气相CBr2的激光诱导荧光光谱

本文报道了在交叉分子束装置中氟原子和二溴甲烷反应生成的CBr_2的气相激光诱导荧光光谱的首次实验结果,位于585—664nm范围内的激光诱导荧光光谱由22个峰组成,被指定为CBr_2的A(V′_1~V′_20)←X(000)(V′_1=0,1;V′_2=0—12)跃迁。从光谱导出ν_(00)=14885cm~(-1),上态振动光谱常数ν′_1=460,ν′_2=189cm~(-1),x′_(12)=3.10,x′_(22)=-0.27cm~(-1)。本实验结果与CBr_2的低温固相光谱进行比较,发现固相光谱较气相光谱明显蓝移,确认了CBr_2是:F+CH_2Br_2过程的两步反应的产物。     

四氟乙烯-全氟4-甲基-3,6-二氧杂△~7辛基磺酰氟共聚物的分子运动

本工作用振簧仪,在-150—80℃范围内,测试了四氟乙烯-全氟4-甲基-3,6-二氧杂△~7辛基磺酰氟共聚物的动态力学性能。样品是含有不同侧基数目的部分结晶共聚物。观察到四个松弛过程,按温度下降次序记为α、γ_1-、γ_2-、γ_3-。α峰(室温附近)系玻璃化转变。γ_1峰(-50℃,～215Hz)为主链有阻碍的短链段分子运动。γ_2-峰(-60℃,～230Hz)为侧基的分子运动。γ_3-峰(-77℃,～260Hz)为的链段运动,并且γ_3-峰的强度随结晶度增加而增强。     

非晶态聚对苯二甲酸乙二酯等温结晶的介电研究

非晶态PET的介电性质温度谱除α_a松弛和β松弛外,在120—130℃之间由于在升温过程中试样的结晶出现一个损耗峰。比较非晶态试样与结晶后试样介电常数ε′和介电损耗ε″的差别,可在97—113℃温度下用ε′和ε″来表征非晶态PET的等温结晶过程。在结晶的初期,ε′随时间的变化符合Avrami方程,即(ε′(t)-ε′(∞))/(ε′(0)-ε′(∞))=exp(-Kt~n)。在结晶的后期,由介电性质的频率谱Cole-Cole图观察介电松弛强度△ε和β参数在结晶过程的变化。     

Schiff碱型双冠醚的合成及性质

用脂链或芳环桥联两个苯并—15—冠—5单元的双冠醚报道较多,而桥联苯并-18-冠-6或苯并-12-冠-4单元的双冠醚报道较少。本文报道以α,ω-二卤代烷或二(对甲苯磺酸)二甘醇酯与邻羟基苯甲醛反应,制成相应的二醛化合物1_(α-∫)后使它们分别与4′-氨基苯并-18-冠-6或4′-氨基苯并-12-冠-4反应,得到脂芳混合桥联的schiff碱型双冠醚2_(b-∫)或3_(?)。     

辅助配体导向合成两个锌金属配位聚合物:结构,稳定性和荧光性质（英文）

以二苯-4,4′-二羧酸和六水硝酸锌为原料,在相同反应条件下,通过改变不同的辅助配体(2,2′-二甲基-4,4′-联吡啶和三乙烯二胺),合成出2个金属有机配位聚合物:{[Zn(DBA)(dmbpy)_(0.5)]·2H_2O}_n(1)和[Zn_2(DBA)_2(dabco)]_n(2)(H_2DBA=二苯-4,4′-二羧酸,dmbpy=2,2′-二甲基-4,4′-联吡啶,dabco=三乙烯二胺)。通过元素分析、红外光谱、差热分析、X射线粉末衍射和X射线单晶衍射等手段对配合物进行了结构表征。结果显示,化合物1为二维(4,4)网络结构,2个二维结构在平行方向上通过互锁进一步形成2D→2D的互锁网络结构。化合物2为一维带状结构。热稳定性表明化合物1能够稳定到370℃;而化合物2稳定性差。荧光分析表明常温固态下配合物1和2均发射蓝色荧光,荧光寿命分别为231.4 ns和2.33 ns。     

VA族元素氢化物的紫外光解和多光子电离——Ⅲ.AsH_3分子的紫外激光光解和多光子电离

通过193nm的ArF激光光解AsH_3,首次在420-650nm之间观察到了AsH_2(■2A_1→X 2B_1)的发射光谱。经过认证之后,获得了v=19928+868v′_2-3v′_2~2-(989v″_2-6v″_2~2)的经验公式,并辨认了七个谱带系。AsH_2(■2A_1)的辐射寿命是(130±20)ns。此外,还观察到四条As(5s→4p)的原子发射谱线和多光子电离信号。     

