Structural and property changes in poly (vinylidene fluoride–trifluoroethylene) 70/30 mol % copolymer induced by proton irradiation

Poly(vinylidene fluoride–trifluoroethylene) 70/30 mol% copolymer has been irradiated with 3 MeV protons at doses ranging from 43 to 200 Mrad. The effects of irradiation on the polarization hysteresis, dielectric properties, lattice spacing, phase transition behavior and electric-field-induced strain have been studied. The irradiated copolymer exhibits the characteristic behavior of a relaxor ferroelectric, including frequency dispersion of the dielectric constant, which follows the Vogel–Fulcher rule. These results indicate that the proton irradiation breaks up the coherent polarization domains in the copolymer into nano-sized regions, thereby converting the copolymer to a relaxor ferroelectric. X-ray diffraction measurements show that the nano-sized regions are in the non-polar phase. Since the lattice spacing of the non-polar phase is substantially different from that of the polar phase, the local phase transformation between these two phases induced by an external electric field gives rise to a large lattice strain and hence a giant electrostrictive response. PACS 77     

Thermal and dielectric investigations of the curie transition in Poly(vinylidene fluoride—trifluoroethylene) copolymers

The ferroelectric-to-paraelectric phase transition in poly(vinylidene fluoride-trifluoroethylene) copolymers has been investigated by differential scanning calorimetry and dielectric techniques. The transition appears to be very dependent on the crystallization kinetics and thermal history. The anomalies accompanying the transition show that the structural transformations are complex. In particular, the 30 mol % TrFE sample presents the most remarkable effects. The results are discussed in terms of the existence of a possible intermediate crystalline phase. The role of defects and of the anchored amorphous phase have also been considered.     

Comparison of the thermal stability of the α, β and γ phases in poly(vinylidene fluoride) based on in situ thermal Fourier transform infrared spectroscopy

The electroactive β phase of poly(vinylidene fluoride) (PVDF) is induced due to the aging time of PVDF solutions. The feasibility of the combination of the three crystalline polymorphs (α, β and γ) is demonstrated where their relative proportion within the PVDF film can be tailored by the simple monitoring of the preparation conditions. To identify all these phases, Fourier transform infrared (FT-IR) spectroscopy is carried out and it is spotlighted that the vibrational bands at 510 and 841 cm^?1 are not sufficient to state the formation of the β phase. The main aim of this work is devoted to develop a better understanding on the thermal stability of these several phases of PVDF, which has a longstanding ambiguity persisting in this area. It has been found that the in situ thermal FT-IR spectroscopy is one of the best alternatives to understand this important issue. It is ascertained that the β phase is the least thermally stable phase among α, β and γ phases, whereas the γ phase is the most thermally stable phase.     

A van der Waals density functional theory study of poly(vinylidene difluoride) crystalline phases

Ferroelectric polymers, such as poly(vinylidene difluoride) (PVDF), have many potential applications in flexible electronic devices. PVDF has six experimentally observed polymorphs, three of which are ferroelectric. In this work we use density functional theory to investigate the structural properties, energetics and polarisation of the stable α-phase, its ferroelectric analogue, the δ-phase, and the β-phase, which has the best ferroelectric properties. The results from a variety of exchange and correlation functionals were compared and it was found that van der Waals (vdW) interactions have an important effect on the calculated crystal structures and energetics, with the vdW-DF functional giving the best agreement with experimental lattice parameters. The spontaneous polarisation was found to strongly correlate with the unit cell volumes, which depend on the functional used. While the relative phase energies were not strongly dependent on the functional, the cohesive energies were significantly underestimated using the PBE functional. The inclusion of vdW interactions is, therefore, important to obtain the correct lattice structures, polarisation and energetics of PVDF polymorphs.     

Crystalline Phase Formation of Poly(vinylidene fluoride) from Tetrahydrofuran/N,N‐dimethylformamide Mixed Solutions

The present work focused on the effect of the interactions between poly(vinylidene fluoride) (PVDF) chains and solvent molecules on the structure and crystallization behavior of PVDF in films obtained by solution casting. In a single solvent system, the film cast from the good solvent of N,N‐dimethylformamide (DMF), showed dominantly β‐phase crystals with the highest PVDF crystallinity (50.6%) and the largest spherulite size, about 4 μm, at the top surface. The samples deposited from good swelling agents, such as tetrahydrofuran (THF) and methyl ethyl ketone (MEK), exhibited mainly the original α phase with some amount of β‐phase crystals; the crystallization behavior and the morphology of the surface were similar to the original PVDF resin, because of the only partially dissolved PVDF chains in these two solvents. In a mixed solvent system (THF/DMF), the β phase formation linearly increased as the DMF component increased, determined by Fourier transform infrared spectroscopy (FTIR) techniques, owing to increased interactions between PVDF chains and DMF molecules. The film surface consisted of β spherulites with average size of about 3 μm, which were smaller than those grown from pure DMF, because of the increased crystallization rate in the mixed solvent.     

