Low-dielectric-constant poly(acetoxystyrenezhi-co-octavinyl-polyhedral oligomeric silsesquioxane)(PAS-POSS) organicinorganic hybrid nanocomposite was successfully synthesized via one-step free radical polymerization a...Low-dielectric-constant poly(acetoxystyrenezhi-co-octavinyl-polyhedral oligomeric silsesquioxane)(PAS-POSS) organicinorganic hybrid nanocomposite was successfully synthesized via one-step free radical polymerization and characterized by FTIR,high-resolution ~1H NMR,^(29)Si NMR,DSC,TGA,AFM,spectroscopic elhpsometry and dielectric constants measurements. The results show T_g and T_(dec) were elevated dramatically due to the incorporation of inorganic POSS cores.Spectroscopic ellipsometry and dielectric consta...展开更多
Al2O3 porous nanosolid was prepared via solvothermal hot-press（SHP） method.The dielectric constant of Al2O3 porous nanosolid is as low as 2.34,while its compressive strength is very poor.In order to improve the comp...Al2O3 porous nanosolid was prepared via solvothermal hot-press（SHP） method.The dielectric constant of Al2O3 porous nanosolid is as low as 2.34,while its compressive strength is very poor.In order to improve the compressive strength and maitain low dielectric constant,polyimide was introduced to prepare Al2O3 /polyimide composite porous nanosolid.Compared to Al2O3 porous nanosolid,Al2O3 /polyimide composite porous nanosolid possesses much higher compressive strength,which reaches its saturation value when the mass loading of polyimide is 7.75%.In addition,the in situ Fourier transformation infrared（FTIR） monitoring result reveals that Al2O3 /polyimide composite porous nanosolid is stable up to 400 °C.展开更多
Because of the increase in the transmission voltage levels,the demand for insulation reliability of power transformers has increasingly become critical.Cellulose insulating paper is the main insulating component of po...Because of the increase in the transmission voltage levels,the demand for insulation reliability of power transformers has increasingly become critical.Cellulose insulating paper is the main insulating component of power transformers.To improve the insulation level of ultrahigh voltage transformers and reduce their weight and size,reducing the dielectric constant of oil-immersed cellulose insulating paper is highly desired.Cellulose is used to produce power-transformer insulating papers owing to its excellent electrical properties,renewability,biodegradability and abundance.The dielectric constant of a cellulose insulating paper can be effectively reduced by chemical or physical modification.This study presents an overview of the foreign and domestic research status of the use of modification technology to reduce the dielectric constant of cellulose insulating papers.All the mentioned methods are analyzed in this study.Finally,some recommendations for future modified cellulose insulating paper research and applications are proposed.This paper can provide a reference for further research on low dielectric constant cellulose insulating paper in the future.展开更多
Epoxy resins with a high dielectric constant and low intrinsic thermal conductivity coefficient cannot meet the current application requirements of advanced electronic and electrical equipment.Therefore,novel fluorine...Epoxy resins with a high dielectric constant and low intrinsic thermal conductivity coefficient cannot meet the current application requirements of advanced electronic and electrical equipment.Therefore,novel fluorine-containing liquid crystal epoxy compounds(TFSAEy)with fluorinated groups,biphenyl units,and flexible alkyl chains are first synthesized via amidation and esterification reactions.Then,4,4′-diaminodiphenylmethane(DDM)is used as a curing agent to prepare the corresponding fluorine-containing liquid crystal epoxy resins.The obtained dielectric constant(ε)and dielectric loss(tanδ)values of TFSAEy/DDM at 1 MHz are 2.54 and 0.025,respectively,which are significantly lower than those of conventional epoxy resins(E-51/DDM,3.52 and 0.038).Additionally,the intrinsic thermal conductivity coefficient(λ)of TFSAEy/DDM is 0.36 W/(m⋅K),71.4%higher than that of E-51/DDM(0.21 W/(m⋅K)).Meanwhile,the corresponding elastic modulus,hardness,glass transition temperature,and heat resistance index of TFSAEy/DDM are 5.73 GPa,0.35 GPa,213.5◦C,and 188.7℃,respectively,all superior to those of E-51/DDM(3.68 GPa,0.27 GPa,107.2℃,and 174.8℃),presenting potential application in high-heating electronic component packaging and printed circuit boards.展开更多
