Reversibly strain-tunable elastomeric photonic crystals

Reversibly strain-tunable polymeric photonic crystals made of thermoplastic polyester elastomer (TPEE) were fabricated by using the self-assembled silica opals as templates. The stop band of the polymeric photonic crystal locates at the near infrared (IR) regime in its transmission spectrum, and exhibits a blue shift with the increase of the incident angle. Because of the elasticity of the TPEE, the stop band of the TPEE photonic crystal can also be reversibly tuned at ambient temperature through to and fro uniaxially or biaxially stretching and recovering by changing the lattice spacing and the symmetry of the crystal along (1 1 1) plane.

Effect of poly(propylene carbonate) on the crystallization and melting behavior of poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate)

The crystallization and melting behavior of poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) (PHBV) and a 30/70 (w/w) PHBV/poly(propylene carbonate) (PPC) blend was investigated with differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The transesterification reaction between PHBV and PPC was detected in the melt-blending process. The interaction between the two macromolecules was confirmed by means of FTIR analysis. During the crystallization process from the melt, the crystallization temperature of the PHBV/PPC blend decreased about 8 degreesC, the melting temperature was depressed by 4 degreesC, and the degree of crystallinity of PHBV in the blend decreased about 9.4%; this was calculated through a comparison of the DSC heating traces for the blend and pure PHBV. These results indicated that imperfect crystals of formed, crystallization was inhibited, and the crystallization ability of PHBV was weakened in the blend. The equilibrium melting temperatures of PHBV and the 30/70 PHBV/PPC blend isothermally crystallized were 187.1 and 179 degreesC, respectively.

Thermal analysis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) irradiated under vacuum

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was irradiated by Co-60 gamma-rays (doses of 50, 100 and 200kGy) under vacuum. The thermal analysis of control and irradiated PHBV, under vacuum was carried out by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile properties of control and irradiated PHBV were examined by using an Instron tensile testing machine. In the thermal degradation of control and irradiated PHBV, a one-step weight loss was observed. The derivative thermogravimetric curves of control and irradiated PHBV confirmed only one weight-loss step change. The onset degradation temperature (T-o) and the temperature of maximum weight-loss rate (T-p) of control and irradiated PHBV were in line with the heating rate (degreesC min(-1)). T-o and T-p of PHBV decreased with increasing radiation dose at the same heating rate. The DSC results showed that Co-60 gamma-radiation significantly affected the thermal properties of PHBV. With increasing radiation dose, the melting temperature (T-m) of PHBV shifted to a lower value, due to the decrease in crystal size. The tensile strength and fracture strain of the irradiated PHBV decreased, hence indicating an increased brittleness.

Modeling of organic light-emitting diodes with graded concentration in the emissive multilayer

We model the electrical behavior of organic light-emitting diodes whose emissive multilayer is formed by blends of an electron transporting material, tris-(8-hydroxyquinoline) aluminum (Alq(3)) and a hole transporting material, N,N-'-diphenyl-N,N-'-bis(1,1(')-biphenyl)-4,4-diamine. The multilayer is composed of layers of different concentration. The Alq(3) concentration gradually decreases from the cathode to the anode. We demonstrate that these graded devices have higher efficiency and operate at lower applied voltages than devices whose emissive layer is made of nominally homogeneous blends. Our results show an important advantage of graded devices, namely, the low values of the recombination rate distribution near the cathode and the anode, so that electrode quenching is expected to be significantly suppressed in these devices.

Copolymerization of dichlorodiphenylsulfone with bis(chlorophthalimide) catalyzed by NiBr2/PPh3/Zn

A new high-performance material, poly(sulfone-imide) was prepared by Ni(0)-catalyzed coupling of aromatic dichlorides containing imide structure and 4,4'-dichlorodiphenylsulfone. The copolymers were produced with high yield and moderate to high inherent viscosities of 0.52-1.13 dL/g. Wide-angle X-ray diffractograms revealed that the polymers were amorphous. Most of the polymers exhibited good solubility and could be readily dissolved in various solvents such as N-methyl-2-pyrrolidinone(NMP) and N,N-dimethylacetamide (DMAc). These polysulfone-imides had glass-transition temperatures between 317 and 345 degreesC and 10% weight loss temperatures in the range of 450476 degreesC in nitrogen atmosphere. The tough polymer films, obtained by casting from cresol solution, had a tensile strength range of 21 158 MPa and a tensile modulus range of 2.1-3.3 GPa.

