Unified Understanding of Ferroelectricity in n-Nylons: Is the Polar Crystalline Structure a Prerequisite?

Modeling Impact of Regiodefects on the Electrocaloric Effect in Poly(VDF-co-TrFE) Copolymers

Impact of regiodefects in the ferroelectric poly(vinylidene difluoride-co-trifluoroethylene) copolymer [poly(VDF-co-TrFE)] on the electrocaloric effect was studied with use of a developed analytical model and molecular dynamics (MD) simulations. It was shown earlier that the electrocaloric effect in these polymers is caused by the first-order phase transition from the ferroelectric β phase to the paraelectric conformationally disordered (condis) phase. MD simulations performed in the current work show that the presence of regiodefects in polymer chains makes this phase transition more gradual, the second order. The proposed analytical model is based on the Landau phenomenological theory of phase transitions, modified to ensure the correct behavior of polymer polarization at low temperatures. The model calculates the polymer polarization, P, and temperature change under adiabatic electric field variation, ΔT, as functions of temperature, applied electric field, and regiodefect concentration. Parameters of the free energy functional are calibrated through MD simulations of the poly(VDF-co-TrFE) crystal. The obtained results show that presence of regiodefects substantially changes the form of dependencies P(T) and ΔT(T), which significantly shifts them closer to experimental data.

Nylons with Applications in Energy Generators, 3D Printing and Biomedicine

Linear polyamides, known as nylons, are a class of synthetic polymers with a wide range of applications due to their outstanding properties, such as chemical and thermal resistance or mechanical strength. These polymers have been used in various fields: from common and domestic applications, such as socks and fishing nets, to industrial gears or water purification membranes. By their durability, flexibility and wear resistance, nylons are now being used in addictive manufacturing technology as a good material choice to produce sophisticated devices with precise and complex geometric shapes. Furthermore, the emergence of triboelectric nanogenerators and the development of biomaterials have highlighted the versatility and utility of these materials. Due to their ability to enhance triboelectric performance and the range of applications, nylons show a potential use as tribo-positive materials. Because of the easy control of their shape, they can be subsequently integrated into nanogenerators. The use of nylons has also extended into the field of biomaterials, where their biocompatibility, mechanical strength and versatility have paved the way for groundbreaking advances in medical devices as dental implants, catheters and non-absorbable surgical sutures. By means of 3D bioprinting, nylons have been used to develop scaffolds, joint implants and drug carriers with tailored properties for various biomedical applications. The present paper aims to collect evidence of these recently specific applications of nylons by reviewing the literature produced in recent decades, with a special focus on the newer technologies in the field of energy harvesting and biomedicine.

Engineering the Dielectric Constants of Polymers: From Molecular to Mesoscopic Scales

Polymers are essential components of modern-day materials and are widely used in various fields. The dielectric constant, a key physical parameter, plays a fundamental role in the light-, electricity-, and magnetism-related applications of polymers, such as dielectric and electrical insulation, battery and photovoltaic fabrication, sensing and electrical contact, and signal transmission and communication. Over the past few decades, numerous efforts have been devoted to engineering the intrinsic dielectric constant of polymers, particularly by tailoring the induced and orientational polarization modes and ferroelectric domain engineering. Investigations into these methods have guided the rational design and on-demand preparation of polymers with desired dielectric constants. This review article exhaustively summarizes the dielectric constant engineering of polymers from molecular to mesoscopic scales, with emphasis on application-driven design and on-demand polymer synthesis rooted in polymer chemistry principles. Additionally, it explores the key polymer applications that can benefit from dielectric constant regulation and outlines the future prospects of this field.

Toward Excellent Energy Storage Performance via Well-Aligned and Isolated Interfaces in Multicomponent Polypropylene-Based All-Organic Polymer Dielectric Films

Polypropylene (PP) serves as an excellent commercialized polymer dielectric film owing to its high breakdown strength, excellent self-healing ability, and flexibility. However, its low dielectric constant causes the large volume of the capacitor. Constructing multicomponent polypropylene-based all-organic polymer dielectric films is a facile strategy for achieving high energy density and efficiency simultaneously. Thereinto, the interfaces between the components become the key factors that determine the energy storage performance of the dielectric films. In this work, we propose to fabricate high-performance polyamide 513 (PA513)/PP all-organic polymer dielectric films via the construction of abundant well-aligned and isolated nanofibrillar interfaces. Laudably, a significant enhancement in the breakdown strength is achieved from 573.1 MV/m of pure PP to 692.3 MV/m with 5 wt % of PA513 nanofibrils. Besides, a maximum discharge energy density of about 4.4 J/cm² is realized with 20 wt % of PA513 nanofibrils, which is about 1.6-folds higher than pure PP. Simultaneously, the energy efficiency of samples with modulated interfaces maintains higher than 80% up to 600 MV/m, which is much higher than pure PP of about 40.7% at 550 MV/m. This work provides a new strategy to fabricate high-performance multicomponent all-organic polymer dielectric films on an industrial scale.

