Time-Resolved Study of the Photo-Curing Process of Dental Resins with the NMR-MOUSE

The photo-curing reaction of dental resins has been examined with unilateral nuclear magnetic resonance (NMR-MOUSE) allowing nondestructive high-resolution measurement of depth profiles as a function of time and space. The NMR signal is sensitive to both the monomer concentration and changes in molecular mobility. Upon irradiation with blue light, it first increases due to molecular mobility enhanced by the reaction heat and then decreases exponentially with the monomer concentration as the polymer signal is lost in the dead time of the instrument upon curing. The space and time dependence of the NMR signal can be described by the photo-polymerization reaction kinetics together with a heuristic approximation of the temperature dependence.     

新型腰果酚基不饱和树脂的结构及其紫外光固化行为的红外光谱研究

以天然产物腰果酚为原料,利用其酚羟基与环氧基的反应活性,通过开环醚化反应制备了两种腰果酚基不饱和树脂单体。通过傅里叶红外光谱研究了合成过程中主要活性基团的变化,结合核磁共振氢谱及凝胶渗透色谱分析进一步确定了合成树脂单体的分子结构,并利用红外光谱法对树脂单体的紫外光固化行为进行了研究,且对其光固化物进行了热重分析。研究表明：分子结构分析确认了目标产物的成功合成,树脂单体的分子结构以及不饱和双键含量对树脂的固化速度和固化物的热稳定性有着重要影响,两种单体在30 s内均已基本达到最高固化水平,光固化物的主分解初始温度均可达到350 ℃以上。     

Formation of a stable polymer blue phase under UV irradiation of Langmuir-Schaefer films of diin N-arylcarbamate derivative

Polymerization under UV irradiation is studied in monolayer Langmuir-Schaefer films of diin N-arylcarbamate derivative. The formation of a stable polymer blue phase of diacetylene derivative stable against excess UV light and heating to a temperature of 120 °C was detected. The formation of the structurally ordered Langmuir monolayer of monomers is studied using Brewster angle microscopy.     

压印光刻中紫外光诱导阻蚀胶固化控制计算

针对压印过程中两类基本的复型缺陷，从实验分析中得出其主要原因是曝光后阻蚀胶的固化程度难以控制．通过分析紫外曝光光源与阻蚀胶的光谱匹配性，得出使得阻蚀胶固化的有效波长为365nm；对光诱导紫外曝光过程中紫外光的传播分析，建立了阻蚀胶中光强分布的数学模型；用粘度来表征阻蚀胶的固化程度，建立了阻蚀胶中的粘度分布函数．分析了阻蚀胶对365nm紫外光的吸收率以及膜厚对阻蚀胶中光强分布均匀性的影响，得出复型后阻蚀胶凸起处的光强分布均匀性对吸收率及膜厚更为敏感的结论．     

Photochemical sensitization and magnetic field effect on aerosol particle formation from a gaseous mixture of glyoxal and acrolein

Under light irradiation at 435.8 nm with a medium pressure mercury lamp, pure acrolein (AC) vapour does not produce any deposits, but a gaseous mixture of glyoxal (GLY) and AC produced sedimentary aerosol particles. The nucleation process of the aerosol particles was investigated by measuring He-Ne laser light intensity scattered by the aerosol particles as formed under light irradiation at 435.8 nm. From the dependence of the scattered light intensity on the partial pressure of GLY, it was found that electronically excited GLY in the nπ? state initiated chemical reactions with AC leading to nucleation of the aerosol particles. Magnetic field effects on the nucleation process were measured for a gaseous mixture of GLY and AC. With the application of a magnetic field of 5.3 kG, the nucleation reaction was accelerated, and the convection of the gaseous mixture was changed due to greater heat release during nucleation reaction between GLY and AC. The magnetic field effect on the gaseous mixture is discussed based on the photochemical behaviour of GLY.     

Cold crystallization from chiral smectic phase

Cold crystallization of liquid crystalline (S)-4’-(1-methylheptyloxycarbonyl) biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-2-fluorobenzoate (3F7HPhF) was studied in isothermal as well as non-isothermal conditions. For isothermal conditions at temperatures between 233 and 250?K X-ray diffraction and differential scanning calorimetry were used. The crystallization kinetics was described by the Avrami–Avramov model, and the values of Avrami exponent, characteristic time and activation energy were determined. The kinetics of the cold crystallization in non-isothermal conditions for chosen heating rates up to 0.5?K/s was studied by differential scanning calorimetry and analyzed using Ozawa, Mo and Augis–Bennett models. Cold crystallization was found to be three-dimensional and controlled by diffusion both in the isothermal and non-isothermal process, however the activation energy determined in the non-isothermal process is about two times smaller than in the isothermal one.     

