光照可逆调控侧链液晶聚合物膜的表面能

对侧链液晶聚合物聚甲基丙烯酸(5-[4-(4-氰基偶氮苯)苯氧基]戊酯)进行溶液铸膜,用473nm线偏振光(LPL)照射使聚合物膜发生光致取向,用锥光成像的方法表征了侧链液晶聚合物的取向。取向前接触角为71.8°,取向后为86.4°;用365nm紫外光照射后,薄膜发生了解取向,解取向后接触角为72.3°。取向使膜表面能由40.1变为30.8mJ/m2,解取向后又恢复到39.8mJ/m2。表明光照能可逆调控侧链液晶聚合物表面能。     

Noncovalent functionalization of graphene with pyrene-terminated liquid crystalline polymer

Pyrene-terminated liquid crystalline polymers (poly [8-(4-cyano-4′-biphenyl)-1-octanoylacrylate] and poly [6-(4-cyano-4′-biphenyl)-1-hexanoylacrylate]) were synthesized and used to functionalize graphene sheets via π–π interactions. The resulting liquid crystalline polymers functionalized graphene sheets were characterized by UV–vis spectroscopy, fluorescence spectroscopy, thermal gravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, atomic force microscopy and Raman spectroscopy. It was found that an intercalated layer structure was formed when polymer was grafted onto graphene sheets. The liquid crystalline polymers were able to effectively disperse graphene in N,N-dimethylformamide that were stable for months. Additionally, a remarkable smaller distance of adjacent mesogenic units was observed, which is attributed to the confinement of the polymer chains between 2D reduced graphene oxide sheets.     

Analysis of stress relaxation on the basis of isolated relaxation spectrum for wet wood

In this study, we investigated the relaxation properties of wet wood based on spectra isolated from the whole wood relaxation spectrum, calculated using Alfrey’s approximation at temperatures ranging from 25 to 85 °C. Three relaxation processes were identified, I, II, and III, in the order of low to high temperature, and these were attributed to local molecular motions of hemicellulose, lignin, and cellulose, respectively. Processes I and II (but not III) depended on temperature and the apparent activation energy, which was calculated from the temperature dependence of their relaxation time and was approximately 85 kJ/mol (20 kcal/mol) for both processes. The peak positions and intensity of the isolated relaxation spectra indicated that the molecular motion of the relaxation processes in the temperature range studied represent not whole molecular motion, but rather local molecular motion of the hemicellulose and lignin matrix. This study also demonstrated that the isolation procedure using a Gaussian function can be used to analyze the relaxation process of wood.     

Filament winding of bicomponent fibers consisting of polypropylene and a liquid crystalline polymer

This paper is concerned with novel wholly thermoplastic composite materials suitable for use in filament winding. Bicomponent fibers consisting of a sheath of polypropylene (PP) of lower melting point and a core of a thermotropic liquid crystalline polymer (TLCP) of higher melting point were produced in a ratio of 30/70(w/w) using a modification of a standard bicomponent spinning process. The modifications were required to handle the necessity of melting the TLCP at a temperature in the range of 320°C while not raising the temperature of PP above 300°C which would lead to significant degradation of PP. The tensile modulus and strength of the fibers were 38.7 GPa and 465 MPa, respectively. A methodology was developed for establishing the conditions for filament winding these bicomponent composite fibers, which would allow adequate consolidation without disrupting the molecular orientation within the TLCP component and hence reinforcing properties. Cylinders and rings were generated with winding angles of 90 and 80°C under conditions in which the PP was melted but the TLCP retained its properties. The degree of consolidation was evaluated using the interlaminar shear strength test and optical microscopy. Because of the uniform distribution of the reinforcing component there was no failure observed in this test. The void content was determined to be 5.2%. The tubes generated from these materials have the potential for transport liquid oxygen and corrosive fluids.     

Structure and mechanical properties of the extruded blends of a liquid crystalline polymer with polypropylene

Blends of a thermoplastic, isotatic polypropylene (PP) and a liquid-crystalline polymer (LCP) based on a copolyester of hydroxynapthoic acid and hydroxybenzoic acid, were extruded. The LCP exhibited a higher viscosity than that of the PP under the extrusion conditions. Calorimetric, microscopic, static and dynamic mechanical tests were performed on these blends. Differential scanning calorimetry thermograms indicated that the crystallization temperature of PP increases slightly with increasing LCP content. Scanning electron microscopy examinations revealed that the LCP phase was elongated into microfibrils in the blends investigated. However, some undeformed spherical droplets were dispersed in the PP matrix in addition to microfibrils for the blends containing high LCP concentrations. Static tensile tests showed that the addition of LCP to PP results in an increase of the modulus of elasticity but a decrease in tensile strength. The storage modulus of the extruded blends was found to increase with the addition of LCP.     