Reorganization of Hydrogen Bonding in Biobased Polyamide 5,13 under the Thermo-Mechanical Field: Hierarchical Microstructure Evolution and Achieving Excellent Mechanical Performance

The hierarchical microstructure evolution of an emerging biobased odd-odd polyamide 5,13 (PA5,13) films under the thermo-mechanical field, stepping from hydrogen bond (H-bond) arrangement to the crystalline morphology, has been investigated systematically. It is found that the reorganization of H-bonds under the thermo-mechanical field plays a crucial role in the crystallization of PA5,13. Especially, it is revealed that the crystallization process under the thermo-mechanical field develops along the chain axis direction, while lamellar fragmentation occurs perpendicular to the chain axis. Consequently, a stable and well-organized H-bond arrangement and lengthened lamellae with significant orientation have been constructed. Laudably, an impressive tensile strength of about 500 MPa and modulus of about 4.7 GPa are thus achieved. The present study could provide important guidance for the industrial-scale manufacture of high-performance biobased odd-odd PAs with long polymethylene segment in the dicarboxylic unit combined with a large difference between the polymethylene segments in the dicarboxylic and diamine units.

Sustainable pathway towards large scale melt processing of the new generation of renewable cellulose-polyamide composites

Modern society's growing demands for accountable high-performance and more environmentally friendly materials is leading to increased interest and fast development of sustainable polymeric composite materials. New generations of "greener" products originating from renewable resources fulfil emerging requirements of low environmental and health & safety impacts and contribute to diminishing global dependence on fossil feedstock. The preparation of sustainable polymeric composites via reliable and reproducible melt-compounding methods is still challenging but has the potential to yield applicable and market competitive products. This literature survey reviews the current state of research involving the use of cellulosic materials, as bio-sourced and sustainable reinforcement in melt-processed polyamides and focuses on the main hurdles that prevent their successful large-scale melt-compounding. Particular emphasis is dedicated to emerging bio-sourced polyamides fitting the performance of engineering materials and at the same time offering additional interesting properties for advanced applications such as piezoelectricity for transducers, sensors, actuators and energy harvesters.

Achieving efficient and large-scale preparation of mesophase-nylon 11 film by random copolymerization of nylon 11 and nylon 611

Nylon 11 is a promising functional material for future electronic devices or energy storage systems. To utilize nylon-11 in these applications, it is important to control the formation of metastable crystal phases such as the γ-phase and δ′-phase. However, controlling the formation of the applicable metastable crystal phase by the processing method is complicated and inefficient. Herein, we report a novel nylon 11-based copolymer synthesized by random copolymerization of nylon 11 and nylon 611, which can directly obtain a metastable crystal phase by simple hot-pressing. Meanwhile, high heterogeneity can stabilize the defective mesophase. Non-isothermal crystallization analysis showed that the crystallization rate decreased gradually with the increase of chemical heterogeneity in the nylon random copolymer. The resulting metastable crystal phase of the nylon copolymer is controlled by crystallization kinetics. This study clarified the mechanism of controlling the crystal structure by copolymerization of nylon 11 and nylon 611, moreover, it is promising to inspire novel nylon copolymers.

Chemical heterogeneity induced and stabilized the mesophase of nylon copolymer.

Unprecedented dipole alignment in α-phase nylon-11 nanowires for high-performance energy-harvesting applications

Dipole alignment in ferroelectric polymers is routinely exploited for applications in charge-based applications. Here, we present the first experimental realization of ideally ordered dipole alignment in α-phase nylon-11 nanowires. This is an unprecedented discovery as dipole alignment is typically only ever achieved in ferroelectric polymers using an applied electric field, whereas here, we achieve dipole alignment in as-fabricated nanowires of 'non-ferroelectric' α-phase nylon-11, an overlooked polymorph of nylon proposed 30 years ago but never practically realized. We show that the strong hydrogen bonding in α-phase nylon-11 serves to enhance the molecular ordering, resulting in exceptional intensity and thermal stability of surface potential. This discovery has profound implications for the field of triboelectric energy harvesting, as the presence of an enhanced surface potential leads to higher mechanical energy harvesting performance. Our approach therefore paves the way towards achieving robust, high-performance mechanical energy harvesters based on this unusual ordered phase of nylon-11.

