Reliability of liquid crystal cell and immiscibility between dual-curable adhesives and liquid crystal

The dual-curable adhesive used to attach thin film transistors (TFTs) to color filters in the construction process of liquid crystal display (LCD) panels requires fast curing by UV irradiation and strong bond strength after thermal-curing. In addition, it is necessary to consider the immiscibility of the dual-curable adhesives with the liquid crystal, because they come directly into contact with the liquid crystal without curing process in the large LCD panel production. In this study, dual-curable adhesives based on partially acrylated epoxy acrylate oligomers were prepared and investigated with nematic liquid crystals using gas chromatography (GC), polarized optical microscopy and the measurement of the transmittance of the liquid crystal.As the concentration of CC bonds was increased, the immiscibility was enhanced due to the fast curing rate of the partially acrylated epoxy acrylate oligomers and reduced visual contamination was observed in the polarized optical microscope images. Moreover, the transmittance of the liquid crystal cells was not changed before and after the dual-curing of the adhesives and was maintained for 100 h.     

Contribution of relaxation processes to adhesive-joint strength of viscoelastic polymers

Relaxation processes accompany all stages of the lifetime of viscoelastic pressure-sensitive polymer adhesives, which can form strong adhesive joints with substrates of various chemical natures under application of a slight external pressure to the adhesive film for a few seconds. This review deals with comparison of the adhesion and relaxation properties of a number of typical pressure-sensitive adhesives based on polyisobutylene, butyl rubber, styrene-isoprene-styrene triblock copolymers, alkyl acrylate copolymers, and silicone adhesives as well as pressure-sensitive adhesives based on blends of high-molecular-mass polyvinylpyrrolidone with oligomeric poly(ethylene glycol). Within all three stages of the lifetime of adhesive joints (under adhesive-bond-forming pressure, upon withdrawal of contact pressure in the course of relaxation of the adhesive material, and under the force detaching an adhesive film from the substrate surface), the strength of adhesive joints has been shown to be controlled by large-scale relaxation processes, which are characterized by long relaxation times in the range 150–800 s. All examined pressure-sensitive adhesives can be arbitrarily divided into two groups. The first group is composed of fluid adhesives that relax comparatively fast and exhibit no residual (unrelaxed) stress. The second group includes elastic adhesives capable storing mechanical energy in the course of deformation that are characterized by appreciably longer relaxation times and display residual stress after relaxation. Conditions of adhesive debonding (e.g., strain amplitude and deformation velocity) significantly affect the relaxation process.     

Preparation and properties of sol–gel waterborne polyurethane adhesive

Waterborne polyurethane (WBPU) sol–gel adhesives were prepared through a prepolymer process followed by a sol–gel reaction of (3-aminopropyl)triethoxysilane (APTES). The terminal amine group of APTES reacted with the NCO group of the prepolymer, and the ethoxy group created Si–O–Si branching by hydrolysis and condensation reactions in water at the dispersion step. Water swelling (%), tensile strength and Young’s modulus of the synthesized WBPU sol–gel adhesives were improved by increasing APTES content. Synthesized WBPU sol–gel adhesives were used for bonding nylon fabrics. A significant improvement in adhesive strength was recorded, and the potential for good adhesive strength under water at moderately high temperature (up to 75 °C) was observed with 6.84 mol% APTES in WBPU sol–gel adhesives.     

Supramolecular Adhesives with Extended Tolerance to Extreme Conditions via Water-Modulated Noncovalent Interactions

Development of supramolecular adhesives with strong tolerance to extreme conditions has emerged as an important research area. In this study, by balancing supramolecular interactions such as hydrogen bonding interactions, electrostatic interactions, π–π stacking interactions, and cation-π interactions, we designed and prepared a series of two-component supramolecular adhesives derived from small organic molecules. Highly efficient interfacial adhesion with maximum adhesion strength of ≈10.0 MPa was realized on various surfaces in air, organic solvents, or liquid nitrogen. Owing to balanced supramolecular interactions, water participation prolonged and increased the tolerance of the adhesives in extreme environments. We demonstrate that the combination of imidazole-based ionic liquids and phenols can be applied for various interfacial adhesions, thereby aiding the development of next-generation adhesives capable of adapting to various extreme conditions in a controlled manner.     

