Fabrication of a graded-index polymer optical fiber preform by using a centrifugal force

We have investigated a fabricating method for a graded index polymer optical fiber preform using a centrifugal force. When two monomers with different densities and refractive indices are polymerized under a centrifugal force, a concentration gradient is generated due to their density difference. Therefore, a graded refractive index can be obtained according to the concentration gradient. When a monomer is polymerized under a centrifugal force, a preform with a hollow is obtained because of volume shrinkage. To compensate for this practically, additional monomer should be filled into the hollow. Monomer should be fed to obtain a continuous gradient of refractive index at the interface before the first polymerized product is perfectly glassified. Two different types of feeding additional monomer were experimented with: monomer-monomer pair (case I) and monomer-polymer pair (case II). The graded index profile with a proper δn (about 0.01) was successfully obtained in either case.     

Preparation of graded index plastic rods doped with Sm3+ by interfacial-gel polymerization

A novel graded index (GI) poly(methyl methacrylate) (PMMA) rod was prepared by interfacial-gel polymerization carried out in a PMMA tube with one closed end. Bromobenzene (BB), a higher refractive index molecule, was used to obtain a graded index distribution and samarium octanoate (SOA) was used as a dye with Sm³⁺ concentrations from 60ppm to 700ppm. For a poly-merization system containing methyl methacrylate (MMA) as monomer, azobis-isobutyronitrile (AIBN) as initiator and dodecyl mercaptan as chain transfer agent, the difference of the refractive index from the centre to the periphery of the rod (Δn) with various BB and Sm³⁺ contents was determined. Experimental results showed that a parabolic profile of refractive index formed on the cross-section of the rod and Δn increased with increase of BB content. SOA has little effect on the profile within the given concentrations. The GI distribution may be calculated by free volume theory. The result is identical with the experimental distribution. © 1998 SCI.     

Preparation and simulation of graded‐index polymer rods by interfacial‐gel polymerization

A graded‐index (GI) polymer rod was prepared by interfacial‐gel polymerization, in which polymerization was performed in a PMMA tube and bromobenzene (BB) was used as a higher refractive index molecules. By using the new technology, a GI polymer rod without any defect of void or bubble was made. A detailed mechanism and simulation of graded‐index formation were given according to the Vrentas‐Duda free volume theory. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3387–3390, 2001     

渐变型聚合物光纤共挤扩散过程的数学模型

基于流变学原理和质量传递原理的分析，建立了一个能够描述渐变型聚合物光纤（GIPOF）共挤扩散制备过程的数学模型。该模型采用基于温度和掺杂剂浓度修正的Carreau黏度方程，利用计算流体动力学软件Fluent模拟求解出拉丝后光纤折射率分布。以聚甲基丙烯酸甲酯为芯皮层原料、苯硫醚为掺杂剂制备了GIPOF，并通过聚焦法测得光纤折射率分布。模拟结果与实验结果基本相符，表明该模型可用来预测和控制光纤折射率分布情况。     

Refractive index distribution of graded poly(methyl methacrylate) preform described by self-diffusion approaches of free-volume theory in a ternary system

A series of graded index poly(methyl methacrylate) (PMMA) preforms with monomer/dopant=5:1, 7:1, 10:1 have been made by an interfacial-gel polymerization procedure, in which polymerization was performed in a PMMA tube and a dopant, bromobenzene (BB), was used as a higher refractive index molecule. The graded index was formed by the diffusion of the molecules. While describing the process of interfacial-gel polymerization, the distribution of the polymer concentration at the radial direction of the tube was assumed to be ω=a(r/R)²+b. According to the self-diffusion approach of the free-volume theory in ternary systems and its application in a high-conversion polymerization system, a model of forming the graded index is established, and a quadratic refractive index (RI) distribution on the cross-section of the preform is obtained. Compared with the theory in a binary system, the result is more identical with experiments in both the changing trend and the value of RI. The RI distributions of preforms prepared with different MMA/BB were simulated. The effect of MMA/BB on the RI distribution was also discussed.     

Preparation and characterization of gradient refractive index plastic rods with small calibers

A series of gradient refractive index (GRIN) plastic rods with diameters of 2–4 mm were fabricated using the centrifugal diffusion polymerization (CDP) technique. Methyl methacrylate (MMA) was used as the monomer having a lower refractive index, and poly‐(methyl methacrylate) (PMMA) was used as a prepolymer dopant. The reactive benzyl methacrylate (BzMA), and an unreactive agent chosen from bromonaphthalene (BN) and diphenyl sulfide (DS) with higher refractive index were used as the second component of the feed mixture. Effects of feed composition, centrifugal conditions, and initiator concentration on the optical characteristics of plastic GRIN rods are investigated. Refractive index profiles and image transmission qualities of the GRIN rods prepared in this investigation are estimated.     

