Development of a novel colorimetric indicator label for monitoring freshness of intermediate-moisture dessert spoilage

A colorimetric mixed pH dye-based indicator with potential for the development of intelligent packaging, as a “chemical barcode” for real-time monitoring of intermediate-moisture dessert spoilage, is described. This on-package indicator contains mixed pH-sensitive dyes, bromothymol blue and methyl red, that respond through visible color change to carbon dioxide (CO₂) as a spoilage metabolite. Both indicator solution and indicator label characteristics were studied, as well as their response to CO₂. A kinetic approach was used to correlate the response of the indicator label to the changes in intermediate-moisture dessert spoilage. Color changes, in terms of total color difference of a mixed pH dye-based indicator, correlated well with CO₂ levels of intermediate-moisture dessert. Trials on golden drop have verified that the indicator response correlates with microbial growth patterns in dessert samples, thus enabling the real-time monitoring of spoilage either at various constant temperatures or with temperature fluctuation.     

氮化镓功率电子器件封装技术研究进展

氮化镓(GaN)高电子迁移率晶体管(high electron mobility transistor, HEMT)以其击穿场强高、导通电阻低、转换效率高等特点引起科研人员的广泛关注并有望应用于电力电子系统中,但其高功率密度和高频特性给封装技术带来极大挑战。传统硅基电力电子器件封装中寄生电感参数较大,会引起开关振荡等问题,使GaN的优良性能难以充分发挥;另外,封装的热管理能力决定了功率器件的可靠性,若不能很好地解决器件的自热效应,会导致其性能降低,甚至芯片烧毁。本文在阐释传统封装技术应用于氮化镓功率电子器件时产生的开关震荡和热管理问题基础上,详细综述了针对以上问题进行的GaN封装技术研究进展,包括通过优化控制电路、减小电感L_g、提高电阻R_g抑制dv/dt、在栅电极上加入铁氧体磁环、优化PCB布局、提高磁通抵消量等方法解决寄生电感导致的开关振荡、高导热材料金刚石在器件热管理中的应用、器件封装结构改进,以及其他散热技术等。     

有机EL器件MEH-PPV/Alq3的光伏特性

制备了ITO/MEH-PPV/Alq3/LiF/Al光伏(PV)器件. MEH-PPV和Alq3分别为电子受体和给体. 光谱响应曲线主要和Alq3的吸收光谱相匹配. 在功率为0.5 mW·cm2的紫外氙灯照射下电池的短路电流为2.4 μA·cm-2, 开路电压为2.6 V, Fill因子为0.71, 电池的能量转换效率达到0.9%. 在直流电的驱动下, 器件具有电致发光的特性并且发出明亮的桔红色光, 在15 V的直流电压驱动下, 最大亮度达到了1 000 cd·cm-2.     

LED感应局部加热封装试验研究

采用感应局部加热技术,对大功率发光二极管(LED)封装进行了试验研究。结果表明,由于感应加热对材料和结构具有选择性,封装过程中仅Cu-Sn合金焊料层加热,实现了芯片和覆铜陶瓷基板间的热键合。封装后的LED性能测试表明,该封装技术不仅降低了热阻,使LED在高电流下(4倍电流)仍能保持较低的工作温度,而且降低了热应力和整体高温对芯片结构的损坏,提高了器件性能和可靠性。     

Hydroxytyrosol and Oleuropein-Enriched Extracts Obtained from Olive Oil Wastes and By-Products as Active Antioxidant Ingredients for Poly (Vinyl Alcohol)-Based Films

Oxidative stability of food is one of the most important parameters affecting integrity and consequently nutritional properties of dietary constituents. Antioxidants are widely used to avoid deterioration during transformation, packaging, and storage of food. In this paper, novel poly (vinyl alcohol) (PVA)-based films were prepared by solvent casting method adding an hydroxytyrosol-enriched extract (HTyrE) or an oleuropein-enriched extract (OleE) in different percentages (5, 10 and 20% w/w) and a combination of both at 5% w/w. Both extracts were obtained from olive oil wastes and by-products using a sustainable process based on membrane technologies. Qualitative and quantitative analysis of each sample carried out by high performance liquid chromatography (HPLC) and nuclear resonance magnetic spectroscopy (NMR) proved that the main components were hydroxytyrosol (HTyr) and oleuropein (Ole), respectively, two well-known antioxidant bioactive compounds found in Olea europaea L. All novel formulations were characterized investigating their morphological, optical and antioxidant properties. The promising performances suggest a potential use in active food packaging to preserve oxidative-sensitive food products. Moreover, this research represents a valuable example of reuse and valorization of agro-industrial wastes and by-products according to the circular economy model.     

