Ultrathin, all-organic, fabric-based ferroelectret loudspeaker for wearable electronics.

All-organic, flexible, and body-compatible loudspeakers have become increasingly attractive for wearable electronics. Due to their remarkable piezoelectric response, ferroelectrets are suitable for loudspeakers. Two distinct kinds of ultrathin ferroelectrets, including cellular polypropylene films and expanded polytetrafluoroethylene (ePTFE) films, were combined with three different types of electrodes ((Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS))-coated fabrics, PEDOT:PSS direct coating, and sputter-coated Au/Pd) for study regarding their frequency-dependent sound intensity and radiation directivity. Among the loudspeakers investigated, the all-fabric loudspeakers with ePTFE ferroelectret and PEDOT:PSS-coated spandex electrodes have a higher frequency dependency. Loudspeakers equipped with PEDOT:PSS-coated spandex electrodes are less angle dependent compared to other loudspeakers evaluated. Moreover, the soft loudspeaker constituted of an all-organic FEP(fluorinated-ethylene-propylene)-ePTFE-based ferroelectret and PEDOT:PSS-coated fabrics presented in this paper is easy to integrate with clothes and has a higher thermal stability. It is naturally compatible with the human body and a competitive candidate for future developments of all-organic loudspeakers for wearable electronic systems.

Poly(cannabinoid)s: Hemp-Derived Biocompatible Thermoplastic Polyesters with Inherent Antioxidant Properties.

The legalization of hemp cultivation in the United States has caused the price of hemp-derived cannabinoids to decrease 10-fold within 2 years. Cannabidiol (CBD), one of many naturally occurring diols found in hemp, can be purified in high yield for low cost, making it an interesting candidate for polymer feedstock. In this study, two polyesters were synthesized from the condensation of either CBD or cannabigerol (CBG) with adipoyl chloride. Poly(CBD-Adipate) was cast into free-standing films and subjected to thermal, mechanical, and biological characterization. Poly(CBD-Adipate) films exhibited a lack of cytotoxicity toward adipose-derived stem cells while displaying an inherent antioxidant activity compared to poly(lactide) films. Additionally, this material was found to be semi-crystalline and able to be melt-processed into a plastic hemp leaf using a silicone baking mold.

Flexible cyclic-olefin with enhanced dipolar relaxation for harsh condition electrification.

Flexible large bandgap dielectric materials exhibiting ultra-fast charging-discharging rates are key components for electrification under extremely high electric fields. A polyoxafluoronorbornene (m-POFNB) with fused five-membered rings separated by alkenes and flexible single bonds as the backbone, rather than conjugated aromatic structure typically for conventional high-temperature polymers, is designed to achieve simultaneously high thermal stability and large bandgap. In addition, an asymmetrically fluorinated aromatic pendant group extended from the fused bicyclic structure of the backbone imparts m-POFNB with enhanced dipolar relaxation and thus high dielectric constant without sacrificing the bandgap. m-POFNB thereby exhibits an unprecedentedly high discharged energy density of 7.44 J/cm3 and high efficiency at 150 °C. This work points to a strategy to break the paradox of mutually exclusive constraints between bandgap, dielectric constant, and thermal stability in the design of all-organic polymer dielectrics for harsh condition electrifications.

All-Organic Flexible Ferroelectret Nanogenerator with Fabric-Based Electrodes for Self-Powered Body Area Networks.

Due to their electrically polarized air-filled internal pores, optimized ferroelectrets exhibit a remarkable piezoelectric response, making them suitable for energy harvesting. Expanded polytetrafluoroethylene (ePTFE) ferroelectret films are laminated with two fluorinated-ethylene-propylene (FEP) copolymer films and internally polarized by corona discharge. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-coated spandex fabric is employed for the electrodes to assemble an all-organic ferroelectret nanogenerator (FENG). The outer electret-plus-electrode double layers form active device layers with deformable electric dipoles that strongly contribute to the overall piezoelectric response in the proposed concept of wearable nanogenerators. Thus, the FENG with spandex electrodes generates a short-circuit current which is twice as high as that with aluminum electrodes. The stacking sequence spandex/FEP/ePTFE/FEP/ePTFE/FEP/spandex with an average pore size of 3 µm in the ePTFE films yields the best overall performance, which is also demonstrated by the displacement-versus-electric-field loop results. The all-organic FENGs are stable up to 90 °C and still perform well 9 months after being polarized. An optimized FENG makes three light emitting diodes (LEDs) blink twice with the energy generated during a single footstep. The new all-organic FENG can thus continuously power wearable electronic devices and is easily integrated, for example, with clothing, other textiles, or shoe insoles.

