Ordering rigid rod conjugated polymer molecules for high performance photoswitchers

Molecules of a rigid rod conjugated polymer, a derivative of poly(para-phenylene ethynylene)s with thioacetyl end groups (TA-PPE), were well aligned by drop-casting the polymer solution onto the friction-transferred poly(tetrafluoroethylene) substrates. TA-PPE molecules were found to be exactly oriented with their conjugated backbones along the PTFE sliding direction. Photoresponse characteristics based on the uniaxially ordered film were significantly improved compared to those of devices with the disordered film. For example, the switch on/off ratio of the photoswitchers with aligned molecules was as high as 330-400, while that of devices without alignment was only 8-12. It was due to the efficient carrier transport along the highly aligned polymer films, in which the molecules of TA-PPE oriented along the carrier transport direction of the devices.     

Permeability of N2, Ar,He, O2, and CO2 through as‐extruded amorphous and biaxially oriented polyester films: Dependence on chain mobility

For as‐extruded amorphous and biaxially orientated polyester films based on poly(ethylene terephthalate), poly(ethylene naphthalate), and copolymers containing poly(ethylene terephthalate) and poly(ethylene naphthalate) moieties, permeability, diffusion, and solubility coefficients are interpreted in terms of chain mobility. The influence of polymer morphology is determined by comparison of the data for as‐extruded amorphous sheets and materials produced with different biaxial draw ratios. The crystallinities of the samples were assessed using differential scanning calorimetry and density measurements. Changes in mobility at a molecular level were investigated using dielectric spectroscopy and dynamic mechanical thermal analysis. The study, in conjunction with our earlier work, leads to the conclusion that the key to understanding differences in gas transport is the difference in local chain motions rather than in free volume. This was illustrated by the permeability results for He, Ar, N₂, and O₂ in the range of polyesters. However, the permeability of CO₂ was found to require alternative explanations because of polymer–penetrant interactions. For biaxially oriented samples, the differences in diffusivity are not only due to differences in local chain motions, but also additional constraints resulting from the increased crystallinity and chain rigidity—which also act to hinder segmental mobility. The effectiveness of the reduction in permeability in the biaxially oriented films is consequently determined by the ability of the polymer chains to effectively align and form crystalline structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2916–2929, 2004     

Molecular orientation study of uniaxially drawn nafion polymer electrolyte membranes utilizing polarized UV–Raman spectra

Nafion® perfluorosulfonic acid polymer electrolyte membranes were uniaxially drawn at a temperature where the α‐relaxation is active. Polarized UV–Raman spectra revealed the anisotropy developed. They strongly suggest that, upon uniaxial drawing, Nafion macromolecular chains are oriented parallel to the drawing axis, while the perfluorinated side chains exhibit a tendency to be oriented perpendicular to the draw axis. The drawing process resulted in the reduction of the membrane thickness in addition to an enhanced mechanical strength along the draw direction, measured with dynamic mechanical analysis. In a parallel study, a preliminary molecular orientation study of uniaxially drawn Teflon samples allowed a better assignment of the Raman bands of Nafion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2509–2517, 2007     

Thermal diffusivity and electrical conductivity of electropolymerized polypyrrole films

This article presents measurement of thermal diffusivity and electrical conductivity of polypyrrole films prepared by electropolymerization. Thermal diffusivity was measured by laser radiometry (former flash radiometry). Electrical conductivity was determined by a conventional four-probe method. Increase of thermal diffusivity is observed when increasing the supporting electrolyte concentration, which is also shared with the increase of electrical conductivity. Both thermal diffusivity and electrical conductivity significantly depended on the types of counter anion incorporating into polymer bulk. Thermal diffusivity of polypyrrole film is larger than that for common nonelectrical conductive polymers. Temperature profile of thermal diffusivity for as-grown polypyrrole films shows that thermal diffusivity increases with increasing temperature (first running profile), whereas remeasured temperature profile of thermal diffusivity (second or third running profiles) shows the decrease of thermal diffusivity with increasing temperature. Electrical conductivity monotonically increases until the significant decrease of it occurs at the temperature above 130°C. Investigation of these temperature profiles of thermal diffusivity and electrical conductivity has been made by corresponding to thermal analysis data. © 1994 John Wiley & Sons, Inc.     