Test methods for the characterization of gas and vapor permeability in polymers for food packaging application: A review

The assessment of the transport properties of different substances in polymeric materials is of crucial importance for the evaluation of packaging performances, aiming to protect packed food products and ensure a prolonged shelf-life. The most relevant substances for such application can be identified in O₂, CO₂ and C₂H₄ (together with N₂ as control) as permanent gases, and water vapor as condensable species. All these penetrants are able to alter significantly food properties, in term of sensory characteristics, textures, and quality in general. All relevant techniques for the experimental characterization of mass transport properties in polymeric films or packages are critically reviewed, focusing in detail on standard methods. Each technique is briefly presented in terms of apparatus requirements and general procedures, followed by a discussion on its main features.     

Ultrasensitive NOX Detection in Simulated Exhaled Air: Enhanced Sensing via Alumina Modification of In‐Situ Grown WO3 Nanoblocks

Seedless growth of vertically aligned nanostructures, which can induce smoother transport and minimize Ohmic contact between substrate and semiconductor, can be fabricated by in situ growth utilizing modified hydrothermal methods. Such devices can be useful in designing non‐invasive ultrasensitive hand‐held sensors for diagnostic identification of volatile organic compounds (VOCs) in exhaled air, offering pain‐free and easier detection of long‐term diseases such as asthma. In the present work, WO₃ nanoblocks, with a high surface area and porosity, have been grown directly over transparent conducting oxide to minimize Ohmic resistance, facilitating smoother electron transfer and enhanced current response. Further modification with porous alumina (γ‐Al₂O₃), by electrodeposition, resulted in the selective and ultrasensitive detection of NO_X in simulated exhaled air. Crystal phase purity of as‐fabricated pristine as well modified samples is validated with X‐ray diffraction analysis. Morphological and microstructural analyses reveal the successful deposition of porous alumina over the surface of WO₃. Improved surface area and porosity is presented by porous alumina in the modified WO₃ device, suggesting more active sites for the gas molecules to get adsorbed and diffuse through the pores. Oxygen vacancies, which are detrimental in the transport phenomenon in the presented sensors, have been studied using X‐ray photoelectron spectroscopic (XPS) analysis. Gas sensing studies have been performed by fabricating chemiresistor devices based on bare WO₃ and Al₂O₃‐modified WO₃. The higher sensitivity for NO_X gas in case of γ‐Al₂O₃‐modified WO₃ based devices, as compared to bare WO₃‐based devices, is attributed to the better surface area and charge transport kinetics. The presented device strategy offers crucial understanding in the design and development of non‐invasive, hand‐held devices for NO gas present in the human breath, with potential application in medical diagnostics.     

Structure–property relationship in high urethane density polyurethanes

The structure–property relationship of polyurethane (PU) homopolymers synthesized by the stoichiometric combination of 1,6‐hexamethylene diisocyanate (HDI) and low‐molecular‐weight glycols with different structure is investigated by the analysis of PU elastic modulus obtained by means of high‐resolution peak force atomic force microscopy. Different experimental techniques are employed to understand the role of block structure influence on hydrogen bonding distribution, crystallinity, thermal transitions, and crystal packaging within the PU. The results show that glycols with bulky side groups have more impediments to self‐assemble into hydrogen‐bonded and packed macromolecular structures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 739–746     

光学方法在微电子封装中的应用

热应力分析在微电子封装的设计和制造中是非常重要的一环。影响微电子封装可靠性的因素包括封装结构中的温度分布、热致变形和关键界面上的层间粘结强度。在微电子封装热应力分析和可靠性评估中，实验力学起着重要的作用。凭借其内在的并行处理能力，实验力学中的光学方法可以提供现场的、具有各种敏感度和解析度的全场位移测量，因而它也被广泛地用于微电子封装领域。本文讨论了光学方法在微电子封装热应力分析中的应用，并举实例来说明光学方法是如何地被用于微电子封装技术的研发以及考核验收。     

Extraction and gas chromatographic evaluation of plasticizers content in food packaging films

Cling films are prepared by adding (5-30% w/w) adipates, citrates, and phthalates. The adverse effects on human health of the plasticizers have been demonstrated, and then their content in food contact plastics and possible migration to foodstuffs must be carefully checked. To offer an easier tool to perform these controls, a Soxhlet extraction by ethyl acetate and a multi residue chromatography analysis, with Flame Ionization Detector, have been optimised for the application in evaluating both the real content of plasticizers in films and freezing bags, and their migrated amounts in simulants. The average extraction yield was 95 ± 10%. The chromatographic analysis was able to determine 16 different compounds, clearly separated, taking only 25 min to complete the assay. The detection limits ranged from 0.07 to 0.7% (w/w). The total amount of plasticizers in the packaging products was comprised between 3 and 10% (w/w). Extracted and migrated amounts were compared, and they resulted in good agreement. No migration of Phthalates, whose presence has been demonstrated in some samples, has been observed. It has been also demonstrated that a prolonged contact (till 60 days) did not increase the amount of migrated plasticizers, and then the risks for health.