The electroactive properties of PVDF-based ferroelectric polymers can be tailored by blending. In order to investigate the tunability of electrocaloric effect (ECE) and ferroelectric responses, ...blends of ferroelectric relaxor poly(vinylidene difluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer and normal ferroelectrics poly(vinylidene difluoride–co–trifluoroethylene) (P(VDF–TrFE)) copolymer are studied. At low copolymer content (<15 wt%), the coupling between the relaxor terpolymer and the nano-phase copolymer converts the copolymer into relaxor and causes an increase in the crystallinity compared with neat terpolymer. As a result, the blends exhibit an enhanced relaxor polarization response and a significant increase in the electrocaloric effect compared with those in the neat terpolymer. At high copolymer content, the blends exhibit mixed structures of the two components. By varying composition, the dielectric and ferroelectric properties of blends can be tuned in the range between the copolymer and terpolymer. This blend system provides a model system to study how random defects influence the polarization response in the normal ferroelectric copolymer, and to understand the relationship between the polarization response and ECE in the blends. The results demonstrate the promise of nanocomposite approaches in tailoring and enhancing ECE and ferroelectric properties in the ferroelectric polymers.
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Q.‐D. Shen and co‐workers demonstrate a simple and low‐cost—yet effective—wearable flexible transducer for non‐invasive and dynamic cardiovascular diagnosis system on page 3640. Constructed from a ...ferroelectric polymer thin film on top of an active semiconducting layer, the device can detect transient pulse waves with fast response and high sensitivity. The transducers have excellent potential for electronic skin and health monitoring applications.
Greatly enhanced energy density in poly(vinylidene fluoride‐chlorotrifluoroethylene) P(VDF‐CTFE) is realized through interface effects induced by a photo cross‐linking method. Being different from ...nanocomposites with lowered dielectric strength, the cross‐linked P(VDF‐CTFE)s possess a high breakdown field as well as remarkably elevated polarization, both of which contribute to the enhanced energy density as high as 22.5 J · cm−3. Moreover, patterned thin films with various shapes and sizes are fabricated by photolithography, which sheds new light on the integration of PVDF‐based electroactive polymers into organic microelectronic devices such as flexible pyroelectric/piezoelectric sensor arrays or non‐volatile ferroelectric memory devices.
Greatly enhanced energy density in P(VDF‐CTFE) is realized through interface effects induced by a photo cross‐linking method. The cross‐linked P(VDF‐CTFE)s possess high breakdown field as well as remarkably elevated polarization, both of which contribute to the enhanced energy density as high as 22.5 J·cm−3. Patterned thin films with various shapes and sizes are fabricated by photolithography, which sheds new light on the integration of PVDF‐based electroactive polymers into micro organic electronic devices.
Ferroelectric polymers are among the most promising materials for flexible electronic devices. Highly ordered arrays of the defect-modified ferroelectric polymer P(VDF-TrFE-CFE) (poly(vinylidene ...fluoride-trifluoroethylene-chlorofluoroethylene)) are fabricated by nanoimprint lithography for nonvolatile memory application. The defective CFE units reduce the coercive field to one-fifth of that of the un-modified P(VDF-TrFE), which can help minimize the energy consumption and extend the lifespan of the device. The nanoimprint process leads to preferable orientation of polymer chains and delicately controlled distribution of the defects, and thus a bi-stable polarization that makes the memory nonvolatile, as revealed by the pulsed polarization experiment.
Bifunctional composite nanoparticles with simultaneous response toward light excitation and external magnetic field are fabricated by electrostatic adsorption of a single layer of conjugated ...polyelectrolytes on the magnetic nanoparticle surfaces. Cell imaging is realized through incubation of the composite nanoparticles with human hepatoma cell Bel-7402. Both fluorescence microscopy imaging and flow cytometry analysis verify that the bifunctional nanoparticles efficiently penetrate the cell membranes. Transmission electron microscopy reveals that the nanoparticles are confined in the endosome and show clear signs of particle aggregation. The cellular uptake efficiencies of the magnetic-fluorescent nanoparticles can be enhanced greatly by a magnetic field. In vitro cell viability results indicate low cytotoxicity of the nanoparticles even after 72 h incubation. The current method of fluorescence labeling of nanomaterials by electrostatic adsorption is applicable to a variety of charged nanomaterials that exist with great diversity in chemistry and morphology, which is necessary for estimation of cell toxicity and fundamental understanding of phenomena related to the development of nanomaterial based diagnostics and therapeutics.