Ultra-low dielectric loss(Df)and low dielectric constant(Dk)materials are urgently required in highspeed and large-capacity transmission,in which the wholly aromatic liquid crystal polymer(LCP)has gained attention due...Ultra-low dielectric loss(Df)and low dielectric constant(Dk)materials are urgently required in highspeed and large-capacity transmission,in which the wholly aromatic liquid crystal polymer(LCP)has gained attention due to its excellent dielectric properties.However,the relationship between molecular structure and dielectric properties is still not clear.In this study,two copolyesters containing phenyl or naphthyl structures are synthesized,as well as the effects of benzene and naphthalene mesogens on dielectric properties are investigated.The synthesized copolyesters containing naphthalene structure have good comprehensive properties with high thermal stability(T_(5%)=479℃ and T_g=195-216℃),inherent flame retardance(LOI=33.0-35.0 and UL-94 V-0 level at 0.8 mm),low Dk(2.9-3.0@10 GHz)and low Df(0.0027-0.0047@10 GHz).Naphthalene mesogen can reduce the dielectric loss more significantly than benzene at high frequency by reducing the density and mobility of polarizable groups,which leads to the effectively limited dipole polarization in copolyesters.Consequently,we proposed a new strategy for designing low Dk and low Df materials.展开更多
An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented.The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromet...An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented.The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromethyl in polymer chains.By using this design strategy,a highly transparent polyimide film with low-k was synthesized from 3,5-diaminobenzotrifluoride(m-TFPDA)and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)through a two-step method.The obtained m-TFPDA/6FDA(CPI)film(~30 pm)possesses high optical transparency(λ_(cutoff)=334 nm,T_(450nm)=85.26%,Haze=0.31)and is close to colorless(L^(*)=96.03,a^(*)=-0.34,b^(*)=2.12,yellow index=3.96).The intrinsic k and dielectric loss value of the film are 2.27 and 0.0013 at 10 kHz,respectively.More importantly,such low dielectric performance could remain stable up to 280℃,and the film shows a low moisture rate(~0.51%),which helps to maintain the low-k property stability in different humid environments.Meanwhile,the film also shows good thermal stability and mechanical properties,with a glass transition temperature(T_(g))of 296℃and the 5 wt%decomposition temperature(T_(d,s%))of 522℃under N_(2).The tensile strength and tensile modulus of the film are 85.1 MPa and 1.96 GPa,respectively.In addition,the film is soluble in common solvents,which allows simple solution processing and low-cost,continuous roll-to-roll processes.This design strategy is beneficial to improving the transparency,lightening yellow color,lowering the dielectric constant and meanwhile maintaining the comprehensive properties of polyimide films,which is mainly due to the introduced meta-substituted and trifluoromethyl structures effectively inhibiting the transfer of charge transfer complex(CTC)effects and increasing the free volume of film.This design strategy could also be extended to other high-performance polymer systems.展开更多
We report an improved method for the preparation of highly dense nickelate ceramics at relatively low temperature. It is found that the introduction of appropriate additives during the ball-milling process facilitates...We report an improved method for the preparation of highly dense nickelate ceramics at relatively low temperature. It is found that the introduction of appropriate additives during the ball-milling process facilitates the formation of nickelate phase through solid state reaction. Moreover, although high-purity nickelate powders can only be obtained by calcining the mixture of starting materials at temperature higher than 1100 ℃. The adoption of powders calcined at 1000 ℃, rather than those calcined at higher temperature, is conductive to the low-temperature densification of nickelate ceramics, which is attributed to the small and dispersive particles, and the solid state reaction of the residual starting materials during sintering. Compared with the conventional process, the improved method can reduce the sintering temperature of nickelate ceramics by about 100 ℃ and decrease the grain size of the obtained ceramics, and therefore makes nickelate meet the fabrication requirements of multi-layer ceramic capacitors（MLCC）.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.90606011, 50472038 and 2097401)PhD Program Foundation of Ministry of Education of China(No.20070255012)+3 种基金Shanghai Leading Academic Discipline Project(No.B603)Open Project of The State Key Laboratory of Crystal Materials(KF0809)the Program of Introducing Talents of Discipline to Universities(No.111-2-04)Doctoral Dissertation Innovation Project(No.BC200907)
文摘Low-dielectric-constant poly(acetoxystyrenezhi-co-octavinyl-polyhedral oligomeric silsesquioxane)(PAS-POSS) organicinorganic hybrid nanocomposite was successfully synthesized via one-step free radical polymerization and characterized by FTIR,high-resolution ~1H NMR,^(29)Si NMR,DSC,TGA,AFM,spectroscopic elhpsometry and dielectric constants measurements. The results show T_g and T_(dec) were elevated dramatically due to the incorporation of inorganic POSS cores.Spectroscopic ellipsometry and dielectric consta...