Luminescent copolymers for applications in multicolor‐light‐emitting devices

Light‐emitting diodes based on organic materials [organic light‐emitting diodes (OLEDs)] have attracted much interest over the past decade. Several different attempts have been made to realize multicolor OLEDs. This article describes a new approach based on energy transfer in a donor/acceptor system. A copolymer containing both donor and acceptor compounds as comonomer units is prepared. The polymer consists of a derivative of a luminescent dye [4‐dicyanmethylene‐2‐methyl‐6‐4H‐pyran (DCM); acceptor compound], which is copolymerized with fluorene (donor compound) to combine the properties of an electroactive polymer with a highly luminescent dye. Photochemical processing is achieved by UV irradiation of this copolymer in the presence of gaseous trialkylsilanes. This reagent selectively saturates the C?C bonds in the DCM comonomer units while leaving the fluorene units essentially unaffected. As a result of the photochemical process, the red electroluminescence of the acceptor compound vanishes, and the blue‐green electroluminescence from the polyfluorene units is recovered. Compared with previous approaches based on polymer blends, this copolymer approach avoids problems associated with phase‐separation phenomena in the active layer of OLEDs. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4317–4327, 2006     

A reversible water-based electrostatic adhesive

Commercial adhesives typically fall into two categories: structural or pressure sensitive. Structural glues rely on covalent bonds formed during curing and provide high tensile strength whilst pressure-sensitive adhesives use physical bonding to provide weaker adhesion, but with considerable convenience for the user. Here, a new class of adhesive is presented that is also reversible, with a bond strength intermediate between those of pressure-sensitive and structural adhesives. Complementary water-based formulations incorporating oppositely charged polyelectrolytes form electrostatic bonds that may be reversed through immersion in a low or high pH aqueous environment. This electrostatic adhesive has the advantageous property that it exhibits good adhesion to low-energy surfaces such as polypropylene. Furthermore, it is produced by the emulsion copolymerization of commodity materials, styrene and butyl acrylate, which makes it inexpensive and opens the possibility of industrial production. Bio-based materials have been also integrated into the formulations to further increase sustainability. Moreover, unlike other water-based glues, adhesion does not significantly degrade in humid environments. Because such electrostatic adhesives do not require mechanical detachment, they are appropriate for the large-scale recycling of, e.g., bottle labels or food packaging. The adhesive is also suitable for dismantling components in areas as varied as automotive parts and electronics.     

Understanding and Designing Thermally Activated Delayed Fluorescence Emitters: Beyond the Energy Gap Approximation

In this article recent progress in the development of molecules exhibiting Thermally Activated Delayed Fluorescence (TADF) is discussed with a particular focus upon their application as emitters in highly efficient organic light emitting diodes (OLEDs). The key aspects controlling the desirable functional properties, e. g. fast intersystem crossing, high radiative rate and unity quantum yield, are introduced with a particular focus upon the competition between the key requirements needed to achieve high performance OLEDs. The design rules required for organic and metal organic materials are discussed, and the correlation between them outlined. Recent progress towards understanding the influence of the interaction between a molecule and its environment are explained as is the role of the mechanism for excited state formation in OLEDs. Finally, all of these aspects are combined to discuss the ability to implement high level design rules for achieving higher quality materials for commercial applications. This article highlights the significant progress that has been made in recent years, but also outlines the significant challenges which persist to achieve a full understanding of the TADF mechanism and improve the stability and performance of these materials.     