Fabrication of a graded‐index polymer optical fiber preform without cavity via the automatic refilling process

When two monomers with different densities and refractive indices are polymerized under a centrifugal force field, a cavity is generated in the rotational axis as a result of inherent volume shrinkage. Accordingly, an additional monomer‐refilling process is necessary to compensate for the undesirable cavity. In this study, we modified the stepwise refilling process to an automatic process and have successfully fabricated a graded‐index polymer optical fiber preform without a cavity. The process could also reduce the processing time and enhance the transmission speed of a polymer optical fiber compared with the stepwise process. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Improvement of Chromatic Aberration of the Plastic Rod‐Lens Array, 2

Summary: We propose in this paper a new plastic rod‐lens with low chromatic aberration. Since a plastic rod‐lens has a parabolic refractive index distribution, it usually also shows a distribution of Abbe number. This Abbe number distribution is thought to cause the chromatic aberration of the plastic rod‐lens array. We have studied novel materials for a new plastic rod‐lens with low chromatic aberration and have provided new transparent polymer blends consisting of two polymers with different refractive indices and with almost equal Abbe numbers by using a fabrication process based on photopolymerization of methacrylate monomer(s) in the presence of other methacrylic polymers. The process can give new transparent polymer blends which cannot be formed using conventional techniques for polymer blend formation. In this work, tricyclo[5,2,1,0^2,6]deca‐8‐yl methacrylate is used as a high refractive index monomer and tert‐butyl methacrylate is used as a low refractive index one. By using polymer blends including these monomer units, we have created a plastic rod‐lens with lower chromatic aberration.

Molecular structures of comonomers in the study.     

环管反应器中聚丙烯颗粒内部的质量与热量传递模型

针对环管反应器中Ziegler-Natta催化剂催化的聚丙烯颗粒增长过程,采用多层模型建立了聚丙烯颗粒内部的质量与热量传递预测模型.通过模型模拟得到聚丙烯颗粒内部的丙烯单体浓度梯度和温度梯度.此外,通过模型分析了聚丙烯颗粒的增长规律.结果表明,环管反应器中的聚丙烯颗粒内部的单体浓度梯度明显,该浓度梯度值随扩散系数的增大而减小,随催化剂初始粒径减小而减小;相比于浓度梯度而言,聚丙烯颗粒内部的温度梯度并不明显,温度值随聚合进行而增加,温度梯度则随催化剂初始粒径的增加而增加;不同大小的催化剂颗粒增长得到的聚丙烯颗粒的增长倍数不同.     

Birefringence of a polymeric cholesteric liquid crystal measured by refractometry

The Abbé refractometer provides a convenient way to measure the refractive indices and birefringence of polymeric liquid crystalline solutions. The cholesteric mesophase formed by (acetoxypropyl) cellulose and its solutions in dibutyl phthalate were examined at 26°C and 50°C. The measured refractive indices were dependent on the direction of shear when the polymer was applied to the refractometer plates. The initial shear-induced nematic-like order relaxed slowly to the equilibrium planar cholesteric structure. The refractive index for the isotropic solutions and the two refractive indices for the anisotropic solutions all varied linearly with polymer concentration, and the width of the intermediate two-phase region was readily determined. The changes in refractive index with polymer concentration and with orientation on the refractometer plate were rationalized with a simple model of the cellulosic mesophase, and an order parameter of 0.7 was estimated. The layer birefringence calculated from optical rotatory dispersion measurements of the cholesteric reflection band intensity was in good agreement with the birefringence measurements.     

对二甲苯氧化反应器非均匀混合模型

对二甲苯氧化是一个复杂的气-液-固三相反应过程。今根据实验测取的对二甲苯氧化反应动力学关系与数据,建立了工业氧化反应器的非均匀混合模型,用以考察气、液相的混合状况及其对反应的影响。模型采用三区串联加区问返混的结构,区间返混参数由工业反应器实测轴向温度分布拟合确定。计算表明,釜内液相混合接近全混、流,而气相氧浓度存在明显的轴向梯度：溶剂蒸发与液相混合相互竞争造成反应器内有一定的温度梯度：氧浓度梯度和温度梯度共同作用使得CO2．CO量增多,燃烧副反应加剧,这其中氧浓度梯度起主要作用。     

紫外／可见光谱在有机光纤研制中应用

有机光导纤维是近十几年来在新型光功能性高分子材料领域中的一支独秀．相对于玻璃光导纤维，有机光导纤维加工容易、口径大、轻而柔软、抗挠曲、抗冲击、耦合容易，更重要的因素是制作成本低和用途广泛．通常光导纤维是一种带包层的透明圆柱型的细丝．芯子的折射率高于包层并且是不变的，这种纤维称为突变型（ＳＩ）光纤．由于ＳＩ型光纤的带宽小，不能满足高信息量传输的需要，因而渐变型（ＧＩ）有机光纤得以发展．在这种光导纤维中，纤芯的折射率是呈抛物线型分布的，其轴心的折射率最大，折射率由纤维轴心沿径向到包层逐渐变小，在芯／…     