Interfacial architecture is key in tuning ferroelectric nanocomposites; however, the dynamic process of energy storage and release at the interface still remains a mystery. Herein, we experimentally ...demonstrated the direct proof of interfacial polarization, and interfacial energy distribution and coupling in ferroelectric nanocomposites by scanning probe microscopy (SPM) techniques. Remarkably, static reconstructions of the decay time (τ2) reveals that the nanocomposite with carboxyl polystyrene nanoparticles (PS–COOH NPs) exhibits a much more obvious interfacial polarization layer than that of the nanocomposite with PS NPs, which is beneficial for achieving high energy density and high discharged efficiency. Besides, the spatial map of the decay time (τ1) indicates that the size of polar nanoregions (PNRs) is scaled down by the cross-linking method, which is beneficial for achieving high energy density. Most importantly, SPM technology offers a means of visualizing the entire process of the energy release at the interface in real time and real space, which is advantageous to design hierarchical interface architecture for nanoscale energy utilization in capacitors, batteries, and fuel cells.
An anaerobe‐inspired drug delivery vehicle is described by Q. D. Shen, Z. Gu, and co‐workers in their Communication on page 2588 ff. The biomimetic nanovesicles are stable in cells with normal ...physiological redox and oxygen balance. Upon disruption by external light stimuli, they show dual synergistic anticancer actions with enhanced therapeutic efficacy.
Healthy weight loss represents a real challenge when obesity is increasing in prevalence. Herein, we report a conjugated polymer nanocarrier for smart deactivation of lipase and thus balancing ...calorie intake. After oral administration, the nanocarrier is sensitive to lipase in the digestive tract and releases orlistat, which deactivates the enzyme and inhibits fat digestion. It also creates negative feedback to control the release of itself. The nanocarrier smartly regulates activity of the lipase cyclically varied between high and low levels. In spite of high fat diet intervention, obese mice receiving a single dose of the nanocarrier lose weight over eight days, whereas a control group continues the tendency to gain weight. Daily intragastric administration of the nanocarrier leads to lower weight of livers or fat pads, smaller adipocyte size, and lower total cholesterol level than that of the control group. Near-infrared fluorescence of the nanocarrier reveals its biodistribution.
Composite nanoparticles with magnetic core and fluorescent shell were facilely prepared by the layer-by-layer deposition of conjugated polyelectrolytes over the negatively charged nanoparticles (NPs) ...of superparamagnetic iron oxide. The alternate assembly of cationic and anionic fluorescent polyelectrolytes leads to reversal in the sign of ζ-potentials. The even numbers of adsorption layer corresponding to the anionic polyelectrolyte (PFS) have negative values (−13 to −24 mV), whereas odd numbers of coating relative to the cationic polyelectrolyte (PFN) have positive values (26 to 28 mV). The composite nanoparticles can respond to both external magnetic field and ultraviolet light excitation. Förster resonance energy transfer (FRET) between oppositely charged polyelectrolytes (PFN and ThPFS) layers was also found, indicating dense packing of the polymer coatings. The fluorescence of the positively charged nanoparticles (NPs/PFN) can be quenched with very high efficiency by a small molecule anionic quencher Fe(CN)6 4−, while the same quencher has far less effect on the fluorescence of the negatively charged nanoparticles (NPs/PFN/PFS).
A nanocomposite was fabricated using poly(vinylidene fluoride) (PVDF) as matrix and poly(p-chloromethyl styrene) (PCMS) grafted with high dielectric constant copper phthalocyanine oligomer (CuPc) ...(PCMS-g-CuPc) as filler. Transmission electron microscopic morphologies reveal that the PCMS-g-CuPc particle size of ca. 80nm in average are dispersed in PVDF matrix, while in PCMS-g-CuPc particles the PCMS acts as “matrix” which contains dispersed CuPc balls with a average size of ca. 25nm 1/20 of that of CuPc in simple blend of PVDF and CuPc (PVDF/CuPc). The nanocomposite with only 15wt% CuPc can realize a dielectric constant of 325 at 100Hz, about 7 times larger than that of PVDF/CuPc, and nearly 40-fold enhancement with respect to that of the pure PVDF. The significant enhancement of dielectric response can be attributed to the remarkably strengthened exchange coupling effect as well as the Maxwell–Wagner–Sillars polarization mechanism.
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