查找使用阿拉丁产品的科研文献

Research on N,N′-carbonyldiimidazole: A novel low-temperature imidization accelerator of polyimide

Lidong Cao,Xingzhong Fang,Guofei Chen

High imidization temperature of polyimides (PIs) brings great restriction to the applications in electronic industry. In this study, N,N ′-carbonyldiimidazole (CDI), a novel low-temperature imidization accelerator with the unique dual function of catalyst and dehydrating agent, was researched to solve this problem. PIs synthesized from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4,4′-oxydianiline were researched as the main object on method A and method B, two preparation methods of PIs, by introduction of CDI, which was found that the PIs prepared by method A achieved complete imidization and basically had no residual CDI and N,N -Dimethylacetamide at 180 °C under vacuum, while the completely imidized PIs prepared by method B were also obtained at 40 °C. Even prepared at low temperature, the PI films with adding CDI both showed satisfactory thermal and mechanical properties, especially in reducing coefficient of thermal expansion. In addition, the universality of the reaction between CDI and poly(amic acid) were also verified by other soluble PI systems. All these results prove the superior performance of CDI in lowering imidization temperature, showing great potentials in low-temperature cured PIs. Graphical

Recovery of N, N-dimethylglycine (DMG) from dimethylglycine hydrochloride by bipolar membrane electrodialysis

Yuqi Zheng,Yang Jin,Nan Zhang,Dong Wang,Yang Yang,Meng Zhang,Guohui Wang,Shaoxiang Lee,Wenjuan Qu

A Bipolar membrane electrodialysis (BMED) was performed to achieve efficient production of N, N-dimethylglycine (DMG) from dimethylglycine hydrochloride. And the two-compartment cell configuration (BP-A) was used to avoid the amino acid macromolecules migrating through the membrane resulting in membrane fouling. Several experiment parameters including current density, initial dimethylglycine hydrochloride concentration and flow rate were discussed and compared. The results indicated that the optimal operation condition was at the current density of 50 A/m 2 , feed mole concentration of 0.3M and flow rate of 15L/h. Under the optimal condition, the energy consumption was 0.45 kWh/kg, the current efficiency was 65% and the recovery ratio for DMG reached 98% by calculation. In addition, the membrane fouling after experiments was conducted and further analyzed. It was observed that there was no appreciable change on the membrane during the BMED process by the SEM images and FTIR spectra. These results show that the harm of BMED process to membranes could be ignored. BMED method has the advantages of high purity, no by-products, low energy consumption and environmental friendliness. And this study can broaden the application of electrodialysis in the purification and preparation of macromolecular amino acids.

Experimental and modeling study of the N, N-dimethylformamide pyrolysis at atmospheric pressure

Du Wang,Zhen-Yu Tian,Zhi-Hao Zheng,Wang Li,Ling-Nan Wu,Jiu-Jie Kuang,Jiu-Zhong Yang

As a polar solvent , N, N-Dimethylformamide (DMF) is a potential source of volatile organic compounds during industrial processing. The potential energy surface and pressure-dependent rate coefficients of DMF primary and secondary thermal decomposition were theoretically investigated by automatic ab initio calculations. A singlet aminohydroxycarbene route generating CO is found to be the most energetically favored channel among the unimolecular initiation reactions with a tight transition state. A kinetic model was proposed for DMF pyrolysis prediction and validated against the speciation data newly obtained from synchrotron vacuum ultraviolet photoionization mass spectrometry in a flow reactor within 773 K–1048 K and literature data in a jet stirred reactor within 450 K–900 K at atmospheric pressure. Satisfactory agreements were obtained for the major intermediates and products, but the model failed to capture the formation of some oxygenated compounds, possibly due to the missing reaction pathway for bimolecular addition. During pyrolysis , DMF is mainly consumed by the hydrogen abstraction reaction as the relatively high C N bond energy hinders the barrierless homolytic cleavage. Unlike aldehydes where the carbonyl site is favored, H-abstraction from DMF methyl sites is prevalent, although the acylamino group readily undergoes decarbonylation and β-scission forming oxygenated and nitrogenous parts. Consequently, CO and HCN are the major pyrolysis products. Besides, by incorporating essential high temperature kinetics, extended validation was conducted against the available intermediate temperature autoignition delay times (1000–1350 K, 2 bar) and laminar burning velocity data, and the reason for the discrepancy between the model prediction and experiments was inferred according to the sensitivity analyses.