Ferroelectric performance of nylons 6-12, 10-12, 11-12, and 12-12

Nylons have great potential for electrical applications requiring high polarizability and low dielectric loss. Recently, the narrow single hysteresis loop with relaxor ferroelectricity and the double hysteresis loop due to antiferroelectricity have been reported in nylon random copolymers, terpolymers, and common even-numbered nylons. Although several studies of ferroelectric nylons have been reported, even–even-numbered and odd–even-numbered nylons have not been sufficiently explored. Here, the ferroelectricity of spin-coated even–even-numbered and odd–even-numbered nylons was investigated. A series of even–even-numbered nylons, including nylons 6-12, 10-12, and 12-12, and an odd–even-numbered nylon, nylon 11-12, were polymerized with 1,10-dodecanedicarboxylic acid (12) and four aliphatic diamines with various methylene units, 1,6-hexanediamine (6), 1,10-decanediamine (10), 1,11-undecanediamine (11), and 1,12-dodecanediamine (12). The obtained nylon polymers were spin coated and then subjected to melt-quenching or thermal annealing followed by quenching. From the X-ray diffraction and the electrical hysteresis loop data, the correlation between the ferroelectricity and the crystal parameters of crystallinity and crystallite size of the γ crystal phase was investigated. Furthermore, the free volume of the nylon samples was estimated to correlate with the ferroelectricity. Temperature-dependent ferroelectricity was investigated for nylon 10-12. At a high temperature, the nylon samples showed a narrow polarization–electric field hysteresis loop and a rhombus-shaped polarization current–electric field hysteresis loop due to the relaxor ferroelectricity. This behaviour was caused by electrically rotating the nanodomains with weakened hydrogen bonds at higher temperatures.

Nylons have great potential for electrical applications requiring high polarizability and low dielectric loss.

Solution-processed transparent ferroelectric nylon thin films

Ferroelectricity, a bistable ordering of electrical dipoles in a material, is widely used in sensors, actuators, nonlinear optics, and data storage. Traditional ferroelectrics are ceramic based. Ferroelectric polymers are inexpensive lead-free materials that offer unique features such as the freedom of design enabled by chemistry, the facile solution-based low-temperature processing, and mechanical flexibility. Among engineering polymers, odd nylons are ferroelectric. Since the discovery of ferroelectricity in polymers, nearly half a century ago, a solution-processed ferroelectric nylon thin film has not been demonstrated because of the strong tendency of nylon chains to form hydrogen bonds. We show the solution processing of transparent ferroelectric thin film capacitors of odd nylons. The demonstration of ferroelectricity, as well as the way to obtain thin films, makes odd nylons attractive for applications in flexible devices, soft robotics, biomedical devices, and electronic textiles.

Advances in the study of piezoelectric polymers

The literature review based on the works published over the last decade concerns the progress in research on innovative piezoelectric materials with current or potential practical applications. At the beginning, the nature of piezoelectric phenomenon is clarified. The main emphasis is put on presentation of polymers, biopolymers and polymer composites as well as hybrid materials with piezoelectric properties. Moreover, carbon nanomaterials are also included. These materials have recently become an intensively developing field, as evidenced by numerous scientific publications. Furthermore, the recently reported main methods of characterizations and selected examples of modern applications of piezoelectric materials in various fields (electronics, industry, medicine) have been discussed.

The bibliography includes 217 references.

The effect of crystal structure on the electromechanical properties of piezoelectric Nylon-11 nanowires

Crystal structure is crucial in determining the properties of piezoelectric polymers, particularly at the nanoscale where precise control of the crystalline phase is possible. Here, we investigate the electromechanical properties of three distinct crystalline phases of Nylon-11 nanowires using advanced scanning probe microscopy techniques. Stiff α-phase nanowires exhibited a low piezoelectric response, while relatively soft δ'-phase nanowires displayed an enhanced piezoelectric response.