Revision of the model of a fibril with amorphous nodules for oriented soft-chain semicrystalline polymers

A critical analysis of literature data about calculations of small-angle x-ray scattering (SAXS) from a model of a fibril with amorphous nodules (FAN) is made. Changes in the SAXS patterns are reviewed for the effect of stretching the FAN. Possibilities of using the calculation results for interpretation of microdeformational behavior of oriented, flexible chain semicrystalline polymers are analyzed. Invoking the FAN model, a retrospective analysis of some literature data and also analysis of new experimental results obtained by SAXS and wide-angle x-ray scattering methods for oriented samples of cellulose triacetate, poly(vinylidene fluoride-co-hexafluoropropylene), and poly(vinyl alcohol) are carried out.     

Vertical phase separation in spin-coated films of a low bandgap polyfluorene/PCBM blend—Effects of specific substrate interaction

We report on the effect of the substrate on the vertical phase separation in spin-coated thin films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole] (APFO-3) blended with [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). Compositional depth profiles of the films are measured by dynamic secondary ion mass spectrometry (SIMS). We found that changing the substrate from silicon to gold affects the composition profile near the substrate interface. This is caused by a specific interaction between the polymer (APFO-3) and the gold surface, as confirmed by X-ray photoelectron spectroscopy (XPS). The composition profile in the area away from the substrate interface, as well as the enrichment of the free surface with APFO-3, remain however unaffected by the choice of substrate. The vertical composition was also analysed for APFO-3:PCBM films spin-coated on indium tin oxide (ITO) coated with a thin layer of (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS).     

Influence of the nematic order on the rheology and conformation of stretched comb-like liquid crystalline polymers

We have studied the rheology and the conformation of stretched comb-like liquid-crystalline polymers. Both the influence of the comb-like structure and the specific effect of the nematic interaction on the dynamics are investigated. For this purpose, two isomers of a comb-like polymetacrylate polymer, of well-defined molecular weights, were synthesized: one displays a nematic phase over a wide range of temperature, the other one has only an isotropic phase. Even with high degrees of polymerization N, between 40 and 1000, the polymer chains studied were not entangled. The stress-strain curves during the stretching and relaxation processes show differences between the isotropic and nematic comb-like polymers. They suggest that, in the nematic phase, the chain dynamics is more cooperative than for a usual linear polymer. Small-angle neutron scattering has been used in order to determine the evolution of the chain conformation after stretching, as a function of the duration of relaxation t _r. The conformation can be described with two parameters only: , the global deformation of the polymer chain, and p, the number of statistical units of locally relaxed sub-chains. For the comb-like polymer, the chain deformation is pseudo-affine: is always smaller than (the deformation ratio of the whole sample). In the isotropic phase, has a constant value, while pincreases as tr. This latter behavior is not that expected for non-entangled chains, in which p varies as t _r ^1/2 (Rouse model). In the nematic phase, decreases as a stretched exponential function of t _r, while p remains constant. The dynamics of the comb-like polymers is discussed in terms of living clusters from which junctions are produced by interactions between side chains. The nematic interaction increases the lifetime of these junctions and, strikingly, the relaxation is the same at all scales of the whole polymer chain. Received 5 May 1999 and Received in final form 18 October 1999     

Study on measurement of refractive index profile of GI-POF by light scattering

This paper is devoted to the study on measurement of refractive index profile of graded-index polymer optical fiber (GI-POF) by light scattering. Using Generalized Airy theory and Debye series of an inhomogeneous cylinder, the scattering intensity distributions are obtained of Airy structure of rainbows for different refractive index profile. The results show that positions of Airy peaks depend closely on refractive index profile of GI-POF. Since each order of rainbow penetrates it to different depths, such methods could be used to provide information of the refractive index profile of GI-POF. For GI-POF with given diameter, positions of Airy peaks of rainbows are simulated as a function of refractive index profile, which can be used to inverse unknown parameters of refractive index profile. The least square method is used in inversion of refractive index profile with the given refractive index of the cladding. The results obtained agree with theoretical values with high precision. The method has the advantages of non-instructive and on-line measurement, and can be used for the measurement of other inhomogeneous droplets.     