基金Supported by the National Natural Science Foundation of China(Nos.50990061,51021062,21073107 and 51102151)the Postdoctoral Science Foundation of China(No.20100481245)+1 种基金the Natural Science Foundation(No.ZR2011EMQ002)the Postdoctoral Innovation Foundation(No.201003077) of shandong Province, China
文摘Al2O3 porous nanosolid was prepared via solvothermal hot-press（SHP） method.The dielectric constant of Al2O3 porous nanosolid is as low as 2.34,while its compressive strength is very poor.In order to improve the compressive strength and maitain low dielectric constant,polyimide was introduced to prepare Al2O3 /polyimide composite porous nanosolid.Compared to Al2O3 porous nanosolid,Al2O3 /polyimide composite porous nanosolid possesses much higher compressive strength,which reaches its saturation value when the mass loading of polyimide is 7.75%.In addition,the in situ Fourier transformation infrared（FTIR） monitoring result reveals that Al2O3 /polyimide composite porous nanosolid is stable up to 400 °C.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51977114 and 51867003)Bagui Young Scholars Program(Grant No.2019AQ16)China Postdoctoral Science Foundation(2022MD713732).
文摘Because of the increase in the transmission voltage levels,the demand for insulation reliability of power transformers has increasingly become critical.Cellulose insulating paper is the main insulating component of power transformers.To improve the insulation level of ultrahigh voltage transformers and reduce their weight and size,reducing the dielectric constant of oil-immersed cellulose insulating paper is highly desired.Cellulose is used to produce power-transformer insulating papers owing to its excellent electrical properties,renewability,biodegradability and abundance.The dielectric constant of a cellulose insulating paper can be effectively reduced by chemical or physical modification.This study presents an overview of the foreign and domestic research status of the use of modification technology to reduce the dielectric constant of cellulose insulating papers.All the mentioned methods are analyzed in this study.Finally,some recommendations for future modified cellulose insulating paper research and applications are proposed.This paper can provide a reference for further research on low dielectric constant cellulose insulating paper in the future.
基金Foundation ofNational Natural Science Foundation of China,Grant/Award Number:51973173+3 种基金Fundamental Research Funds for the Central UniversitiesUndergraduate Innovation and Business Program in Northwestern Polytechnical UniversityInnovation Foundation for Doctor’s Dissertation of Northwestern Polytechnical University,Grant/Award Number:CX2023026Polymer Electromagnetic Functional Materials Innovation Team of Shaanxi Sanqin Scholars。
文摘Epoxy resins with a high dielectric constant and low intrinsic thermal conductivity coefficient cannot meet the current application requirements of advanced electronic and electrical equipment.Therefore,novel fluorine-containing liquid crystal epoxy compounds(TFSAEy)with fluorinated groups,biphenyl units,and flexible alkyl chains are first synthesized via amidation and esterification reactions.Then,4,4′-diaminodiphenylmethane(DDM)is used as a curing agent to prepare the corresponding fluorine-containing liquid crystal epoxy resins.The obtained dielectric constant(ε)and dielectric loss(tanδ)values of TFSAEy/DDM at 1 MHz are 2.54 and 0.025,respectively,which are significantly lower than those of conventional epoxy resins(E-51/DDM,3.52 and 0.038).Additionally,the intrinsic thermal conductivity coefficient(λ)of TFSAEy/DDM is 0.36 W/(m⋅K),71.4%higher than that of E-51/DDM(0.21 W/(m⋅K)).Meanwhile,the corresponding elastic modulus,hardness,glass transition temperature,and heat resistance index of TFSAEy/DDM are 5.73 GPa,0.35 GPa,213.5◦C,and 188.7℃,respectively,all superior to those of E-51/DDM(3.68 GPa,0.27 GPa,107.2℃,and 174.8℃),presenting potential application in high-heating electronic component packaging and printed circuit boards.
