Haloform adsorption on crystalline copolymer films of vinylidene fluoride with trifluoroethylene

Reversible bromoform adsorption on crystalline polyvinylidene fluoride with 30% of trifluoroethylene, P(VDF-TrFE 70:30) was examined by photoemission and inverse photoemission spectroscopies. The adsorption of bromoform on this polymer surface is associative and reversible. Molecular bromoform adsorption appears to be an activated process at 120 K with enhanced adsorption following the initial adsorption of bromoform. Strong intermolecular interactions are also implicated in the presence of a weak shake off or screened photoemission final state, whose intensity scales with the unscreened photoemission final state.     

Infrared Emission of Air Pollutants Induced by a CO2 Laser

Abstract

A possible method for the measurement of air pollutants is described. It is based on infrared emission from gases at specific wavelengths induced by a CO₂ laser. The emission level can be increased by adding a sensitizing gas (e.g. SF.) to the sample gas. Although the mechanism of the emission is not fully understood experimental data indicate that the emission is of thermal origin. Spectra of some air polluting gases are included in this paper.     

Random and sequential radical cotelomerizations of 3,3,3‐trifluoropropene (H2CCHCF3) with vinylidene fluoride (F2CCH2)

The synthesis of original cotelomers based on 3,3,3‐trifluoropropene (TFP) and vinylidene fluoride (VDF) with a general formula: R_F‐[CH₂? CF₂]_n? [CH₂? CH(CF₃)]_m? I (where n = 1–63, m = 2–640, and R_F = (CF₃)₂CF) was achieved by sequential and random cotelomerizations in the presence of R_FI. The radical cotelomerizations were initiated by thermal decomposition of different peroxide and persulfate initiators either in bulk, in solution (in the presence of acetonitrile or 1,1,1,3,3‐pentafluorobutane as the solvents), and in aqueous process (emulsion). Different adducts were obtained in good yield (50–70 wt %) with a relative proportion of each adduct depending on (i) the R₀ = [R_FI]₀/([TFP]₀+[VDF]₀) initial molar ratio, (ii) the reaction temperature, and (iii) C₀ = [In]₀/([TFP]₀+[VDF]₀). Random cotelomerization gave higher yields than those obtained from the sequential cotelomerization. When the concentration of the chain transfer agent increased, the molecular weights of the resulting poly(VDF‐co‐TFP) cotelomers decreased and showed that the R₀ ratio targeted the molecular weights (～700–66,000 g mol^?1). Some of the obtained molecular weights were exceptionally high for a (co)telomerization. The kinetics of the radical cotelomerization of VDF and TFP led to the determination of the reactivity ratios of both comonomers (r_VDF = 0.28 ± 0.07 and r_TFP = 2.35 ± 0.26 at 75 °C). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3964–3981, 2009     

Highly Emissive Diborylphenylene‐Containing Bis(phenylethynyl)benzenes: Structure–Photophysical Property Correlations and Fluoride Ion Sensing

A series of 2,5‐bis(dimesitylboryl)‐1,4‐bis(arylethynyl)benzenes 1 – 6 that contain various p‐substituents on the terminal benzene rings, including NPh₂ ( 1 ), OMe ( 2 ), Me ( 3 ), H ( 4 ), CF₃ ( 5 ), and CN ( 6 ) groups, were synthesized, and the effects of the p‐substituents on the absorption and fluorescence properties were investigated both in solution and in the solid state. Linear relationships were obtained not only between the Hammett σ_p⁺ constants of the p‐substituents and the absorption and fluorescence maxima, quantum yields, and excited‐state dynamics parameters in solution, but also between the σ_p⁺ constants and the fluorescence quantum yields in the solid state. An important finding extracted from these results is that the suppressed fluorescence quenching in the solid state is a common feature for the present laterally boryl‐substituted π‐conjugated skeletons. Hence, the diborylphenylene can serve as a useful core unit to develop highly emissive organic solids. In fact, most of the derivatives showed more intense emission in the solid state than in solution. In addition to these studies, the titration experiment of 1 by the addition of nBu₄NF was conducted, which showed the stepwise bindings of two fluoride ions with high association constants as well as a drastic change in the fluorescence spectra, while constantly maintaining high quantum yields (0.61–0.76), irrespective of the binding modes. This result also demonstrated the potential utility of the present molecules as an efficient fluorescent fluoride ion sensor.     

CaF2晶体的生长与光学性能

采用导向温度梯度法(TGT)生长CaF2晶体,建立了生长炉内的垂直温度梯度场.研究表明影响晶体质量及光学性能的主要因素包括坩埚材料、温度场、生长程序及原料纯度等.从大量的实验中总结出TGT法生长高质量CaF2晶体的生长条件如下:石墨坩埚;轴向梯度≤2℃/mm;生长降温速率1.5～2.5℃/h;冷却速率≤40℃/h.     