VA族元素氢化物的紫外光解和多光子电离Ⅲ. AsH3分子的紫外激光光解和多光子电离

通过193 nm的ArF激光光解AsH_3, 首次在420-650 nm之间观察到了AsH_2(Ã ~2A_1→X ~2B_1)的发射光谱。经过认证之后, 获得了v=19928+868v′_2-3v′_2~2-(989v″_2-6v″_2~2)的经验公式, 并辨认了七个谱带系。AsH_2(Ã ~2A_1)的辐射寿命是(130±20)ns。此外, 还观察到四条As(5s→4p)的原子发射谱线和多光子电离信号。     

3,3＇,5,5＇-四苯基-2,2＇-双亚硫杂环己二烯与四氰代对二次甲基苯醌和碘的复合物

自发现四硫富瓦烯(TTF)与四氰代对二次甲基苯醌(TCNQ)电荷转移复合物具有金属导电性以来,高电导有机化合物的研究已引起广泛兴趣。本文报道有关3,3′,5,5′-四苯基-2,2′-双亚硫杂环己二烯(2,2′DIPSΦ_4)与TCNQ和碘的复合物的合成及物理性能的研究。 2, 2′DIPSΦ_4的紫外一可见光谱在整个吸收范围内都比TTF有更强吸收,并一直延伸到700nm。另外,它的第一、第二半波电位亦比TTF小,与4,4′DIPSΦ_4,相似(表1)。由此可见,它有希望与合适的电子受体形成高电导的电荷转移复合物。     

1,1′-(四甲基二硅撑)双[环戊二烯基三羰基钼配合物]的合成及结构

1,2-二环戊二烯基四甲基二硅烷与正丁基锂作用生成(四甲基二硅撑)双[环戊二烯基负离子盐],后者随即与六羰基钼反应即形成1,1′-(四甲基二硅撑)双[环戊二烯基三羰基钼负离子盐],(Me_2SiSiMe_2)[Cp′(CO)_3~-Li~+]_2(1)、1分别与四种不同的卤化物反应,生成在钼原子上发生烃基化的产物(Me_2SiSiMe_2)[Cp′Mo(CO)_3R]_2(R:CH_3,2;C_2H_5,3;=PhCH_2,4;CH_2COOC_2H_5,5).1与林醋酸作用,随即分别与CCl4及NBS反应,生成相应的钼氯化物和钼溴化物(Me_2SiSiMe_2)[Cp′MO(CO)_3X]_2(X:Gl,6;Br,7).1与Fe_2(SO_4)_3/H_3O~+作用发生氧化偶联反应,生成Mo—Mo键双核产物(Me_2SiSiMe_2)[Cp′Mo(CO)_3]_2(8).8在氯仿中与碘反应,又生成Mo—Mo键断裂的钼碘化物(Me_2SiSiMe_2)[Cp′Mo(CO)_3I]_2(9).以元素分析、IR及~1H NMR表征了2—9的结构.并对5的单晶进行了X射线衍射分析.它的晶体属三斜晶系,Pl空间群,晶体学数据:a=1.1447(2),b=1.36(?)0(4),c=1.4125(2)nm;β=60.01(1)~°.V=1.6336nm~3,Z=2,D_o=1.583g·cm~(-2).μ=8.7cm~(-1),F(000)=788.偏差因子R=0.043,R_w=0.055.     

由4,4'-二甲基-2,2'-联苯二甲酸配体构筑的锌(Ⅱ)和镉(Ⅱ)双核配合物的合成、晶体结构、荧光及光催化性质（英文）

采用水热方法,用4,4′-二甲基-2,2′-联苯二甲酸配体(H_2dbda)和菲咯啉(phen)、2,2′-联吡啶(2,2′-bipy)分别与ZnCl_2或CdCl_2·H_2O反应,合成了3个零维双核配合物[Zn_2(μ-dbda)_2(phen)_2(H_2O)_2](1)、[Zn_2(μ-dbda)_2(2,2′-bipy)_2](2)和[Cd_2(μ-dbda)_2(2,2′-bipy)_2(H_2O)_2]·2H_2O (3),并对其结构、荧光和光催化性质进行了研究。结构分析结果表明3个配合物分别属于三斜和单斜晶系的P1和P2_1/n空间群。配合物1～3都具有零维双核结构,而且这些双核单元通过O-H…O氢键作用进一步形成了三维超分子框架。研究表明,配合物1～3在室温下能发出蓝色荧光。另外,研究了3个配合物对有机染料亚甲基蓝的光催化降解性能,结果表明配合物3可以高效地降解亚甲基蓝。     