渐变型聚合物光纤共挤扩散过程工艺参数的正交优化研究

基于相关数学模型，对共挤扩散过程的芯皮层体积流量比、总体积流量、扩散温度等工艺参数进行了正交优化试验，利用计算流体动力学软件FLUENT求解出模拟试验结果。为了合理方便地评价试验结果的优劣，提出了一个评判标准，较好地评价了模拟试验所得光纤折射率分布曲线与抛物线型折射率分布曲线的吻合程度。本研究中，该值约在10^-4～10^-2之间，其值越小说明两者吻合程度越好。正交优化分析表明，芯皮层体积流量比、总体积流量是影响光纤折射率分布的主要工艺参数，当两者分别在1：1、6．9cm^3／min附近时，对应的模拟试验所得光纤折射率分布最接近抛物线型分布。     

一种制备梯度型聚合物光纤预制棒的新方法及其折射率分布的调控

针对现有制备方法对梯度型聚合物光纤（GI—POF）折射率分布（RID，直接影响带宽）的调控能力有限的特点，提出了一种制备GI-POF预制棒的新方法，可以实现对RID的自如调控。通过理论计算阐述了这种方法制备预制棒时RID的调控方法。结果表明，制备预制棒时所用物料的层数越多，预制棒的RID越接近理想分布，最终实际所得预制棒的RID与理论计算十分一致。     

高分子梯度玻璃的研制和表征

利用溶胶凝胶法制备高分子梯度玻璃前体 ,在这个体系中加入钛酸丁酯 ,形成高分子梯度玻璃。采用X射线散射能谱 (EDAX)、吸收光谱仪、隧道扫描电子显微镜 (SEM)、射线衍射仪 (XRD)对产品进行了表征 ,发现在样品(棒状 )中钛离子浓度由中心向边缘逐渐降低 ,呈梯度分布 ,样品在可见光范围内无明显的吸收峰 ,说明样品有较好的光学透明性 ,材料的颗粒分布均匀 ,粒径的大小为 40～ 6 0nm ,说明其有机相和无机相是均匀混合的 ,材料中没有明显的晶态物质     

A novel method for preparing gradient index (GI) plastic rods

Summary The initiator diffusion technique was used in this study to prepare the gradient index(GI) plastic rods, in which two kinds of initiators were used, i.e., thermal initiator and redox initiator. Experimental results showed that a GI plastic rod with a parabolic profile of refractive index was obtained by the initiator diffusion technique. The difference of the refractive index from the center to the periphery (n) of the plastic rods was in the range of 0.004–0.014. n increased with increasing temperature due to the increase of the gel effect and diffusion rates of monomers at a higher temperature. Furthermore, the GI plastic rod had substantially less defects, e.g., bubbles and opaqueness, than that prepared from interfacial-gel copolymerization.     

竖直窄矩形通道内环状流的流动传热特性

为了研究竖直窄矩形通道内环状流的流动传热特性,建立了窄矩形通道内环状流的数学物理模型,并进行了实验验证。通过数值求解环状流的数学物理模型得到了环状流区域的压降梯度、沸腾传热系数和液膜内的速度分布。结果表明窄矩形通道内的环状流模型能够很好地预测环状流区域的压降梯度和沸腾传热系数,而且环状流液膜内速度在法向的分布是非线性的,在层流边界层区速度梯度较大。热通量和窄矩形通道的尺寸对液膜的流速有很大影响,随热通量的增加和窄矩形通道尺寸的减小液膜的流速逐渐增加,然而质量流速对液膜流速的影响较小,而且随质量流速的增加液膜的速度逐渐减小。     

Preparation and electrooptical properties of liquid crystal dispersed film by electron-beam irradiation

Polymer films consisting of nematic liquid crystal (LC) droplets and polymer networks were prepared by using a low-energy electron beam to irradiate a homogeneous mixture of nematic LC and bifunctional methacrylate monomer. Influences of such polymerization conditions as polymerization temperature, monomer concentration, and radiation energy on electrooptical properties of the compound films were examined. The polymer yield, affecting to a large extent the film properties, depended on the monomer concentration and the radiation energy. Compound films, which have a switching function from the scattering state to transparency by applying approximately 20–30 V between the two sides of the film, were obtained. In addition, it was found that a compound film with excellent electrooptical properties was prepared by changing impure LC in the droplets into pure LC. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1675–1681, 1997     

Gradient polymers by diffusion polymerization

Gradient polymers are multicomponent polymers whose structures or compositions are not macroscopically homogeneous, but vary as a function of position in the sample. One method to prepare such polymers is by diffusing a guest monomer into a host polymer and then polymerizing the monomer in position to retain the concentration gradient created by the diffusion. One series of such type of materials was prepared by diffusing acrylonitrile into polystyrene. The gradient profile was determined by analyzing the nitrogen content in succeeding layers of the sample. These gradient polymers exhibit improved resistance to hydrocarbon solvents. The second series of gradient polymers was made by diffusion of methyl acrylate into poly(methyl methacrylate). These materials are shown to possess substantially increased fracture strain. Eyring's stress-biased activated rate theory of yielding was used to rationalize the observed toughening effect in gradient polymers.