Nonsolvent-induced dewetting of thin polymer films

The process of nonsolvent-induced dewetting of thin polystyrene (PS) films on hydrophilic surfaces at room temperature has been studied by using water as a nonsolvent. It is observed that the process of nonsolvent-induced dewetting is greatly different from other previous dewetting processes. The PS film is found in nonviscous state in our study. A mechanism of nonsolvent-induced dewetting is deduced in an order of penetration, replacement, and coalescent, and it is different from other previous dewetting mechanisms. The results of experiments are analyzed from thermodynamics and dynamics to support the hypothetical mechanism.

Study of self-assembly of symmetric coil-rod-coil ABA-type triblock copolymers by self-consistent field lattice method

The self-assembly of symmetric coil-rod-coil ABA-type triblock copolymer melts is studied by applying self-consistent field lattice techniques in a three-dimensional space. The self-assembled ordered structures differ significantly with the variation of the volume fraction of the rod component, which include lamellar, wave lamellar, gyroid, perforated lamellar, cylindrical, and spherical-like phases. To understand the physical essence of these phases and the regimes of occurrence, we construct the phase diagram, which matches qualitatively with the existing experimental results. Compared with the coil-rod AB diblock copolymer, our results revealed that the interfacial grafting density of the separating rod and coil segments shows important influence on the self-assembly behaviors of symmetric coil-rod-coil ABA triblock copolymer melts. We found that the order-disorder transition point changes from f(rod)=0.5 for AB diblock copolymers to f(rod)=0.6 for ABA triblock copolymers. Our results also show that the spherical-like and cylindrical phases occupy most of the region in the phase diagram, and the lamellar phase is found stable only at the high volume fraction of the rod.

Enhanced electrochemical properties of nanocomposite polymer electrolyte based on copolymer with exfoliated clays

In this present work, a polymer electrolyte based on polymer/clay nanocomposite has been developed. Montmorillonite (MMT) clay was used as the filler. due to its special size in length and thickness, and its sandwich type structure. The obtained gel polymer electrolytes have high ionic conductivity up to 2.5 mS cm(-1) with high cationic transference number (about 0.64) at room temperature. The influences of the filler on the membrane morphology. the solvent uptake, the ionic conductivity, and the cation transport number were investigated, and thus the significant contribution from the exfoliated organophilic MMT was identified.

Relaxation time and conductivity of comb-like gel polymer electrolytes

Using the copolymer of acrylonitrile (AN), methyl methacrylate (MMA), and poly(ethylene glycol) methyl ether methacrylate as a backbone and poly(ethylene glycol) methyl ether (PEGME) with 1100 molecular weight as side chains, comb-like gel polymers and their Li salt complexes were synthesized. The dynamic mechanical properties and conductivities were investigated. Results showed that the gel copolymer electrolytes possess two glass transitions: alpha-transition and beta-transition. Based on the time-temperature equivalence principle, a master curve was constructed by selecting T. as reference temperature. By reference to T-0 = 50 degrees C, the relation between log c, and c was found to be linear. The master curves are displaced progressively to higher frequencies as the content of plasticizer is increased. The relation between log tau(p) and the content of plasticizer is also linear.

Organic/inorganic nanocomposite polymer electrolyte

The organic/inorganic nanocomposites polymer electrolytes were designed and synthesized. The organic/inorganic nanocomposites membrane materials and their lithium salt complexes have been found thermally stable below 200 degrees C. The conductivity of the organic/inorganic nanocomposites polymer electrolytes prepared at room temperature was at magnitude range of 10(-6) S/cm. (c) 2007 Li Qi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Applications of scanning probe microscopy in intrinsically conducting polymer research

The applications of scanning probe microscopy (SPM) in intrinsically conducting polymer research is briefly reviewed, including morphology observation, nanofabrication, microcosmic electrical property measurements, electrochemistry researches, in-situ measurements of film thickness change, and so on. At the same time, some important variations of SPM and the related techniques are briefly introduced. Finally, the future development of SPM in the study of intrinsically conducting polymers is prospected.

Efficient multilayer white polymer light-emitting diodes with aluminum cathodes

Efficient multilayer white polymer light-emitting diodes (WPLEDs) with aluminum cathodes are fabricated. The multilayer structure is composed of a water soluble hole-injection layer, a toluene-soluble emissive layer, and an alcohol-soluble emissive layer. The polarity difference of the solvents used for spin coating these polymers allows for realization of the multilayer polymer structure. The recombination zone confined at the interface of the two emissive polymers avoids exciton quenching by electrodes, and white emission is realized by harvesting photons emitted from the two emissive polymers. A maximum luminous efficiency of 16.9 cd/A and a power efficiency of 11.1 lm/W are achieved for this WPLED.

