聚对苯二甲酸乙二酯非晶态膜片单轴热——拉伸中的结晶与松弛

用动态力学损耗温度谱作为测试手段,研究了非晶态PET膜片在78—112℃温度范围内的单轴拉伸。实验结果说明,在较低温度下所得结晶的拉伸试样,完全由于应变诱发结晶,发生在应力-应变曲线的屈服后应力开始上升的阶段。在较高温度下(90℃或更高)拉伸可得非晶态而且光学各向同性的试样,是由于分子链的小尺度取向在拉伸过程中已完全热松弛所致,而分子链的大尺度取向要通过高弹态流动而松弛,其速率较慢,用拉伸后试样两端固定时的应力松弛进行了观察。在较低温度下应力松弛后仍为非晶态,在较高温度下应力松弛到起始应力的1O％下才开始结晶。FTIR研究表明在这种状态下的结晶有一结晶诱导期,其时间尺度与应力松弛阶段相当。     

Preparation of the individual compact single-chain globular particulates of Poly(N-isopropylacrylamide)

The compact single-chain (SC) particulates of Poly(N-isopropylacrylamide) (PNIPAM), which have been formed above its lower critical solution temperature in an aqueous solution containing the surfactant of sodium n-dodecyl sulfate (SDS), were recovered from the solution by freeze-drying. Under scanning electron microscopy, the compact particulate appears as a spherical or elliptical particulate individually dispersed in SDS, which acts as a solid solvent to prevent agglomeration. The conformation of the compact SC particulates of PNIPAM dispersed in SDS had been studied by the solid-state high-resolution ¹³C NMR spectroscopy. The ¹³C spin-lattice relaxation time T ₁ of the SC sample was determined in comparison with that of the original one. It was found that the T ₁ of the methyl carbon in the isopropyl group of the SC sample was about 45% higher than that in the original multichain sample, which revealed the differences in the motion of the methyl group in the different condensed states and illuminated the characteristic conformation of the compact SC globular particulates of PNIPAM.     

Second-order Green's function calculations of the ionization potential of a (H2)7 chain embedded in a homogeneous electric field

Summary The vertical ionization potential and the related pole strength of a model alternant chain of 14 hydrogen atoms subject to a homogeneous electric field, parallel to the chain and of increasing intensity are calculated, in the framework of a 6–31G** basis set, at the second-order level of the many-body Green's function theory. Trends observed with orbital relaxation, pair removal and pair relaxation effects are interpreted in terms of deformations of the electron density.     

Studies on the Phase Properties of Winsor Ⅰ-Ⅲ Type Microemulsions with Dielectric Relaxation Spectroscopy

The dielectric relaxation spectroscopy （DRS） of Winsor I -Ⅲ microemulsions for nonionic surfactant octyl polyglucoside CsG1.46/1-butanol/cyclohexanedwater system was studied. The experiment shows that the permittivity decreases with the increase in the frequency and clear dielectric relaxation phenomena were observed. Permittivity obviously decreases with the change of the microstructure of the microemulsion, W/O, B.C. and O/W can be distinguished by the permittivity.     

Dielectric behaviour of a side-chain-bearing liquid-crystalline polysiloxane

The relaxation of electric field-induced polar orientation in a side-chain-bearing liquid-crystalline polysiloxane was measured by means of thermally stimulated depolarization currents. Different relaxation mechanisms were identified and characterized: the glass transition cooperative relaxation exhibits compensation behaviour. On the other hand, lowerT _g and upperT _g discharges were observed and their molecular nature is discussed.     

The pockels coefficient of new polymers for nonlinear optics and its time dependence after poling,compared with dielectric measurements

Epoxy polymers with donor–acceptor type side groups were synthesized for application in nonlinear optics. The stability of the Pockels coefficient was measured in thin films after poling. The relaxation times and their temperature dependence seem to be correlated with dielectric measurements. Guest–host systems (polystyrene and polymethylmethacrylate with dimethylaminonitrostilbene) were investigated for comparison.     

Relaxational behavior of birefringence of aqueous carboxymethylcellulose under an alternating electric field at frequencies ranging from 0.1 Hz to 100 kHz

The d. c. component of birefringence of aqueous carboxymethylcellulose (CMC) under an a. c. electric field was measured at frequencies ranging from 0.1 Hz to 100 kHz. Three samples of different molecular weights were studied with varying degree of neutralization, polymer concentration and added salt concentration. The dispersion curve of birefringence consists of three relaxation bands,A, B andC in order of decreasing frequency. RelaxationB with a negative relaxation strength is ascribed to end-over-end rotation of almost rodlike CMC molecules. RelaxationA with a positive strength is attributed to the relaxation of electrical polarizability along the minor axis of molecule. RelaxationC possesses also a positive strength and is induced by clusters of CMC molecules.Dedicated to Prof. Dr. F. H. Müller.     

Dielectric Studies of Glycine–Ethylene Glycol–Water Solutions Using Time Domain Reflectometry

Time domain reflectometry (TDR) has been used for dielectric relaxation measurements on the glycine–ethylene glycol–water ternary system (TDR) at 25, 30, 35, and 40°C in the frequency range from 10 MHz to 10 GHz. Glycine–ethylene glycol–water solutions are prepared with different concentrations of ethylene glycol (0, 5, 10, 15, 20, and 30%) and also for different glycine molar concentrations (0, 0.2, 0.4, 0.6, 0.8, and 1 M). The dielectric relaxation parameters are measured for aqueous glycine solutions also to compare the results with those for the glycine–ethylene glycol–water ternary system. For all the solutions considered, only one relaxation peak was observed in this frequency range. The complex permittivity spectra for the aqueous glycine solutions can be well described by the Cole–Davidson expression, whereas that for the ternary system can be well described by the Havriliak–Negami expression. The logarithm of the relaxation time log() shows a nonlinear relation with the glycine molar concentration that implies a change in the relaxation mechanism with glycine concentration. The dielectric strength increases with an increase in glycine molar concentration, whereas it decreases with an increase in ethylene glycol concentration.     

Electroosmosis through a Cation-Exchange Membrane: Effect of an ac Perturbation on the Electroosmotic Flow

Electroosmosis experiments through a cation-exchange membrane have been performed using NaCl solutions in different experimental situations. The influence of an alternating (ac) sinusoidal perturbation, of known angular frequency and small amplitude, superimposed to the usual applied continuous (dc) signal on the electroosmotic flow has been studied. The experimental results show that the presence of the ac perturbation affects the electroosmotic flow value, depending on the frequency of the ac signal and on the solution stirring conditions. In the frequency range studied, two regions have been observed where the electroosmotic flow reaches a maximum value: one at low frequencies (Hz); and another at frequencies of the order of kHz. These regions could be related to membrane relaxation phenomena.