Influence of Particle Nucleation in Pressure Sensitive Adhesive Properties: Miniemulsion versus Emulsion Polymerization

Miniemulsion polymerization is a promising approach to produce and tailor pressure sensitive adhesives (PSAs). In this paper, a systematic comparison of the adhesive properties of latexes produced by miniemulsion and conventional emulsion polymerization is presented. Specifically, the influence of the total surfactant concentration, chain transfer agent concentration and chemical composition on the final adhesive properties of the polymer 2-ethyl hexyl acrylate/methyl methacrylate/acrylic acid was discerned using a 2³ factorial design for each polymerization method. In addition to the adhesive properties (i.e., loop tack, peel strength and shear strength), molecular weight distribution, particle size distribution (PSD) and glass transition temperature were analyzed. The results show that under the conditions used in this work, it is possible to produce PSAs using miniemulsion polymerization, a process wherein monomer droplet nucleation is the dominant particle nucleation mechanism. The use of a miniemulsion polymerization process, as opposed to the conventional emulsion technique, produced several differences such as larger particles sizes and narrower molecular weight distributions. Focusing on the PSA films that exhibited adhesive rather than cohesive failure, the PSA films generated via miniemulsion polymerization displayed higher values of loop tack and peel strength compared to those produced via conventional emulsion polymerization. Shear strength results were strongly dependent on the amount of gel content and sol molecular weight for both cases.     

白光有机电致发光器件中Rubrene超薄层的发光性能

以黄光荧光染料5,6,11,12-Tetraphenylnaphthacene(Rubrene)作为超薄层, 制备了白光有机电致发光器件, 并采用改变荧光超薄层厚度的方法, 通过表征器件的电致发光光谱, 分析了超薄层中染料浓度对器件性能的影响. 研究结果表明, 在荧光染料Rubrene的厚度为0.3 nm时, 器件可以同时实现黄光和蓝光的等强度发射, 从而得到性能优良的白光器件, 最高亮度达到3700 cd/m², 颜色坐标为(0.32, 0.33). 器件中蓝光来自N,N′-Bis-(1-naphthyl)-N,N′- biphenyl-1,1′-biphenyl-4,4′-diamine(NPB)的电致发光, 而器件优良的光电性能是由于Rubrene分子直接载流子陷阱(DCT)效应和NPB分子向Rubrene分子传递能量的协同作用所致.     

Design and fabrication of gecko-inspired adhesives

Recently, there has been significant interest in developing dry adhesives mimicking the gecko adhesive system, which offers several advantages compared to conventional pressure-sensitive adhesives. Specifically, gecko adhesive pads have anisotropic adhesion properties; the adhesive pads (spatulae) stick strongly when sheared in one direction but are non-adherent when sheared in the opposite direction. This anisotropy property is attributed to the complex topography of the array of fine tilted and curved columnar structures (setae) that bear the spatulae. In this study, we present an easy, scalable method, relying on conventional and unconventional techniques, to incorporate tilt in the fabrication of synthetic polymer-based dry adhesives mimicking the gecko adhesive system, which provides anisotropic adhesion properties. We measured the anisotropic adhesion and friction properties of samples with various tilt angles to test the validity of a nanoscale tape-peeling model of spatular function. Consistent with the peel zone model, samples with lower tilt angles yielded larger adhesion forces. The tribological properties of the synthetic arrays were highly anisotropic, reminiscent of the frictional adhesion behavior of gecko setal arrays. When a 60° tilt sample was actuated in the gripping direction, a static adhesion strength of ~1.4 N/cm(2) and a static friction strength of ~5.4 N/cm(2) were obtained. In contrast, when the dry adhesive was actuated in the releasing direction, we measured an initial repulsive normal force and negligible friction.     

Thermal behavior and dismantlability of adhesives containing various inorganic salts

As a fundamental study on the development of dismantlable adhesives containing chemically reactive materials, the thermal behavior and dismantlability of an epoxy adhesive containing one of the twenty-seven inorganic salts (chlorides, perchlorates, and nitrates) were observed. In the thermal behavior measured by the differential scanning calorimetry, epoxy adhesives with inorganic salts containing iron, copper, zinc, and aluminum cations released heats of reaction at lower temperatures than the adhesive alone or the adhesives with other inorganic salts. Since such inorganic salts were considered to be effective candidates as fillers in dismantlable adhesives, the adhesion strengths of their mixtures with the adhesive were observed after heat aging at 270 °C for 30 min. The results showed that both chloride and perchlorate salts specifically decreased the adhesion strength after heating. On the other hand, the effect of nitrate salts on the decrease in adhesion strength was low in comparison with the chloride and perchlorate salts.     

