The equationε_(eff)■/φ_(c)φ)^(s)which shows the relationship between effective dielectric constant(ε_(eff))and the filler concentration(φ),is widely used to determine the percolation behavior and obtain paramete...The equationε_(eff)■/φ_(c)φ)^(s)which shows the relationship between effective dielectric constant(ε_(eff))and the filler concentration(φ),is widely used to determine the percolation behavior and obtain parameters,such as percolation thresholdφc and 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 toφ_(c)is almost independent of the matrix.展开更多
Composites have been extensively studied for dielectric and related applications.This is a reviewof polymer based 0-3 composites that exhibit a high dielectric constant.These composites areclassified into two types.Di...Composites have been extensively studied for dielectric and related applications.This is a reviewof polymer based 0-3 composites that exhibit a high dielectric constant.These composites areclassified into two types.Dielectric-dielectric composite and conductor-dielectric composite.The physical principles and related models are presented with associated assumptions and ap-proximations.In general,a dielectric-dielectric composite needs a higher concentration of thefillers to reach a high dielectric constant than a conductor-dielectric composite.The high dielectric constant observed in the conductor-dielectric composites is usually associated with ahigh dielectric loss and a low electric breakdown field.The experimental results are summarized toillustrate the principles for,and the achievements in,the development of these composites.The challenges facing the fundamental understanding and the further development of these compo-sites for diferent applications are discussed.展开更多
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...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=y_(max)^(e-T/t)is 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.展开更多
Influence of the coupling agent on microstructure and dielectric properties of ceramic-polymer composites is systematically studied using CaCu_(3)Ti_(4)O_(12)(CCTO)as the filler,trichloro-(1H,1H,2H,2H-perfluorooctyl)-...Influence of the coupling agent on microstructure and dielectric properties of ceramic-polymer composites is systematically studied using CaCu_(3)Ti_(4)O_(12)(CCTO)as the filler,trichloro-(1H,1H,2H,2H-perfluorooctyl)-silane(Cl_(3)-silane)as coupling agent,and P(VDF-CTFE)88/12 mol.%copolymer as the matrix.It is demonstrated that Cl_(3)-silane molecules can be attached onto CCTO surface using a simple process.The experimental results show that coating CCTO with Cl_(3)-silane can improve the microstructure uniformity of the composites due to the good wettability between Cl_(3)-silane and P(VDF-CTFE),which also significantly improves the electric breakdown field of the composites.It is found that the composites using CCTO coated with 1.0 wt.%Cl_(3)-silane exhibit a higher dielectric constant with a higher electric breakdown field.For the composites with 15 vol.%CCTO that is coated with 1.0 wt.%Cl_(3)-silane,an electric breakdown field of more than 240 MV/m is obtained with an energy density of more than 4.5 J/cm^(3).It is also experimentally found that the dielectric constant can be used to easily identify the optimized content of coupling agent.展开更多
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 th...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.展开更多
The analytical solution is reported for one-dimensional(1D)dynamic conduction heat transfer within a mulilayer system that is the typical structure of electrocaloric devices.Here,the multilayer structure of typical el...The analytical solution is reported for one-dimensional(1D)dynamic conduction heat transfer within a mulilayer 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 extemal electic 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 N terms of the series.The formula for calculating the value of N is 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 N is 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 N is 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.展开更多
Various designs have been introduced to build heat pumps using the electrocaloric effect (ECE). Each of all the curent designs usesat least one moving part, which significantly reduces the reliability of the pump and ...Various designs have been introduced to build heat pumps using the electrocaloric effect (ECE). Each of all the curent designs usesat least one moving part, which significantly reduces the reliability of the pump and adds complexities. In this work, a new all-soliddesign 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. Moreimportantly, 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 simlulate the device's performance by using the newly introducedanalytical solutions for the heat conduction in the system. It is concluded that a continuous heat transformation from the source tosink at the same temperature can be achieved when the contacting cofficient, K_(ε)=√(k^(c)p^(c)c^(c)_(p))/(k^(o)p^(o)c^(o)_(p)), is very small, where k,ρ, and Cp are thermal conductivity, density, and heat capacity, respectively, while the superscript c and 0 represent the ECM andsource/sink, respectively.展开更多
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,w...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.展开更多
基金This work was supported by an USDA grant and an AU-IGP grant.