The influence of core-shell structured modifiers on the toughness of poly (vinyl chloride)

The core-shell structured grafted copolymer particles of polybutadiene grafted polymethyl methacrylate (PB-g-PMMA, MB) were prepared by emulsion polymerization. The MB particles were used to modify poly (vinyl chloride) (PVC) by melt blending. The mechanical properties of the PVC blends were investigated. The micro-morphology of the PVC blends was observed by scanning electron microscopy (SEM). The results indicated that the samples with the best impact strength could be obtained when the core-shell weight ratio of PB to PMMA is lower than 93:7, the mechanical properties correlated well with SEM morphologies, the addition of modifier with the ratio core to shell of 93:7 could reduce the domain size of the dispersed phase. Furthermore, the compatibility and properties of the blends were greatly enhanced and improved. The modifier particles could be well dispersed in the PVC matrix.

Study on crystalline morphology of poly(L-lactide)-poly(ethylene glycol) diblock copolymer

Crystallization behavior, structural development and morphology evolution in a series of diblock copolymers Of poly(L-lactide)-blockpoly(ethylene glycol) (PLLA-b-PEG) were investigated via differential scanning calorimetry, wide-angle X-ray diffraction, polarized optical microscopy and atomic force microscopy. In these copolymers, both blocks are crystallizable and biocompatible. It was interesting that these PLLA-b-PEG diblock copolymers could form spherulites with banded textures, which was undercooling dependent. Single crystals with an abundance of screw dislocations were also observed via AFM. Such results indicated that these ringed spherulites and single crystals were formed during the crystallization of the PLLA blocks.

Preparation of fully cross-linked CNBR/PP-g-GMA and CNBR/PP/PP-g-GMA thermoplastic elastomers and their morphology, structure and properties

Binary CNBR/PP-g-GMA and ternary CNBR/PP/PP-g-GMA thermoplastic elastomers were prepared by reactive blending carboxy nitrile rubber (CNBR) powder with nanometer dimension and polypropylene functionalized with glycidyl methacrylate (PP-g-GMA). Morphology observation by using an atomic force microscope (AFM) and TEM revealed that the size of CNBR dispersed phase in CNBR/PP-g-GMA binary blends was much smaller than that of the corresponding CNBR/PP binary blends. Thermal behavior of CNBR/PP-g-GMA and CNBR/PP blends was studied by DSC. Comparing with the plain PP-g-GMA, T, of PP-g-GMA in CNBR/PP-g-GMA blends increased about 10degreesC. Both thermodynamic and kinetic effects would influence the crystallization behavior of PP-g-GMA in CNBR/PP-g-GMA blends. At a fixed content of CNBR, the apparent viscosity of the blending system increased with increasing the content of PP-g-GMA. FTIR spectrum verified that the improvement of miscibility of CNBR and PP-g-GMA was originated from the reaction between carboxy end groups of CNBR and epoxy groups of GMA grafted onto PP molecular chains. Comparing with CNBR/PP blends, the tensile strength, stress at 100% strain, and elongation at break of CNBR/PP-g-GMA blends were greatly improved.

White electrolumineseence from a single-polymer system with simultaneous two-color emission: Polyfluorene as the blue host and a 2,1,3-benzothiadiazole derivative as the orange dopant on the main chain

New single-polymer electroluminescent systems containing two individual emission species - polyfluorenes as a blue host and 2,1,3-benzothiadiazole derivative units as an orange dopant on the main chain - have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue(lambda(max) = 421 nm/445 nm) and orange emission (lambda(max) = 564 nm)from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light-emitting diodes (PLEDs) based on the single-polymer systems has been investigated. The introduction of the highly efficient 4,7-bis(4-(N-phenyl-N-(4-methylphenyl)amino)phenyl)-2,1,3-benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single-layer device fabricated in air (indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure-white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m(-2), luminance efficiency of 7.30 cd A(-1), and power efficiency of 3.34 lm W-1 can be obtained.

Blue light-emitting polymer with polyfluorene as the host and highly fluorescent 4-dimethylamino-1,8-naphthalimide as the dopant in the sidechain

The dopant/host concept, which is an efficient approach to enhance the electroluminescence (EL) efficiency and stability for organic light-emitting diodes (OLEDs) devices, has been applied to design efficient and stable blue light-emitting polymers. By covalently attaching 0.2 mol % highly fluorescent 4-dimethylamino-1,8-naphthalimide (DMAN) unit (photoluminescence quantum efficiency: Phi(PL)=0.84) to the pendant chain of polyfluorene, an efficient and colorfast blue light-emitting polymer with a dopant/host system and a molecular dispersion feature was developed. The single-layer device (indium tin oxide/PEDOT/polymer/Ca/Al) exhibited the maximum luminance efficiency of 6.85 cd/A and maximum power efficiency of 5.38 lm/W with the CIE coordinates of (0.15, 0.19). Moreover, no undesired long-wavelength green emission was observed in the EL spectra when the device was thermal annealed in air at 180 degrees C for 1 h before cathode deposition. These significant improvements in both efficiency and color stability are due to the charge trapping and energy transfer from polyfluorene host to highly fluorescent DMAN dopant in the molecular level.