Thermal optimization of high power LED arrays with a fin cooling system

In this paper, we describe an optimization process of thermal design for the light lamp which utilizes the Light Emitting Diode (LED) module as a lighting source. The thermal performance of the LED module was shown to significantly improve by the optimization process of cooling system attached with it. A wind circulating cooling system was designed for the LED arrays with the input power of 60?Watts and another heat pipe cooling system was designed for the input power of 144?Watts. The effects of design parameters such as air temperature and air velocity on the thermal performance of LED lamp were investigated. Thermal performance of the two cooling systems was compared for practical application.     

Anisotropic Thermal Processing of Polymer Nanocomposites via the Photothermal Effect of Gold Nanorods

By embedding metal nanoparticles within polymeric materials, selective thermal polymer processing can be accomplished via irradiation with light resonant with the nanoparticle surface plasmon resonance due to the photothermal effect of the nanoparticles which efficiently transforms light into heat. The wavelength and polarization sensitivity of photothermal heating from embedded gold nanorods is used to selectively process a collection of polymeric nanofibers, completely melting those fibers lying along a chosen direction while leaving the remaining material largely unheated and unaffected. Fluorescence‐based temperature and viscosity sensing was employed to confirm the presence of heating and melting in selected fibers and its absence in counter‐aligned fibers. Such tunable specificity in processing a subset of a sample, while the remainder is unchanged, cannot easily be achieved through conventional heating techniques.     

Thermodynamics of isothermal vitrification by chemical reactions in a liquid

Summary We report here first observations of the decrease in heat capacity during isothermal vitrification of a thermosetting polymer. A new experimental method has been developed for this study which allows simultaneous measurements of both the heat capacity and the enthalpy released as chemical reactions occur in quasi-isothermal conditions. During the curing the heat capacity of a thermoset first increases slightly, undergoes an abrupt decrease in a narrow range of time and thereafter slowly decreases. The abrupt decrease represents the irreversible transition of the liquid to a vitreous solid which is equivalent to the reversible glass transition appearing in a supercooled liquid when the temperature is lowered.     

Locally-induced permanent birefringence by polymer-stabilization of liquid crystal in cells and photonic crystal fibers

The aim of this work was to induce permanent birefringence both in typical liquid crystal cells and photonic crystal fibers (PCFs) by photo-polymerization. For this purpose three different liquid crystalline materials, namely E7, 5CB, and 6CHBT were combined with a mixture of RM257 monomer and a UV sensitive initiator with the percentage weight less than 10%. Due to the photo-polymerization process it was possible to achieve polymer-stabilized liquid crystal orientation inside LC cells and micro-sized cylindrical glass tubes. In particular, periodic change in spatial molecular orientation was achieved by selective photo-polymerization. Successful results obtained in these simple geometries allowed for the experimental procedure to be repeated in PCFs leading to locally-induced permanent birefringence in PCFs.     

Hybrid Isothermal Model for the Ferrohydrodynamic Chemically Reactive Species

A hybrid isothermal model for the homogeneous-heterogeneous reactions in ferrohydrodynamic boundary layer flow is established. The characteristics of Newtonian heating and magnetic dipole in a ferrofluid due to a stretchable surface is analyzed for three chemical species. It is presumed that the isothermal cubic autocatalator kinetic gives the homogeneous reaction and the first order kinetics gives the heterogeneous (surface) reaction. The analysis is carried out for equal diffusion coefficients of all autocatalyst and reactions. Heat flux is examined by incorporating Fourier's law of heat conduction. Characteristics of materialized parameters on the magneto-thermomechanical coupling in the flow of a chemically reactive species are investigated. Further, the heat transfer rate and friction drag are depicted for the ferrohydrodynamic chemically reactive species. It is evident that the Schmidt number has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for specific cases is found an excellent agreement.     

