Core‐shell structured Al/PVDF nanocomposites with high dielectric permittivity but low loss and enhanced thermal conductivity

Surface modification of core‐shell structured Al (Al@Al₂O₃) nanoparticles was performed using γ‐(Aminopropyl)‐triethoxysilane (APS) and dopamine (DA), respectively, and the microstructures, dielectric properties and thermal conductivities of the Al/poly(vinylidene fluoride) (PVDF) nanocomposites were investigated. Both DA and APS enhance the interfacial bonding strength between the fillers and the matrix, leading to homogeneous dispersion of Al nanoparticles in PVDF matrix. Compared with raw Al nanoparticles, surface‐treated Al/PVDF exhibit much higher dielectric permittivity due to the enhanced interfacial interactions between the two components, whereas, the dielectric loss and electric conductivity of the nanocomposites still remain at rather low levels owing to the insulating alumina shell preventing effectively core Al from direct contact. The dynamic dielectric properties results reveal that dielectric constant and loss increase with temperature due to the gradually enhanced mobility of molecular chain segments of PVDF for the raw Al/PVDF and treated Al/PVDF nanocomposites. Additionally, the PVDF nanocomposites with Al treated with APS and DA show enhanced thermal conductivities compared with raw Al/PVDF under the same filler loading because of reduced thermal interfacial resistance promoting phonon transfer across the interfaces. POLYM. ENG. SCI., 59:103–111, 2019. © 2018 Society of Plastics Engineers     

对加入功能性微细纤维的新型高填纸的探讨

探讨用微细纤维和填料PCC（沉淀碳酸钙）替代部分纤维后文化用纸的结构和性能的变化。这种新配方可使文化用纸中PCC的加入量提高至50%～60%。与传统高填文化用纸相比,新配方纸可具有更高的强度性能和光学性能。     

北美特种纸行业概况

从市场总量、产品分类、生产设备以及行业现状等方面,概括分析了北美地区特种纸行业的整体状况。北美地区58家特种纸公司每年产量总计约为300万t,其中5大特种纸公司各自所占市场份额均超过7%,排名前12位的公司总计占市场份额总量的69%。北美地区特种纸机平均产能居全球第一,但平均技术年龄也最高。造成这一局面的原因在于北美地区特种纸行业发展成熟、市场饱和,近年来对本行业的新投资远落后于全球其他地区。随着各种新技术、新材料的诞生以及对环保、可再生能源等领域的重视,北美特种纸行业将迎来新的发展机遇。     

基于气相色谱-离子迁移色谱分析不同贮藏方式对洋葱浆馕风味的影响

采用气相色谱-离子迁移谱（gas chromatography-ion mobility spectrometry，GC-IMS）对洋葱浆馕6 种不同贮藏条件下挥发性物质进行分析，包括低温贮藏、室温贮藏、真空贮藏、脱氧贮藏、保鲜剂贮藏和保鲜剂结合脱氧贮藏。研究表明：在洋葱浆馕中共鉴定出66 种挥发性风味物质，其中包括醇类9 种、酮类4 种、醛类18 种、酯类4 种、呋喃衍生物3 种，酸类1 种和未能识别的化合物27 种。随着贮藏时间的延长，低温贮藏和真空贮藏洋葱浆馕在贮藏期内醛类挥发性有机物基本不变，其他处理组的醛类挥发性有机物在贮藏期内变化呈降低的趋势。结合主成分分析和欧氏距离可以发现低温贮藏和其他贮藏方式的第0天挥发性物质种类和浓度较为接近，主成分分析图中点的位置也相聚在一起，说明低温贮藏馕的挥发性物质变化不明显。该研究建立不同贮藏方式洋葱浆馕挥发性气味指纹图谱，可视化出洋葱浆馕挥发性成分轮廓，为洋葱浆馕贮藏期间风味变化规律提供信息。     

深共融溶剂催化制备二酯类化合物

二酯类化合物广泛应用于有机中间体、药物、增塑剂、香料等领域,开发其绿色、高效的合成新方法具有重要意义.报道了以二元羧酸(或二羧酸酐)和脂肪醇为原料,以深共融溶剂(DESs)为催化剂催化合成二酯类化合物.以n(氯化胆碱):n(对甲苯磺酸)=1:2为催化剂,产率最高可达95％,并且DESs使用8次后产率仍保持在88％以上.运用1HNMR和13CNMR对产物进行了结构表征.该方法具有操作简单、产率高、易分离和催化剂可循环使用等优点.     

