再生丝素/丝胶蛋白水溶液的微流体静电纺丝研究

以再生丝素蛋白(SF)水溶液和丝胶蛋白(SS)水溶液为纺丝液,微流体多通道芯片为纺丝器,成功制备了SF/SS和SF/SS/SF纤维毡。制备SF/SS纤维毡时,上述两流体在微通道中以层流方式流动,到达芯片出口处既不共混也不分层,而是各自独立成丝,通过扫描电镜可以观察到粗细差异较大的两种纤维共存,形貌较好。以SS水溶液为微通道的中心流体,SF水溶液为两侧流体,通过微流体静电纺制得SF/SS/SF纤维毡,SF部分与SS部分可能形成了三明治螺旋特殊结构。纺丝液流速会对纤维毡形态结构产生影响,SF溶液流速保持不变,增加SS溶液的流速,纤维粘连严重且容易出现断裂;保持SS流速不变,增大SF溶液流速,纤维粘连性得到改善,且形貌变好。     

道康宁推出新型芯片粘合剂

<正>5月18日,道康宁宣布推出一种先进新型材料,进一步丰富了其微机电系统(MEMS)传感器解决方案产品组合。新型Dow Corning~ DA-6650芯片粘合剂将低模量特性、宽温度范围与专利填料技术相结合,可大幅度地减少小型MEMS芯片在封装装配过程中的开裂现象。道康宁的新型粘合剂适用于单一或堆叠芯片,有助于提升相机传感器、高灵敏度MEMS传感器,如压力、温度和其它指     

纳米流体在芯片微通道中的流动与换热特性

对去离子水及体积分数分别为0.15%和0.26%的水基γ-Al₂O₃纳米流体在当量直径为194.5 μm的硅基梯形芯片微通道内的层流流动和换热特性进行了实验研究。考察了Reynolds数、Prandtl数以及体积分数对流动换热的影响。结果发现,使用纳米流体后,压降无明显增加,纳米流体的流动阻力特性与去离子水基本相同;对流换热Nusselt数较去离子水有明显提高,且随着体积分数的增加而增加;相同泵功下换热热阻显著下降。实验还发现纳米流体的强化传热效果在较高温度时更加明显。根据实验数据得到了梯形硅微通道内低浓度纳米流体的层流对流换热关联式。研究结果对于集成高效芯片散热系统设计具有重要意义。     

微通道里流速分布对大功率LED散热性能的模拟分析

本文以大功率LED水冷散热为研究对象,利用FLUENT软件模拟微通道里流体流速的分布对大功率LED芯片表面温度的影响。分析了微通道流速分布与LED散热之间的关联机制,探讨在相同的入口流速下,微通道里流体流速的均匀性对大功率LED芯片表面温度的影响。模拟结果表明:在同一入口流速下,微通道的深宽值越大,微通道里流体流速分布就越均匀,大功率LED芯片表面的温度越低。FLUENT能够合理地模拟仿真大功率LED芯片的温度分布以及微通道里流体流速的分布,为设计合理微通道结构参数并对其进行优化,从而获得理想的流速均布结果提供理论基础。     

T型微流控芯片中微液滴破裂的数值模拟

利用VOF模型对T型结构微流控芯片中微液滴的三维破裂过程进行了数值模拟,获得了液滴发生破裂和不会破裂两种流型。一定轴向长度的微液滴对应着一个临界毛细数,当主流流体的毛细数大于此临界毛细数时,微液滴发生破裂并分别流向T型结构两侧;否则不会发生破裂,微液滴流向任意一侧。通过多个工况的计算,拟合了临界毛细数与微液滴相对轴向长度的关系,探讨了黏度比对微液滴破裂的影响。发现黏度比越小,微液滴越易发生破裂。     

新款Dow Corning~(道康宁)DA-6650芯片黏合剂着力提升高灵敏度MEMS传感器产量和可靠性

<正>2017年5月18日,密歇根州米德兰市—陶氏化学全资子公司、全球有机硅、硅基技术领导者道康宁今日宣布推出一种先进新型材料,进一步丰富了其日益增长的微机电系统(MEMS)传感器解决方案产品组合。新型道康宁DA-6650芯片黏合剂将低模量特性、宽温度范围与专利填料技术相结合,可以最大幅度地减少小型MEMS芯片在封装装配过程中的开裂现象。道康宁的新型粘合剂适用于单一或堆叠芯片,有助于提升相机传感器、高灵敏度MEMS传感器,如压     