Total‐reflection X‐ray diffraction study of friction‐transferred poly(tetrafluoroethylene) film

The orientational structure of the friction‐transferred poly(tetrafluoroethylene) (PTFE) film, which consists of highly oriented polymer strands, was evaluated with energy‐dispersive total‐reflection X‐ray diffractometry. In the film, each PTFE molecule is oriented along the friction direction, and PTFE crystallites have a preferred orientation with respect to the substrate surface. The orientational distribution of the chain direction was quantitatively evaluated. The half‐width of the distribution was determined to be about 3°. The dependence of the orientational distribution on temperature is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 432–438, 2001     

Anisotropic thermal transport in a crosslinked polyisoprene rubber subjected to uniaxial elongation

Anisotropic thermal transport in a crosslinked polyisoprene (natural rubber) subjected to uniaxial elongation is investigated experimentally. Using a novel optical technique based on forced Rayleigh scattering, two components of the thermal diffusivity tensor are measured as a function of stretch ratio. The thermal diffusivity is found to increase in the direction parallel, and decrease in the direction perpendicular, to the stretch direction. The level of anisotropy for the natural rubber is substantially lower than that reported by Tautz 50 years ago but comparable to that found in our previous studies on molten polymers, quenched thermoplastics, and other crosslinked elastomers. Thermal diffusivity data along with measurements of the tensile stress were used to evaluate the stress‐thermal rule, which was found to be valid over the entire range of stretch ratios. In contrast, failure of the stress‐optic rule was observed at stretch ratios well below the largest value at which the stress‐thermal rule was valid. This suggests that the degree of anisotropy in thermal conductivity depends on both orientation and stretch of polymer chain segments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

超拉伸聚乙烯的弹性模量和导热性能

为了揭示聚合物分子链伸展、取向的本征特性，发展了两个新的测量方法和实验装置，用于研究拉伸比高达２００的超拉伸聚乙烯凝胶的弹性性能、传热性能和聚合物结构的关系．应用激光脉冲热致超声法给出材料拉伸方向和横向杨氏模量，应用激光脉冲光热辐射法给出拉伸方向，横向和厚度方向的导热系数．随拉伸比λ的增加，轴向杨氏模量急剧的增加，而横向的仅有少许减小．导热系数具有相似的特性．本文发现当λ＝２００时，这种拉伸取向聚乙烯的轴向模量可达钢的８０％，而导热系数甚至可达２倍，直至成为热的良导体，这是由于在高拉伸比时形成了相当数量的伸展分子链构成的针状晶体———晶桥．本文提出晶桥作为短纤维分散相的取向聚合物的结构模型，对于超拉伸聚乙烯的上述特性可以进行统一描述和定量化分析，和实验结果很好符合．     

Relaxation behavior of ultradrawn poly(ethylene) film by temperature wave analysis

A new sensitive thermal analysis for the observation of re-orientation behavior in the melting region of the ultradrawn poly(ethylene) film was proposed by the simultaneous measurement of thermal diffusivity and birefringence under optical microscope in a constant heating rate. Thermal diffusivity was obtained by the phase delay of temperature wave passed through the thickness direction of the specimen. The results correspond with each other over wide temperature range including melting temperature. It was concluded that the thermal diffusivity measurement was more sensitive not only to detect the molecular relaxation in a continuous heating run, but also to find out the delicate variation of chain direction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Templating α-helical poly(L-lysine)/polyanion complexes by nanostructured uniaxially oriented ultrathin polyethylene films

