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The development of electrocaloric materials (ECMs) with strong electrocaloric effect (ECE) in recent years offers a great opportunity for the development of solid-state heat pumps without using environmentally unfriendly vapor-based technologies. Currently existing ECE-based heat pumps (CEHPs) use one ECM layer that has to be moved back and forth between the thermal source (SO) and sink (SI), which raises reliability and safety concerns. Here, a design, which uses two layers of an ECM and the electric field on each layer is independently controlled with a special pattern, is introduced to develop ECE-based heat pumps with a high cooling power. In the design, the two ECM layers are permanently bound together and used as a single ECM module. The performance of the heat pumps is calculated using the newly introduced analytical solutions. First of all, it is found that the cooling power of CEHPs is strongly dependent on, while the cooling power of heat pumps using the two-ECM-layers module (TELM) is insensitive to, the materials used as the SO/SI. This would significantly expand the application of ECE-based heat pumps since in many applications there is no freedom to choose the materials to be used as the SO/SI. Secondly, the heat pumps using the TELM exhibit a high cooling power. For example, when different materials are used as the SO/SI, the cooling power of CEHPs would be changed over more than 100 times, while it is only changed less than 2 times when the TELM is used to replace the ECM layer used in CEHPs. And the cooling power of heat pumps using the TELM can be more than 7 times higher than the highest cooling power obtained in CEHPs. More importantly, the TELM can be permanently bound to the SO (or the SI) (i.e., the ECM is not moved at all during the operation), which would result in a high reliability. In this case, the cooling power of the heat pumps using the TELM can only be changed less than 25 % when different materials are used as the SO/SI and this cooling power is close to the highest cooling power obtained in the CEHPs.

An all-organic composite system using newly developed PPy nanoclips is developed. The composites have a uniform microstructure due to the unique preparation process. The composites have a very low percolation threshold (<8wt%) and exhibit a high dielectric constant. At room temperature, the composites exhibit a dielectric constant of more than 1000. At temperatures higher than 98°C, the composites exhibit a dielectric constant of about 2000. More interestingly, the high dielectric constant reported here is associated with a loss much smaller than the loss reported for other CDCs using 1-D fillers. It is indicated that a new dielectric relaxation process is induced due to the mixture of PPy with P(VDF-TrFE), whose relaxation time decreases with increasing PPy content. The loss observed in the composites at low temperature including room temperature is mainly determined by this relaxation process rather than the conductivity. If this relaxation process has a strong contribution to the dielectric constant, the widely used percolation formula describing relationship between the dielectric constant and the composite cannot be used.

Electron-irradiated poly(vinylidene fluoride−trifluoroethylene) [P(VDF−TrFE)] copolymer exhibits a very high electromechanical performance that is attractive for many applications. A study of recrystallization of irradiated P(VDF−TrFE) 65/35 mol % copolymer is reported in this paper. The structure and morphology of the recrystallized samples were determined using DSC and X-ray diffraction, and the polarization behavior of the recrystallized samples was studied. The nonpolar phase content of the recrystallized samples was much lower than that of the irradiated samples. For irradiated samples that exhibited the best electromechanical performance, the corresponding recrystallized material had a high polar phase content, with a correspondingly high remanent polarization. For samples irradiated with higher doses, although the polarization level was low immediately after irradiation, after recrystallization the material exhibited a much higher polarization level with a very small remanent polarization, an attractive combination for many electromechanical applications.

In this study, we investigated the influence of annealing conditions before irradiation on the ferroelectric and electromechanical properties of uniaxially stretched high-energy-electron-irradiated poly(vinylidene fluoride trifluoroethylene) (HEEIP) copolymer (68/32 mol %) films. For films annealed at one fixed temperature before the irradiation (one-step annealing), the highest crystallinity, which was highly desirable for enhancing the electromechanical response, was obtained only for films annealed between 132 and 136 °C. In addition, annealing over 10 h in this temperature window resulted in a large increase in the crystal lamellar thickness, which was required for reducing the polarization hysteresis to a minimum in the HEEIP samples. For improvements in the mechanical qualities of the uniaxially stretched films, a two-step annealing procedure was investigated; that is, before the irradiation, the films were first annealed at a lower temperature to release the mechanical stress in the films due to the stretching and then were annealed in the high-temperature window to raise the crystallinity and crystalline size. The experimental results indicated that this approach could produce uniaxially stretched HEEIP films with much improved mechanical qualities. Furthermore, the uniaxially stretched HEEIP films with this two-step annealing exhibited the same electromechanical response as or an even higher one than that from the one-step-annealed HEEIP films. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 797–806, 2003

In poly(vinylidene fluoride-trifluoroethylene) copolymer spin cast films, it has been observed that the polarization switching time increases as the film thickness is reduced. We will show that this change with thickness can be divided into two thickness regimes, those above a critical thickness and below this critical thickness. For films above the critical thickness, the change is in the switching behavior is mainly due to interface effect. While for films below the critical thickness, there is an additional and very large increase of the switching time with reduced film thickness, which is caused by a large drop of the crystallinity in this thickness range. It has been observed that this critical thickness, below which the crystallization in the polymer films is strongly hindered, depends on the film annealing conditions and is directly related to the thermodynamic stable crystallite thickness.