On the piezoelectricity of collagen/natural rubber blend films

We studied the physicochemical, piezoelectric and dielectric properties of collagen-natural rubber (NR) films. The piezoelectric strain tensor element d₁₄, and the dielectric permittivity ε₁₁ were obtained for the collagen-NR blends. Resonance measurement of the piezoelectric strain constant d₁₄ of collagen gives 0.057 pC/N. It was observed that for the addition of 10% of NR we have a decrease of the piezoelectricity to 0.042 pC/N. Our results also show that the presence of NR contributes to the increase of the thermal stability of the collagen films. The denaturation temperatures of collagen increases with the presence of NR. For the blend with 25% of NR (S2--Col75bn25), one has the highest denaturation temperature (109.6 °C). We also believe that the presence of NR lead to the decrease of the organization of the microscopic structure of the films, which results in the decrease of the piezoelectricity.     

Experimental characterization of hexatic smectic phases through electro-optic studies and dielectric relaxation spectroscopy

The electro-optic and complex dielectric behaviour of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl 4'-(n-butanoyloxyprop-1-oxy)biphenyl-4-carboxylate, having chiral SmC_A* and hexatic smectic phases, have been investigated. Complex dielectric permittivities were measured as a function of frequency, d.c. bias field and temperature. Spontaneous polarization was measured by the current reversal technique; tilt angle was measured under a polarizing microscope using a low frequency electric field. The electro-optic properties and dielectric behaviour of the material are compared with results obtained by DSC and polarizing optical microscopy. Dielectric relaxation processes in SmC_A* and hexatic smectic phases were determined. The dielectric strength at the SmC_A* to hexatic smectic phase transition is discussed in terms of coupling between the long range bond orientational order and smectic C director. It seems from the results of spontaneous polarization and dielectric relaxation spectroscopy that the material might possess an additional phase between the SmC_A* and hexatic smectic I* phases.     

Temperature Dependent Microwave Dielectric Characterization of Associated Liquids

The present paper reports static dielectric constants, densities, viscosities, and refractive indices of the binary mixtures of ethanol with DMSO measured at 303 K, 308 K, 313 K. These measured parameters are used to obtain the derived properties, such as the Bruggeman factor, the molar polarization, the excess molar volume, the excess viscosity, the excess static dielectric constant, and the excess molar polarization. The variation in magnitudes of these quantities with composition and temperature is used to discuss the type, strength, and nature of binary interactions. The excess parameters are fitted to the Redlich Kister (R-K) fit equation. The evaluated values of the excess dielectric constant and the excess molar polarization infer that deviations of their mixture values occur from the mole-fraction mixture law. The results confirm that there are dipole-dipole interactions between unlike molecules of ethanol+DMSO mixtures and that 1:1 complexes are formed. The excess static dielectric constant indicates that there is a decrease in the total number of parallel aligned effective dipoles that contribute to the mixture dielectric polarization. It is observed that the excess molar volume becomes more and more positive with the corresponding increase in the temperature. This observation certainly leads to the inference that the intermolecular interaction strength decreases with the temperature.     

Experimental characterization of hexatic smectic phases through electro-optic studies and dielectric relaxation spectroscopy

The electro-optic and complex dielectric behaviour of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl 4′-(n-butanoyloxyprop-1-oxy)biphenyl-4-carboxylate, having chiral SmC_A* and hexatic smectic phases, have been investigated. Complex dielectric permittivities were measured as a function of frequency, d.c. bias field and temperature. Spontaneous polarization was measured by the current reversal technique; tilt angle was measured under a polarizing microscope using a low frequency electric field. The electro-optic properties and dielectric behaviour of the material are compared with results obtained by DSC and polarizing optical microscopy. Dielectric relaxation processes in SmC_A* and hexatic smectic phases were determined. The dielectric strength at the SmC_A* to hexatic smectic phase transition is discussed in terms of coupling between the long range bond orientational order and smectic C director. It seems from the results of spontaneous polarization and dielectric relaxation spectroscopy that the material might possess an additional phase between the SmC_A* and hexatic smectic I* phases.     