We report a templating effect of uniaxially oriented melt-drawn polyethylene (MD-PE) films on α-helical poly(L-lysine)/poly(styrenesulfonate) (α-PLL/PSS) complexes deposited by the layer-by-layer (LBL) method. The melt-drawing process induced an MD-PE fiber texture consisting of nanoscale lamellar crystals embedded in amorphous regions on the MD-PE film surface whereby the common crystallographic c axis is the PE molecular chain direction parallel to the uniaxial melt-drawing direction. The MD-PE film and the α-PLL/PSS deposit were analyzed by atomic force microscopy (AFM) and in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) using polarized light as a complementary method. Both methods revealed that α-PLL/PSS complexes adsorbed at the MD-PE surface were anisotropic and preferentially oriented perpendicular to the crystallographic c direction of the MD-PE film. Quantitatively, from AFM image analysis and ATR-FTIR dichroism of the amide II band of the α-PLL, mean cone opening angles of 12-18° for both rodlike α-PLL and the anisotropic α-PLL/PSS complexes with respect to the PE lamellae width direction were obtained. A model for the preferred alignment of α-PLL along the protruding PE lamellae is discussed, which is based on possible hydrophobic driving forces for the minimization of surface free energy at molecular and supermolecular topographic steps of the PE surface followed by electrostatic interactions between the interconnecting PSS and the α-PLL during layer-by-layer adsorption. This study elucidates the requirements and mechanisms involved in orienting biomolecules and may open up a path for designing templates to induce directed protein adsorption and cell growth by oriented polypeptide- or protein-modified PE surfaces.     

Novel biodegradable poly(butylene succinate)/poly(ethylene oxide) blend film with compositional and spherulite‐size gradients

Biodegradable poly(butylene succinate) (PBS)/poly(ethylene oxide) (PEO) polymer blend film with compositional gradient in the film thickness direction was prepared using a method of interdiffusion across the interface between the PBS and PEO layers at a temperature above the melting points of both the component polymers. The miscibility between PBS and PEO was confirmed by observation of the glass transition temperature by differential scanning calorimetry. The compositional gradient structure of PBS/PEO was characterized by microscopic mapping measurement of Fourier transform infrared spectra and dynamic mechanical thermal analysis. Furthermore, a new method for confirming the crystalline/crystalline compositional gradient structure through observing the crystallization behavior by POM (polarized optical microscopy) was put forward. A continuous gradient of the spherulite size along the film thickness direction was succeessfully generated in the PBS/PEO blend film. The compositional gradient blend was found to have significantly improved physical properties that cannot be realized for pure PBS, pure PEO, and even their homogeneous miscible blend system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 368–377, 2005     

Thermal diffusivity of polymer films by the flash radiometry method

We have developed a flash radiometry technique for the determination of the thermal diffusivity of polymer films that consists of flashing a laser pulse on the front surface of the sample and monitoring the thermal radiation from the rear surface as a function of time using an infrared detector. This method is applicable to polymer films of thickness 14–250 μm in the wide temperature range between 150 and 500 K. We have performed measurements on four polymers, including polycarbonate, polyimide, polyvinylidene fluoride, and polyethylene terephthalate. The temperature dependence of the thermal conductivity of polycarbonate can be understood by considering the phonon mean free path, and the crystallinity and orientation dependence of the thermal conductivity of polyethylene terephthalate can be explained in terms of the two-phase model proposed by Choy and Young.     

Thermal conductivity and thermal expansivity of thermotropic liquid crystalline polymers

The thermal conductivity and thermal expansivity of a thermotropic liquid crystalline copolyesteramide with draw ratio λ from 1.3 to 15 have been measured parallel and perpendicular to the draw direction from 120 to 430 K. The sharp rise in the axial thermal conductivity K_par; and the drastic drop in the axial expansivity α_∥ at low λ, and the saturation of these two quantities at λ > 4 arise from the corresponding increase in the degree of chain orientation revealed by wide-angle x-ray diffraction. In the transverse direction, the thermal conductivity and expansivity exhibit the opposite trends but the changes are relatively small. The draw ratio dependences of the thermal conductivity and expansivity agree reasonably with the predictions of the aggregate model. At high orientation, K_par; of the copolyesteramide is slightly higher than that of polypropylene but one order of magnitude lower than that of polyethylene. In common with other highly oriented polymers such as the lyotropic liquid crystalline polymer, Kevlar 49, and flexible chain polymer, polyethylene, α_par; of the copolyesteramide is negative, with a room temperature value differing from those of Kevlar 49 and polyethylene by less than 50%. Both the axial and transverse expansivity show transitions at about 390 and 270 K, which are associated with large-scale segmental motions of the chains and local motions of the naphthalene units, respectively. ©1995 John Wiley & Sons, Inc.     

