Other affiliations: Chinese Academy of Sciences, Center for Excellence in Education, Johns Hopkins University ...read more
Bio: Kailiang Ren is an academic researcher from Guangxi University. The author has contributed to research in topics: Piezoelectricity & Materials science. The author has an hindex of 24, co-authored 58 publications receiving 3403 citations. Previous affiliations of Kailiang Ren include Chinese Academy of Sciences & Center for Excellence in Education.
Papers published on a yearly basis
TL;DR: It is demonstrated that a very high energy density with fast discharge speed and low loss can be obtained in defect-modified poly(vinylidene fluoride) polymers by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants.
Abstract: Dielectric polymers with high dipole density have the potential to achieve very high energy density, which is required in many modern electronics and electric systems. We demonstrate that a very high energy density with fast discharge speed and low loss can be obtained in defect-modified poly(vinylidene fluoride) polymers. This is achieved by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants, to avoid the electric displacement saturation at electric fields well below the breakdown field. The results indicate that a very high dielectric constant may not be desirable to reach a very high energy density.
TL;DR: In this article, the bimorph-based piezoelectric nanogenerators (P/TENG) were integrated into the triboelectrics to construct a hybrid piezo/triboelectrical NG for highly efficient mechanical rotation-energy harvesting.
Abstract: To develop highly efficient energy harvesting means to sustainably driving miniaturized portable electronic devices, the hybrid nanogenerators (NGs) are emerging to compensate for the respective shortcomings of either type of NG. However, the crucial factors affecting the output performances of hybrid NGs still exist, such as the driving frequency, phase difference and mismatched impedance. Here, the bimorph-based piezoelectric NG was integrated into the triboelectric NG to construct a hybrid piezo/triboelectric NG (H-P/TENG) for highly efficient mechanical rotation-energy harvesting. Systematic measurements and analyses illustrated the output performance of H-P/TENG was independent of the rotation speed (driving frequency) due to the invariable periodic deformation degree of the H-P/TENG. Both NGs in the H-P/TENG had the identical phase and matched impedance in the same magnitude, which were beneficial for direct coupling of their individual rectified output signals and avoided unnecessary energy loss from the utilization of transformer. Under a low rotation speed of 100 rpm, the proposed H-P/TENG delivered high output voltage, output current and large average power/power density at ~210 V, 395 μA and 10.88 mW/6.04 mW cm−2, respectively. The output voltage/current of the sophisticated H-P/TENG could retain at ~210 V/400 μA under rotation speeds from 50 to 250 rpm. Through integrating an energy managing circuit with the H-P/TENG, we developed a DC power source (stable DC output at 3.6 V) to sustainably drive RF wireless temperature sensing network and commercial electronics. The H-P/TENG was also capable of producing high output voltage (150 V) and current (150 μA) at wind speed of 14 m/s to power 50 LEDs in parallel connection. The distinctive structure and outstanding performance of this hybrid NG is promising for the practical application of self-powered systems and the large-scale energy conversion.
TL;DR: In this paper, the authors studied the effect of the solution concentration and collecting distance on the piezoelectric properties of polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE) nanofibers.
Abstract: Since the last decade, piezoelectric polymer nanofibers have been of great interest in the stimulation of cell growth and proliferation for tissue engineering and wound healing applications. To date, there is no clear understanding of how the piezoelectric properties of piezoelectric materials can be affected by electrospinning parameters and how the piezoelectricity from the electrospun polymer nanofibers produced under optimized electrospinning conditions in vivo would affect cell growth, proliferation and elongation. In this paper, it is shown for the first time how electrospinning parameters, such as solution concentration and collecting distance (from the needle to the rotating mandrel), can affect the piezoelectricity of the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) nanofibers. Here, the optimized electrospinning conditions for P(VDF-TrFE) nanofibers were achieved and these nanofiber scaffolds (NFSs) were used for implanted energy harvester in SD rats, cell proliferation and cell alignment growth applications. During the process of slightly pulling implanted site of SD rats, the implanted PVDF-TrFE NFSs generated a maximum voltage and current of 6 mV and ~6 nA, respectively. With great cytocompatibility and relatively large piezoelectric effect, fibroblast cells grew and aligned perfectly along the electrospinning direction of P(VDF-TrFE) nanofiber direction and cell proliferation rate was enhanced by 1.6 fold. Thus, electrospun P(VDF-TrFE) NFSs show great promise in tissue engineering and wound healing applications.
TL;DR: Comparison with a magnetic-based energy harvesting system suggests that electrostrictive energy harvesting systems are preferable for "small" energy harvesting applications with low-frequency excitation.