The microstructural changes in high-energy electron-irradiated poly(vinylidene fluoride−trifluoroethylene) 68/32 mol % copolymer have been studied by X-ray diffraction, FTIR spectroscopy, and differential scanning calorimetry. The macroscopic polarization response in these materials was investigated by examining the dielectric and polarization behavior in a broad temperature and frequency range. It was found that besides reducing crystallinity in the copolymer film, irradiation produces significant changes in the ferroelectric-to-paraelectric phase transition behavior. The irradiation leads to a reduction in the polar domain size to below a critical size (a few nanometers), resulting in the instability of the macroscopic ferroelectric state and transforming the structure of the crystalline region in the copolymer from a polar all-trans ferroelectric to a nonpolar state represented by a trans−gauche conformation. However, a reentrant polarization hysteresis was observed in the copolymers irradiated with higher doses (>75 Mrad). Therefore, there is an optimized dose that generates a copolymer with a nonpolar structure but relatively high crystallinity whose electromechanical performance is the best. In the copolymers in this optimum dose range, FT-IR data revealed that there is not much change in the molecular conformation with temperature, even as the temperature passes through the dielectric peak, indicating that there is no symmetry breaking in both the macroscale and local level. Although the lattice spacing of the crystalline region along the molecular chain direction discontinuously changes between two special cases, the interchain spacing continuously changes with the irradiation dose, reflecting a strong intrachain coupling between the nonpolar and polar regions. On the other hand, the X-ray data reveal that the crystalline size perpendicular to the polymer chain does not change with irradiation until at doses exceeding 85 Mrad.

Using a solution casting method, a high dielectric constant composite based on a copper-phthalocyanine (CuPc) oligomer and a poly(vinylidene fluoride-trifluoroethylene) copolymer is developed. The experimental data show that the low field dielectric constant of the composites (with 55 wt % CuPc) can reach 1000 and the loss is ~0.5 at room temperature and 100 Hz. Because of the long-range electron delocalization in CuPc, which results in a strong space charge response of the composite to the external field, there is a strong frequency dispersion of the dielectric properties. In addition, the dielectric properties exhibit a nonlinear behavior with electric field. At a field of 10 kV/cm, the dielectric constant at 10 Hz reaches 4500; meanwhile the dielectric loss is also high. One of the unique attributes of the composite is its mechanical properties that remain very much the same as those of the polymer matrix. Even for a composite with 55 wt % CuPc (the volume fraction of CuPc in the composite is also in the similar range), the composite film is still flexible, with a Young's modulus of 1.2 GPa at room temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 70–75, 2001

The low elastic modulus and the ability to withstand high strain without failure make the conducting polymer attractive for a wide range of acoustic applications based on high-strain electroactive polymers. In this article, we examine the electric and electromechanical performance of all-polymer electromechanical systems, fabricated by painting conductive polyaniline (PANI) doped with camphor sulfonic acid (HCSA) on both sides of electrostrictive Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer films, and compare them with those from the same copolymers with gold electrodes. The all-polymer composite films are flexible, with strong coherent interfaces between the electrostrictive polymer layer and the conductive polymer layer. The electric performance such as dielectric properties and polarization hysteresis loops from P(VDF-TrFE)/PANI film is nearly identical to those of P(VDF-TrFE)/gold films in a wide temperature (from −50 to 120°C), and frequency range (from 1 Hz to 1 MHz). The all-polymer systems also show a similar or even larger electric field induced strain response than that of films with electrodes under identical measurement conditions. The results demonstrate that the polyaniline/HCSA is good candidate material as the electrodes for electroactive polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 945–951, 2000