Oriented polymers from solution. I. A novel method for producing polyethylene films

A novel method for the production of uniaxially oriented polyethylene film is demonstrated, it being an extension of the “surface growth” method for obtaining polyethylene fibers from solution using a Couette apparatus. The film growth is found to be affected by temperature, rotor speed, rotor material, and surface roughness. Together with its possible practical importance, film growth is presented as a useful means of sample preparation and as a way to increased linear fiber growth rates. In addition, its use for studies on solution grown polypropylene fibers is indicated as well as its implications for “surface growth” of polymer crystals in general.     

Features of the delocalized crazing of high-density polyethylene in poly(ethylene oxide) solutions

It is shown that the deformation of high-density polyethylene films in poly(ethylene oxide) solutions occurs via the delocalized-crazing mechanism and leads to the formation of polymer blends. With an increase in the draw ratio, the concentration of poly(ethylene oxide) in the blend increases and significantly exceeds the theoretical values calculated from the polyethylene porosity and the poly(ethylene oxide) concentration in the solution. It is suggested that the high concentration of poly(ethylene oxide) in the blends is due to its adsorption on a highly developed surface of polyethylene deformed via the crazing mechanism. The composition of the resulting blends is independent of the strain rate.     

Dynamic mechanical investigations on drawn samples of isotactic polypropylene/EPM–Rubber blend

The physical behavior of isotropic and oriented samples of an isotactic polypropylene (iPP)/ethylene–propylene–copolymer (EPM) reactor blend was studied by performance of dynamic mechanical measurements over a wide temperature range (DMTA). The influence of thermal history and drawing procedure was examined. The results showed that with increasing draw ratio the uniaxial elastic modulus of the material was considerably enhanced, whereas the intensity and strength of the amorphous relaxations of both components were reduced. At a certain draw ratio, the glass transtions of iPP and EPM phenomenologically merged and appeared as a single relaxation. The crystalline relaxation of iPP emerged with increased draw ratio at higher temperatures and was better seperated and easier to detect. The effects observed were attributed to the orientation of the crystallites in a fibrillar structure and to the restricted molecular mobility in amorphous regions. Measurements by differential scanning calorimetry (DSC) and x-ray diffraction of several drawn samples were performed to determine the effects of drawing on the melting behavior and the crystal orientation in the semicrystalline polymer. For comparison, some results of analogous studies on neat isotactic PP are presented and discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1439–1448, 1997     

Recovery as a measure of oriented crystalline structure in poly(ether ester)s based on poly(ethylene oxide) and poly(ethylene terephthalate) used as shape memory polymers

Poly(ether ester)s consisting of poly(ethylene oxide) and poly(ethylene terephthalate) segments, EOET copolymers, could be used as shape memory polymers (SMP). Crystalline structural characters of the copolymers during the memory process were investigated by dynamic mechanical analysis, differential scanning calorimeter, wide-angle X-ray diffraction, polarizing microscopy, and recovery measurements. PEO crystals in stretched EOET copolymer preferentially oriented along fiber axis or stretch direction. During stretching, the structure of the copolymer undertake a transformation from spherulite to fiber, resulting in a crystalline morphology similar to shish-kebab, and recovery properties of stretched EOET samples were dependent on as-described crystalline structural characters that can be influenced by draw ratio. Driving forces for contraction come from the oriented chains, and only oriented or extended chains can be contributive to the recovery of deformation; these extended chains involve both crystalline and amorphous segments. The recovery process in shape memory behavior was noticed to be deorientation of oriented chains due to thermodynamic entropy effect, and was divided into three stages. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 101–112, 1999     