Abstract: The recent development of electrostrictive polymers has generated new opportunities for high-strain actuators. At the current time, the investigation of using electrostrictive polymer for energy harvesting, or mechanical to electrical energy conversion, is beginning to show its potential for this application. In this paper we discuss the mechanical and electrical boundary conditions for maximizing the energy harvesting density and mechanical-to-electrical coupling of electrostrictive materials. Mathematical models for different energy harvesting approaches were developed under quasistatic assumptions. Energy harvesting densities then are determined for representative electrostrictive material properties using these models. Comparison with a magnetic-based energy harvesting system suggests that electrostrictive energy harvesting systems are preferable for "small" energy harvesting applications with low-frequency excitation.
TL;DR: In this article, the main characteristics of the electroactive phases of polyvinylidene fluoride and copolymers are summarized, and some interesting potential applications and processing challenges are discussed.
Abstract: Poly(vinylidene fluoride), PVDF, and its copolymers are the family of polymers with the highest dielectric constant and electroactive response, including piezoelectric, pyroelectric and ferroelectric effects. The electroactive properties are increasingly important in a wide range of applications such as in biomedicine, energy generation and storage, monitoring and control, and include the development of sensors and actuators, separator and filtration membranes and smart scaffolds, among others. For many of these applications the polymer should be in one of its electroactive phases. This review presents the developments and summarizes the main characteristics of the electroactive phases of PVDF and copolymers, indicates the different processing strategies as well as the way in which the phase content is identified and quantified. Additionally, recent advances in the development of electroactive composites allowing novel effects, such as magnetoelectric responses, and opening new applications areas are presented. Finally, some of the more interesting potential applications and processing challenges are discussed.
TL;DR: Electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin akin to human skin.
Abstract: Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.
TL;DR: In this paper, the authors focus on the important role and challenges of high-k polymer-matrix composites (PMC) in new technologies and discuss potential applications of highk PMC.
Abstract: There is an increasing need for high-permittivity (high-k) materials due to rapid development of electrical/electronic industry. It is well-known that single composition materials cannot meet the high-k need. The combination of dissimilar materials is expected to be an effective way to fabricate composites with high-k, especial for high-k polymer–matrix composites (PMC). This review paper focuses on the important role and challenges of high-k PMC in new technologies. The use of different materials in the PMC creates interfaces which have a crucial effect on final dielectric properties. Therefore it is necessary to understand dielectric properties and processing need before the high-k PMC can be made and applied commercially. Theoretical models for increasing dielectric permittivity are summarized and are used to explain the behavior of dielectric properties. The effects of fillers, fabrication processes and the nature of the interfaces between fillers and polymers are discussed. Potential applications of high-k PMC are also discussed.
TL;DR: Crosslinked polymer nanocomposites that contain boron nitride nanosheets have outstanding high-voltage capacitive energy storage capabilities at record temperatures and have been demonstrated to preserve excellent dielectric and capacitive performance after intensive bending cycles, enabling broader applications of organic materials in high-temperature electronics and energy storage devices.
Abstract: Dielectric materials, which store energy electrostatically, are ubiquitous in advanced electronics and electric power systems. Compared to their ceramic counterparts, polymer dielectrics have higher breakdown strengths and greater reliability, are scalable, lightweight and can be shaped into intricate configurations, and are therefore an ideal choice for many power electronics, power conditioning, and pulsed power applications. However, polymer dielectrics are limited to relatively low working temperatures, and thus fail to meet the rising demand for electricity under the extreme conditions present in applications such as hybrid and electric vehicles, aerospace power electronics, and underground oil and gas exploration. Here we describe crosslinked polymer nanocomposites that contain boron nitride nanosheets, the dielectric properties of which are stable over a broad temperature and frequency range. The nanocomposites have outstanding high-voltage capacitive energy storage capabilities at record temperatures (a Weibull breakdown strength of 403 megavolts per metre and a discharged energy density of 1.8 joules per cubic centimetre at 250 degrees Celsius). Their electrical conduction is several orders of magnitude lower than that of existing polymers and their high operating temperatures are attributed to greatly improved thermal conductivity, owing to the presence of the boron nitride nanosheets, which improve heat dissipation compared to pristine polymers (which are inherently susceptible to thermal runaway). Moreover, the polymer nanocomposites are lightweight, photopatternable and mechanically flexible, and have been demonstrated to preserve excellent dielectric and capacitive performance after intensive bending cycles. These findings enable broader applications of organic materials in high-temperature electronics and energy storage devices.
TL;DR: A number of materials have been explored for their use as artificial muscles, but dielectric elastomers appear to provide the best combination of properties for true muscle-like actuation, and widespread adoption of DEs has been hindered by premature breakdown and the requirement for high voltages and bulky support frames.
Abstract: A number of materials have been explored for their use as artificial muscles Among these, dielectric elastomers (DEs) appear to provide the best combination of properties for true muscle-like actuation DEs behave as compliant capacitors, expanding in area and shrinking in thickness when a voltage is applied Materials combining very high energy densities, strains, and efficiencies have been known for some time To date, however, the widespread adoption of DEs has been hindered by premature breakdown and the requirement for high voltages and bulky support frames Recent advances seem poised to remove these restrictions and allow for the production of highly reliable, high-performance transducers for artificial muscle applications