铽配合物荧光及在农用光波长转换塑料薄膜中的应用

选择荧光效应强的稀土元素铽,以磺基水杨酸作为第一配体,以聚乙烯醇、聚乙二醇2000等为协配体,对乙醇溶液和水溶液两个体系中形成的配合物荧光进行了研究。试验确定了铽、磺基水杨酸以及聚乙烯醇、聚乙二醇2000为优良协配体的最佳用量。进一步研究发现,表面活性剂的加入对不同配合物的荧光均会产生增强效果,十二烷基磺酸钠效果最好;同时探索了酸度对体系荧光强度的影响。对于获得的铽-磺基水杨酸-聚乙烯醇配合物,其荧光激发波长为342 nm,而荧光发射波长为545 nm,将该配合物以适当比例掺加到农用塑料薄膜中,制备出可以使太阳光的紫外部分转换为作物光合作用需要的绿光的稀土光转换膜。     

Structural control of photoluminescence of four poly(urethane-urea-co-1,3,5-triazine)s: Synthesis and characterization

A series of segmented poly(urethane-urea)s containing 1,3,5 triazine in the hard block and hexamethylene spacers in the soft block was prepared. The hard to soft segment ratio was varied systematically, to afford a series of polymers in which the chromophore concentration varied from 4.2% to 18.1%. Although triazine emission is located in the UV region, the films with higher content of the chromophore emitted a visible blue light (425 nm) when excited at the very red-edge of the absorption band. The photophysical properties of the materials were strongly dependent on the relative amount of triazine moieties along the main chain. Isolated moieties emit in copolymers with small amount of triazine groups, indicating that even though in solid state, these moieties tend to be apart. Two photophysical consequences were observed when the amount of triazine increases: there is some energy transfer process involving isolated moieties with consequent decrease of the lifetime and an additional red-edge emission attributed to aggregated lumophores. The mono-exponential decay observed for the isolated form is substituted by a bi-exponential decay of the aggregated species. The materials were not strong emitters, but since the N-containing triazine moieties are good electron transport groups, the polymers have potential application as electron transport enhancers in various applications.     

Effect of melt viscosity and surface tension of polymers on the percolation threshold of conductive-particle-filled polymeric composites

The electrical conductivities of carbon-black-filled low-density polyethylene (LDPE), poly(methyl methacrylate) (PMMA), and poly(vinyl chloride)-vinyl acetate (PVC/ VAc) copolymer were measured as functions of carbon content and melt viscosity of the matrix at the temperatures at which the composites were prepared. Sharp breaks in the relationship between the carbon filler content and the conductivity of composites were observed in all specimens at some content of the carbon filler. The conductivity jumps as much as 10 orders of magnitude at the break point. This phenomenon has been known as the “percolation threshold”. The critical carbon content corresponding to the break point     

Investigation on crystalline structure and dielectric relaxation behaviors of hot pressed poly(vinylidene fluoride) film

The dielectric relaxation behaviors of hot pressed poly(vinylidene fluoride) (PVDF) film have been studied using dielectric spectroscopy in the frequency domain from 20 Hz to 5 MHz at temperatures between 20 °C and 200 °C. Crystalline/amorphous interphase is suggested with methods of FTIR, XRD, and DSC. Frequency and temperature dependence of dielectric spectroscopy reveals the relaxation behavior and structural dynamics of the samples, and three types of relaxation processes are suggested, α_Ac relaxation process contributed by the hopping transport process near the periphery of conduction band or valence zones at Fermi energy, α_c relaxation process related to the structure change of crystal lattice trapped dipoles in crystalline regions, and α_a relaxation process arising from segmental dipole rearrangement of interphases in amorphous regions. Cole-Cole and Havriliak-Negami experimental equations were utilized to analyze these relaxation processes, and differences of Arrhenius parameters for α_Ac and α_c relaxation processes obtained from Cole-Cole and Havriliak-Negami equations were discussed in detail. Activity energy of different relaxation processes obtained from Arrhenius equation and VFT equation indicates non-single thermal activation mechanism for hot pressed PVDF film.     

