Dynamic crack propagation and unloading behavior of brittle polymers

The method of caustics in combination with a Cranz–Schardin high-speed camera was utilized to study dynamic crack propagation and unloading behavior of epoxy, PMMA and Homalite-100 specimens. Dynamic stress intensity factor K _ID and crack velocity were evaluated in the course of crack propagation. Caustic patterns at the loading points were also recorded to estimate load P applied to the specimen. Unloading rate , the time derivative of P, was determined as a function of time t, and its time correlation with K _ID or was examined. The findings showed that the change in was qualitatively in accord with the change in K _ID or . However, there existed slight differences among the values of t giving the maximum , and K _ID, so that their order was , and K _ID. This revised version was published online in July 2006 with corrections to the Cover Date.     

纳米SiO_2/聚甲基丙烯酸甲酯透明复合材料的制备及透光率

首先利用γ-甲基丙烯酰氧基丙基三甲氧基硅烷(MPS)对纳米SiO_2进行表面改性(SiO_2-MPS),再通过原位聚合法在SiO_2-MPS表面接枝聚甲基丙烯酸甲酯(PMMA)。采用熔融共混法将未改性和改性SiO_2与PMMA共混制成预分散母料,再分别与PMMA熔融共混制备纳米SiO_2/PMMA透明复合材料。用FTIR、TG和SEM对不同表面处理的纳米SiO_2和纳米SiO_2/PMMA复合材料的结构进行表征,并对其冲击强度、接触角和透光率进行表征。结果表明:SiO_2-MPS/PMMA复合材料中纳米SiO_2与MPS、MPS与PMMA间形成化学键,接枝率分别达到10.01%和22.95%,SiO_2-MPS-PMMA在PMMA中分散性最好,团聚现象明显减少,与纯PMMA相比,SiO_2/PMMA、SiO_2-MPS/PMMA和SiO_2-MPS-PMMA/PMMA复合材料的冲击强度、与水接触角均略有提升,透光率达到90%左右,最高可达94.2%。     

PMMA光子晶体及PMMA/TiO2光子晶体的制备及表征

用无皂乳液聚合法,制备单分散的聚甲基丙烯酸甲酯（PMMA）微球,并使其在重力和表面张力作用下自组装成PMMA光子晶体。用SEM研究其表面形貌,并对其进行光学性质的研究。此外还制备了PMMA／TiO2光子晶体,用AFM表征了其形貌,XRD表征了混合体系的TiO2的晶型。经光学性质研究表明,TiO2纳米粒子提高了光子晶体的折射率比,光子带隙红移。     

用正交设计研究PVDF/PVC/PMMA共混中空纤维膜

制备了PVDF(聚偏氟乙烯)/PVC(聚氯乙烯)/PMMA(聚甲基丙烯酸甲酯)三元共混中空纤维膜,讨论了影响膜性能的主要因素.正交实验结果表明:在PVDF/PVC/PMMA体系中,聚合物总浓度是影响膜的水通量的主要因素;PVDF浓度对膜强度影响最大;PMMA对膜的亲水性有较大的贡献.得到优化的制膜条件为:铸膜液中PVDF∶PVC∶PMMA=7∶1.2∶1.8(质量比),聚合物溶质的总质量分数为17%;添加剂吐温-80的质量分数为6%.     

真空气相沉积生长PTCDI C8 N型有机薄膜晶体管

在大气环境下N型有机薄膜晶体管(OFET)的性能不稳定,为提高晶体管在大气环境稳定性,该文分别制作了SiO2单绝缘层器件和SiO2/PMMA双绝缘层器件。采用N型新材料PTCDI-C8作为有源层,Ag作为源、漏电极,对制作的不同绝缘层的器件进行聚对二甲苯的封装,对有源层进行形貌和晶体结构分析。并进行电流-电压(I-V)曲线测试。在相同工作电压下,双绝缘层器件比单绝缘层器件具有更大的场效应迁移率、开关电流比和更小的阈值电压。     

溶胶-凝胶法在固体染料激光制备中的应用

固体染料激光性能优良,其制备方法有多种,溶胶-凝胶掺入法是其中较好的一种.但传统的溶胶-凝胶法还存在许多不利于制做固体染料激光的缺点.我们主要叙述了近年来发展的两种改性方法-有机改性硅酸盐法(ORMOSILS)和在溶胶-凝胶制备过程中掺入聚甲基丙烯酸甲酯(PMMA)法,并通过一系列的比较,说明有机改性硅酸盐的溶胶-凝胶法能更好的应用于固体染料激光的制备工艺中.     

Efficiency shifts of prism coupling into polymer waveguides subject to environmental variations

The effect of changing environmental conditions on the coupling efficiency of a prism–film coupler is studied for polymer waveguides. A large shift of the coupling efficiency is observed subject to environmental changes. Two processes, change of water content and loss of residual solvent in the polymer waveguides, lead to the efficiency change of the prism coupler. Experimental results show that the index change in the waveguide film is the dominant reason behind the efficiency change. Variation of water content in polymer material is the key contribution to the index change.     

Synthesis of stereoblock poly(methyl methacrylate) via transformation of isotactic-specific living polymer anion to syndiotactic-specific anion

Polymerization of methyl methacrylate (MMA) by isotactic poly(methyl methacrylate) (PMMA) living anion, prepared with t-C₄H₉MgBr in toluene at ?60°C, was carried out at ?78°C in the presence of trialkylaluminiums (R₃Al; R = CH₃, C₂H₅, and n-C₄H₉) to obtain a stereoblock PMMA, isotactic PMMA-block-syndiotactic PMMA. Among the R₃Als, (CH₃)₃Al gave most effectively the steroblock PMMA with narrow molecular weight distribution. The fraction of rr triad in the syndiotactic PMMA block increased with increase in the ratio of Al/Mg and reached about 76% at a ratio of Al/Mg ≥ 6. The method was also used to prepare stereoblock copolymer comprising isotactic PMMA block and syndiotactic block of butyl methacrylate. Stereocomplex formation and solution viscosity of the stereoblock PMMA were also studied.     

Hydrolysis induced formation of macrovoids in poly(methyl methacrylate)

In the PMMA with saturated methanol and ethanol desorbed in the distilled water, because of the phase inversion, the macrovoids are produced. The size and the quantity of macrovoids near the surface layer are larger than those inside of the specimens. If the hydrolysis temperature is lower, the macrovoids formed tend to be of close‐type. On the contrary, if the temperature is higher, there will be open‐type macrovoids. Because of the occurrence of macrovoids, the size of which is smaller than the visible wavelength, the light will scatter, thereby reducing the transmittance of the specimens. The transmittance decreased as the hydrolysis temperature and hydrolysis time was increased. This phenomenon is much obvious when using ethanol, instead of methanol, as the solvent. The scattering intensity of the specimens after hydrolysis is inversely proportional to the visible wavelength with an exponent, n, in the range from 0.03 to 2.40 for methanol and 0.02 to 0.15 for ethanol. The exponent is equal to 4 corresponding to the Rayleigh scattering. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3451–3465, 2006     

PBT／PMMA共混体系的研究

通过PBT/PMMA、PB/PMMA/PC共混物的拉伸行为、动态力学行为和形态,讨论了PC对PBT/PMMA共混体系的性能及形态的影响。指出PC的存在导致共混物中PMMA的粒径变小,使PMMA对PBT显示出增韧效应,但对PBT-PMMA的相容性无明显影响。