Enhancement of stability of polymer light-emitting diodes by post annealing

We investigate the effect of thermal annealing before and after cathode deposition on the stability of polymer light-emitting diodes (PLEDs) based on green fluorescent polyfluorene derivative. The annealed PLEDs exhibit improved charge transport and red-shift emission compared to the as-fabricated device. The stability of the PLEDs is largely enhanced by post-annealing before and after Ca deposition, which is attributed to the enhanced charge transport and the intimate contact between the cathode and the emissive layer.

Enhanced electrical conductivity of highly crystalline polythiophene/insulating-polymer composite

Poly(3-butylthiophene) (P3BT)/insulating-polymer composites with high electrical conductivity have been prepared directly from the solution. These composites exhibit much higher conductivity compared to pure P3BT with the same preparation method provided that P3BT content is higher than 10 wt %. Morphological studies on both the pure P3BT and the composites with insulating polymer show that P3BT highly crystallizes and develops into whisker-like crystals. These nanowires are homogeneously distributed within the insulating polymer matrix and form conductive networks, which provide both extremely large interface area between conjugated polymer and insulating polymer matrix and highly efficient conductive channels through out the whole composite. In contrast, the conductivity enhancement of P3HT/PS composite is not so obvious and drops down immediately with increased PS content due mainly to the absence of highly crystalline whisker-like crystals and much larger scale phase separation between the components. The results presented here could further illuminate the origin of conductivity formation in organic semiconducting composites and promote applications of these polymer semiconductor/insulator composites in the fields of organic (opto-)electronics, electromagnetic shielding, and antistatic materials.

Toward high-performance polymer solar cells: The importance of morphology control

Polymer solar cells have the potential to become a major electrical power generating tool in the 21st century. R&D endeavors are focusing on continuous roll-to-roll printing of polymeric or organic compounds from solution-like newspapers-to produce flexible and lightweight devices at low cost. It is recognized, though, that besides the functional properties of the compounds the organization of structures on the nanometer level-forced and controlled mainly by the processing conditions applied-determines the performance of state-of-the-art polymer solar cells. In such devices the photoactive layer is composed of at least two functional materials that form nanoscale interpenetrating phases with specific functionalities, a so-called bulk heterojunction. In this perspective article, our current knowledge on the main factors determining the morphology formation and evolution is introduced, and gaps of our understanding on nanoscale structure-property relations in the field of high-performance polymer solar cells are addressed. Finally, promising routes toward formation of tailored morphologies are presented.

Progress in polymer solar cell

This review outlines current progresses in polymer solar cell. Compared to traditional silicon-based photovoltaic (PV) technology, the completely different principle of optoelectric response in the polymer cell results in a novel configuration of the device and more complicated photovoltaic generation process. The conception of bulk-heterojunction (BHJ) is introduced and its advantage in terms of morphology is addressed. The main aspects including the morphology of photoactive layer, which limit the efficiency and stability of polymer solar cell, are discussed in detail. The solutions to boosting up both the efficiency and stability (lifetime) of the polymer solar cell are highlighted at the end of this review.

Effect of doped dye on the charge-carrier transport and electroluminescent performance in molecularly doped polymer light-emitting diodes

The effects of the concentration of 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6, 78-i,j)quinolizin-11-one (C545T) as dopant in polyfluorene (PFO) on the charge-carrier transport and electroluminescence (EL) performance were investigated by steady-state and transient EL measurements. A fully green emission from C545T was observed and the EL performance depends strongly on the C545T concentration. The mobility in the C545T-doped PFO film was determined by transient EL. The dopant concentration dependence of the current-voltage relationship indicated clearly the carrier trapping by the C545T molecules. The mobility in C545T:PFO changed significantly with the C545T concentration, and showed a nontrivial dependence on the doping level. The behavior may be understood in terms of the formation of an additional energy disorder due to potential fluctuation caused by the Coulomb interaction of the randomly distributed doping molecules.

Improvement of amplified spontaneous emission performance by doping tris(8-hydroxyquinoline) aluminum (Alq3) in dye-doped polymer thin films

A well-known red fluorescent dye 4-(dicy-anomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB) was codoped with an electron transport organic molecule tris(8-hydroxyquinohne) aluminum (Alq3) in a host matrix of polystyrene (PS), and the amplified spontaneous emission (ASE) was studied by optically pumping. It was found that the ASE performance was significantly improved by the introduction of Alq3. The Alq3:DCJTB:PS blending thin films showed a low threshold (2.4 mu J/pulse) and a high net gain coefficient (109.95 cm(-1)) compared with the pure DCJTB:PS system (threshold of 15.2 mu J/pulse and gain of 35.94 cm(-1)). The improvement of the ASE performance was considered to be attributable to the effective Foster energy transfer from Alq(3) to DCJTB. Our results demonstrate that the Alq(3):DCJTB could be a promising candidate as gain medium for red organic diode lasers.