Intercomparison of slip flow velocity measurements of filled polymers by capillary extrusion rheometry

Slip flow can complicate both the measurement of the shear flow behaviour of polymers and the modelling of moulding processes. However, the understanding of the reliability of methods for measuring slip flow behaviour is limited. The results of an intercomparison on the measurement of slip flow behaviour by capillary extrusion rheometry of two polymer melts—a filled high-density polyethylene and a filled ethylene–vinyl acetate copolymer—are reported. Slip velocities were calculated, following the Mooney method, from the dependence of the shear stress–shear rate behaviour on the extrusion die diameter. Both compounds exhibited wall slip: in one case the slip velocity accounted for ≈80% of the total flow rate. Slip velocity results were typically within ≈±20% of the average values for the materials, although scatter up to ≈±40% was obtained for one material at high shear stresses. An analysis of slip velocity measurements indicated that uncertainties of 40–50% are typical (95% confidence level) although significantly higher uncertainties could result if testing conditions (primarily die diameters) are not optimised.     

Correlations between dynamic fragility and dynamic mechanical properties of several amorphous polymers

In the present paper, dynamic mechanical properties were measured for several amorphous polymers ranging from strong to fragile. The results indicate that the storage modulus changes steadily, and the loss modulus peak and the tanδ peak are broader for strong glass-forming polymers. Three variables, the steepness index (S), the transition wideness (W) of storage modulus and the integration area (A) of tanδ, were defined to illustrate the potential correlation between the dynamic fragility index (m) and the dynamic mechanical properties. It is found that W and A can be correlated with m by power law equations, while an exponential relationship between S and m is observed. Moreover, as m decreases, the tanδ peak is more and more apart from the loss modulus peak and the point where the storage modulus begins to drop. These phenomena are interpreted in terms of chain packing efficiency.     

Optical, electrical and photovoltaic properties of thermally annealed PPHT:DDE blend thin films

We have investigated the optical, electrical and photovoltaic properties of devices based on 1,2-diazoamino diphenyl ethane (DDE) and poly(3-phenyl hydrazone thiophene) (PPHT):DDE blend. It is observed from the J-V characteristics of the Al/DDE/ITO (ITO—indium tin oxide) device that the electron current injected from Al contact was shown to be space charge limited (SCL), indicating that Al forms nearly ohmic contact for electron injection into lowest unoccupied molecular orbital (LUMO) of DDE. The effect of thermal annealing and composition, on the optical, electrical and photovoltaic response of blend of PPHT and DDE sandwiched between a transparent ITO electrode and an Al back contact are investigated. The observed absorption quenching in the PPHT:DDE blend is attributed to the disordering of PPHT chains and charge transfer between PPHT and DDE as evidenced by FTIR spectra. The observed red shift in the absorption peak on thermal annealing is due to the improvement in the ordering and increases in conjugation length in PPHT. The observed dark current-voltage curves agree well with trap-controlled SCL transport theory. The photophysics of the blend material and influence of thermal annealing on the performance and morphology of these devices were discussed. Annealing process results in the formation of PPHT:DDE complex and increase in the ordering of polymer chain, that increases the incident photon to current efficiency (IPCE) and power conversion efficiency of the photovoltaic devices.     

Kac Polymers

We show how a polymer in two dimensions with a self-repelling interaction of Kac type exhibits a diffusive–ballistic transition if considered on the appropriate scale.     

Surface free energy of ultra-high molecular weight polyethylene modified by electron and gamma irradiation

Surface free energy of biocompatible polymers is important factor which affects the surface properties such as wetting, adhesion and biocompatibility. In the present work, the change in the surface free energy of ultra-high molecular weight polyethylene (UHMWPE) samples, which is produced by electron beam and gamma ray irradiation were, investigated. Mechanism of the changes in surface free energy induced by irradiations of doses ranging from 25 to 500 kGy was studied. FTIR technique was applied for sample analysis. Contact angle measurements showed that wettability and surface free energy of samples have increased with increasing the irradiation dose, where the values of droplet contact angle of the samples decrease gradually with increasing the radiation dose. The increase in the wettability and surface free energy of the irradiated samples are attributed to formation of hydrophilic groups on the polymer surface by the oxidation, which apparently occurs by exposure of irradiated samples to the air.     

Dynamics at the air-water interface revealed by evanescent wave light scattering

A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle illumination. Peak width and height are affected by the interfacial profile and the focusing of the beam. In addition, the propagation of capillary waves was studied at the surface of pure water and in the presence of latex particles and amphiphilic diblock copolymers. The range of the scattering vectors where propagating surface waves were detected is by far wider than standard surface quasi-elastic light scattering (SQELS) and comparable with those of X-ray photon correlation spectroscopy (XPCS).     

Effect of non-zero Schottky barrier on the J-V characteristics of organic diodes

Current-voltage (J -Vcharacteristics of poly(3-hexylthiophene) (P3HT) are studied at different temperatures upto high voltages ∼ 20 V in the hole-only device configuration. The characteristics are studied in the temperature range 310-210K. In the intermediate voltage range the J -V characteristics follow J V ^l+1 , where l > 1 . As the voltage increases to high values J still varies as a power law i.e. as V^m, but contrary to the literature result m becomes < 2 . This behavior is explained theoretically in terms of non-zero injection Schottky barriers. The complete analytical expressions for the actual trap filled limit voltage (V′ _TFL) and J -V curves beyond V′ _TFL are presented.     

Optical and photoluminescent properties of plasma polymer films used in electroluminescent display structures

The optical and photoluminescent properties of plasma polymer layers synthesized from hexamethyldisiloxane are examined. The value of the polymer layer transparence is in the limits from 55% at 400 nm to 88% at 800 nm. Photoluminescence is stimulated by using the spectral line λ=365 nm emitted by a Hg spectral lamp.The organosilicon plasma polymers are included as protective and capsulating layers in electroluminescent (EL) structures. The structure obtained is characterized by a significant increase in emission brightness, compared to inorganic protective layers. For EL structures with a chalcogenide protective layer the increase is more than 6 times and for structures with heterogeneous matrix on the base of TiO₂ it is more than 20 times. As a stable covering the organosilicon plasma polymer increases the lifetime of the EL structures too.     

Structural and thermal studies of PVA:NH4I

Proton-conducting polymer electrolytes based on poly vinyl alcohol (PVA; 88% hydrolyzed) and ammonium iodide (NH₄I) has been prepared by solution casting method with different molar ratios of polymer and salt using DMSO as solvent. DMSO has been chosen as a solvent due its high dielectric constant and also its plasticizing nature. The ionic conductivity has been found to increase with increasing salt concentration up to 25 mol% beyond which the conductivity decreases and the highest ambient temperature conductivity has been found to be 2.5×10⁻³ S cm⁻¹. The conductivity enhancement with addition of NH₄I has been well correlated with the increase in amorphous nature of the films confirmed from XRD and differential scanning calorimetry (DSC) analyses. The temperature-dependent conductivity follows the Arrhenius relation. The polymer-proton interactions have been analyzed by FTIR spectroscopy.     

共轭导电聚合物电致发光元件的原理与进展

共轭导电聚合物是一种极有应用前途的有机半导体材料。本文综述了共轭导电聚合发光二极管和导电聚合物电化学发光电池的原理及进展。