Structural adhesives with increased deformation resistance

The radiation-resistant cold-setting adhesive compositions with increased elasticity have been developed based on epoxy-diane resin modified by low-molecular two- and three-functional diluents. The presented adhesives can operate in the temperature range of −196 to +150°C, and they yield a high shear strength of the adhesive joint for aluminum alloys (16–23 MPa) and peeling strength for the joint between organic fabrics and aluminum alloys (1.75–2.4 kN/m).     

In Search of the Driving Factor for the Microwave Curing of Epoxy Adhesives and for the Protection of the Base Substrate against Thermal Damage

This study used controlled microwaves to elucidate the response of adhesive components to microwaves and examined the advantages of microwave radiation in curing epoxy adhesives. Curing of adhesives with microwaves proceeded very rapidly, even though each component of the adhesive was not efficiently heated by the microwaves. The reason the adhesive cured rapidly is that microwave heating was enhanced by the electrically charged (ionic) intermediates produced by the curing reaction. In contrast, the cured adhesive displayed lower microwave absorption and lower heating efficiency, suggesting that the cured adhesive stopped heating even if it continued to be exposed to microwaves. This is a definite advantage in the curing of adhesives with microwaves, as, for example, adhesives dropped onto polystyrene could be cured using microwave heating without degrading the polystyrene base substrate.     

A Novel Production Route for Nylon-6: Aspects of Microwave-Enhanced Catalysis

Summary: Microwave irradiation was used for the amidation of a nitrile with an amine with a freshly prepared zirconium-based heterogeneous catalyst. Microwave irradiation selectively heats the catalyst which enhances its activity as compared to conventional heating. The difference between microwave heating and conventional heating disappears when Zr(OH)₄ is used instead of ZrO₂, indicating a microwave-induced shift in the hydrolysis equilibrium, i.e. the distribution of ZrO₂, ZrO(OH)₂ and Zr(OH)₄, of the zirconium-based catalyst. The catalyst efficiently catalyzes the amidation of valeronitrile with n-hexylamine with conventional as well as with microwave heating. Zr(OH)₄ was also used for the polymerization of 6-aminocapronitrile using conventional and microwave heating. With both heating methods a relatively low molecular weight polymer with a M_n of 4000 g/mol was obtained in a sealed vessel, due to the presence of water and ammonia. A post-polymerization step under microwave irradiation, with active removal of water and ammonia shifts M_n to 10000 g/mol. Pressure decrease to facilitate water removal resulted in products with higher molecular weights. A pressure reduction to 50 Pa and operation in an argon atmosphere at 230 °C resulted in nylon-6 with a M_n of 65000 in rather short reaction times. Lower pressures led to end-biting and evaporation of the volatile ε-caprolactam at 230 °C. As a consequence the resulting product has than a much lower molecular weight. The combination of a heterogeneous zirconium based catalyst and microwave heating is promising for process intensification for nylon-6 production.     

Thermally activated delayed fluorescence molecules and their new applications aside from OLEDs

Thermally activated delayed fluorescence molecules (TADF) molecules have been found to undergo efficient intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes, which benefit their successful applications in organic light emitting diodes (OLEDs). Due to their long-lived delayed fluorescence, TADF molecules can also be applied in time-resolved luminescence imaging. Besides their special singlet properties, their excited triplet characteristics provide their potential applications in triplet-triplet annihilation upconversion (TTA-UC), photodynamic therapy (PDT) and organic photocatalytic synthesis by used as a triplet photosensitizer.     

Adhesion of molded polyethylene using polyethylene gels by microwave heating

Adhesive effect of polyethylene gels on the molded polyethylene by heating with microwaves has been investigated. Polyethylene gels in polar organic solvents such aso-xylene, chlorobenzene,o-dichlorobenzene,m-dichlorobenzene, 1,1,1,2-tetrachloroethane, and 1,1,2,2-tetrachloroethane were used as adhesives. All of these gels showed adhesive effect when heated with microwaves. In particular, the gels in 1,1,2,2-tetrachloroethane showed such strong adhesion that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking by heating for 8 min in a 500 W (2450 MHz) microwave oven.     