The reversible enthalpy change of the metallic glass Fe40Ni40B20 — Experiments and simulation in the activation energy spectrum model

The activation energy spectrum model can be used quite successfully to explain various aspects of the kinetics of structural relaxation in metallic glasses. In order to describe the often observed reversible component in a more quantitative way in the framework of this model an expression for the temperature dependence of the reversible part of the activation energy spectrum is derived. Using this expression three experiments concerning the reversible enthalpy change during structural relaxation are simulated and the results are compared with the actual experimental traces.     

Interactions of a liquid crystalline polymer with polycarbonate and poly(ethylene terephthalate)

Thermal behaviour of blends of a liquid crystalline copoly(ester amide) (Vectra B950) with two isotropic polymers has been studied by differential scanning calorimetry. One of the isotropic polymers is an amorphous polymer – polycarbonate, the other is a semi-crystalline polymer – poly(ethylene terephthalate). It was found that the glass transition temperature of polycarbonate decreases with increasing Vectra concentration in the blend, suggesting a partial miscibility between the Vectra liquid crystalline polymer (LCP) and polycarbonate. The miscibility is enhanced through heat treatment at elevated temperatures presumably due to a transesterification reaction. Moreover, the presence of the amorphous poly- carbonate hinders the crystallization of the liquid crystalline polymer in the blends. It was also observed that heat treatment of the Vectra LCP and poly(ethylene terephthalate) blends causes a loss in crystallinity and shifts in transition temperatures of poly(ethylene terephthalate), indicating that exchange reactions occur between Vectra B950 and poly(ethylene terephthalate). Based on these results, a new strategy, in situ compatibilization, is proposed to improve the interfacial adhesion between an LCP and an isotropic polymer. This revised version was published online in November 2006 with corrections to the Cover Date.     

Modeling multiaxial impact behavior of a glassy polymer

In many applications of polymers, impact performance is a primary concern. Impact tests experimentally performed on molding prototypes yield useful data for a particular structural and impact loading case. But, it is generally not practical in terms of time and cost to experimentally characterize the effects of a wide range of design variables. A successful numerical model for impact deformation and failure of polymers can provide convenient and useful guidelines on product design and therefore decrease the disadvantages that arise from purely experimental trial and error. Since the specimen geometry and loading mode for multiaxial impact test provides a close correlation with practical impact conditions and can conveniently provide experimental data, the first step of validating a numerical model is to simulate this type of test. In this paper, we create a finite element analysis model using ABAQUS/Explicit to simulate the deformation and failure of a glassy ABS (acrylonitrile-butadiene-styrene) polymer in the standard ASTM D3763 multiaxial impact test. Since polymers often exhibit different behavior in uniaxial tensile and compression tests, the uniaxial compression or tensile tests are generally not representative of the three-dimensional deformation behavior under impact loading. A hydrostatic pressure effect (controlled by the parameter γ) is used to generalize a previously developed constitutive model ("DSGZ" model) so that it can describe the entire range of deformation behavior of polymers under any monotonic loading modes. The generalized DSGZ model and a failure criterion are incorporated in the FEA model as a user material subroutine. The phenomenon of thermomechanical coupling during plastic deformation is considered in the analysis. Impact load vs. displacement and impact energy vs. displacement curves from FEA simulation are compared with experimental data. The results show good agreement. Finally, equivalent stress, strain, strain rate and temperature distributions in the polymer disk are presented. Electronic Publication     

Effect of frequency on dielectric properties of liquid crystal doped with side-chain liquid crystalline polymer

The frequency and applied bias voltage dependence of the dielectric properties and dielectric anisotropy of liquid crystal (LC) doped with side-chain liquid crystalline polymer (SLCP) mixture have been investigated using the admittance spectroscopy method (C–V and G/ω–V) in the frequency range of 10 kHz to 10 MHz at room temperature. The liquid crystal used in this experiment is E63. The doping material used in this study is SLCP and its concentration is ensured 1 wt % in E63. Dielectric constant (?′), dielectric loss (?), dielectric loss tangent (tan δ) and real and imaginary parts of electrical modulus (M′ and M″) of the E63/SLCP mixture was also calculated. Moreover, dielectric anisotropy (Δ?) as a function of frequency was obtained. Results show that the values of the all dielectric parameters are strong functions of frequency and applied bias voltage. After a critical frequency, dielectric anisotropy has negative values according to p/n type changing.     