三链核酸poly(U)·poly(A)·poly(U)主链的振动位移

基于三链核酸 poly(U)· poly(A)·poly(U)的螺旋对称性 ,利用晶格动力学方法 ,计算了三链核酸分子 poly(U)·poly(A)·poly(U)主链振动的本征矢 ,探讨了振动位移矢量和线二色光谱的关系。结果表明 ,对应着磷酸双氧的反对称振动谱线可以用于直接确定磷酸根的取向 ,精度大约为 1°。其他谱线必须通过对分子的简正分析来帮助确定分子的结构。     

三螺旋DNA分子poly(dT)·poly(dA)·poly(dT)的构型和振动谱

我们计算了ｐｏｌｙ（ｄＴ）·ｐｏｌｙ（ｄＡ）·ｐｏｌｙ（ｄＴ）的Ｈｏｗａｒｄ模型的原子笛卡尔坐标，并利用晶格动力学方法对模型进行了简正分析。结果发现其０ Ｐ ０对称振动模式位于８０４ｃｍ－１，这和８１０ｃｍ－１附近没有拉曼和红外谱线的实验结果不符。在８００～１０００ｃｍ－１的范围内只有四个振动模式，明显少于拉曼和红外光谱在该范围内的谱线数目。所以我们认为Ｈｏｗａｒｄ模型需要进一步地完善和修正，ｐｏｌｙ（ｄＴ）·ｐｏｌｙ（ｄＡ）·ｐｏｌｙ（ｄＴ）必须具有三条不完全一致的脊骨     

Enhanced β Crystalline Phase in Poly(vinylidene fluoride) via the Incorporation of Graphene Oxide Sheets assisted by Supercritical CO2 Treatment

Graphene oxide (GO) sheets were pre-modified with a typical piezoelectric polymer, poly(vinylidene fluoride) (PVDF), using a simple supercritical carbon dioxide (SC CO₂) method, and then the PVDF-decorated GO was added into a PVDF matrix by solution blending. Transmission electron microscopy (TEM) revealed that the decorating degree of PVDF on the surface of the GO increased significantly with increasing of SC CO₂ pressure and PVDF concentration. The mechanism of the polymer adsorption on the GO sheets through favorable interaction between the GO and PVDF chains was identified via Fourier transform infrared spectroscopy (FTIR). Further, the crystallization behavior of PVDF/GO composites was investigated by differential scanning calorimetry (DSC), FTIR and polarized optical microscopy (POM). Interestingly, the composite with PVDF-decorated GO as the filler showed higher β-phase content compared to the composite with pristine GO as the filler. The study showed that the supercritical fluid-induced epitaxial crystallization process has significant potential for fabricating functional GO-based nanocomposties containing piezoelectric or conducting materials.     

Effect of trifluoroethylene monomers on molecular conformation of poly（vinylidene fluoride-trifluoroethylene） copolymer

Hartree－Fock and density functional theory (DFT) methods were employed to study poly (vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] molecular chains with different VDF contents. The dependence of dipole moment of P(VDF-TrFE) chains on VDF content obtained from our calculation is in good agreement with the experiment. The TrFE monomer plays an important role in introducing the gauche bond into copolymer chains. A possible mechanism was interpreted.     

Thermodynamics of poly(α-olefin) solutions

The Maron theory of polymer solutions was used to examine the 30°C vapor pressure data of Tait and Livesey on solutions of polyheptene-1, polydecene-1, polydodecene-1, and polyoctadecene-1 in toluene. For polyheptene-1 and polydecene-1, excellent agreement was obtained between theory and experiment over the entire concentration range studied. However, for the other two polymers, deviations were observed between the calculated and observed vapor pressures at higher solution concentrations. These deviations were used to show the presence of crystallinity in these and to ascertain the amounts. Further, it was shown that only one crystalline form of the polymer was present in the polydodecene-1, whereas in the polyoctadecene-1 two crystalline forms were detected. These observations, confirmed by measurements with a differential thermal analyzer (DTA), indicate that for polydodecene-1 and one of the crystalline forms in polyoctadecene-1 the crystallization involves alignment of both backbone and side chains; however, the lower melting form in polyoctadecene-1 appears to have only the side chains aligned in the crystal lattice.     

