Optical and Mechanical Properties of Hot-Pressed Cesium Iodide

Polycrystalline CsI disks were fabricated by hot-pressing in a nitrogen-purged glove box. Densification during hotpressing occurred by plastic flow resulting from lattice dislocation glide. Primary recrystallization and extensive grain growth were observed. Both the optical and mechanical properties of this material were significantly affected by grain growth, but in opposite ways. Transmittance increased and strength decreased as grain size increased. The hot-pressed CsI had transmittance of about 85% in the extra-long-wavelength infrared range, a value equivalent to that of single-crystal CsI. The flexural strength of the CsI that was hot-pressed under conditions that minimized grain growth was about 8 times higher than that of single-crystal CsI.     

UV-Curable Adhesives For Optical Communications

UV-curable optical adhesive systems featuring refractive indices in the 1.45 to 1.59 region controllable to within 0.005 are developed using new fluoro-epoxies and fluoro-epoxy (meth) acrylates. These adhesives possess excellent refractive index matching with optical glass and optical fibres, and the joints exhibit high bonding strength and good durability. These high performance adhesives are readily applicable as optical adhesives in fabricating optical components, attaching fibres to optical waveguides, and splicing optical fibres for optical communications.     

Optical and Mechanical Properties of α/β Composite Sialons

Two-phase α/β composites have been produced with a combination of high hardness, fracture toughness, and strength. Compared with a single-phase α-sialon, the composite showed around a twofold increase in both fracture toughness and bending strength, with only minimal reduction in hardness. Despite being a two-phase material, the optical properties of the composite were very good, showing transparency in sections of around 0.5 mm thickness. The optical properties were in fact better for the composite than for the single-phase α-sialon. Work to date on transparent sialons has focused on single-phase α-materials, which have inherently low fracture toughness unless elongated microstructures are developed. However, this microstructural development appears to adversely affect optical transparency. In this work it has been shown that good combination of mechanical properties can be achieved while maintaining optical transparency in two-phase composite sialons. The development of such materials should widen their range of application.     

光学胶粘剂在透镜应用中的发展

介绍了光学胶的应用和发展情况,以及对光学胶的技术要求。     

Mechanical Behavior of Butyl Adhesives

Butyl adhesives are widely used to bond elastomeric membranes. The results of uniaxial tension tests and simple shear tests conducted on bulk samples of butyl adhesives are presented in this paper. Butyl adhesives were found to have a rate-sensitive mechanical response with very low tensile and shear strengths. The stress-strain curves of the adhesive are characterized by an initial elastic response followed by a region of large plastic flow. A three-element viscoelastic model was used to model the stress-strain behavior of the adhesive. The model effectively combines a viscous dashpot and a network spring to capture the plastic flow in the material after the initial yield. The parameters of the model are calibrated to simulate a wide range of mechanical response of the adhesive.     

GAP推进剂粘合剂固化体系力学性能的研究

在保证推进剂加工工艺性能和能量性能的前提下,通过化学共聚的方法,选用主链柔顺性较好、且在推进剂中可单独用作含能粘合剂的3,3-双(叠氮甲基)氧丁环/四氢呋喃的共聚物(BAMO/THF)来改善聚叠氮缩水甘油醚(GAP)交联网络结构,在此基础上再加入合适的扩链剂和交联剂,所得弹性体的力学性能有大幅度的提高。当固化参数R=1.3,m(GAP)∶m(BAMO/THF)=75∶25,以1,4-丁二醇(BDO)为扩链剂,异佛尔酮二异氰酸酯(IPDI)/多异氰酸酯(N100)为固化剂,胶片的拉伸强度可达到1.03MPa,断裂伸长率达到505.3%。     

Mechanical and Optical Properties of Polyamide 6/Clay Nanocomposite Cast Films: Influence of the Degree of Exfoliation

PA6 nanocomposite films with different nanoclay dispersion degrees are prepared by melt compounding and cast extrusion. The dispersion of the MMT platelets (homogeneity and degree of exfoliation) is evaluated qualitatively by TEM and quantitatively by rheology and NMR; it ranges from microcomposites to highly exfoliated nanocomposites. Compared to neat PA6, the optical properties (clarity, gloss, haze) are worse for the microcomposites and better for the nanocomposites. The mechanical properties depend strongly on the exfoliation level. Better exfoliation leads to higher stiffness. The strain at break decreases compared to neat PA6 films even in the case of highly exfoliated nanocomposites films. At low MMT content, the microcomposite has a higher ductility than well exfoliated nanocomposites films.