Excitation wavelength dependence and magnetic field effect on aerosol particle formation from a gaseous mixture of carbon disulphide and glyoxal

Upon excitation of carbon disulphide (CS₂) molecules under UV light irradiation at 313?nm a gaseous mixture of CS₂ and glyoxal deposited sedimentary aerosol particles only. The nucleation process of the aerosol particles was investigated by measuring the He–Ne laser light intensity scattered by the aerosol particles formed under light irradiation at 313?nm, and the chemical structure of the sedimentary particles was analysed by measuring the FT-IR and X-ray photoelectron spectra. On application of a magnetic field of up to 5?T, the nucleation process was decelerated and the chemical species originating from CS₂ were less abundant. The results were compared with those obtained under visible light irradiation at 435.8?nm reported previously. Chemical reactions between CS₂ and glyoxal molecules, which were responsive to the magnetic field, are discussed briefly.     

紫外光致聚合物和制造镭射玻璃的技术

本文论述了制造镭射玻璃的技术和材料。技术包括：清洗玻璃板；将紫外光致聚合物材料涂到玻璃板上；将镭射玻璃母版粘贴到涂有光致聚合物的玻璃板上；紫外光曝光固化；丝网印刷；真空镀膜；涂保护层。紫外光致聚合物材料是由光引发剂、单体、预聚体和其它添加剂组成。实验结果表明：此种镭射玻璃具有很高的抗酸、碱、热和紫外照射的能力     

真空罐内应用的太阳模拟灯阵热设计

为了解决太阳模拟灯阵整体放在真空罐内使用时的导热问题,采用热管导热的方案,设计了专门的氙灯导热机构。计算了液氮系统的导热能力,结果显示,真空罐液氮冷却系统的温度升高ΔT为2074 1 K,小于其过冷度4 K,表明真空罐液氮冷却系统完全可以将太阳模拟灯阵的热量导出。采用热管导热技术,设计了导热机构,用有限元分析法进行了热仿真分析,分析结果表明,氙灯阴阳极温度维持在100 ℃左右,氙灯灯泡维持在655 ℃左右,满足氙灯正常工作的温度条件;积分器和反射镜组件温度维持在200 ℃左右,椭球镜温度维持在135 ℃左右,亦满足正常工作的温度条件,从而验证了热设计的正确性。     

一种廉价紫外光源对维生素D2合成的研究

开发了一种新型廉价紫外荧光光源,采用中波透紫玻璃作为灯管,灯管玻璃本身可以吸收254nm以下的紫外光,因此反应器不需要滤光液。得到了光照时间与麦角固醇转化率及前维生素D₂选择性得率之间的关系。初步研究了该光源紫外光强度随时间的衰减变化,并对光强衰减与光化学反应结果的影响进行了研究。结果表明,该廉价光源在65min可以使反应达到65.5%的转化率,选择性得率为60.4%,且光源强度在300h内仅衰减13%。该光源成本较低,寿命较长,且反应器不需要滤光液,设备投资较少,是一种理想的可用于工业化生产的廉价光源。     

Simulation and improvement of temperature distributions of a framed mould during the autoclave composite curing process

It is recognized that the uniformity of mould temperature fields during the composite curing process has a vital important effect on the component and, thereby, the product quality. Previous studies mainly considered the temperature along the thickness direction of the mould or composite component, or under a rather simple external environment, leading to some deviations from the actual composite autoclave curing process. In this paper, taking into consideration some factors such as auxiliaries, framed mould and forced convection phenomenon inside an autoclave, a simulation model has been established on the mould curing temperature field in an autoclave. On this basis, simulation and thermal analysis of the framed mould temperature fields with regard to composite structure and material system in the aviation industry have been performed. Besides, the influences of the time of heat preservation, heating rate have been also investigated, and two nondimensional factors are introduced for evaluating temperature uniformity and heating quality. It is found that increasing the time of heat preservation and the number of periods could improve the uniformity significantly, and, thus, the improvements of heating efficiency and uniformity of temperature field are achieved, and that a smaller heating rate would give much better heating quality.     

