Preparation and characterization of emulsifier-free core–shell interpenetrating polymer network-fluorinated polyacrylate latex particles

The emulsifier-free core–shell interpenetrating polymer network (IPN) fluorinated polyacrylate latex particles with fluorine rich in shell were prepared by emulsifier-free seeded emulsion polymerization with water as the reaction medium. The fluorinated copolymer could be fixed on the particle surface due to the formation of interpenetrating polymer network. The resultant core–shell particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS) analysis, Fourier transform infrared (FTIR) spectrometry, X-ray photoelectron spectroscopy (XPS) analysis and thermogravimetric analysis (TGA). The core–shell particles possessed very narrow monomodal particle size distributions. XPS analysis of the latex film displayed that perfluoroalkyl groups had the tendency to enrich at surface and there was a gradient concentration of fluorine in the structure of the latex film from the film–air interface to the film–glass interface. In addition, compared with the latex film of crosslinked polyacrylate prepared under the same condition, the emulsifier-free core–shell IPN-fluorinated polyacrylate latex film showed better thermal stability, higher contact angle and lower water uptake.     

聚氨酯/聚丙烯酸酯复合乳液粒子热力学平衡形态预测

以水性聚氨酯分散液为种子采用无皂乳液聚合新技术合成出了具有核壳结构的聚氨酯/聚丙烯酸酯（PU/PA）复合聚合物乳液。采用界面张力简化计算方法计算了聚合物与聚合物之间以及聚合物和水之间的界面张力,通过界面自由能变化最小的热力学判据对合成的复合乳液粒子的热力学平衡形态进行了预测。并利用透射电子显微镜观察和用接触角法测定的膜的表面极性对其进行了证实。结果表明：界面自由能变化的最小判据可以推广到PU/PA 体系,本文给出的界面张力的简化计算方法是可行的。     

Fabrication of Selenium/Carbon Core–Shell Submicrowires and Carbon Submicrotubes by a Facile Solution Process

We show a facile one‐step surfactant‐assisted solution process to fabricate selenium/carbon (Se/C) coaxial core–shell submicrowires and their transformation into carbon submicrotubes by dissolution of the Se cores at ambient temperature. The formation process of the Se/C core–shell submicrowires was investigated. The results of the investigation and further experiments confirm that the thickness of the carbon shell could be tailored by controlling the experimental conditions. The as‐synthesized Se/C core–shell submicrowires and the carbon submicrotubes are potentially useful in applications such as in nanodevices or biomedicine.     

Encapsulation of silica nanoparticles by redox-initiated graft polymerization from the surface of silica nanoparticles

This study describes a facile and versatile method for preparing polymer-encapsulated silica particles by ‘grafting from’ polymerization initiated by a redox system comprising ceric ion (Ce⁴⁺) as an oxidant and an organic reductant immobilized on the surface of silica nanoparticles. The silica nanoparticles were firstly modified by 3-aminopropyltriethoxysilane, then reacted with poly(ethylene glycol) acrylate through the Michael addition reaction, so that hydroxyl-terminated poly(ethylene glycol) (PEG) were covalently attached onto the nanoparticle surface and worked as the reductant. Poly(methyl methacrylate) (PMMA), a common hydrophobic polymer, and poly(N-isopropylacrylamide) (PNIPAAm), a thermosensitive polymer, were successfully grafted onto the surface of silica nanoparticles by ‘grafting from’ polymerization initiated by the redox reaction of Ce⁴⁺ with PEG on the silica surface in acid aqueous solutions. The polymer-encapsulated silica nanoparticles (referred to as silica@PMMA and silica@PNIPAAm, respectively) were characterized by infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. On the contrary, graft polymerization did not occur on bare silica nanoparticles. In addition, during polymerization, sediments were observed for PMMA and for PNIPAAm at a polymerization temperature above its low critical solution temperature (LCST). But the silica@PNIPAAm particles obtained at a polymerization temperature below the LCST can suspend stably in water throughout the polymerization process.     

金纳米核壳局域表面等离子体激元的消光特性研究

采用离散偶极近似(Discrete Dipole Approximation,DDA)方法考察核壳比和外界介质折射率对ITO/Au、CdS/Au、Nb-Sn/Au纳米核壳粒子表面等离子体共振消光特性的影响,并利用杂化理论对其物理本质解释。仿真结果表明,ITO/Au和CdS/Au纳米核壳的ω-模式对应的共振峰峰位随核壳比的增加逐渐红移,而Nb-Sn/Au纳米核壳对应的共振峰峰位随核壳比的增加逐渐蓝移;ω+模式对应的四极共振峰峰位随核壳比的增大缓慢蓝移;集中在金壳两极点的振荡电荷对核壳球模式和腔模式的耦合作用以及电场分布有显著影响;相同尺寸纳米核壳的消光能力由强到弱依次是ITO/Au、Nb-Sn/Au、CdS/Au。     

Factors affecting the microstructure and mechanical properties of Ti-Al3Ti core-shell-structured particle-reinforced Al matrix composites

This work studied the effects of matrix powder and sintering temperature on the microstructure and mechanical properties of in situ formed Ti–Al₃Ti core–shell-structured particle-reinforced pure Al-based composites. It has been shown that both factors have significant effects on the morphology of the reinforcements and densification behaviour of the composites. Due to the strong interfacial bonding and the limitation of the crack propagation in the intermetallic shell during deformation by soft Al matrix and Ti core, the composite fabricated using fine spherical-shaped Al powder and sintered at 570 °C for 5 h has the optimal combination of the overall mechanical properties. The study provides a direction for the optimum combination of high strength and ductility of the composites by adjusting the fabrication parameters.     