     

Effect of Aging on the Mechanical Properties of UV Curable Optical Fiber Coatings

Abstract

A dual-layer urethane acrylate UV-cured coating is widely used to protect optical fibers because of its well-balanced mechanical properties, weathering resistance and rapid curing. The long-term mechanical behavior of fiber coatings is important for the reliability of optical fibers. Long-term exposure of UV-cured polyether urethane acrylate films was carried out in dry air and in water at elevated temperatures. Tensile testing was performed to reveal changes in mechanical properties and dynamic mechanical analysis to determine both the glass transition temperature and the crosslink density. The equilibrium swelling allowed assessment of the crosslink density. Tensile testing and strip force measurements were performed on virgin and aged optical fibers. Initially the fracture strengths of the secondary coatings increased under all aging conditions indicating post-curing reactions and the possible loss of uncrosslinked species. Aging under wet conditions led at a later stage to hydrolytic degradation of the network and to a decrease in the fracture stress. The equilibrium swelling and equilibrium modulus measurements showed good correlation with the changes in strength. The primary coatings showed a decrease in mechanical strength after only 2–4 weeks under all conditions.     

双组分豆粕基胶黏剂的流变行为研究

以改性胶液作为组分1,豆粕粉作为组分2,通过常温复配的技术手段制备了一种双组分豆粕基胶黏剂,并利用旋转流变仪对其流变行为进行了研究。结果表明：添加改性胶液的双组分豆粕基胶黏剂黏度增加,但剪切变稀现象与添加自来水的豆粕基胶黏剂保持一致;豆粕粉添加量对胶黏剂在高剪切速率下的流变行为的影响较为明显;Z试剂对胶黏剂在低配比（豆粕粉添加量≤10%）、低剪切速率（≤500 s^-1）下的流变行为影响较大;填料和表面活性剂只影响豆粕基胶黏剂的黏度而不改变其剪切流变行为。     

The Efficient Design of Adhesive Bonded Joints

A concise method of analysis is used to study the numerous parameters influencing the stress distribution within the adhesive of a single lap joint. The formulation includes transverse shear and normal strain deformations. Both isotropic or anisotropic material systems of similar or dissimilar adherends are analysed. Results indicate that the primary Young's modulus of the adherend, the overlap length, and the adhesive's material properties are the parameters most influential in optimizing the design of a single lap joint.     

The Effect of Moisture Content in Epoxy Film Adhesives on their Performance. III: Bulk Properties

Humidity absorbed by epoxy film adhesives during low temperature storage or exposure to atmosphere may result in reversible changes and irreversible modifications. Vacuum treatment may partially remedy the reversible changes. The consequences of vacuum drying are manifested in enhancement of both the peel and shear properties of bonded joints (Part I and Part II of this series of papers) and the thermal, physical and mechanical properties of the bulk adhesive, characterized in the present study.

Experimental results have shown that the bulk properties of structural epoxy based adhesives are highly correlated with the aging processes caused by water absorption in the prepolymerized adhesive. Applying the vacuum process is harmful to fresh unaged adhesive due to devolatization of low molecular species of the film adhesive.

The characterization of bulk properties for the purpose of following the aging and recovery processes is advantageous, since the bulk is independent of geometrical and interfacial effects which dominate in the case of property evaluation of the adhesive in a bonded joint.     

The Effect of Moisture Content in Epoxy Film Adhesives on their Performance. III: Bulk Properties

Humidity absorbed by epoxy film adhesives during low temperature storage or exposure to atmosphere may result in reversible changes and irreversible modifications. Vacuum treatment may partially remedy the reversible changes. The consequences of vacuum drying are manifested in enhancement of both the peel and shear properties of bonded joints (Part I and Part II of this series of papers) and the thermal, physical and mechanical properties of the bulk adhesive, characterized in the present study.

Experimental results have shown that the bulk properties of structural epoxy based adhesives are highly correlated with the aging processes caused by water absorption in the prepolymerized adhesive. Applying the vacuum process is harmful to fresh unaged adhesive due to devolatization of low molecular species of the film adhesive.

The characterization of bulk properties for the purpose of following the aging and recovery processes is advantageous, since the bulk is independent of geometrical and interfacial effects which dominate in the case of property evaluation of the adhesive in a bonded joint.     

UV-Curable Transparent Adhesives for Fabricating Precision Optical Components

UV-curable transparent epoxy adhesives have been specifically developed for the fabrication of optical communictions precision devices. The newly developed adhesives using cylohexane type fluoro-epoxy as the base resin and speherical quartz filler have extremely low volume shrinkage of 1.2% during curing and the cured adhesives have low thermal expansion coefficient of less than 2 × 10^-5/°C. Sheets of the adhesives are colorless and transparent to visible light because the refractive index of the epoxy matrix resin is matched to that of the quatz filler. These highly transparent adhesives can be cured to a depth of more than 5 mm by using 10 mW/cm² UV-irradiation for 30 min. They also have high adhesive strength and good durability. Therefore, they can be used in the fabrication of optical components that require submicron positioning accuracy.     