Transparent Electrothermal Film Defoggers and Antiicing Coatings based on Wrinkled Graphene

Fog, frost, ice, and other natural phenomena can inevitably affect human life and the function of equipment. Therefore, removal or prevention is an urgent problem to be solved. As a new type of 2D material, graphene possesses great application potential in defogging and antiicing. In this work, a graphene film with intentionally increased defects and uniformly distributed wrinkles is synthesized on copper–zinc alloy substrates by chemical vapor deposition, and transparent electrothermal film defoggers are prepared based on such material. The defoggers can completely remove fog within 5 s when supplying a safe voltage of 28 V. The surface resistance of the defoggers is sensitive to humidity and it can monitor the defogging process in real time. Such outstanding performance is attributed to the ultrafast evaporation mechanism, which can prevent excessive water accumulation. The antiicing performance of wrinkled graphene (WG) is further studied. The antiicing coatings can delay freezing for 1.25 h at ?15 °C or 2.8 h at ?10 °C. The superior performance of WG can be explained by its unique surface structure and nanoscale roughness. Taken together, WG is expected to be used in antifog glass, rearview mirror defogging, aircraft surface deicing, and other applications.     

自动电位滴定仪示值误差测量不确定度评定

按照JJG 814-2015规定,自动电位滴定仪需进行电计示值误差和仪器示值误差检定,本文例举对这两项检定结果进行不确定度评定,供相关人员参考。     

Formation of Uniform Water Microdroplets on Wrinkled Graphene for Ultrafast Humidity Sensing

Portable humidity sensors with ultrafast responses fabricated in wearable devices have promising application prospects in disease diagnostics, health status monitoring, and personal healthcare data collecting. However, prolonged exposures to high‐humidity environments usually cause device degradation or failure due to excessive water adsorbed on the sensor surface. In the present work, a graphene film based humidity sensor with a hydrophobic surface and uniformly distributed ring‐like wrinkles is designed and fabricated that exhibits excellent performance in breath sensing. The wrinkled morphology of the graphene sensor is able to effectively prevent the aggregation of water microdroplets and thus maximize the evaporation rate. The as‐fabricated sensor responds to and recovers from humidity in 12.5 ms, the fastest response of humidity sensors reported so far, yet in a very stable manner. The sensor is fabricated into a mask and successfully applied to monitoring sudden changes in respiratory rate and depth, such as breathing disorder or arrest, as well as subtle changes in humidity level caused by talking, cough and skin evaporation. The sensor can potentially enable long‐term daily monitoring of breath and skin evaporation with its ultrafast response and high sensitivity, as well as excellent stability in high‐humidity environments.     

Co-precipitation synthesis of ZnAl2O4: Cr3+ phosphor for better light penetration in pc-LED

Cr doped ZnAl₂O₄ spinel samples were prepared by the traditional solid state reaction and co-precipitation synthetic route, and the results suggest that the co-precipitation method has some superiority in contrast to the solid state reaction method. XRD, FT-IR, and XPS spectra confirmed that the well-crystallized spinel cubic phase of ZnAl₂O₄: Cr³⁺ samples were successfully formed. The morphology of the samples was investigated by FE-SEM and FE-TEM, and the results show that the samples by the co-precipitation route can generate a smaller size of particles compared to the solid state reaction. Photoluminescence excitation spectra monitored at 686 nm are comprised of two broad excitation bands near 530 nm and 395 nm, and the emission spectra show emissions ranging from 640 to 780 nm, due to the ²E?→?⁴A₂ spin-forbidden transition of Cr³⁺ ions in spinel lattices. The optimized concentration monitored at 686 nm is 1%, while at 693 nm is 3.5%. Compared with the samples by solid state reaction method, the samples by co-precipitation method show preferable luminescent properties, such as the higher photoluminescence intensity and higher quantum efficiency. Several phosphor-converted LEDs were to investigate the applicability of the prepared samples. The results confirm that the phosphor has potential applications in plant growth and supplementing the red region in white-LEDs and the phosphors prepared by co-precipitation are more suitable to be used in phosphor-converted LED devices due to their preferable luminescent properties.

     

Decentralized optimal tracking control for large-scale nonlinear systems with tracking error constraints

In this article, a decentralized optimal tracking control strategy is proposed for a class of nonlinear systems with tracking error constraints by utilizing adaptive dynamic programming (ADP). It should be noted that ADP technology cannot be directly used to solve decentralized optimal tracking problem of large-scale interconnected nonlinear system with nonzero equilibrium points, since that an infinite domain performance index function may result in an unsolvable solution. In addition, by introducing a smooth function, the constrained tracking error is transformed into an unconstrained one. Then, the error dynamics and a new infinite domain performance index function are designed, such that ADP technology can be used. Following the designed performance index function, the tracking error can be ensured within a small neighborhood of zero. Finally, the feasibility and the effectiveness of the proposed decentralized optimal control scheme are verified through two simulation examples.