The effect of hydrostatic pressure up to 1,361 atms on the dielectric properties of a segmented polyurethane elastomer (Dow 2103-80AE) is studied at temperatures from 0°C to 80°C. The experimental results show that the relaxation time for both the I–process, associated with the molecular motions in the hard segments, and the α–process, associated with the glass transition, increases with pressure, and this shift is more pronounced for the I–process. Besides the glass transition, it is found that the I–process can be described by the Vogel–Fulcher (V–F) and Williams–Landel–Ferry (WLF) relations. At atmospheric pressure, Tg and T0 for the I–process are 235.9 K and 4.2 × 10³ K, respectively. Based on the V–F and WLF relations and experimental results, it is found that a parameter, C1, in the WLF relation is independent of the pressure. Thus, a method is introduced to determine the values of both the characteristic transition temperature (Tg) and activation energy (T0) for the processes at different pressures. As the pressure increases from atmospheric to 1,361 atms, the increase of Tg for the I–process is about 30°C. The results also show that, for both the I– and the α–processes, T0 decreases with increasing pressure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 983–990, 1999

The conduction behavior at high current density at room temperature and above of polyaniline (PANI) films doped with HCl and camphor sulfonic acid (HCSA), respectively, is reported. It is found that the current density deviates strongly from the linear relation with the electric field in high current density region, and a saturation of the current density is observed. The maximum current density Jm seems to be proportional to the conductivity of the sample and hence, for PANI doped with HCl, Jm is about 200 A/cm^2, whereas for HCSA doped samples, Jm can reach more than 1,200 A/cm². The saturation of current density is interpreted as being caused by space charge accumulation at the insulating barrier regions and a dedoping effect in the conduction domains due to the detraping of the ions under high fields. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2845–2850, 1999

As discussed in a previous paper [B. G. Martin etal., J. Acoust. Soc. Am. 87, 193–200 (1990)], Chebyshev theory can be used in designing wideband acoustic multilayer antireflection (ar) coatings. For some situations, however, the required Chebyshev layer impedances may be difficult to match with commonly available materials. In such cases, the Chebyshev layer can be replaced by an acoustic symmetric multilayer (ASM) with equivalent properties. ASM dispersion effects, however, somewhat degrade the originally designed ar behavior. To explore this problem, an experimental investigation was made by using ASMs as layer replacements in the fabrication of Chebyshev ar coatings for normally incident ultrasonic waves. It is concluded from this investigation that the ar properties of the Chebyshev coating is only moderately degraded by the use of optimized ASM replacements.

Chebyshev filter theory can be applied to the design of wideband acoustic multilayer antireflection (ar) coatings. However, in many cases the acoustic impedance required for a particular layer is not readily available among common materials. In such cases, this study shows that the Chebyshev layer can be replaced by an acoustic symmetric multilayer (ASM) with the prescribed impedance. On the other hand, ASMs are dispersive, i.e., their reflection properties are a function of frequency. Consequently, the ASM replacement will somewhat degrade the performance of the resulting Chebyshev ar coating. In this study, theoretical results are obtained for a number of ASM replacement designs. For each design, normal‐incidence reflection coefficient versus frequency is calculated. It is concluded that the performance of a Chebyshev ar coating is only slightly degraded by the use of ASM replacements, provided that the ASM dispersion is kept as small as possible. Accordingly, the ASM technique offers a useful means for the practical design of acoustic Chebyshev ar coatings.

The analytical solution is reported for one-dimensional (1D) dynamic conduction heat transfer within a multilayer system that is the typical structure of electrocaloric devices. Here, the multilayer structure of typical electrocaloric devices is simplified as four layers in which two layers of electrocaloric materials (ECMs) are sandwiched between two semi-infinite bodies representing the thermal sink and source. The temperature of electrocaloric layers can be instantaneously changed by external electric field to establish the initial temperature profile. The analytical solution includes the temperatures in four bodies as a function of both time and location and heat flux through each of the three interfaces as a function of time. Each of these analytical solutions includes five infinite series. It is proved that each of these series is convergent so that the sum of each series can be calculated using the first Nterms of the series. The formula for calculating the value of Nis presented so that the simulation of an electrocaloric device, such as the temperature distribution and heat transferred from one body to another can be performed. The value of Nis dependent on the thickness of electrocaloric material layers, the time of heat conduction, and thermal properties of the materials used. Based on a case study, it is concluded that the Nis mostly less than 20 and barely reaches more than 70. The application of the analytical solutions for the simulation of real electrocaloric devices is discussed.

Various designs have been introduced to build heat pumps using the electrocaloric effect (ECE). Each of all the current designs uses at least one moving part, which significantly reduces the reliability of the pump and adds complexities. In this work, a new all-solid design is introduced, in which two layers of an electrocaloric material (ECM) are permanently sandwiched in the source and sink, which would significantly increase the device’s reliability since nothing moves and all are permanently bound together. More importantly, the electric fields applied on two ECM layers are independently controlled. A special sequence for the electric fields on two ECM layers is introduced. Numerical calculation was used to simulate the device’s performance by using the newly introduced analytical solutions for the heat conduction in the system. It is concluded that a continuous heat transformation from the source to sink at the same temperature can be achieved when the contacting coefficient, Kε=(kcρccpc)∕(koρocpo), is very small, where k, ρ, and cpare thermal conductivity, density, and heat capacity, respectively, while the superscript cand orepresent the ECM and source/sink, respectively.