几种生物芯片的研发应用进展

生物芯片的概念来源于计算机芯片，计算机芯片是指将不同功能单元集成在一块微型器件上。生物芯片借用了计算机芯片的集成化特点，将生物活性大分子（目前主要指核酸、蛋白质）或组织、细胞等密集排列固定在固相载体（主要有玻璃片、硅片、硝酸纤维膜、PVDFM膜等）上形成微型检测器件。目前，生物芯片主要包括基因芯片、蛋白质芯片、微球体芯片、微流体芯片及芯片实验室。     

一种基于非接触式介电泳捕获微颗粒和癌细胞的微流控芯片的研究

介电电泳(DEP)是一种基于尺寸或电性质分离和鉴定悬浮在介质溶液中的微颗粒技术。为了克服传统接触式介电泳电极污染样品和芯片工艺复杂等问题,采用液体电极代替金属电极或薄膜电极。在该芯片中,电极通过电介质阻挡层电容耦合到流体通道,用非接触式液体沟道电极代替传统接触式金属电极。实验中,分别考察了电压和频率对液体电极捕获微球和细胞的影响。结果表明,电压和频率对液体电极捕获微球和细胞均有重大影响,同时没有发现被捕获的细胞有裂解现象,活力良好。芯片中不同细胞的电旋转速度明显不同,说明该芯片具有通过微颗粒/细胞自身独特电特性捕获和识别不同微颗粒/细胞的能力。     

基于离心力驱动微流控芯片的研究进展

离心力驱动微流控芯片具有制作成本低、集成度高等优势,是一种不可多得的微流体驱动技术,文中介绍了离心力驱动微流控芯片的驱动原理和加工方法并对其优缺点进行了比较,综述了离心式芯片在生物、医疗和化工等领域应用及发展前景。     

静电纺丝装置:设计静电纺丝工艺制备纳米纤维

纳米纤维可以产泛用于制备多种材料,如过滤材料、生物传感器、军用防护涂层、三维组织支架、复合材料、药物释放、敷料以及电子器件.为了制备具有所要求物理化学性能的纳米纤维,研究人员提出了多种静电纺丝工艺,如利用特别设计的收集屏、微电机械加工而成的喷嘴以及利用辅助电极稳定纺丝射流;而且,开发新的静电纺丝工艺仍在继续,目的是为了获得某种场合专用的纳米纤维.通过这些工艺,像纤维取向以及纤维网的三维结构等参数最终可以得到控制.讨论了最近提出的静电纺丝工艺,这些工艺可以赋予纤维特定的功能,同时详细叙述了使用的工艺参数与获得的纤维物理性能之间的关系,最后提出了未来的设计方向,即设计出能够制备最佳结构纳米纤维的静电纺丝装置.     

Strengthening of the adhesive bond using a mixture of adhesives between dissimilar adherends in a single lap joint

Abstract

Adhesive bonding is the best alternative to riveting in aircraft structures but the strength of the adhesive bonded joint is low and is limited by strength of adhesive. Strengthening of adhesive bonding is an important requirement. In this work, an attempt has been made to strengthen the adhesive bonding by mixing different quantities of brittle adhesive in the ductile adhesive and vice-versa. Two different adhesives, one brittle (AV138) and another ductile (Araldite-2015) adhesive have been considered. Initially single lap joint has been constructed between the CFRP and aluminium with individual adhesives, then the mixture of adhesives have been used in the bonded region in varied proportions. The X-ray radiography and ultrasonic testing have been performed to check the quality of bonding. Uniaxial tensile tests have been conducted on the lap joints along with Digital Image Correlations (DIC) to obtain the individual and mixed adhesive bond strength. The failure patterns have been identified using optical and scanning electron microscope. These studies indicate that strengthening of the adhesive bonding achieved by mixing of two adhesives and highest bond strength obtained when the mixture of AV138 and Araldite-2015 adhesives are used in equal proportions.     