一种高电导率PVA聚合物电解质的制备与表征

通过溶液浇注法制备了一种polymer in salt型PVA KOH H2O聚合物电解质.对该电解质进行了X射线衍射、热性质及电化学性质测试与分析.X射线衍射显示PVA和KOH在聚合物电解质中均以非晶态存在.随着KOH含量的增加,聚合物的玻璃转化点温度逐渐上升,而电解质电导率也随之增加.该电解质的电化学窗口可达1.4V,阻抗测试显示当电解质组成PVA/KOH为1/3(质量比)时,室温电导率可达0.15S/cm,电导率与温度关系符合Arrhenius方程.该电解质热力学稳定性好,机械强度高、电化学性质优越.     

Syntheses and structural characterization of two new nanostructured Bi(III) supramolecular polymers via sonochemical method

Two new bismuth(III) coordination supramolecular polymers, {[Bi₂(Hbpp)(bpp)(μ-I)₂I₆](Hbpp)·MeOH}_n (1) and [Bi(Hbpp)(Br₄)] (2), (bpp = 1,3-di(pyridin-4-yl)propane) were prepared and were structurally characterized by single crystal X-ray diffraction. Single crystalline one-dimensional materials were prepared using a heat gradient applied a solution of the reagents using the branched tube method. The structural determination by single crystal X-ray crystallography shows that compounds 1 and 2 form monoclinic polymers with symmetry space group P2₁ in the solid state. These new nanostructured Bi(III) supramolecular compounds, {[Bi₂(Hbpp)(bpp)(μ-I)₂I₆](Hbpp)·MeOH} (1) and [Bi(Hbpp)(Br₄)] (2), were also synthesized by sonochemical method. The nanostructures were characterized by Field Emission-scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and IR spectroscopy.     

Ultrasonic synthesis of two nanostructured cadmium(II) coordination supramolecular polymers: Solvent influence,luminescence and photocatalytic properties

Two nanoparticles of cadmium(II) coordination polymers (CPs) formulated as [Cd(L)(DCTP)]_n (1) and [Cd(L)₂(DCTP)·2H₂O]_n (2) (L = 1,2-bis(2-methylbenzimidazol-1-ylmethyl)benzene, H₂DCTP = 2,5-dichloroterephthalic acid) were prepared by the sonochemical approach in different solvents and characterized by elemental analysis, IR spectra, scanning electron microscopy (SEM), and powder X-ray diffraction. Structural determination reveals that CP 1 displays a 2D four-connected sql net layer, Whilst CP 2 exhibits a 1D “V”-like chain structure. Luminescence properties, thermal behavior, and photocatalytic activities of the nanoparticles of CPs 1 and 2 on the degradation of methylene blue were investigated. The photocatalytic mechanism is carried out by introducing t-butyl alcohol (TBA) as a widely used OH scavenger. Furthermore, the influence of solvents, reaction time, and ultrasound irradiation temperature on the morphology and size of the nanostructure CPs 1 and 2 were investigated. The results indicated that an increase of time and ultrasound irradiation temperature decreased the nanostructured size.     

Kinetics of Formation and Evolution of Phase Structure in Multipolymer: 1. The Application of Semilogarithmic Plot Method to Early Stage of Phase Dispersion

Kinetics of phase dispersion of binary blends of polypropylene and poly(cis-butadiene) rubber during the processing in a batch mixer was investigated by a back small-angle laser scattering (BSALS) online system. It was found experimentally that the scattering intensity I(q, t) followed an exponential growth with time during the early dispersion stage from 1 s to 65 s, while at t > 65 s, the slope levels off with time. A theory in which two critical parameters, W(q) and D_d, were calculated was proposed to describe the early stage of phase dispersion; the former parameter is defined as the rate of decreasing dispersed phase dimension, and the latter, evaluated from the slope of W(q) versus q² plot, is the dispersion coefficient. W(q) remains constant with the increment of dispersed phase. W(q) has a self-similarity with q for different compositions. The slope β, defined as the dispersion acceleration evaluated by linear fit in the nonscaling interval, was determined to explain the similar evolution mechanisms for the different velocity distributions of W(q). The dispersion coefficient D_d increases with the increment of the dispersed phase, and does not vary with shear rates.     