To overcome the low discharging efficiency of ceramic-polymer composites using ferroelectric polymers as matrix and to take the advantage in fabrication offered by the polar polymer, a polar but non-ferroelectric polymer – poly(methyl methacrylate) (PMMA) – was selected as the matrix in the development of high performance composites for energy storage. Ba0.5Sr0.5TiO3(BST) nanoparticles were selected as the filler. Freestanding and flexible BST-PMMA ceramic-polymer nanocomposites with BST content up to 30 vol.% were fabricated in thickness of about 5 μm using spin-coating process and were systemically studied. Due to the strong interaction between the polar groups of PMMA and the hydroxyl groups on the surface of BST nanoparticles, the suspension of BST nanoparticles in PMMA solution exhibits excellent stability and, hence, the nanocomposite films have excellent microstructure uniformity and compatibility between the BST nanoparticles and PMMA matrix. All the BST-PMMA films exhibit excellent frequency (100 Hz to 1 MHz) and temperature (−90 to 100 °C) stabilities in their dielectric properties with a high energy-storage density of more than 11 J/cm3. Most importantly, an ultra-high discharging efficiency of almost 100% is obtained in all the nanocomposites.

A complication of yellow nail syndrome after pleurodesis is presented. After endotracheal extubation the patient developed delayed acute laryngeal oedema requiring re-intubation. We postulate that the combination of lymphatic defect and airway trauma from the double lumen endotracheal tube were contributory to the oedema. If endotracheal intubation is performed, these patients should be observed for 48 h. (Heart, Lung and Circulation 2000; 9: 36-38)

Conductor–dielectric 0–3 nanocomposites using spherical nickel nanoparticles as filler and poly(vinylidene fluoride–trifluoroethylene) 70/30mol.% as matrix are prepared using a newly developed process that combines a solution cast and a hot-pressing method with a unique configuration and creates a uniform microstructure in the composites. The uniform microstructure results in a high percolation threshold φc(>55vol.%). The dielectric properties of the nanocomposites at different frequencies over a temperature range from −70∘C to 135∘C are studied. The results indicate that the composites exhibit a lower electrical conductivity than the polymer matrix. It is found that the nanocomposites can exhibit an ultra-high dielectric constant, more than 1500 with a loss of about 1.0 at 1kHz, when the Ni content (53 vol.%) is close to percolation threshold. For the nanocomposites with 50 vol.% Ni particles, a dielectric constant more than 600 with a loss less than 0.2 is achieved. It is concluded that the loss including high loss is dominated by polarization process rather than the electrical conductivity. It is also found that the appearance of Ni particles has a strong influence on the crystallization process in the polymer matrix so that the polymer is converted from a typical ferroelectric to a relaxor ferroelectric. It is also demonstrated that the widely used relationship between the dielectric constant and the composition of the composites may not be valid.

The characteristics of the electromechanical response observed in an ionic-electroactive polymer (i-EAP) are represented by the time (t) dependence of its bending actuation (y). The electromechanical response of a typical i-EAP — poly(ethylene oxide) (PEO) doped with lithium perchlorate (LP) — is studied. The shortcomings of all existing models describing the electromechanical response obtained in i-EAPs are discussed. A more reasonable model: y=ymaxe−τ∕tis introduced to characterize this time dependence for all i-EAPs. The advantages and correctness of this model are confirmed using results obtained in PEO-LP actuators with different LP contents and at different temperatures. The applicability and universality of this model are validated using the reported results obtained from two different i-EAPs: one is Flemion and the other is polypyrrole actuators.

Pyroelectric composites of triglycine sulfate (TGS)-polyvinylidene difluoride (PVDF) doped with graphene are studied. It is found that the graphene can effectively improve the polling efficiency and thermal property of the composites so that the infrared detective performance can be significantly improved. For example, by adding about 0.83 wt.% of graphene, the infrared detective property can be improved by more than 30%. It is also found that the size of the graphene plays a critical role on the property improvement. For example, the small-sized graphene prepared by ultrasonic exfoliation (UE) method is more effective than the big-sized graphene prepared by electrochemical exfoliation (EE) method.