Flexible Temperature-Invariant Polymer Dielectrics with Large Bandgap.

Flexible dielectrics operable under simultaneous electric and thermal extremes are critical to advanced electronics for ultrahigh densities and/or harsh conditions. However, conventional high-performance polymer dielectrics generally have conjugated aromatic backbones, leading to limited bandgaps and hence high conduction loss and poor energy densities, especially at elevated temperatures. A polyoxafluoronorbornene is reported, which has a key design feature in that it is a polyolefin consisting of repeating units of fairly rigid fused bicyclic structures and alkenes separated by freely rotating single bonds, endowing it with a large bandgap of ≈5 eV and flexibility, while being temperature-invariantly stable over -160 to 160 °C. At 150 °C, the polyoxafluoronorbornene exhibits an electrical conductivity two orders of magnitude lower than the best commercial high-temperature polymers, and features an unprecedented discharged energy density of 5.7 J cm-3 far outperforming the best reported flexible dielectrics. The design strategy uncovered in this work reveals a hitherto unexplored space for the design of scalable and efficient polymer dielectrics for electrical power and electronic systems under concurrent harsh electrical and thermal conditions.

Graphene and Poly(3,4-ethylene dioxythiophene):Poly(4-styrenesulfonate) on Nonwoven Fabric as a Room Temperature Metal and Its Application as Dry Electrodes for Electrocardiography.

Highly conductive, metal-like poly(ethylene terephthalate) (PET) nonwoven fabric was prepared by coating poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) containing dimethyl sulfoxide (DMSO) onto PET nonwoven fabric previously coated with graphene/graphite. The sheet resistance of the original nonwoven fabric decreases from >80 MΩ□-1 to 1.1 Ω□-1 after coating with 10.7 wt % graphene and 5.48 wt % PEDOT:PSS with a maximum current at breakdown of 4 A. This sheet resistance is lower than previously reported sheet resistances of fabrics coated with graphene films, PEDOT:PSS films, or PEDOT:PSS coated fabrics from the literature. The effect of temperature on the resistance of graphene/PEDOT:PSS coated fabric has revealed that the resistance decreases with increasing temperature, analogous to semiconductors, with a clear semiconductor-metal transition occurring at 290 K. Finally, a coating of 18 wt % graphene/graphite and 2.5 wt % PEDOT:PSS (Rs = 5.5 Ω□-1) screen printed on the nonwoven fabric was shown to function as an electrode for electrocardiography without any hydrogel and with dry skin conditions. This composite coating finds application in wearable electronics for military and consumer sectors.

Sn-Polyester/Polyimide Hybrid Flexible Free-Standing Film as a Tunable Dielectric Material.

Flexible films having high dielectric constants with low dielectric loss have promising application in the emerging area of high-energy-density materials. Here, for the first time, an organometallic, Sn-polyester-containing hybrid free-standing film in polyimide matrix is reported. Polyimide, pBTDA-HDA, is used with poly(dimethyltin glutarate) and poly(dimethyltin-3,3-dimethyglutarate) (pDMTDMG) for having a processable film with tunable dielectric properties. Hybrid film with 60% pDMTDMG and 40% PI (HB2) is found to have improved dielectric features over previously synthesized organic polyimide and organometallic Sn-polyester homopolymers. These novel organometallic-organic hybrid systems expanded a new area of dielectrics for next-generation electronics with superior overall electrical performance.

Screen-Printed PEDOT:PSS Electrodes on Commercial Finished Textiles for Electrocardiography.

Electrocardiography (ECG) is an essential technique for analyzing and monitoring cardiovascular physiological conditions such as arrhythmia. This article demonstrates the integration of screen-printed ECG circuitry from a commercially available conducting polymer, PEDOT:PSS, onto commercially available finished textiles. ECG signals were recorded in dry skin conditions due to the ability of PEDOT:PSS to function as both ionic and electronic conductors. The signal amplifies when the skin transpires water vapor or by applying a common lotion on the skin. Finally, PEDOT:PSS wires connected to PEDOT:PSS electrodes have been shown to record ECG signals comparable to Ag/AgCl connected to copper wires.