Shear strength of adhesively bonded polyolefins with minimal surface preparation

Interest in polyethylene and polypropylene bonding has increased in the last years. However, adhesive joints with adherends which are of low surface energy and which are chemically inert present several difficulties. Generally, their high degree of chemical resistance to solvents and dissimilar solubility parameters limit the usefulness of solvent bonding as a viable assembly technique. One successful approach to adhesive bonding of these materials involves proper selection of surface pre-treatment prior to bonding. With the correct pre-treatment it is possible to glue these materials with one or more of several adhesives required by the applications involved. A second approach is the use of adhesives without surface pre-treatment, such as hot melts, high tack pressure-sensitive adhesives, solvent-based specialty adhesives and, more recently, structural acrylic adhesives as such 3M DP-8005^® and Loctite 3030^®.In this paper, the shear strengths of two acrylic adhesives were evaluated using the lap shear test method ASTM D3163 and the block shear test method ASTM D4501. Two different industrial polyolefins (polyethylene and polypropylene) were used for adherends. However, the focus of this study was to measure the shear strength of polyethylene joints with acrylic adhesives. The effect of abrasion was also studied. Some test specimens were manually abraded using 180 and 320 grade abrasive paper. An additional goal of this work was to examine the effect of temperature and moisture on mechanical strength of adhesive joints.     

Determination of traction-separation laws on an acrylic adhesive under shear and tensile loading

Structural acrylic adhesives are of special interest because those adhesives are cured at room temperature and can be bonded to oily substrates. To use those adhesives widely for structural bonding, it is necessary to clarify the methodology for predicting strengths of bonding structures with those adhesives. Recently, cohesive zone models (CZMs) have been receiving intensive attentions for simulation of fracture strengths of adhesive joints, especially when bonded with ductile adhesives. The traction-separation laws under mode I and mode II loadings require to estimate fracture toughness of adhesively bonded joints. In this paper, the traction-separation laws of an acrylic adhesive in mode I and mode II were directly obtained from experiments using Arcan type adhesively bonded specimens. The traction-separation laws were determined by simultaneously recording the J-integral and the opening displacements in the directions normal and tangential to the adhesive layer, respectively.     

Bonding performance of melamine-urea-formaldehyde and phenol-resorcinol-formaldehyde adhesives in interior grade glulam

Wood moisture content (MC) affects the glued laminated beam (glulam) bonding strength. Selected adhesives were Phenol-Resorcinol-Formaldehyde (PRF) and Melamine-Urea-Formaldehyde (MUF) adhesives with 1, 1.5 and 2% (w/w) carboxymethyl cellulose (CMC) formic acid solutions. Douglas fir (pseudotsuga menziesii) from North America was used in the test. The bonding behavior of these adhesives with wood at 12 and 18% MC were investigated. The study focused on the effect of 18% MC on shear strength performance of MUF and PRF adhesives and optimizing the formula of CMC formic acid solution. Compressive shear strength of wood with MUF adhesive with 2% (w/w) formic acid solution at 12 and 18% MC stabilized at 10.6 and 10.0 MPa, respectively, which were 17 and 16% higher than that with PRF adhesive at the same condition. At 12–18% MC, MC had a little effect on bonding strength. However, 18% MC wood with PRF adhesive had 52.2% less initial strength increasing rate than that of 12% MC wood. 18% MC wood with MUF adhesives with 1, 1.5 and 2% (w/w) CMC formic acid solutions had 16.0, 15.5 and 27.0% less initial strength increasing rates than that of 12% MC wood, respectively. MUF adhesive using 2% CMC formic solution required the shortest press time at 12 and 18% MC about 1.6 and 2.7 h, respectively. The strength of PRF adhesive was significantly affected by wood MC and enough press time is essential for the proper bonding strength.     

新型可见光固化口腔正畸粘合剂研制

介绍了一种新型可见光固化正畸粘合剂的组成、性能及正畸粘接的工艺。此粘合剂由一种单组分液体底胶和单组分糊剂组成。与化学固化粘合剂相比,其操作使用方便,固化时间短。这种新型粘合剂的粘接强度完全满足了正畸粘合剂的要求。     