Laser transmission welding of poly(ethylene terephthalate) and biodegradable poly(ethylene terephthalate) – Based blends

Joining of Poly(Ethylene Terephthalate) PET and its biodegradable derivatives is of high relevance to ensure good productive rate, low cost and operational safety for fabrication of medical and electronic devices, sport equipments as well as for manufacturing of food and drug packaging solutions. In the present investigation, granules of PET and PETs modified by organic additives, which promote biodegradation of the polymeric chains, were prepared by extrusion compounding. The achieved granules were subsequently re-extruded to shape thin (330 μm) flat sheets. Substrates cut from these sheets were joined by Laser Transmission Welding (LTW) with a continuous wave High Power Diode Laser (cw-HPDL). First, based on a qualitative evaluation of the welded joints, the most suitable operational windows for PETs laser joining were identified. Second, characterization of the mechanical properties of the welded joints was performed by tensile tests. Accordingly, Young's modulus of PET and biodegradable PET blends was studied by Takayanagi's model and, based on the experimental results, a novel predicting analytical model derived from the mixture rule was developed. Lastly, material degradation of the polymeric joints was evaluated by FT-IR analysis, thus allowing to identify the main routes to thermal degradation of PET and, especially, of biodegradable PET blends during laser processing.     

Improvement of ammonia sensing properties of poly(pyrrole)–poly (n-methylpyrrole) composite by ion irradiation

In the present investigation we have electrochemically synthesized polypyrrole–poly (n-methylpyrrole) composite film with optimized process parameters (viz. concentration of monomers and dopant, applied current density, deposition time, pH of electrolyte etc.) on platinum substrate. The composite film of polypyrrole–poly (n-methylpyrrole) was subjected to electrical, spectral and morphological characterizations and its sensing response to various concentration of ammonia was also studied. Later, the synthesized composite films were irradiated under high vacuum (∼5×10⁻⁶ Torr) at room temperature with 85 MeV O⁷⁺ ion beam at various fluences from 1×10⁵ to 1×10⁷ ions/cm². We have observed remarkable improvements in electrical and morphological properties suitable for gas-sensing applications. The irradiated composite film was evaluated for the sensing of various concentrations of ammonia and excellent improvement in terms of sensitivity, lower detection limit and response time was observed.     

The dipolar and exchange contributions to the spin-lattice relaxation of the imino protons in poly(rA)· poly(rU)

Selective, semiselective, and biselective excitation has been used to study the spin-lattice relaxation of the hydrogen-bonded imino protons in the sonicated, double-stranded RNA polymer poly(rA)· poly(rU). The spin-lattice relaxation of the imino protons has contributions from both dipolar interactions and exchange with the solvent, and the relative contribution of each to the observed rate depends on temperature. When exchange is slow compared to the dipolar contribution, the two components can be resolved by measuring the relaxation rate with and without prior inversion of the solvent peak. When exchange is fast, the contributions can be resolved by comparing the initial selective relaxation rate with the rate of saturation transfer when the solvent peak is inverted. This allows the exchange and dipolar contributions to be separated at temperatures well below the duplex melting temperatures and provides an easy way to study the mechanism of proton exchange with the solvent.     

Nanostructured Thermosetting Blends of Phenolic Thermosets and Poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) Triblock Copolymer

The amphiphilic triblock copolymer, poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) (PEO‐b‐PPO‐b‐PEO) was incorporated into novolac resin to prepare thermosetting blends. The morphology of the thermosetting blends was investigated by means of atomic force microscopy (AFM) and small‐angle x‐ray scattering (SAXS) and the nanostructures were obtained. It was identified that the reaction‐induced phase separation occurred in the blends of phenolic thermosets with the model poly(propylene oxide) (PPO), whereas poly(ethylene oxide) (PEO) was miscible with novolac resin after and before the curing reaction. In terms of miscibility and phase behavior of the subchains of the triblock copolymer with novolac resin, it was demonstrated that the formation of nanostructures in the thermosets followed a mechanism of reaction‐induced microphase separation.     

Poly(dA)·poly(dT)结构的喇曼光谱和晶格动力学研究

我们成功地获得了溶液中poly(dA)·poly(dT)的喇曼光谱,并利用晶格动力学方法对于异规模型进行了简正分析.根据势能分布矩阵(PED)对每一个模式进行了指定.结果表明异规模型的简振频率和poly(dA)·poly(dT)的喇曼光谱符合得相当好,这说明溶液中的poly(dA)·poly(dT)完全有可能保留了固体纤维中的异规模型结构.     