Solvent-induced novel morphologies in diblock copolymer blend thin films

We report the morphology and phase behaviors of blend thin films containing two poly styrene-b-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymers with different blending compositions induced by a selective solvent for the PMMA block, which were studied by transmission electron microscopy (TEM). The neat asymmetric PS-b-PMMA diblock copolymers employed in this study, respectively coded as a(1) and a(2), have similar molecular weights but different volume fractions of PS block (f(PS) = 0.273 and 0.722). Another symmetric PS-b-PMMA diblock copolymer, coded as s, which has a PS block length similar to that of a(1), was also used. For the asymmetric a(1)/a(2) blend thin films, circular multilayered structures were formed. For the asymmetric a(1)/symmetric s blend thin films, inverted phases with PMMA as the dispersed domains were observed, when the weight fraction of s was less than 50%. The origins of the morphology formation in the blend thin films via solvent treatment are discussed. Combined with the theoretical prediction by Birshtein et al. (Polymer 1992, 33, 2750), we interpret the formation of these special microstructures as due to the packing frustration induced by the difference in block lengths and the preferential interactions between the solvent and PMMA block.

Polyimides derived from 3,3 '-bis(N-aminophthalimide)

A novel diamine, 3,3'-bis(N-aminophthalimide) (BAPI), was prepared from 3,3'-bis(N-phenylphthalimide). Its structure was determined via IR, H-1 NMR, N-15 NMR, elemental analysis, and single-crystal X-ray diffraction analysis. A series of homo- and copolyimides were synthesized by a conventional one-step method in p-chlorophenol. The characteristic IR absorption bands of hydrazine-based imide groups were near 1780, 1750, 1350, 1100, and 730 cm(-1). The polymers showed good solubility in polar aprotic solvents and phenols at room temperature. The temperatures of 5% weight loss (T-5%) of the polyimides ranged from 495 to 530 degrees C in air. DMTA analyses indicated that the glass-transition temperatures (Tgs) of the polyimides were in the range 371-432 degrees C. These polymers had cutoff wavelengths between 350 and 400 nm. The polyimide films of 6FDA/BAPI and 4,4'-HQPDA/BAPI were colorless; other films were pale yellow or yellow.

Dewetting and phase behaviors for ultrathin films of polymer blend

Dynamics of dewetting and phase separation in ultrathin films (thickness is ca. one radius of gyration, approximate to 1 R-g) of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) blends on Si substrate has been studied by in situ atomic force microscopy (AFM). In the miscible region, a "spinodal-like" dewetting driven by a composition fluctuation recently predicted by Wensink and Jerome (Langmuir 2002, 18, 413) occurs. In the two-phase region, the dewetting of the whole film is followed by phase separation in the droplets, coupling with the wetting of the substrate by the PMMA extracted by the strong attractive interaction between them.

Stabilization of polymer bilayers by introducing crosslinking at the interface

Bisphenol A solid epoxy serves as an effective reaction compatibilizer to the bisphenol A polycarbonate (PC)/PMMA bilayer systems. Addition of epoxy to the bottom PMMA layer can retard or even prevent the dewetting of PC films by introducing crosslinking between both components at the interface. This is the first investigation of polymer bilayers stabilized by chemical reactions.

White electroluminescence from a poly(N-vinylcarbazole) layer doped with CdSe/CdS core-shell quantum dots

Hybrid organic/inorganic white light-emitting diodes (LEDs) were fabricated of semiconductor polymer poly(N-vinylcarbazole) (PVK) doped with CdSe/CdS core-shell semiconductor quantum dots (QDs). The device, with a structure of indium-tin-oxide (ITO)vertical bar 3,4-polyethylene-dioxythiophene- polystyrene sulfonate (PEDOT:PSS)vertical bar PVK:CdSe/CdS vertical bar Al, emitted a pure white light spanning the whole visible region from 400 to 800 nm. The Commission Internationale del'Eclairage coordinates (CIE) remained at x = 0.33, y = 0.34 at wide applied voltages. The maximum brightness and electroluminescence (EL) efficiency reached 180 cd m(-2) at 19 V and 0.21 cd A(-1) at current density of 2 mA cm(-2), respectively. The realization of the pure white light emission is attributed to the incomplete energy and charge transfer from PVK to CdSe/CdS core-shell QDs.