文摘The equationε_(eff)■/φ_(c)φ)^(s)which shows the relationship between effective dielectric constant(ε_(eff))and the filler concentration(φ),is widely used to determine the percolation behavior and obtain parameters,such as percolation thresholdφc and 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 toφ_(c)is almost independent of the matrix.
文摘Composites have been extensively studied for dielectric and related applications.This is a reviewof polymer based 0-3 composites that exhibit a high dielectric constant.These composites areclassified into two types.Dielectric-dielectric composite and conductor-dielectric composite.The physical principles and related models are presented with associated assumptions and ap-proximations.In general,a dielectric-dielectric composite needs a higher concentration of thefillers to reach a high dielectric constant than a conductor-dielectric composite.The high dielectric constant observed in the conductor-dielectric composites is usually associated with ahigh dielectric loss and a low electric breakdown field.The experimental results are summarized toillustrate the principles for,and the achievements in,the development of these composites.The challenges facing the fundamental understanding and the further development of these compo-sites for diferent applications are discussed.
基金National Science Foundation through the Auburn University IGERT(Award#:1069004)NSF-IGERT and USDA-NIFA(Grant#:2014-60722-21694).
文摘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=y_(max)^(e-T/t)is 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.
文摘Influence of the coupling agent on microstructure and dielectric properties of ceramic-polymer composites is systematically studied using CaCu_(3)Ti_(4)O_(12)(CCTO)as the filler,trichloro-(1H,1H,2H,2H-perfluorooctyl)-silane(Cl_(3)-silane)as coupling agent,and P(VDF-CTFE)88/12 mol.%copolymer as the matrix.It is demonstrated that Cl_(3)-silane molecules can be attached onto CCTO surface using a simple process.The experimental results show that coating CCTO with Cl_(3)-silane can improve the microstructure uniformity of the composites due to the good wettability between Cl_(3)-silane and P(VDF-CTFE),which also significantly improves the electric breakdown field of the composites.It is found that the composites using CCTO coated with 1.0 wt.%Cl_(3)-silane exhibit a higher dielectric constant with a higher electric breakdown field.For the composites with 15 vol.%CCTO that is coated with 1.0 wt.%Cl_(3)-silane,an electric breakdown field of more than 240 MV/m is obtained with an energy density of more than 4.5 J/cm^(3).It is also experimentally found that the dielectric constant can be used to easily identify the optimized content of coupling agent.
基金The authors gratefully acknowledge financial support from Natural Science Foundation of China(NSFC Grant No.51572216 and No.61604122)This work has been financially supported by NSFC Major Research Program on Nanomanufacturing(Grant No.91323303)+2 种基金the industrial science and technology research project in Shaanxi province(2015GY005)111 Program(No.B14040)the open projects from Institute of Photonics and Photo-Technology,Provincial Key Laboratory of Photoelectronic Technology,Northwest University,China.
文摘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.
文摘The analytical solution is reported for one-dimensional(1D)dynamic conduction heat transfer within a mulilayer 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 extemal electic 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 N terms of the series.The formula for calculating the value of N is 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 N is 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 N is 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.
文摘Various designs have been introduced to build heat pumps using the electrocaloric effect (ECE). Each of all the curent designs usesat least one moving part, which significantly reduces the reliability of the pump and adds complexities. In this work, a new all-soliddesign 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. Moreimportantly, 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 simlulate the device's performance by using the newly introducedanalytical solutions for the heat conduction in the system. It is concluded that a continuous heat transformation from the source tosink at the same temperature can be achieved when the contacting cofficient, K_(ε)=√(k^(c)p^(c)c^(c)_(p))/(k^(o)p^(o)c^(o)_(p)), is very small, where k,ρ, and Cp are thermal conductivity, density, and heat capacity, respectively, while the superscript c and 0 represent the ECM andsource/sink, respectively.
基金supported by an USDA(2014-67022-21694)grant and a NASA grant(Grant#G00007275).
文摘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.