Viscoelastic Properties of Pressure-Sensitive Adhesives

Recent studies on the correlation of viscoelastic properties of pressure-sensitive adhesive (PSAs) with industry standard performances such as peel, tack and shear are reviewed and discussed. One notewothy feature in these correlations is the separation of the bonding and debonding steps in PSA adhesion, which specifies the characteristic bonding and debonding frequencies of different PSA tests. Viscoelastic windows (VW) for different types of pressure-sensitive adhesives (PSAs) proposed by these workers are also compared and discussed. The observed good correlations reaffirm the importance of bulk viscoelastic properties to PSA adhesion performances.     

Accurate High-speed Assembly of Optical Components in Optical Scanning Systems using UV-curing Adhesives: A Positional and Stability Study

In the miniaturized designs of optical scanning systems, UV-curing adhesives have been substituted for screws and bolts. The assembly of delicate optical components enforces stringent requirements on positional accuracy and stability after temperature and humidity cycle testing. The influence of the UV-curing adhesive is mainly determined by its polymerization shrinkage (typically more than 6%). With low amounts of Aerosil® fillers (5% by weight), shrinkage values of 3% can be attained. Optimized adhesive constructions lead to close positional tolerances (0.5 μm) and angular displacements (0.1 mrad).     

Hygrothermal Properties of Epoxy Film Adhesives

The hygrothermal response of high performance epoxy film adhesives, in their bulk state, has been characterized over a wide range of temperatures, following exposure to a combination of humidity (95% R.H.) and heat (50°C).

Experimental results have indicated that the testing temperature has a pronounced effect on both tensile modulus and strength of the adhesives, while the effect of moisture content varies with respect to the adhesive type. The moduli of the film adhesives, which have a wide range of glass transition temperatures (T_g), have been related to both moisture level in the adhesive and testing temperature. This has been accomplished by employing a dimensionless temperature, which incorporates the wet and dry T_g and the testing, as well as a reference, temperature. The strength properties have shown a higher degree of scatter using the abovementioned dimensionless temperature.

Scanning electron microscopy of the fracture surfaces have shown a good agreement between the effects of moisture and the mechanical properties. Adhesives which exhibited good moisture resistance, as manifested by the stability in their tensile properties, showed minor changes in their fracture surfaces regardless of moisture conditioning. Distinctively, the effect on strength properties has been correlated with typical moisture-induced fracture mechanisms.     

Hygrothermal Properties of Epoxy Film Adhesives

The hygrothermal response of high performance epoxy film adhesives, in their bulk state, has been characterized over a wide range of temperatures, following exposure to a combination of humidity (95% R.H.) and heat (50°C).

Experimental results have indicated that the testing temperature has a pronounced effect on both tensile modulus and strength of the adhesives, while the effect of moisture content varies with respect to the adhesive type. The moduli of the film adhesives, which have a wide range of glass transition temperatures (T_g ), have been related to both moisture level in the adhesive and testing temperature. This has been accomplished by employing a dimensionless temperature, which incorporates the wet and dry T_g and the testing, as well as a reference, temperature. The strength properties have shown a higher degree of scatter using the abovementioned dimensionless temperature.

Scanning electron microscopy of the fracture surfaces have shown a good agreement between the effects of moisture and the mechanical properties. Adhesives which exhibited good moisture resistance, as manifested by the stability in their tensile properties, showed minor changes in their fracture surfaces regardless of moisture conditioning. Distinctively, the effect on strength properties has been correlated with typical moisture-induced fracture mechanisms.     

m-LLDPE／纳米SiO2的力学性能和光学性能研究

采用熔融共混法制备了m-LLDPE／纳米SiO2复合材料，并对该体系的力学性能和光学性能进行了系统研究。结果表明，纳米SiO2对m-LLDPE具有一定的增强、增韧作用。复合材料的红外吸收能力较m-LLDPE明显提高，此外，m-LLDPE／纳米SiO2复合材料的可见光透光度有所降低，雾度却有明显的上升。通过SEM电镜得出，表面处理方法对纳米SiO2在基体中的分散性能有显著影响。     

BOPP消光膜制备及其光学与力学性能研究

将3种无机填料及PET树脂作为消光剂与载体树脂共混制备消光母料,并加工成消光膜。对薄膜的光学性能和力学性能进行了分析,并采用扫描电镜观察了消光母料的表面形貌。结果表明:载体树脂直接影响消光膜的消光性能和力学性能,PET消光体系的各项指标均优于无机填料消光体系。     

m-LLDPE/纳米SiO_2的力学性能和光学性能研究

采用熔融共混法制备了m-LLDPE/纳米SiO2复合材料,并对该体系的力学性能和光学性能进行了系统研究。结果表明,纳米SiO2对m-LLDPE具有一定的增强、增韧作用。复合材料的红外吸收能力较m-LLDPE明显提高,此外,m-LLDPE/纳米SiO2复合材料的可见光透光度有所降低,雾度却有明显的上升。通过SEM电镜得出,表面处理方法对纳米SiO2在基体中的分散性能有显著影响。