An overview of solvents in resin–dentin bonding

Resin bonding to dentin is less durable than bonding to enamel. Bonding to dentin had been a great challenge till date. Though the current dental adhesive systems have tremendously improved the complex dentin bonding, there are still challenges that need to be addressed. Improper handling of the dental adhesive systems is one of the several reasons for the decrease in durability of resin–dentin bonds over time. Improper handling includes inappropriate storage and inaccurate method(s) of application. Solvents incorporated in the dental adhesive systems are known to dissolve methacrylate monomer/co-monomer blends and the initiator/co-initiator systems. These solvents are volatile and they play several important roles in achieving successful and durable bond to dentin. Lack of knowledge about the role of solvents used in dental adhesives could be one of the reasons for improper handling of the dental adhesive systems. This overview discusses the solvent aspects of current dental adhesive systems and their applications in bonding. The overview consists of published literature retrieved from “Pubmed”, by using specific key words “solvents”, “resin adhesives”, “dentin”, “bonding”. The relevant literature was retrieved after screening the titles and the abstracts. Further relevant articles that were included for the overview were retrieved from the reference lists of the initially retrieved articles. The literature seems to indicate that solvent type, solvent content and other factors, like storage of the adhesives and methods of application play a major role in dentin bonding. The knowledge acquired on the solvents and their roles in dentin bonding would enable the users of the dental adhesives to handle them appropriately and consequently achieve strong and durable resin–dentin bonds.     

特种胶粘剂的研究进展

介绍了在特殊环境下具有特殊粘接效果的特种胶粘剂(包括耐高温胶粘剂、耐低温胶粘剂、密封胶、医用胶、真空胶、耐碱胶和点焊胶等)的研究进展和应用现状,并对特种胶粘剂的发展进行了展望。     

Eco-economical polyurethane wood adhesives from cellulosic waste: Synthesis, characterization and adhesion study

This study reports the preparation of polyurethane adhesives using polyols obtained from cellulosic waste and detailed study on its adhesive strength in wood joints. Keeping in view the environmental hazards related to the huge paper-waste generation across the world, low-viscosity polyols have been prepared using magazine paper waste and vegetable oils with different physicochemical properties and were used to prepare two-component polyurethane adhesives for wood bonding. Polyurethane was analyzed by FTIR spectroscopy and TGA was used for the analysis of thermal properties. The adhesive strength was measured and compared with commercially available adhesives under different environmental conditions. The synthesized adhesive with NCO/OH ratio of 1.2 and curing time of 5 days was found to be superior to the commercial adhesives Fevicol™ and Araldite™ when compared simultaneously for the single-lap shear strength in different environmental conditions.     

Water-based adhesive formulations for rubber to metal bonding developed by statistical design of experiments

Waterborne adhesives for rubber to metal bonding have been available since 1990. However, published information about their formulation has been limited, as proprietary restrictions are exercised by companies. As a consequence, the way these adhesives interact with substrates has not been studied extensively. With the aim of investigating the effect the components of a waterborne adhesive have on rubber to metal bonding, fractional factorial and surface response methodologies of design of experiments were employed in this study. Twenty six formulations were prepared with a polychloroprene latex as the adhesive polymer. Viscosity, wettability and non-volatile solids content were measured with each liquid adhesive, while the mechanical strength was evaluated by applying a tensile mechanical stress over cured solid adhesive films. Adhesion properties were evaluated by using a single lap-shear test on metal to metal joints and a pull-out test on rubber to metal joints. The results showed that the components with the largest relative influence on cohesive and adhesives forces were tackifier resin, silicon dioxide and polychloroprene latex type. In order to better understand the contributions of these variables, mathematical models correlating them with the response variables were obtained. This study is valuable in explaining how, through statistical methods, a waterborne adhesive for rubber to metal bonding can be formulated with a reasonably low number of experiments.     

Accelerated-curing epoxy structural film adhesive for bonding lightweight honeycomb sandwich structures

Accelerating the curing of epoxy/aromatic amine adhesives and improving their toughness are challenges in heat-resistant epoxy structural adhesives. Herein, we report an epoxy/aromatic amine adhesive accelerated curing system with an oxo-centered trinuclear (chromium III) complex, which is toughened using a thermoplastic block copolymer (TPBC). The reaction characteristics, heat resistance, microstructure, and bonding properties of the accelerated epoxy adhesives were analyzed. The reaction peak temperature of the epoxy with 3% catalyst was 113.1°C, which was 113.6°C lower than that of epoxy without catalyst, and the modified epoxy resin demonstrated a potential for rapid curing at medium temperature. The glass transition temperature of the TPBC-toughened epoxy adhesive was 125°C after curing, indicating excellent thermal stability after medium temperature curing. The introduction of the TPBC increased the single-lap shear strength of the epoxy adhesive without reducing its heat resistance. The shear strength at room temperature and 120°C of the modified epoxy adhesive with 50 phr of TPBC was 25.2 and 10.9 MPa, respectively. Moreover, the epoxy film adhesive exhibited outstanding bonding properties when used in the bonding of lightweight honeycomb sandwich structures.