单轴取向聚对苯二甲酸乙二酯非等温结晶动力学研究

采用等速升温DSC方法对单轴取向聚对苯二甲酸乙二酯 (PET)的结晶过程进行了研究 ,发现单轴取向PET的冷结晶峰表现为多重结晶峰 .等温DSC方法的研究结果进一步证实结晶重峰的存在 .为此 ,本文提出了一种依据非等温DSC曲线解析高聚物结晶动力学参数的新方法 .对单轴取向PET的研究结果表明 ,与其他方法相比较 ,由新方法计算出的理论曲线与实验数据能更好地吻合 .单轴取向PET的总的结晶过程由三个子结晶过程组成 .根据不同拉伸比 ,各个子过程的Avrami指数和质量分数的变化 ,对结晶机理进行了解释 .与各向同性PET样品相比 ,单轴取向PET在低温部分的结晶速率明显增快     

Development of oriented structure and properties on drawing of poly(vinylidene fluoride) by solid‐state coextrusion

Gel films of poly(vinylidene fluoride) (PVDF) consisting of α‐form crystals were drawn uniaxially by solid‐state coextrusion to extrusion draw ratios (EDR) up to 9 at an optimum extrusion temperature of 160 °C, about 10°C below the melting temperature (T_m). The development of an oriented structure and mechanical and electrical properties on coextrusion drawing were studied as a function of EDR. Wide‐angle X‐ray diffraction patterns showed that the α crystals in the original gel films were progressively transformed into oriented β‐form crystals with increasing EDR. At the highest EDR of 9 achieved, the drawn product consisted of a highly oriented fibrous morphology with only β crystals even for the draw near the T_m. The dynamic Young's modulus along the draw direction also increased with EDR up to 10.5 GPa at the maximum EDR of 9. The electrical properties of ferroelectricity and piezoelectricity were also markedly enhanced on solid‐state coextrusion. The D–E square hysteresis loop became significantly sharper with EDR, and a remanent polarization P_r of 100 mC/m² and electromechanical coupling factor along the thickness direction k_t of 0.27 were achieved at the maximum EDR of 9. The crystallinity value of 73–80% for the EDR 9 film, estimated from these electrical properties, compares well with that calculated by the ratio of the crystallite size along the chain axis to the meridional small‐angle X‐ray scattering (SAXS) long period, showing the average thickness of the lamellae within the drawn β film. These results, as well as the appearance of a strong SAXS maximum, suggest that the oriented structure and properties of the β‐PVDF are better explained in terms of a crystal/amorphous series arrangement along the draw axis. Further, the mechanical and electrical properties obtained in this work are the highest among those ever reported for a β‐PVDF, and the latter approaches those observed for the vinylidene fluoride and trifluoroethylene copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1371–1380, 2001     

Visualization of temperature-induced structural rearrangements in oriented amorphous polymers

Thermally stimulated shrinkage of amorphous poly(ethylene terephthalate) and poly(vinyl chloride) oriented above their glass transition temperatures over a broad range of strain rates was studied by direct microscopic examination. The principle of revealing structural rearrangements is as follows. Before annealing, an oriented sample is coated with a thin (a few nanometers) metal layer. Subsequent annealing, which entails a change in the geometric dimensions of a polymer, leads to the appearance of a surface relief in the coating. The direct microscopic examination of the microrelief provides information on structural rearrangements in the polymer substrate. It was shown that identical microreliefs were formed in PVC independently of its preliminary stretching. For PET, it was found that the self-extension process in the direction of the draw axis was effected along with contraction during annealing. The superimposition of these processes is imaged as relief with two perpendicular folded structures. The obtained results give direct information on stress fields responsible for processes that occur in oriented polymers during their annealing; such information is difficult or even impossible to gain by any other means.     

Thermal diffusivity of polycaprolactone/poly(bisphenol A carbonate) blends by flash radiometry

This article presents thermal diffusivity (D) measurement by flash radiometry for the polymer blend of polycaprolactone (PCL) and poly(bisphenol A carbonate) (PC) with a lower critical solution temperature (LCST) phase diagram. The dependence of D on temperature is significantly changed by annealing above the cloud point. D is largely increased by the growth of PCL crystallite in the blends. In the miscible state, D is smaller than that predicted by the rule of mixtures, whereas the dependence of D on the weight fraction of PC for the immiscible (phase‐separated) state is well expressed by the rule of mixtures. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 745–749, 1999