Effects of salicylate 2-hydroxybenzoate on ionic liquid N-hexadecane-N-methylpyrrolidinium bromide

Liuchen Zhao,Hui Zhang,Wanxu Wang,Guoyong Wang

Surface tension, steady-shear viscosity, and antibacterial activity were investigated when salicylate 2-hydroxybenzoate (NaSal) was added to the micellar solution of N-hexadecane-N-methylpyrrolidinium bromide (C16MPB). It was found that for the mixed system, two flat portions appeared on the surface tension curve with the existence of NaSal in the low-concentration range. The equilibrium contact angle of droplets was decreased with the increase of NaSal concentration. In addition, the steady-shear viscosity abruptly increased with the increase of the concentration of mixture, even if the concentration of NaSal is low. However, this high-viscosity solution exhibited temperature-sensitive property, and white precipitate formation below 18°C. Moreover, the bactericidal capability of C16MPB was affected severely by the mixture of high concentration. All of these features could be attributed to the special interactions between C16MPB and NaSal molecules, among which intramolecular hydrogen bonding of NaSal plays a key role, which have been primely demonstrated by the package of Gaussian09 in this work.

ZnO/GaN n-n heterojunction porous nanosheets for ppb-level NO2 gas sensors

Zhilin Feng,Hongtao Wang,Yaodan Zhang,Dan Han,Yongqiang Cheng,Aoqun Jian,Shengbo Sang

The development of NO 2 gas sensors with lower operating temperature and good thermal stability is always a challenge to solve. In this work, 2D loose porous ZnO/GaN heterogeneous nanosheets were synthesized by ultrasonic mixing, in which ZnO nanosheets and GaN nanoparticles were prepared by hydrothermal method and solid-state pyrolysis , respectively. BET characterization result showed that the specific surface area of loose porous ZnO nanosheets was 57.24 m 2 /g, and XPS tests proved that the formation of heterogeneous interface between ZnO and GaN can effectively increase the number of negative oxygen ion species on the surface. Noticeably, 15 mol % ZnO/GaN composites (Ga:Zn) exhibited the highest response of 134.5–2 ppm of NO 2 at 125 °C and lower limit of detection of 20 ppb. Furthermore, it showed outstanding selectivity, repeatability and long-term stability. The excellent gas-sensing properties can be attributed to the loose porous structure of ZnO and the formation of n-n heterojunction between ZnO and GaN. The gas-sensing mechanism of ZnO/GaN composites to NO 2 was also discussed in detail.

Fmoc N-hydroxysuccinimide ester: A facile and multifunctional role in N-glycan analysis

Chang Wang,Yike Wu,Sheng Liu,Liang Zhang,Bi-Feng Liu,Xin Liu

N-glycans that are fluorescently tagged by glycosylamine acylation have become a promising way for glycan biomarker discovery . Here, we describe a simple and rapid method using Fmoc N-hydroxysuccinimide ester (Fmoc-OSu) to label N-glycans by reacting with their corresponding intermediate glycosylamines produced by microwave-assisted deglycosylation . After optimizing reaction conditions, this derivatization reaction can be effectively achieved under 40 °C for 1 h. Moreover, the comparison of fluorescent intensities for Fmoc-OSu, Fmoc-Cl and 2-AA labeling strategies were also performed. Among which, the fluorescent intensities of Fmoc-OSu labeled glycan derivatives were approximately 5 and 13 times higher than that labeled by Fmoc-Cl and 2-AA respectively. Furthermore, the developed derivatization strategy has also been applied for analyzing serum N-glycans, aiming to screen specific biomarkers for early diagnosis of lung squamous cell cancer. More interestingly, the preparation of free reducing N-glycan standards have been achieved by the combination of HPLC fraction of Fmoc labeled glycan derivatives and Fmoc releasing chemistry . Overall, this proposed method has the potential to be used in functional glycomic study.

Measurements and calculations of thermal conductivity for liquid n-octane and n-decane

Xiong Zheng,Dan Qu,Fa Zhang,Yu Liu,Guangzhao Qin

Hydrocarbons play an important role in lots of industrial processes. Thermal conductivity is an important thermophysical property of fluids in energy conversion process, such as the design of the heat transfer system and the evaluation of thermodynamic cycle. Thus, it is of great significance to acquire solid experimental data and develop reliable models for achieving accurate thermal conductivity of hydrocarbons. In this work, thermal conductivity of two common fuels, n-octane and n-decane, were studied by combining experimental and theoretical methods. Using the transient hot wire method, the thermal conductivity is measured with temperature ranging from 303 to 523 K and pressures ranging from 0.1 to 15 MPa. Excellent agreement is achieved by comparing our experimental results with literatures. Furthermore, the mechanism for the influence of temperature and pressure on thermal conductivity of liquid n-octane and n-decane was explored preliminarily based on Bridgman's theory. In addition, we proposed a modified model considering the critical thermal conductivity enhancement, with which the average absolute deviations are 0.49% and 0.43% for n-octane and n-decane, respectively. It is shown that our proposed model has better predictive ability for representing thermal conductivity than the four traditional theoretical models (Assael model, Sun and Teja model, Huber and Perkins model, Liu model), especially at the vicinity of the critical point. The achievements in the present study are not only useful for relevant industrial application but also helpful for understanding the thermal conductivity critical enhancement when approaching the liquid-gas critical point for n-alkanes.