Electro-active nanofibres electrospun from blends of poly-vinyl cinnamate and a cholesteric liquid crystalline silicone polymer

Electrospinning was used to generate polymer nanofibres from blends of poly-vinyl cinnamate (PVCN) and a cholesteric silicone polymer. Only blends that contained at least 40 % of PVCN produced fibres. Both differential scanning calorimetry and electron dispersion spectroscopy data indicate that the samples are miscible over a wide temperature interval. The variation of fibre diameter with concentration is nonlinear with a well-defined minimum corresponding to an 80 % PVCN blend. The fibres are birefringent with Kerr constants similar to that of cholesteric liquid crystals. Although not significant, the Kerr constant increases with increasing silicone polymer concentration.     

Morphology evolution of a liquid crystalline polymer in polycarbonate matrix enhanced by the addition of glass beads

Polycarbonate (PC)/liquid crystalline polymer (LCP)/glass bead (GB) composites filled with various volume fractions of GB were melt blended and characterized with rheological measurements and morphological observation. The study showed that the morphology evolution of LCP droplets from spheres and ellipsoids to long fibrils during the flow was enhanced by the addition of GB. Increasing shear rate also promoted the fibrillation of LCP. At the first glimpse, increasing the apparent shear rate significantly decreased the viscosity ratio (p) and increased the capillary number (Ca), which facilitated the deformation and fibrillation of LCP, while adding GB affected these parameters less. But a 5% incorporation of GB produced a more pronounced fibrillation effect than an 8-time increase of the apparent shear rate. Image analysis and model establishment were conducted to demonstrate that a high local shear, existing between the closely nearby rotating spheres, increased Ca effectively and promoted the LCP fibrillation even at lower apparent shear rates.     

氢键组装PVA侧链液晶高分子材料的合成

以异烟酸、对硝基苯酚为主要原料首先合成了一种介晶基元异烟酸对硝基苯酚酯,然后以聚乙烯醇(PVA)分子的羟基氢为电子受体,异烟酸对硝基苯酚酯分子中的氮原子为电子供体,通过氢键自组装制备了氢键组装PVA侧链液晶高分子.用IR和1HNMR对介晶基元异烟酸对硝基苯酚酯和氢键组装PVA侧链液晶高分子的结构进行了表征,用DSC和热台偏光显微镜(POM)对它们的液晶行为进行了分析.结果表明,所合成的异烟酸对硝基苯酚酯和氢键组装PVA侧链液晶高分子均显示出热致液晶性能.     

Mechanical properties of injection moulded blends of polypropylene with thermotropic liquid crystalline polymer

Blends of a thermotropic liquid crystalline polymer (LCP) with polypropylene (PP) were injection moulded. The LCP exhibited a higher viscosity than that of PP. Static and dynamic mechanical measurements, Izod impact tests, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were performed on these blends. The static tensile tests show that the tensile modulus and strength of PP are improved with the addition of LCP. The improvement in mechanical properties is associated with the formation of LCP fibrils as evidenced by SEM observations. Dynamic studies on these blends show an increase in the storage modulus but a decrease in loss factor with the addition of LCP. Furthermore, TGA measurements show that the thermal stability of PP is improved substantially with the addition of LCP.     

Environmental crazing in a glassy polymer: the role of solvent absorption

According to a recent theory of Andrews and Bevan, the work of solvent craze formation, ₀ is governed by the cavitation properties of a solvated zone of polymer at the craze tip. In particular, the shear yield stress of this zone and its temperature dependence dictate the variation of ₀ with temperature. In order to investigate this matter further, samples of poly-methylmethacrylate were swollen to equilibrium in a variety of alcohols at different temperatures, and the equilibrium polymer fraction ₂ determined as a function of temperature and solvent. The variation of yield stress with ₂, solvent and temperature was also investigated, and the glass transition temperatures determined as functions of ₂ and solvent.The temperature at which the equilibrium swelling was just sufficient to depress the polymerT _g to a co-incident value was found to correspond closely to the characteristic temperature, identified by Andrews and Bevan, at which the temperature dependence of ₀ changes abruptly. This is shown to be in complete accord with the cavitation theory referred to.     

Dipole gap effects in low energy excitation spectrum of amorphous solids. Theory for dielectric relaxation

The influence of the long-range interaction of two-level systems in dielectric glasses on the density of low-energy excitations and the dielectric properties is studied. The AC dielectric susceptibiliy is analyzed under rapid switching on the external DC electric field. The instantaneous increase in the dielectric susceptibility and its subsequent logarithmic relaxation, recently observed in Ref. 1, are qualitatively explained in a framework of a weakly interacting two-level systems model. The temperature and frequency dependencies of the logarithmic relaxation rate are discussed.