Influence of UV light irradiation on film thickness distribution of tin oxide films by photochemical vapour deposition

Tin oxide (non-doped) films have been prepared by a photochemical vapour deposition (photo-CVD) from Tetramethyltin (TMT) (Sn(CH₃)₄) and O₂ (containing O₃). A low-pressure mercury lamp was used as the light source. The effect of the UV light irradiation on the film thickness distribution along 5 cm×5 cm area was examined. By piling Teflon films on the surface of the suprasil window, the light intensity of 184.9 nm UV wavelength of the low-pressure mercury lamp was controlled, while that of 253.7 nm wavelength through the Teflon hardly changed. As a result, the uniformity of the film thickness distribution was improved as the light intensity (184.9 nm) increased. The UV 184.9 nm light irradiation may have improved the uniformity of the reactive species distribution in the vapour phase, which may result in the formation of the uniform thickness distribution.     

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). III. Rheological Kinetics of Cross‐Linking Reaction

Abstract

The kinetics of the thermally activated cross‐linking reaction of poly(vinyl methyl ether) (PVME) were investigated rheologically by evaluating the viscoelastic material functions such as elastic storage modulus, G′, viscous loss modulus, G″ and complex dynamic viscosity, η*, during the curing process, both isothermally and nonisothermally. The isothermal kinetics reaction was described using a phenomenological equation based on the Malkin and Kulichikhin model, which was predicated originally for the isothermal curing kinetics of thermosetting polymers followed by differential scanning calorimetery (DSC) and was found to be applicable for rheokinetic reactions as well. An excellent representation of the data was obtained using this model; the rate of the reaction was found to be second order regardless of the temperature, which is in good agreement with literature data. The temperature dependence of the cross‐linking rate constant was described by an Arrhenius plot with an apparent activation energy equal to 60–62 kJ mol^?1, in reasonable agreement with the value obtained previously from the temperature dependence of gel time, t _gel. The nonisothermal kinetics reaction rate was described by a model that included the classical rate equation, the Arrhenius equation, and the time–temperature relationships. The apparent activation energy obtained nonisothermally was found to be frequency independent and equal to 72 kJ mol^?1, in very good agreement with the value obtained isothermally from the temperature dependence of t _gel in part II.     

Multiphase modelling of the growth kinetics of precipitates in Al-Cu alloys during artificial aging

ABSTRACT

In the aluminum industry, the needs of predictability of the kinetics of precipitation during the artificial aging processes increase as the targeted applications require the maximisation of properties at the lowest costs possible. In this regard, kinetics modelling can be helpful to design the heat treatment processes. Despite using many fitting parameters, available models show a lack of fitting with experimental data, especially for the apparent heat capacity measured at high temperatures by a differential scanning calorimeter (DSC). To address this issue, a mixed-mode model was recently developed for isothermal heat treatment, whereas non-isothermal heat treatment must be considered to compare the calculated results with those measured by isochronal heating in a DSC. In this contribution, the model is extended to non-isothermal heat treatments. To this end, the growth kinetics pathway and sequence of precipitation in a binary Al-Cu alloy have been simulated, optimising the pre-exponential factor and the activation energy of the interfacial mobility of the secondary phases. This calibration of the interfacial mobilities allowed a very good reproduction of the evolution of the apparent heat capacity with temperature. The model and calibrated interfacial mobilities were then used to compute the size evolution of θ′ precipitates in an Al-4?wt%Cu. The isothermal growth rates calculated at 4 temperatures were in good agreement with those measured and reported by independent researchers. The good predictability of the model indicates that the assumptions made were suitable and well funded, especially regarding the growth rates of embryos emerging from the subcritical growth regime.     

Durability of Ultra-Thin Silver Films and Silver-Gold Alloy Films under UV Irradiation

Silver films(Ag) and silver-gold films(Ag-Au) with thickness ~15nm are coated on Bk7 glasses through thermal evaporation.After doping gold of 5.2%,the grain size of the Ag film reduces from 13.6nm to 9.1nm,also the surface roughness decreases from 1.45 nm to 0.94 nm.A UV lamp is used as the irradiation light source to accelerate the corrosion process in the atmosphere.After 17 h irradiation,the pure silver film surface turns dark,and the transmittances reduce from 350 nm to 500 nm,while the Ag-Au film degrades much less,almost negligibly after UV radiation.Additional x-ray photoelectron spectroscopy and atomic force micrographs data are provided to show atomic content of Sims and their surface morphologies.It is suggested that small grain size and high packing density of alloy film prevent reaction of silver with oxygen in the atmosphere,which leads to high stability of the Ag-Au Elm.