In Vitro and In Vivo Characterization of Biodegradable Reactive Isocyanate‐Terminated Three‐Armed‐ and Hyperbranched Block Copolymeric Tissue Adhesives

Tissue adhesives are an attractive class of biomaterials, which can serve as a treatment for meniscus tears. In this study, physicochemical and adhesive properties of novel biodegradable three‐armed‐ and hyperbranched block copolymeric adhesives are evaluated. Additionally, their degradation in vitro and in vivo, and the tissue reaction after subcutaneous injection in rats are assessed. The developed adhesives have sufficient adhesive strength to meniscus tissue after curing (66–88 kPa). Networks based on the three‐armed adhesive have tensile properties that are in the same range as human meniscus. After 26 weeks, networks based on the hyperbranched adhesive show a faster mass loss (25.4%) compared to networks prepared from the three‐armed ones (5.5%). Both adhesives induce an inflammatory reaction, however, no necrosis and only initial toxic effects on peripheral tissues are observed. The proposed materials are suitable candidates for the use as resorbable tissue adhesives for meniscus repair.     

微波场对固态氧离子导体上的甲烷氧化偶朕的影响

研究了微波场下甲烷在具有Bi2O3结构的固态氧离子导体上氧化偶联反应行为．与常规加热条件下的反应结果相比较,微波辐照下的反应有如下特点;（1）在达到相同甲烷转化率时,微波辐照下所需床层温度要远低于常规加热条件下所需床层温度;（2）微波辐照下,甲烷氧化偶联产物中C2烃的选择性普遍较高,在低温区尤为突出．微波场下甲烷偶联产物乙烷、乙烯的再氧化得到一定程度的抑制,致使微波场下的甲烷氧化偶联反应通常有较低的烯／烷比．     

Development in the area of UV-crosslinkable solvent-based pressure-sensitive adhesives with excellent shrinkage resistance

Solvent-based UV-crosslinkable pressure-sensitive adhesives (PSA) present a new class of products that offers the potential to produce a novel generation of ultraviolet cured self-adhesive products with excellent shrinkage resistance. A variety of solvent-based pressure-sensitive adhesives were prepared by synthesis in ethyl acetate with solid content on 50 wt.% with 2-ethylhexyl acrylate, methyl acrylate, acrylic acid, N-vinyl caprolactam and unsaturated photoinitiators: 4-acryloyloxy benzophenone, allyl benzoine and phenyl-(1-acryloyloxy)-cyclohexyl ketone. The main emphasis is given to the influence of viscosity and molecular mass of synthesized adhesive on their shrinkage. Further trials show the effect of the UV-crosslinking process with UV-lamp and comparison with acrylics PSA crosslinked with metal chelates aluminium acetylacetonate and titanium acetylacetonate on shrinkage. Further examinations describe the influence of various factors such as UV exposure time and UV dose on very relevant PSA performance such as shrinkage on coated PVC carrier.     

微波作用下的细粉煤脱水研究

在煤炭开采和加工工业中 ,泥煤的脱水问题变得越来越重要。改进细粉煤脱水效果的方法主要有物理方法和化学方法两类。现有的物理方法主要是提高过滤压力 ,使滤饼的结构变得致密 ,从而挤出其中的水分 ;微波加热脱水是指煤饼中的极性分子水在微波场的作用下快速摆动 ,产生类似于摩擦的作用 ,而以热的形式表现出来 ,使水分蒸发[1] 。本文是在微波加热条件下 ,探讨了微波对脱水效果的影响以及微波脱水的最佳工艺条件。1　实验部分1 1　原料　实验样品为朱仙庄气煤、山家林肥煤、西曲焦煤、青龙山瘦煤。其工业分析见表 1,其中空气干燥基水分为块…