LIQUID CRYSTALS
·
2019
·
IF 3.078
Liyuan Ren,Longyan Duan,Qaing Weng,Pei Chen,Aiai Gao,Xinbing Chen,Zhongwei An
Terminal vinyl-based benzoxazole liquid crystalline compounds, 2-(3-fluoro-4ʹ-alkoxy-1,1ʹ-biphenyl −4-yl)-5-(2-propenyloxymethyl)-benzoxazole (nPPF(2)BP), were synthesised and their structures were confirmed by infrared (IR) spectra, proton nuclear magnetic resonance (1H-NMR) spectra, gas chromatography with electron impact-mass spectrometry (GC/EI-MS), matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry and elemental analysis (EA). The compounds show enantiotropic smectic/nematic phases with mesophase ranges are 71–97 °C and 87–136°C on heating and cooling processes for nPPF(2)BP, respectively. They give low melting points due to lateral fluoro substituent and flexible terminal 2-propenyloxymethyl chain. It is found that the compounds nPPF(2)BP with shorter alkoxy chain (n = 3, 4) exhibit a wide range of nematic mesophase, which is ascribed to enhanced π–π interaction caused by terminal vinyl moiety, whereas further elongation of the terminal alkoxy chain results in supressing nematic phase and increasing smectic mesophase. Compared with methyl terminated analogues, 2-propenyloxymethyl terminated compounds nPPF(2)BP display much lower melting points and wider or comparable mesophase range both in heating and cooling.
研究领域:
材料科学
·
化学
✓ 已验证
DOI
高影响因子
Energy Storage Materials
·
2025
·
IF 20.2
Xinru Yang,Yang Feng,Peiyan Liu,Liuhao Jiang,Shuo Zhang,Yifan Wu,Shengtao Li
The rapid development of electronic and electrical power equipment has increased the demand for dielectric materials with high-temperature energy storage performances. However, the mutual restrictions imposed by the glass transition temperature ( T g ) and bandgap ( E g ) limit the use of commercial polyetherimide (PEI) under extreme conditions. In this work, we propose a strategic modular structure design to balance a high T g and large E g by modulating the substituents in the biphenyl structure of modified PEI. Both experimental results and theoretical simulations indicates that owing to its electron-withdrawing nature, a bulky -CF 3 substituent not only increases the bandgap but also decreases the conjugation effect of the biphenyl structure, while having a minimal effect on T g . This significantly shortens the hopping distance of the carriers, ultimately improving the high-temperature breakdown strength ( E b ) and thus the capacitance performance of PEI. The modified PEI with the bulky -CF 3 achieves a discharge energy density ( U e ) of 8.01 J/cm 3 with an efficiency ( η ) of 91.9 % at 150 °C and an U e of 5.3 J/cm 3 with an η of 90.4 % at 200 °C, which exceeds the performance of most of current high-temperature dielectric polymers. The results of this study provide technical support for the developing of high-performance, flexible dielectric capacitors.
研究领域:
材料科学
·
电子工程
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF POLYMER RESEARCH
·
2024
·Vol. 31
·期 4
·1-10
·
IF 2.6
Yang Changlei,Wang Yanping,Liu Yufei,Qin Jun,He Min,Qin Shuhao,Yu Jie
The investigation of the polymerization kinetics and thermal degradation kinetics of maleic anhydride copolymers is of significant reference value for the synthesis of multifunctional and high-performance maleic anhydride-based copolymers and their applications in different fields. In this study, anhydride (MAH) derived styrene copolymers, namely Poly( N -phenylmaleimide-alt-styrene) (PNS), Poly( N -(4-carboxyphenyl)maleimide-alt-styrene) (PCS), andpoly(N-fluorine-phenylmaleimide-alt-styrene) (PFS), were prepared using a solution copolymerization method. The copolymerization kinetics and thermal degradation kinetics of MAH derived styrene copolymers were investigated using nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA), as well as the Arrhenius equation and Kim-Park method. The study revealed that the incorporation of carboxyl and fluorine groups had varying degrees of influence on maleic anhydride-styrene copolymers. The copolymerization rate constant ( K value) followed the order PNS>PCS>PFS, while the copolymerization activation energy ( E a ) followed the order PNS
研究领域:
高分子化学
·
材料科学
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF MOLECULAR LIQUIDS
·
2023
·
IF 6
Chenhe Yao,Jiaxing Tang,Ran Chen,Zihao Mao,Xinbing Chen,Pei Chen,Zhongwei An
A series of liquid crystals (LCs) containing bis-tolane, lateral fluorine substituents and 2,2-difluorovinyloxyl group were designed and synthesized. Their LC phase behavior, birefringence, dielectric anisotropy and viscosity properties were discussed by comparing with previously reported LCs with high birefringence and large electrical anisotropy. Meanwhile, the effects of lateral fluorine numbers on the melting point, birefringence and dielectric anisotropy of these LCs were explored, and density functional theory (DFT) calculations of molecular conformation and polarizability were used to correlate the experimental results. Research results indicated that the 2,2-difluorovinyloxyl terminal group decreased the melting points of these LCs, and these LCs showed relatively low melting point (<113.7 ℃), broad nematic-phase temperature interval, high birefringence (>0.4), and large dielectric anisotropy (35.87). Furthermore, performance in high birefringence LC mixture demonstrated that they could effectively improve the birefringence and dielectric anisotropy, and maintain low viscosity, which is expected to possess widespread applications in fast response LC optical devices.
研究领域:
材料科学
·
物理化学
✓ 已验证
产品关联
DOI
高影响因子
危险品化学品经营许可证（带存储）