Dynamic Scaling and Fractal Behavior of Phase Dispersion in Multicomponent Polymer Blends

Dynamic scaling and fractal behavior of phase dispersion in a binary polymer mixture of polypropylene with poly(cis-butadiene) rubber during processing in a batch mixer was studied by means of a back small-angle laser scattering (BSALS) online system. In the late stage of phase dispersion, a special fractal behavior was found; different overlapped line groups existed simultaneously and the temporal distribution was stochastic. We defined the special behavior as quasi-self-similarity and calculated the fractal dimension, D _p, by using the power spectrum method. The results show that the evolution of different fractal dimensions with time is consistent with average chord length of the dispersed phase.     

The effect of severe plastic deformation and annealing conditions on mechanical properties and restoration phenomena in an ultrafine-grains Fe-28.5%Ni steel

The effect of annealing condition on the microstructure evolution, together with mechanical properties of Fe-28.5Ni steel processed by one and six cycles of accumulative roll bonding (ARB), was explored. The evolution of microstructure was studied by means of Electron Backscattered Diffraction method. The ARB-processed specimens were annealed for 30 minutes between 500°C and 600°C, and the effect of these annealing processes was elaborated. Results showed a significantly reduced martensite phase during ARB process cycles. Moreover, a refined and stabilised ultrafine structure was obtained in 6-cycle ARB-processed specimen. Results also show that by annealing the 1-cycle specimen at 550°C, no significant microstructural change and mechanical properties variation are identified. As such, no significant microstructural change and mechanical properties variation were notified for annealing of 6-cycle ARB-processed specimen at 500°C. However, annealing at 600°C in both conditions led to a complete recrystallisation of the deformed structure. Annealing at 550°C in 6-cycle ARB-processed specimen showed partial recrystallisation as well as an abnormal grain growth characteristic. The abnormal grain growth was seen by annealing of 1-cycle ARB-processed specimen at 600°C. The changing features of dislocations were discussed in these specimens in terms of changing the dynamics of low- and high-angle grain boundaries. Tensile test results also showed a significant increase in the yield/ultimate tensile strengths with the application of ARB cycles. Although ARB process led to a rapid reduction of total elongation, full restoration during high-temperature annealing returned this value back to the initial, non-deformed, condition.     

Growth and crystalline structure of Co layers on Cu(0 0 1)

The crystalline structure of Co layers deposited on the Cu(0 0 1) surface was investigated with the use of the directional elastic peak electron spectroscopy (DEPES). For clean Cu(0 0 1) the experimental DEPES profiles obtained for different energies of the primary electron beam exhibit intensity maxima corresponding to the close packed rows of atoms. The Auger peak kinetics recorded during continuous Co deposition suggest the layer-by-layer growth mode. The DEPES profiles recorded for 10 monolayers (ML) of Co on Cu(0 0 1) reflect a short-range order in the adsorbate. Intensity maxima observed in the DEPES profiles for Co along [1 0 0], [0 1 0], and [1 1 0] azimuths of Cu(0 0 1) are characteristic of the face centered cubic (fcc) Co(0 0 1) layers. Low-intensity reflections and considerable background intensities were found in the low energy electron diffraction (LEED) patterns recorded from 10 ML of Co, which indicates a weak long-range order in the adsorbate. The adsorption of about 20 ML of Co results in considerable background contribution to DEPES. No reflections but a large background were observed with the use of LEED for this layer. The heating of the Co/Cu(0 0 1) system at T = 770 K leads to an increase of the short- and long-range order in the overlayer, observed in the DEPES profiles and LEED patterns, respectively. The theoretical DEPES profiles were obtained with the use of a multiple scattering approximation. A very good agreement between experimental and theoretical scans was found for the clean and covered copper substrate. The latter proves the epitaxial growth of Co layers on Cu(0 0 1).     