Thermodynamical study of the thermoelectric effect for magnesium silicide

The thermoelectric effect of magnesium silicide is studied by using a thermodynamical method in the presence of an electric field. The thermoelectric potential is evaluated from the partial derivative of free energy with respect to charge in which the free energy is calculated at the B3LYP/6-31G(d,p) level of density functional theory. This free energy is also utilized to determine the average dipole moment from which the polarizability, alpha; molar polarization, Psi; and dielectric constant can be computed. The present calculation for the dielectric constant (approximately 24-20) is in very good agreement with the experimental value (20). This accurate dielectric constant can be used to derive the relation of the thermoelectric potential with respect to temperature, from which the thermoelectric power or the Seebeck coefficients are calculated. The present result shows good agreement with experiment measurement for the Seebeck coefficients. In comparison, that calculation from the energy band structure theory is far off from the experimental values.     

Persistent polarization in poly(vinylidene fluoride). III. Depolarization and pyroelectricity of poly(vinylidene fluoride) thermoelectrets

Persistent polarization in poly(vinylidene fluoride) thermoelectrets prepared under high electric field has been studied by measurements of depolarization and pyroelectricity. Various polarizations are examined in detail; the polarizations related to a characteristic molecular motion near 60°C and the polarizing temperature are not responsible for the major piezoelectric effect in β-form electrets. The piezoelectricity is attributed to a polarization appearing near the melting temperature. The persistent polarization corresponding to d₃₁ of 2 × 10^?11 coul/N is about 5 × 10^?6 coul/cm². The pyroelectricity of β-form electrets is linearly correlated with the piezoelectricity.     

Persistent polarization in poly(vinylidene fluoride). II. Piezoelectricity of poly(vinylidene fluoride) thermoelectrets

The piezoelectricity of PVDF thermoelect rets formed with vacuum-coated aluminum electrodes has been investigated in detail. The piezoelectricity depends on the β-form crystal structure of PVDF homopolymer and copolymers. However, the piezoelectricity is not attributed to the stress dependence of the spontaneous polarization of β-form crystals, but rather to the persistent polarization arising from trapped charges. The trapping mechanism is discussed.     

Molecular motion and phase transitions of clathrate hydrates**

Abstract

Heat capacities and complex dielectric permittivities of three clathrate hydrates of type II, encaging tetrahydrofuran (THF), acetone (Ac), and trimethylene oxide (TMO), were measured at low temperatures. The heat capacity measurement was done in the temperature range 13–300 K by using an adiabatic calorimeter with a built-in cryorefrigerator. The permittivities were measured in the temperature range 20–260 K and in the frequency range 20 Hz-1 MHz. For pure samples, with a glass transition due to freezing out of water, reorientational motion of the host lattice was observed calorimetrically at 85 K for THF and at 90 K for Ac hydrates, respectively. Spontaneous temperature drift rates of the calorimetric cell were measured under adiabatic conditions to derive the characteristic time for enthalpy relaxation. The enthalpy relaxation times thus derived were well correlated in an Arrhenius plot with the dielectric relaxation times derived from the dielectric relaxation of orientation polarization. The situation is the same as hexagonal ice which has a similar four co-ordinated hydrogen-bonded network.     

Persistent polarization in poly(vinylidene fluoride). I. Surface charges and piezoelectricity of poly(vinylidene fluoride) thermoelectrets

Persistent polarization in poly(vinylidene fluoride) (PVDF) thermoelectrets prepared under high electric field strengths has been studied by measurements of surface charge and piezoelectricity. An anomalous heterocharge appears after the normal homocharge disappears. A model is proposed to explain the surface charge phenomena; the anomalous heterocharge is expressed as a sum of a hidden homocharge and a hidden heterocharge. It is concluded that the anomalous heterocharge as well as the apparent homocharge are not responsible for the piezoelectricity of PVDF electrets. The piezoelectricity is shown to depend on the structure of the original PVDF films or the amount of β-form crystals. However, the piezoelectricity is not attributed to stress dependence of the spontaneous polarization in the β-form crystal of PVDF, but to the hidden polarization which bring about the anomalous heterocharge. The hidden polarizations are attributed to trapped charges.     

The effect of increased crystallization on the electrical properties of nylon-12

The dielectric properties of 30% crystalline dry Nylon-12 have been measured over the frequency range 10–10⁵ Hz and temperature range 300–450 K, and the effect of its annealing at 423 K investigated both by dielectric measurement and differential scanning calorimetry. Annealing causes its crystallization to α phase, which increase the dc conductivity and decreases the contribution to orientation polarization, but does not alter the shape of the relaxation spectrum. The orientation polarization in Nylon-12 involves two processes, each of which occurs above the glass-transition temperature of Nylon-12, but only the spectra of the lowest temperature process could be clearly resolved. © 1993 John Wiley & Sons, Inc.