach. While the focus of this progress report is in experimental methods, their concerted use with theoretical‐computational approaches towards the establishment of a robust material by design methodology is also discussed, which can pave the way for the development of novel materials possessing unprecedented mechanical properties.  相似文献   

4.
The electrocaloric effect (ECE) in dielectric materials has great potential in realizing solid‐state cooling devices with compact size and high efficiency, which are highly desirable for a broad range of applications. This paper presents the general considerations for dielectric materials to achieve large ECE and reviews the experimental efforts investigating ECE in various polar dielectrics. For practical cooling devices, an ECE material must possess a large isothermal entropy change besides a large adiabatic temperature change. We show that polar dielectrics operated at temperatures near order–disorder transition have potential to achieve large ECE due to the possibility of large change in polarization induced by electric field and large entropy change associated with the polarization change. We further show that indeed the ferroelectric poly(vinylidene fluoride–trifluoroethylene)‐based polymers display a large ECE, i.e., an isothermal entropy change of more than 55 J (kgK)?1 and an adiabatic temperature change of more than 12 °C, at temperatures above the order–disorder transition.  相似文献   

5.
The introduction of composite materials is having a profound effect on the design process. Because these materials permit the designer to tailor material properties to improve structural, aerodynamic and acoustic performance, they require a more integrated multidisciplinary design process. Because of the complexity of the design process numerical optimization methods are required. The present paper is focused on a major difficulty associated with the multidisciplinary design optimization process—its enormous computational cost. We consider two approaches for reducing this computational burden: (i)development of efficient methods for cross-sensitivity calculation using perturbation methods; and (ii) the use of approximate numerical optimization procedures. Our efforts are concentrated upon combined aerodynamic-structural optimization. Results are presented for the integrated design of a sailplane wing. The impact of our computational procedures on the computational costs of integrated designs is discussed.  相似文献   

6.
All‐optical switching—controlling light with light—has the potential to meet the ever‐increasing demand for data transmission bandwidth. The development of organic π‐conjugated molecular materials with the requisite properties for all‐optical switching applications has long proven to be a significant challenge. However, recent advances demonstrate that polymethine dyes have the potential to meet the necessary requirements. In this review, we explore the theoretical underpinnings that guide the design of π‐conjugated materials for all‐optical switching applications. We underline, from a computational chemistry standpoint, the relationships among chemical structure, electronic structure, and optical properties that make polymethines such promising materials.  相似文献   

7.
The electronic functionalities of metal oxides comprise conductors, semiconductors, and insulators. Metal oxides have attracted great interest for construction of large‐area electronics, particularly thin‐film transistors (TFTs), for their high optical transparency, excellent chemical and thermal stability, and mechanical tolerance. High‐permittivity (κ) oxide dielectrics are a key component for achieving low‐voltage and high‐performance TFTs. With the expanding integration of complementary metal oxide semiconductor transistors, the replacement of SiO2 with high‐κ oxide dielectrics has become urgently required, because their provided thicker layers suppress quantum mechanical tunneling. Toward low‐cost devices, tremendous efforts have been devoted to vacuum‐free, solution processable fabrication, such as spin coating, spray pyrolysis, and printing techniques. This review focuses on recent progress in solution processed high‐κ oxide dielectrics and their applications to emerging TFTs. First, the history, basics, theories, and leakage current mechanisms of high‐κ oxide dielectrics are presented, and the underlying mechanism for mobility enhancement over conventional SiO2 is outlined. Recent achievements of solution‐processed high‐κ oxide materials and their applications in TFTs are summarized and traditional coating methods and emerging printing techniques are introduced. Finally, low temperature approaches, e.g., ecofriendly water‐induced, self‐combustion reaction, and energy‐assisted post treatments, for the realization of flexible electronics and circuits are discussed.  相似文献   

8.
Heterogeneous materials in which the characteristic length scale of the filler material is in the nanometer range—i.e., nanocomposites—is currently one of the fastest growing areas of materials research. Polymer nanocomposites have expanded beyond the original scope of polymer–nanocrystal dispersions for refractive‐index tuning or clay‐filled homopolymers primarily pursued for mechanical reinforcement, to include a wide range of applications. This article highlights recent research efforts in the field of structure formation in block copolymer‐based nanocomposite materials, and points out opportunities for novel materials based on inclusion of different types of nanoparticles. The use of block copolymers instead of homopolymers as the matrix is shown to afford opportunities for controlling the spatial and orientational distribution of the nanoelements. This, in turn, allows much more sophisticated tailoring of the overall properties of the composite material.  相似文献   

9.
Polymeric dielectrics play a key role in the realization of flexible organic electronics, especially for the fabrication of scalable device arrays and integrated circuits. Among a wide variety of polymeric dielectric materials, aromatic polyimides (PIs) are flexible, lightweight, and strongly resistant to high‐temperature processing and corrosive etchants and, therefore, have become promising candidates as gate dielectrics with good feasibility in manufacturing organic electronic devices. More significantly, the characteristics of PIs can be conveniently modulated by the design of their chemical structures. Herein, from the perspective of structure optimization and interface engineering, a brief overview of recent progress in PI‐based dielectrics for organic electronic devices and circuits is provided. Also, an outlook of future research directions and challenges for polyimide dielectric materials is presented.  相似文献   

10.
Artificial molecular machines are able to produce and exploit precise nanoscale actuations in response to chemical or physical triggers. Recent scientific efforts have been devoted to the integration, orientation, and interfacing of large assemblies of molecular machines in order to harness their collective actuations at larger length scale and up to the generation of macroscopic motions. Making use of such “hierarchical mechanics” represents a fundamentally new approach for the conception of stimuli-responsive materials. Furthermore, because some molecular machines can function as molecular motors—which are capable of cycling a unidirectional motion out of thermodynamic equilibrium and progressively increasing the work delivered to their environment—one can expect unique opportunities to design new kinds of mechanically active materials and devices capable of autonomous behavior when supplied by an external source of energy. Recently reported achievements are summarized, including the integration of molecular machines at surfaces and interfaces, in 3D self-assembled materials, as well as in liquid crystals and polymer materials. Their detailed functioning principles as well as their functional properties are discussed along with their potential applications in various domains such as sensing, drug delivery, electronics, optics, plasmonics, and mechanics.  相似文献   

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