Relationship between the microstructure and the microscopic piezoelectric response of the <Emphasis Type="Italic">α</Emphasis>- and <Emphasis Type="Italic">β</Emphasis>-phases of poly(vinylidene fluoride)

The piezoelectric and pyroelectric properties of PVDF mainly depend on its β-phase. This work reports the study by scanning force microscopy in a piezoresponse mode of the variations in the topological morphology and piezoelectric surface response of β-PVDF prepared by the main preparation methods of this phase. Clear differences in the poled region distribution and size, as well as in the local piezoactivity, have been identified. The piezoelectric activity at a mesoscale reflects the semicrystalline phase of the polymer.     

The coil → blob transition in atactic poly(styrene) films

The structure of atactic poly(styrene) in films prepared from chloroform solutions was studied by small-angle X-ray scattering and electron microscopy. It was shown that the density fluctuations in films corresponding to dilute poly(styrene) solutions are associated with the aggregates of particles with the radius R ₀ close to the hydrodynamic radius of the coil. The value of R ₀ in the films decreases with an increase in the poly(styrene) concentration due to the coil entanglement and the blob formation. The coil (its fractal dimension is D = 2) → blob (D = 3) transition leads to an increase in the density and glass transition temperature of films, which is caused by enhancing interchain and intrachain interactions of segments in the solid state of atactic poly(styrene).     

Solid polymer electrolytes in a poly(butadiene-acrylonitrile)–LiBr system

Poly(nitriles) are among the polymer matrices providing high salt solubility and, in some cases, superionic lithium conductivity at ambient temperatures observed in highly concentrated solvent-free polymer electrolytes. However, the properties of these electrolytes in which ionic aggregation prevails remain difficult to reproduce and predict, as current theories do not adequately model their attributes. The development of new concepts for ion transport in highly concentrated solid polymer electrolytes (SPEs) requires a better understanding of the fundamentals of structure formation in a polymer–salt system over a wide concentration range including salt precipitation. In an attempt to approach this goal, a series of fundamental studies was carried out on the systems based on a rubbery random copolymer of butadiene and acrylonitrile (abbreviated as PBAN). In the present work, LiBr with monatomic halide anion was used as a lithium salt. The effect of LiBr concentration (0.05 to 3.35 mol kg^?1) on phase composition, ion–molecular interactions, glass transition temperature, and ionic conductivity was studied by optical microscopy, FTIR, X-ray diffraction, DSC, and impedance measurements. The results were compared with those of PBAN–LiClO₄ and PBAN–LiAsF₆ studied previously. Low salt solubility and separation of a metastable cubic CsCl-type polymorph of LiBr were established. The highest conductivity of ～10^?4 S cm^?1 at >50 °C was observed for heterogeneous samples comprising this phase. While the conductivity of PBAN–LiBr was lower than that of PBAN–LiClO₄ and PBAN–LiAsF₆, this study provides a new insight into the nature of polymer electrolyte systems.     

Synthesis and Characterization of Terpolymers of poly(L-lactide-glycolide-ε-caprolactone)

Random terpolymers of poly(L-lactide-glycolide-ε-caprolactone) (PLLGC) was prepared by ring-opening polymerization of L-lactide, glycolide and ε-caprolactone monomers initiated with stannous octanoate. Fourier transform infrared spectra, nuclear magnetic resonance and gel permeation chromatography were employed to characterize the obtained PLLGC terpolymers. The effects of polymerization temperature, reaction time, the amount of initiator and the polymerization pressure on the weight average molecular mass and polydispersity index of the PLLGC were investigated. In addition, the water contact angle of the PLLGC was also tested. The characterization of chemical structure showed that the PLLGC was successfully synthesized. For instance, a PLLGC terpolymer with a weight average molecular mass of about 12.435?×?10⁴?Da and a polydispersity index of 1.28 was obtained when the polymerization was conducted with a molar ratio of monomer to initiator ([M]/[I]) of 2000, polymerization temperature of 140?°C, polymerization pressure of 5.0?Pa and reaction time of 24?h. The random incorporation of ε-CL monomer units decreased the wettability of the PLGA copolymers.     

Control on β conformation of poly(9,9-di-n-octylfluorene)via solvent annealing

Films of poly(9,9-dioctylfluorene)(PFO) are of great importance in fabricating light emitting diodes.In practice, theβ-phase of PFO is expected due to its high efficiency in the transport of charge carrier.To promote the formation of β-phase,PFO films are immersed and annealed in the mixture of solvent/nonsolvent.The effects of temperature, solvent/nonsolvent ratio, and annealing time are examined systematically.It is found that the fraction of β-phase can be highly improved by increasing the ratio of solvent/nonsolvent.The reconfiguration of PFO molecules for β-phase in annealing is generally finished in 10 min.The finding in this study demonstrates that solvent-assisted annealing offers a fast and economic approach for mass annealing.