PEDOT:PSS "Wires" Printed on Textile for Wearable Electronics.

Herein, the fabrication of all-organic conductive wires is demonstrated by utilizing patterning techniques such as inkjet printing and sponge stencil to apply poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) onto nonwoven polyethylene terephthalate (PET) fabric. The coating of the conducting polymer is only present on the surface of the substrate (penetration depth ∼ 200 µm) to retain the functionality and wearability of the textile. The wires fabricated by different patterning techniques provide a wide range of resistance, i.e., tens of kΩ/□ to less than 2 Ω/□ that allows the resistance to be tailored to a specific application. The sheet resistance is measured to be as low as 1.6 Ω/□, and the breakdown current is as high as 0.37 A for a 1 mm wide line. The specific breakdown current exceeds the previously reported values of macroscopic carbon nanotube based materials. Simple circuits composed of the printed wires are demonstrated, and resistance of the circuit from the measurement agrees with the calculated value based on Kirchhoff's rules. Additionally, the printed PEDOT:PSS wires show less than 6.2% change in sheet resistance after three washing and drying cycles using detergent.

Optimization of Organotin Polymers for Dielectric Applications.

Recently, there has been a growing interest in developing wide band gap dielectric materials as the next generation insulators for capacitors, photovoltaic devices, and transistors. Organotin polyesters have shown promise as high dielectric constant, low loss, and high band gap materials. Guided by first-principles calculations from density functional theory (DFT), in line with the emerging codesign concept, the polymer poly(dimethyltin 3,3-dimethylglutarate), p(DMTDMG), was identified as a promising candidate for dielectric applications. Blends and copolymers of poly(dimethyltin suberate), p(DMTSub), and p(DMTDMG) were compared using increasing amounts of p(DMTSub) from 10% to 50% to find a balance between electronic properties and film morphology. DFT calculations were used to gain further insight into the structural and electronic differences between p(DMTSub) and p(DMTDMG). Both blend and copolymer systems showed improved results over the homopolymers with the films having dielectric constants of 6.8 and 6.7 at 10 kHz with losses of 1% and 2% for the blend and copolymer systems, respectively. The energy density of the film measured as a D-E hysteresis loop was 6 J/cc for the copolymer, showing an improvement compared to 4 J/cc for the blend. This improvement is hypothesized to come from a more uniform distribution of diacid repeat units in the copolymer compared to the blend, leading toward improved film quality and subsequently higher energy density.

Rational Co-Design of Polymer Dielectrics for Energy Storage.

Although traditional materials discovery has historically benefited from intuition-driven experimental approaches and serendipity, computational strategies have risen in prominence and proven to be a powerful complement to experiments in the modern materials research environment. It is illustrated here how one may harness a rational co-design approach-involving synergies between high-throughput computational screening and experimental synthesis and testing-with the example of polymer dielectrics design for electrostatic energy storage applications. Recent co-design efforts that can potentially enable going beyond present-day "standard" polymer dielectrics (such as biaxially oriented polypropylene) are highlighted. These efforts have led to the identification of several new organic polymer dielectrics within known generic polymer subclasses (e.g., polyurea, polythiourea, polyimide), and the recognition of the untapped potential inherent in entirely new and unanticipated chemical subspaces offered by organometallic polymers. The challenges that remain and the need for additional methodological developments necessary to further strengthen the co-design concept are then presented.

Poly(dimethyltin glutarate) as a prospective material for high dielectric applications.

Poly(dimethyltin glutarate) is presented as the first organometallic polymer, a high dielectric constant, and low dielectric loss material. Theoretical results correspond well in terms of the dielectric constant. More importantly, the dielectric constant can be tuned depending on the solvent a film of the polymer is cast from. The breakdown strength is increased through blending with a second organometallic polymer.

Effect of incorporating aromatic and chiral groups on the dielectric properties of poly(dimethyltin esters).

High-dielectric constant materials are critical for numerous applications such as photovoltaics, photonics, transistors, and capacitors. There are numerous polymers used as dielectric layers in these applications but can suffer from having a low dielectric constant, small band gap, or ferroelectricity. Here, the structure-property relationship of various poly(dimethyltin esters) is described that look to enhance the dipolar and atomic polarization component of the dielectric constant. These polymers are also modeled using first principles calculations based on density functional theory (DFT) to predict such values as the total, electronic, and ionic dielectric constant as well as structure. A strong correlation is achieved between the theoretical and experimental values with the polymers exhibiting dielectric constants >4.5 with dissipation on the order of 10(-3) -10(-2) .