SERS study on surface chain geometry of atactic poly (methyl methacrylate) film and nanosphere

The surface chain geometry of atactic poly (methyl methacrylate) (a‐PMMA) film and nanosphere (NS) was revealed by surface‐enhanced Raman scattering (SERS) spectra. The Ag nanoparticles and nanoplates were prepared by electrochemical deposition and chemical synthesis for SERS substrates. The experimental results suggested that the molecular chain axis of a‐PMMA film adopted a trans‐conformation on bonding to Ag surface ascribed to the short‐range chemical (CHEM) effect according to the SERS selection rules. However, for the well‐coated monolayer of a‐PMMA NSs, the α‐CH₃ in polymer chains stood vertically to the Ag surface due to the giant local electromagnetic effect, then the chain conformation presented in the interface between a‐PMMA NSs and Ag metal was adopted the opposite orientation compared with a‐PMMA film. The Raman enhancement of the Ag nanoparticles was more prominent than that of the Ag nanoplates due to the free energies of face‐centered cubic crystal faces in nanoparticles, but the single crystals with (111) plane of Ag nanoplates could improve the stability of SERS signals when the annealed temperature was above T_g of a‐PMMA NSs. The present work can provide some useful information of surface chain geometry and conformation of NSs for designing various materials with well‐defined structure via a‐PMMA NSs template. Copyright © 2013 John Wiley & Sons, Ltd.     

Structural properties of diamond fine particles and clusters prepared by detonation and decomposition of TNT

The thermal parameter B for three different particle sizes of diamond samples (bulk powder 1–4 μm, fine particle 144–195 Å and cluster 55–61 Å) was determined by the grazing incidence X-ray diffraction method. The values of B were found to be in the range 0.50–0.70 Å² for particles in the size range 195–55 Å and 0.27 Å² for 1–4 μm. All of them are larger than that of diamond bulk. A clear size dependence of B, increasing with decreasing particle size, was found. By analysing X-ray diffraction data at several temperatures the magnitude of B was found to be due to B_S (static part) instead of B_T (dynamic part). The average B_S values obtained were 0.04 Å², 0.19 Å² and 0.27 Å² for bulk powder, fine particle and cluster samples respectively. Ultrahigh resolution transmission electron microscope (TEM) observation confirmed the presence of strain, distortion, roughness and dislocation lines in many particles. TEM images of particles indicate that the clusters were not spherical in shape; they were mostly cubiform and some were truncated prism-like polyhedral. The present study reveals that the B_S component is responsible for the large B value in diamond fine particles and clusters. No clear surface local atomic distortion was found in the particles.     

Electrochemical characterization of poly(vinylidenefluoride)-zinc triflate gel polymer electrolyte and its application in solid-state zinc batteries

Gel polymer electrolyte (GPE) films comprising of poly(vinylidenefluoride), propylene carbonate, ethylene carbonate and zinc trifluoromethane sulfonate are prepared and characterized. The composition of GPE is optimized to contain minimum liquid components with a maximum specific conductivity of 3.94×10⁻³ S cm⁻¹ at (25±1) °C. A detailed investigation on the properties such as ionic conductivity, transport number, electrochemical stability window, reversibility of Zn/Zn²⁺ couple and Zn/gel electrolyte interfacial stability have been carried out. The ionic conductivity follows a VTF behaviour with an activation energy of about 0.0014 eV. Cationic transport number varies from 0.51 at 25 °C to 0.18 at 70 °C. Several cells have been assembled with GPE as the electrolyte, zinc as the anode, γ-MnO₂ as the cathode and their charge–discharge behaviour followed. Capacity values of 105, 82, 64 and 37 mAh/g of MnO₂ have been achieved at 10, 50, 100 and 200 μA/cm² discharge current densities, respectively. The discharge capacity values are almost constant for about 55 cycles for all values of current densities. Cyclic voltammetric study of MnO₂ electrode in Zn/GPE/MnO₂ cell clearly shows intercalation/deintercalation of Zn²⁺.