Fe-rich Fe-Co-B magnetostrictive alloys have been considered as good high-frequency sensor materials. In this paper, Fe-rich Fe-Co-B thin films with the composition of Fe57Co29B14, Fe55Co28B17, Fe53Co27B20, Fe51Co26B23 and Fe49Co25B26 were fabricated. The structure, morphology, magnetic property and resonant behavior of the films were studied. Among the different compositions, Fe55Co28B17has the highest Q value and relatively high amplitude, which is beneficial for sensor application. Au/Fe55Co28B17/Au magnetostrictive particles (MSPs) were prepared by electrodeposition and microfabrication. The 500 μm×100 μm×6 μm MSP shows a resonant frequency of 3.320 MHz and Q value of 127. Fe-Co-B thin film sensors with good performance can be potentially utilized for high-frequency application and food safety detection.

0-3 dielectric composites with high dielectric constants have received great interest for various technological applications. Great achievements have been made in the development of high performance of 0-3 composites, which can be classified into dielectric–dielectric (DDCs) and conductor–dielectric composites (CDCs). However, predicting the dielectric properties of a composite is still a challenging problem of both theoretical and practical importance. Here, the physical aspects of 0-3 dielectric composites are reviewed. The limitation of current understanding and new developments in the physics of dielectric properties for dielectric composites are discussed. It is indicated that the current models cannot explain well the physical aspects for the dielectric properties of 0-3 dielectric composites. For the CDCs, experimental results show that there is a need to find new equations/models to predict the percolative behavior incorporating more parameters to describe the behavior of these materials. For the DDCs, it is indicated that the dielectric loss of each constituent has to be considered, and that it plays a critical role in the determination of the dielectric response of these types of composites. The differences in the loss of the constituents can result in a higher dielectric constant than both of the constituents combined, which breaks the Wiener limits.

The equation εeff∝ (ϕc- ϕ)-swhich shows the relationship between effective dielectric constant (εeff) and the filler concentration (φ), is widely used to determine the percolation behavior and obtain parameters, such as percolation threshold φcand the power constant s in conductor–dielectric composites (CDCs). Six different systems of CDCs were used to check the expression by fitting experimental results. It is found that the equation can fit the experimental results at any frequency. However, it is found that the fitting constants do not reflect the real percolation behavior of the composites. It is found that the dielectric constant is strongly dependent on the frequency, which is mainly due to the fact that the frequency dependence of the dielectric constant for the composites close to φcis almost independent of the matrix.

GaAs/InGaAs quantum-well lasers have been demonstrated by metallorganic chemical vapor deposition on virtual Ge substrates on Si via aspect-ratio trapping (ART) and epitaxial lateral overgrowth (ELO). Laser-structure growth is achieved in two steps: The first step is growing uncoalesced defect-free Ge stripes on a SiO2trench-patterned silicon substrate via ART, whereby the misfit defects originating from the Ge/Si interface are trapped by laterally confining sidewalls. Defects arising from above the SiO2film are reduced by using an optimized ELO process followed by chemical mechanical polishing to provide a planar Ge surface. The second step is overgrowing a GaAs/InGaAs laser structure on the virtual Ge substrate. A number of GaAs/Ge integration issues, including Ge autodoping and antiphase domain defects in GaAs, have been overcome. Despite unoptimized laser structures with high series resistance and large threshold current densities, pulsed room-temperature lasing at a wavelength of 980 nm has been demonstrated using a combination of ART and ELO. This technique is very promising for the achievement of reliable GaAs-based optoelectronic devices on Si.

Several new methods for the synthesis of 2-alkyl-2-oxo-1,3,2-dioxa-phosphorinane (1) and -phosphepane (2) were conducted based on Arbuzov rearrangement, alcoholysis of RP(O)Cl2 with glycol using dilution method or alkylation of cyclic phosphite under PTC condition. The solvent effect on the 31P NMR chemical shift and the characteristic behaviours of the 13C NMR spectra of 1 was investigated. It was found that compd 1 with R=CH3 existed in an equilibrium of e and a forms. The mass spectra of 1 and 2 showed that the ring opening was in competition with the cleavage of P-C bond. According to the fragmentation pathway, 1 can be classified in two categories involving ring opening and cleavage of C-C or P-C bond. For compd 2 the ring opening was a dominant process. Alkaline hydrolysis of 1 and 2 was studied in aqueous dioxane. The hydrolytic process is classified as an AE reaction. Quantitative structure-reactivity relationship was established by multiple regressionanalysis involving the rate constant and the structural parameters of the exocyclic substituents on phosphorus. The difference between the hydrolytic performance of cyclic alkylphosphonates and carboxylates was discussed in terms of various structural changes between ground state and transition state during the hydrolysis.