全氟甲基乙烯基醚和其它含氟单体乳液共聚合的竞聚率测定

分别通过气相色谱法测定了全氟甲基乙烯基醚 (PMVE)与偏氟乙烯 (VDF)以及PMVE与四氟乙烯(TFE)二元乳液共聚反应中的气相单体组成和共聚物组成 ,然后用非线性回归法 (RREVM )计算得TFE PMVE及VDF PMVE乳液共聚合反应的表观竞聚率分别为γTFE =3 89和γPMVE =0 0 5以及γVDF =1 0 6和γPMVE =0 11.结合已经测定的TFE VDF二元乳液共聚的表观竞聚率 ,计算了由VDF TFE PMVE三元乳液共聚合反应合成的共聚物组成 ,后者与由1 9F NMR实测的共聚物组成吻合     

聚偏氟乙烯凝胶电解质组成间相互作用及其凝胶化研究

通过冷却聚偏氟乙烯 (PVDF) 丙烯碳酸酯 (PC)或PVDF PC LiClO4的溶液 ,制备了数个聚合物凝胶 .实验表明 ,聚合物凝胶的凝胶化时间 (tgel)与凝胶温度、聚合物浓度有关 ,且强烈地依赖于体系中盐的浓度 ,因为盐会缩短体系的tgel.凝胶体系中LiClO4的存在提高了其凝胶熔融温度 (Tgm) ,LiClO4的含量越大 ,相应凝胶的Tgm 越高 .用DSC和落球法所测凝胶的Tgm 有较大的差别 .这说明凝胶中可能存在热稳定性好和热稳定性相对较差的两种不同结构部分 .FT IR的研究结果表明 ,凝胶电解质的各组成 (LiClO4,PC和PVDF)间存在较强的相互作用 .对含盐和不含盐的两类凝胶体系的对比研究表明 ,两者不同的凝胶化现象和Tgm 归因于盐与聚合物或溶剂间的络合作用     

BaY2F8∶Ce, Eu中Ce3+→Eu2+的能量传递和Ce3+→Eu3+的电子转移

采用高温固相反应法制备了 Ba Y2 F8∶ Ce3 + ,Ba Y2 F8∶ Eu2 + 和 Ba Y2 F8∶ Ce,Eu,测定了它们的激发、发射和漫反射光谱 .首次发现并研究了在 Ba Y2 F8共掺 Ce F3 和 Eu F3 体系中存在 Ce3 + → Eu2 + 的能量传递和Ce3 +→ Eu3 +的电子转移两种过程及其竞争 .根据光谱数据 ,讨论了 Ce4 +的可能取代格位     

Hydrogen bonding. Part 77. Molecular orbital study of C–HF hydrogen bonds in tetramethylammonium fluoride; potential effects on solid state structure

The infrared (IR) spectrum of tetramethylammonium fluoride suggests that it contains the strongest C–HF⁻ hydrogen bonds yet observed. Ab initio 3-21G(^*) calculations were used to examine potential solid state arrangements of cation about anion. The favored state is one in which four cations surround each F⁻ in a D_2d arrangement and four F⁻ surround each cation. Each F⁻ acts as acceptor of four hydrogen bonds of −10.8 kcal mol⁻¹, one from each cation. This arrangement, similar to that of tetramethylammon chloride, is consonant with the IR spectrum of the cation in solid tetramethylammonium fluoride. In the preferred form of the monomeric gas phase ion-pair F⁻ lies against one triangular face of the T_d cation with three CHF hydrogen bonds of −11.5 kcal mol⁻¹ each. Constraint of F⁻ in the gas phase ion-pair to interaction with a single cation hydrogen results in a tightly bound molecular complex between HF and trimethylammonium methylide with an interaction energy of −27 kcal mol⁻¹; however, this structure is not seen elsewhere and apparently does not play a role in the solid salt.     

氟化铅晶体的生长新技术及其Cherenkov辐射效应

氟化铅晶体是一种性能优异的Cherenkov辐射材料,在实验高能物理领域被用作Cherenkov探测器,有广泛的应用前景,但传统的生长方法不仅生长成本高,而且晶体性能差,难以满足实用要求。文章介绍的掺脱氧剂非真空生长新技术既摆脱了真空法中设备投资大和工艺复杂的缺点,而且生长出的晶体性能优越,其透光率,吸收边、透光均匀性,能量分辨率和抗辐照损伤能力中满足实用要求,处于世界领先水平。