基金financially supported by the National Natural Science Foundation of China(Nos.51991351 and 51991350)the Fundamental Research Funds for the Central Universities+1 种基金the 111 Project(No.B20001)the Sichuan Science and Technology Program(No.2020YFH0016)。
文摘Ultra-low dielectric loss(Df)and low dielectric constant(Dk)materials are urgently required in highspeed and large-capacity transmission,in which the wholly aromatic liquid crystal polymer(LCP)has gained attention due to its excellent dielectric properties.However,the relationship between molecular structure and dielectric properties is still not clear.In this study,two copolyesters containing phenyl or naphthyl structures are synthesized,as well as the effects of benzene and naphthalene mesogens on dielectric properties are investigated.The synthesized copolyesters containing naphthalene structure have good comprehensive properties with high thermal stability(T_(5%)=479℃ and T_g=195-216℃),inherent flame retardance(LOI=33.0-35.0 and UL-94 V-0 level at 0.8 mm),low Dk(2.9-3.0@10 GHz)and low Df(0.0027-0.0047@10 GHz).Naphthalene mesogen can reduce the dielectric loss more significantly than benzene at high frequency by reducing the density and mobility of polarizable groups,which leads to the effectively limited dipole polarization in copolyesters.Consequently,we proposed a new strategy for designing low Dk and low Df materials.
基金supported by the Scientific Research Inn ovation Plan of Sha nghai Education Commission(No.2019-01-07-00-03-E0001)the National Natural Science Foundation of China(Nos.21774019,21975040,51903038)+2 种基金the Program of Shanghai Academic Research Leader(No.18XD1400100)the Natural Science Foundation of Shanghai(No.18ZR1400600)the DHU Distinguished Young Professor Program.
文摘An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented.The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromethyl in polymer chains.By using this design strategy,a highly transparent polyimide film with low-k was synthesized from 3,5-diaminobenzotrifluoride(m-TFPDA)and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)through a two-step method.The obtained m-TFPDA/6FDA(CPI)film(~30 pm)possesses high optical transparency(λ_(cutoff)=334 nm,T_(450nm)=85.26%,Haze=0.31)and is close to colorless(L^(*)=96.03,a^(*)=-0.34,b^(*)=2.12,yellow index=3.96).The intrinsic k and dielectric loss value of the film are 2.27 and 0.0013 at 10 kHz,respectively.More importantly,such low dielectric performance could remain stable up to 280℃,and the film shows a low moisture rate(~0.51%),which helps to maintain the low-k property stability in different humid environments.Meanwhile,the film also shows good thermal stability and mechanical properties,with a glass transition temperature(T_(g))of 296℃and the 5 wt%decomposition temperature(T_(d,s%))of 522℃under N_(2).The tensile strength and tensile modulus of the film are 85.1 MPa and 1.96 GPa,respectively.In addition,the film is soluble in common solvents,which allows simple solution processing and low-cost,continuous roll-to-roll processes.This design strategy is beneficial to improving the transparency,lightening yellow color,lowering the dielectric constant and meanwhile maintaining the comprehensive properties of polyimide films,which is mainly due to the introduced meta-substituted and trifluoromethyl structures effectively inhibiting the transfer of charge transfer complex(CTC)effects and increasing the free volume of film.This design strategy could also be extended to other high-performance polymer systems.
基金supported by the Natural Science Foundation of Fujian Province(2015j01231)the Chunmiao Project of Haixi Institute of Chinese Academy of Sciences(CMZX-2014-005)the National Key Research and Development Program of China(2016YFB0701003)
文摘We report an improved method for the preparation of highly dense nickelate ceramics at relatively low temperature. It is found that the introduction of appropriate additives during the ball-milling process facilitates the formation of nickelate phase through solid state reaction. Moreover, although high-purity nickelate powders can only be obtained by calcining the mixture of starting materials at temperature higher than 1100 ℃. The adoption of powders calcined at 1000 ℃, rather than those calcined at higher temperature, is conductive to the low-temperature densification of nickelate ceramics, which is attributed to the small and dispersive particles, and the solid state reaction of the residual starting materials during sintering. Compared with the conventional process, the improved method can reduce the sintering temperature of nickelate ceramics by about 100 ℃ and decrease the grain size of the obtained ceramics, and therefore makes nickelate meet the fabrication requirements of multi-layer ceramic capacitors（MLCC）.