基于高速摄像实验的开放腔体圆柱壳入水空泡流动研究

基于高速摄像方法,针对入水空泡流动特征和机理,进行了开放腔体圆柱壳垂直入水实验研究.通过对实验现象的观测,发现开放腔体圆柱壳入水运动会形成波动流动和云化流动两种流动方式,结合影像数据,分别描述了两种流动状态下的空泡形态特征,并获得了空泡波动参数的变化规律;对比不同入水速度实验,分析了入水速度对入水空泡流动方式和流动参数的影响;依据流体力学基本理论,分析了入水空泡波动和云化现象的形成机理.结果表明:随入水速度增加,入水空泡依次呈现波动和云化两种流动状态,波动频率与入水速度无关,闭合发生时间随入水速度增加而减小,与Froude数呈线性关系;入水导致开放空腔内部气体涨缩,引起开放端压力场和速度场周期性扰动,空泡截面扩展程度出现差异,形成空泡波动现象;空泡闭合后尾部形成回射流,回射流触及空泡壁面引起壁面流动转捩,形成空泡云化现象.     

Effect of hydrostatic pressure on diamagnetic susceptibility of hydrogenic donor impurity in core/shell/shell spherical quantum dot with Kratzer confining potential

Dependencies of diamagnetic susceptibility ${\chi }_{dia}$ on parameter $r_0$ for different values of hydrostatic pressure for 1s state.Dependence of diamagnetic susceptibility ${\chi }_{dia}$ on hydrostatic pressure $P$ for different values of $r_0$ for 1s state.

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棕榈壳酶解-温和酸解木质素的结构及热解特性研究

采用酶解/温和酸解法提取了棕榈壳和麦秆的木质素(EMALs),利用傅里叶红外光谱(FT-IR)、裂解器-气相色谱质谱联用(Py-GC/MS)和热重-红外联用(TG-FTIR)技术,对两种EMALs的化学结构和热解特性进行了对比研究,并采用Ozaw a-Flynn-Wall方法计算了其热解反应的活化能。结果表明,棕榈壳EM AL和麦秆EM AL均为HGS型木质素。500℃下,两种EMALs的热解产物主要包括酚类、酸类和少量的醇类、醛酮类等化合物;棕榈壳EMAL热解酚类产物中H、G、S型单体酚类的比例分别为47.61%、25.64%和17.18%,而麦秆EMAL分别为23.66%、51.90%和15.50%。在热解反应主失重区(200-380℃),棕榈壳EM AL的主失重速率(50.80%/min)低于麦秆EM AL(78.63%/min);但棕榈壳EM AL热解同时存在肩状失重峰(265℃,27.40%/min),这与其较多H结构产物的释放相关。H型结构产物释放的放热效应降低了棕榈壳EMAL热解初期的活化能(20%,127.92 k J/mol),同时使其热解过程(20%-80%)的平均活化能(152.32 k J/mol)低于麦秆EMAL(161.75 k J/mol)。     

Rapid and effective sample cleanup based on graphene oxide-encapsulated core–shell magnetic microspheres for determination of fifteen trace environmental phenols in seafood by liquid chromatography–tandem mass spectrometry

In this study, graphene oxide-encapsulated core–shell magnetic microspheres (GOE-CS-MM) were fabricated by a self-assemble approach between positive charged poly(diallyldimethylammonium) chloride (PDDA)-modified Fe₃O₄@SiO₂ and negative charged GO sheets via electrostatic interaction. The as-prepared GOE-CS-MM was carefully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer analysis (VSM), and X-ray photoelectron spectroscopy (XPS), and was used as a cleanup adsorbent in magnetic solid-phase extraction (MSPE) for determination of 15 trace-level environmental phenols in seafood coupled to liquid chromatography–tandem mass spectrometry (LC–MS/MS). The obtained results showed that the GOE-CS-MM exhibited excellent cleanup efficiency and could availably reduce the matrix effect. The cleanup mechanisms were investigated and referred to π–π stacking interaction and hydrogen bond between GOE-CS-MM and impurities in the extracts. Moreover, the extraction and cleanup conditions of GOE-CS-MM toward phenols were optimized in detail. Under the optimized conditions, the limits of detection (LODs) were found to be 0.003–0.06 μg kg⁻¹, and satisfactory recovery values of 84.8–103.1% were obtained for the tested seafood samples. It was confirmed that the developed method is simple, fast, sensitive, and accurate for the determination of 15 trace environmental phenols in seafood samples.