Color-tuning neutrality for flexible electrochromics via a single-layer dual conjugated polymer approach.

A method to color-tune electrochromic devices through the use of theoretical calculations is demonstrated to achieve neutrality using only three monomers that form two distinct copolymers. These devices exhibit photopic contrasts up to ca. 38%, high neutrality, color uniformity, and switch speeds of less than 1 s. In addition, this method is used to fabricate a large-area flexible electrochromic device of 75 cm(2) , exceeding the size of small displays.

Rational design of all organic polymer dielectrics.

To date, trial and error strategies guided by intuition have dominated the identification of materials suitable for a specific application. We are entering a data-rich, modelling-driven era where such Edisonian approaches are gradually being replaced by rational strategies, which couple predictions from advanced computational screening with targeted experimental synthesis and validation. Here, consistent with this emerging paradigm, we propose a strategy of hierarchical modelling with successive downselection stages to accelerate the identification of polymer dielectrics that have the potential to surpass 'standard' materials for a given application. Successful synthesis and testing of some of the most promising identified polymers and the measured attractive dielectric properties (which are in quantitative agreement with predictions) strongly supports the proposed approach to material selection.

Neutral color tuning of polymer electrochromic devices using an organic dye.

Herein, we present a facile, one-step method to color tune electrochromic devices (ECDs) that switch between two neutral colors via in situ electrochemical polymerization of electroactive monomers in the presence of a small molecule organic yellow dye using all commercially available materials. These devices exhibited photopic contrasts of ca. 30% without background correction when assembled on flexible PET-ITO substrates. In addition, devices exhibited switching speeds as low as 1 second, color uniformity, and stability. Large defect free ECDs of 100 cm(2) were fabricated exceeding the active switch area required for goggles, lenses, and small display applications.

Rationally designed polyimides for high-energy density capacitor applications.

Development of new dielectric materials is of great importance for a wide range of applications for modern electronics and electrical power systems. The state-of-the-art polymer dielectric is a biaxially oriented polypropylene (BOPP) film having a maximal energy density of 5 J/cm(3) and a high breakdown field of 700 MV/m, but with a limited dielectric constant (∼2.2) and a reduced breakdown strength above 85 °C. Great effort has been put into exploring other materials to fulfill the demand of continuous miniaturization and improved functionality. In this work, a series of polyimides were investigated as potential polymer materials for this application. Polyimide with high dielectric constants of up to 7.8 that exhibits low dissipation factors (<1%) and high energy density around 15 J/cm(3), which is 3 times that of BOPP, was prepared. Our syntheses were guided by high-throughput density functional theory calculations for rational design in terms of a high dielectric constant and band gap. Correlations of experimental and theoretical results through judicious variations of polyimide structures allowed for a clear demonstration of the relationship between chemical functionalities and dielectric properties.

Acrylated poly(3,4-propylenedioxythiophene) for enhancement of lifetime and optical properties for single-layer electrochromic devices.

We utilized our in situ method for the one-step assembly of single-layer electrochromic devices (ECDs) with a 3,4-propylenedioxythiophene (ProDOT) acrylate derivative, and long-term stability was achieved. By coupling the electroactive monomer to the cross-linkable polymer matrix, preparation of the electrochromic ProDOT polymer can occur followed by UV cross-linking. Thus, we achieve immobilization of the unreacted monomer, which prevents any degradative processes from occurring at the counter electrode. This approach eliminated spot formation in the device and increased stability to over 10 000 cycles when compared to 500 cycles with conventional ProDOT devices wherein the monomer is not immobilized. The acrylated electrochromic polymer exhibits similar electrochromic properties as conventional ProDOT devices, such as photopic contrast (48% compared to 46%) and switch speed (both 2 s). This method can be applied to any one-layer electrochromic system where improved stability is desired.

Solid-state high-throughput screening for color tuning of electrochromic polymers.

Diffusion of two monomers and their oxidative copolymerization inside a solid-state gel electrolyte is utilized as a method to match the monomer feed ratio to a color resulting from a conjugated copolymer having a single absorption in the visible region. Here, a combination of two monomers is used to generate a solid-state electrochromic device of any color, except black and green, in the colored state with all other colors going to transmissive sky blue in the bleached state.