Design and preparation of 3D printing intelligent poly N,N-dimethylacrylamide hydrogel actuators

Shengzhu Zhou,Qiang Zhou,Chang Lu,Zhihui Zhang,Luquan Ren

The intelligent poly N , N -dimethylacrylamide hydrogel material system with high mechanical strength and the 3D printable property was prepared via in situ free radical polymerization under vacuum successfully. With the increase in nanofibrillated cellulose (NFC) content, stress and strain of hydrogels increased gradually. As the effective reinforcement, NFC enhanced the crosslinking density, which realized the controllable regulation of rheology behaviors including viscosity, storage modulus, and loss modulus of hydrogels. Combined with the swelling rate and the existence of the gel–sol transition point, a hydrogel with 10 mg/mL NFC was treated as the 3D printing ink of hydrogel actuators. Variation of printing parameters significantly affected self-driven deformations. The hydrogel actuators with 90°/0° and 45°/135° configurations owned bending and spiral deformations, respectively. Actuators with a larger length–width ratio owned a lower pitch value. The precise anisotropic swelling property of the printed bilayer structure was the self-driven deformation mechanism of hydrogel actuators, which provided material candidates for the preparation of soft robots and actuators.

CO2-switchable surfactant-free microemulsion consisted of N,N-dimethylcyclohexylamine, ethanol and water

Daixue Xu,Hongsheng Lu,Dongfang Liu,Xiaojiang Li

Novel SO2 Phase-Change Absorbent: Mixture of N,N-Dimethylaniline and Liquid Paraffin

Muyuan Chai,Wenbo Zhao,Genming Li,Shengchao Xu,Qingming Jia,Yuan Chen

In order to avoid the high energy consumption in SO2 capture with aqueous amine absorbents, a liquid–liquid SO2 phase-change absorbent (SPCA) was developed in the present work using N,N-dimethylaniline (DMA) as absorbent, and high-boiling liquid paraffin was used as solvent to adjust the boiling point of the solution. The homogeneous solution would form two immiscible liquid phases after SO2 bubbling, only the SO2-rich phase needed to be desorbed, which could effectively reduce the energy consumption. Different from the liquid–solid phase-change absorbents developed in our previous work, the liquid–liquid phase-change absorbent avoid their shortcomings such as difficulties in separation of absorption products. The absorption product of SPCA was proved to be a charge-transfer complex DMA·SO2 by NMR and FTIR characterization, and the phase-change mechanism was attributed to the polarity variation between DMA and DMA·SO2. The viscosities of SPCAs was lower than 11.65 mPa·s, and the viscosity of SO2-rich phase was 3.9 mPa·s at 30 °C. The mass absorption capacity was found to be 0.89 g SO2/g DMA at 1 atm and 20 °C by ignoring liquid paraffin. The SPCA exhibited extremely high mass selectivity of SO2/CO2 with the value of 351. In addition, it was found that water had no effect on the structure of the absorption product and the SO2 capacity of SPCA. SPCA could be completely regenerated in 50 min at 80 °C. All the results showed that the SPCAs composed of DMA/liquid paraffin have a good application prospect.

Phase transition of layered titanate under supercritical N,N-dimethylformamide and supercritical water

Changqing Liu,Guoxin Hu

Supercritical fluid exfoliation of layered titanate is an efficient way to prepare titania nanosheets. However, a phase transition may occur under high temperature and high pressure conditions. We have studied the phase transition process of H1.07Ti1.73O4·H2O in two solvents (N,N-dimethylformamide (DMF) and water) under supercritical conditions by XRD measurements. Experimental results show that exfoliation is found in supercritical DMF, while in supercritical water exfoliation and the phase transition occur concurrently, transforming it into anatase. An interpretation of the phase transition is proposed: as water is a protic solvent, it can supply H+ under high temperature and high pressure conditions; the phase transition is caused by dissolution and recrystallization, which is confirmed by XRD and SEM results. The suitable solvents shall be selected for the preparation of titania nanosheets by supercritical exfoliation.

Multi-Responsive Wormlike Micelles Based on N-alkyl-N-Methylpiperidinium Bromide Cationic Surfactant

Zhihu Yan,Caili Dai,Mingwei Zhao,Guang Zhao,Yuyang Li,Xuepeng Wu,Yifei Liu,Mingyong Du

A noncovalent bonding method was utilized for forming multiresponsive surface-active ionic liquids in mixed N -alkyl- N -methylpiperidinium bromide (C 16 MDB) and potassium phthalic acid (PPA). Rheology, cryogenic-transmission electron microscopy, dynamic light scattering and nuclear magnetic resonance were used to investigate the aggregation property of surface-active ionic liquids in aqueous solution. The efficiency of the shielding effect in the form of hydrophobic effects and electrostatic attraction between PPA and the C 16 MDB headgroup under diverse pH conditions is found to be the root cause of a shift in the aggregate's morphological transformation. In addition, the molecular motion of surfactant molecules becomes more active as the temperature increase provides the property of thermoresponsive to the surface-active ionic liquid system.