Recovery performance and characteristics in shape memory effects of aliphatic polyether urethane

The analysis on the recovery performance and characteristics in shape memory effects is helpful for the optimal design and engineering applications of shape memory polymers and their composites. To investigate the relationships among recovery performance, material parameters, and loading conditions, by taking aliphatic polyether urethane as an example, the researchers simulate the shape memory behaviors numerically using a three‐dimensional viscoelastic model. The material parameters for this model are taken from stress relaxation tests, rather than dynamic mechanical analysis tests. Both the unconstrained and the constrained recovery behaviors during strain‐controlled shape memory processes are analyzed. The results reveal that the unconstrained recovery occurs at the same temperature regardless of the applied strain values. Another interesting result is that the shape recovery temperature in unconstrained recovery situations increases and the maximum recovery stress under constrained recovery conditions decreases with the increase of heating rates. Copyright © 2013 John Wiley & Sons, Ltd.     

A sensitive mercury (II) sensor based on CuO nanoshuttles/poly(thionine) modified glassy carbon electrode

Shuttle-like copper oxide (CuO) was prepared by a hydrothermal decomposition process. The resulting material was characterized by scanning electron microscopy and X-ray diffraction. It was then immobilized on the surface of a glassy carbon electrode modified with a film of poly(thionine). A pair of well-defined and reversible redox peaks for Hg(II) was observed with the resulting electrode in pH 7.0 solutions. The anodic and cathodic peak potentials occurred at 0.260 V and 0.220 V (vs. Ag/AgCl), respectively. The modified electrode displayed excellent amperometric response to Hg(II), with a linear range from 40 nM to 5.0 mM and a detection limit of 8.5 nM at a signal-to-noise ratio of 3. The sensor exhibited high selectivity and reproducibility and was successfully applied to the determination of Hg(II) in water samples.     

An amperometric sensor for hydrazine based on nano-copper oxide modified electrode

A sensitive hydrazine sensor has been fabricated using copper oxide nanoparticles modified glassy carbon electrode (GCE) to form nano-copper oxide/GCE. The nano-copper oxide was electrodeposited on the surface of GCE in CuCl₂ solution at −0.4 V and was characterized by Scanning electron microscopy and X-ray diffraction. The prepared modified electrode showed a good electrocatalytic activity toward oxidation of hydrazine. The electrochemical behavior of hydrazine on nano-copper oxide/GCE was explored. The oxidative current increased linearly with improving concentration of hydrazine on nano-copper oxide/GCE from 0.1 to 600 μM and detection limit for hydrazine was evaluated to be 0.03 μM at a signal-to-noise ratio of 3. The oxidation mechanism of hydrazine on the nano-copper oxide/GCE was also discussed. The fabricated sensor could be used to determine hydrazine in real water.     

La(OH)3凝聚的形态和粒径分布研究

在形态空间中对La(OH)_3凝聚体系统的形态分布进行了描述。在此基础上, 对La(OH)_3凝聚体的粒径分布进行了模拟, 进而提出了La(OH)_3凝聚体的形成机制。     

Adaptive robust maneuvering control for nonlinear systems via dynamic surface technique

In this paper, the adaptive robust controller based on dynamic surface technique is investigated for the maneuvering problem of uncertain nonlinear systems with external disturbances. As preliminary, the definition of semi-globally uniformly practically asymptotically stable and its Lyapunov criterion are presented. The static part of controller with smooth robust compensator and adaptive law is designed to achieve the geometric task of maneuverability, and the dynamic control is proposed to reach the speed task by filtered-gradient update law. Moreover, utilizing first-order filter, the problem of “dimensional explosion” is avoided in controller design. Simulation is conducted for three-mecanum-wheeled mobile robot actuated by DC motors to illustrate the effectiveness of the control strategy.

     

Predicting shape memory characteristics of polyurethane in three‐point bending deformation

As a kind of an exceptional material, the temperature‐responding shape memory polymer can fix a temporary shape when cooled down and recover to its original shape when reheated up. Several models have been developed to describe the process. In the present work, we use the generalized Maxwell model to predict the shape memory characteristics of polyurethane in three‐point bending deformation by means of three‐dimensional finite element simulation. The deformation–temperature–stress behavior is obtained numerically. The results reveal that under the condition of accelerating reheating rates at the stage of stress‐free recovery, the maximum recovery rate occurs at higher temperature whereas the recovery ratio decreases. When the deformation degree enlarges, the maximum recovery stress increases in the situation of constrained recovery. The micro‐motion theory of polymer segments is used to explain the characteristics in the shape memory cycle. The simulated results agree well with previous researches, which demonstrate that the simplified model and the numerical simulation method are helpful for both scientific research and engineering development about shape memory polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of 14 whitening active components in cosmetics by ultra-high performance liquid chromatography-triple quadrupole mass spectrometryEI北大核心CSCD

A method based on ultra high performance liquid chromatography-triple quadrupole mass spectrometry (UPLC-MS/ MS) was developed for the analysis of 14 whitening active components in oilycosmetics. The 14 whitening active components were extracted from cosmetics by supersonic extraction with 20 mmol / L potassium dihydrogen phosphate solution, purified by HLB solid phase extraction column and filtered with 0. 22 μm filter membrane. Shim-pack GIST C18 AQ chromatographic column was used for the separation of the whitening active components. Methanol-0. 1% formic acid solution(containing 5 mmol / L ammonium acetate)was employed as mobile phase for gradient elution, and the analytes were detected by electrospray ionization source with positive and negative ion alternate scanning mode and multiple reaction monitoring mode (MRM). The results showed that an effective separation was achieved within 10 min under the optimized conditions, 14 whitening active components exhibited good linear relationships in the respective linear range with the correlation coefficient more than 0. 999. The limits of detection were in the range of 0. 15-2. 5 mg / kg, and the limits of quantitation were in the range of 0. 5-7. 5 mg / kg. The recoveries were from 70% to 117%, and the relative standard deviations were between 0. 2% and 12% . © 2022, Youke Publishing Co.,Ltd. All rights reserved.     

Boehmite sol properties and preparation of two-layer alumina membrane by a sol-gel process

A two layer ultrafiltration alumina membrane was prepared by a sol-gel process using boehmite sol as precursor. The sol was prepared by hydrolysation of aluminium tri-sec-butoxide. Sol properties, such as viscosity as a function of concentration and acidity, were investigated by using capillary viscometry, transmission electron microscopy and laser scattering photometry etc. The viscosity increased with an increase in concentration and a decrease in pH, while the particle shape and size of the sol were mainly determined by pH. The membrane prepared by a dipping procedure was characterized by both scanning electron microscopy and transmission electron microscopy. The results showed that the membrane thickness and surface morphology were affected by the dipping time, the viscosity and the temperature.