Solid-state dye-sensitized solar cells based on ZnO nanoparticle and nanorod array hybrid photoanodes

The effect of ZnO photoanode morphology on the performance of solid-state dye-sensitized solar cells (DSSCs) is reported. Four different structures of dye-loaded ZnO layers have been fabricated in conjunction with poly(3-hexylthiophene). A significant improvement in device efficiency with ZnO nanorod arrays as photoanodes has been achieved by filling the interstitial voids of the nanorod arrays with ZnO nanoparticles. The overall power conversion efficiency increases from 0.13% for a nanorod-only device to 0.34% for a device with combined nanoparticles and nanorod arrays. The higher device efficiency in solid-state DSSCs with hybrid nanorod/nanoparticle photoanodes is originated from both large surface area provided by nanoparticles for dye adsorption and efficient charge transport provided by the nanorod arrays to reduce the recombinations of photogenerated carriers

Toughening mechanisms in a multi-phase alloy of nylon 6,6/polyphenylene oxide

Toughening mechanisms in a nylon 6,6/polyphenylene oxide (PA/PPO) alloy are studied. This alloy consists of well dispersed PPO particles (containing an elastomeric phase) in a PA matrix. Both crazing and shear yielding mechanisms are found to be sequentially operative in this alloy. When a crack propagates in the material, a crazed zone forms ahead of the crack tip. This crazed zone then transforms into a shear yielded zone as the crack propagates through it. The crazes inside the original crazed zone are closed or distorted by the shear yielding process. In the transformed region, the shear yielded material is oriented at different angles as the crack propagates. These findings are consistent with the notion that hydrostatic tension has to be dissipated in order for the remaining deviatoric stress to reach the critical value for yielding. It is possible to partially attribute the increase in toughness to both crack blunting and zone shielding mechanisms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44694/1/10853_2004_Article_BF00553180.pd

Deformation behaviour of a polycarbonate plate with a circular hole: finite elements model and experimental observations

The unique and complex deformation behaviour of ductile polymers has received considerable attention in the polymer field. Much research has been conducted to study the yielding and post-yielding behaviour of polymers. In the case of two-phase polymer alloy systems, however, the deformation behaviour near the interface between the two phases has rarely been studied. The present paper describes the use of two-dimensional (2-D) finite element methods (FEM) to simulate the deformation behaviour of a polycarbonate plate with a circular hole as a special case of two-phase polymer alloys. The FEM model involves consideration of the non-linear behaviour of the material. The FEM simulation results reveal that the maximum octahedral shear stress ([tau]oct) shifts from the equatorial region toward the 45[deg] region at the interface between the hole and the ductile matrix phase. How far the maximum [tau]oct shifts along the interface depends on the stress concentration near the interface and the strain increment between the yield and the strain hardening regions. The shift in maximum [tau]oct is due to the yield and strain softening character of ductile polymers. These results are verified by polycarbonate/hole (PC/hole) experiments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27172/1/0000169.pd

Stable smectic phase in suspensions of polydisperse colloidal platelets with identical thickness

6 pages, 6 figures.-- PACS nrs.: 61.30.Eb, 64.70.M−, 81.16.Dn, 82.70.Dd.-- ArXiv pre-print available at: http://arxiv.org/abs/0909.2625We report the nematic and smectic ordering in an aqueous suspension of monolayer α-Zirconium phosphate platelets possessing a high polydispersity in diameter but uniform thickness. We observe an isotropic-nematic transition as the platelet volume fraction increases, followed by the formation of a smectic, an elusive phase that has been rarely seen in discotic liquid crystals. The smectic phase is characterized by x-ray diffraction high-resolution transmission electron microscopy, and optical microscopy. The phase equilibria in this highly polydisperse suspension are rationalized in terms of a theoretical approach based on density-functional theory.Acknowledgment is made to the donors of ACS Petroleum Research Fund (Grant No. 45303-G7) and to the Dow Chemical Co. This work has been partly financed by start-up funds from Texas Engineering Experimental Station and Texas A&M University, by Grants No. NANOFLUID, No. MOSAICO, and No. S-0505/ESP-0299 from Comunidad Autónoma de Madrid (Spain), and Grants No. FIS2005-05243-C02-01, No. FIS2007-65869-C03-01, No. FIS2008-05865-C02-02, and No. FIS2007-65869-C03-C01 from Ministerio de Educación y Ciencia (Spain).Publicad

Interfacial adhesion and toughening mechanisms in an alloy of polycarbonate/polyethylene

Interfacial adhesion and toughening mechanisms in an alloy of polycarbonate/polyethylene (PC/PE) are investigated using transmission electron microscopy. In contrast to the general speculation, it is found that the PE particles strongly adhere to the PC matrix. The toughening mechanisms in the PC/PE blend are found to be debonding of the PC/PE interface, which relieves the triaxial tension in front of the crack tip, followed by shear banding of the PC matrix. Possible causes for such an unexpected strong interfacial adhesion between PC and PE are discussed. Also, the importance of the cavitational strength of the toughener phase in toughness optimization is addressed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30378/1/0000780.pd

Porous SnO2-Cu x O nanocomposite thin film on carbon nanotubes as electrodes for high performance supercapacitors.

Metal oxides are promising materials for supercapacitors due to their high theoretical capacitance. However, their poor electrical conductivity is a major challenge. Hybridization with conductive nanostructured carbon-based materials such as carbon nanotubes (CNTs) has been proposed to improve the conductivity and increase the surface area. In this work, CNTs are used as a template for synthesizing porous thin films of SnO2-CuO-Cu2O (SnO2-Cu x O) via an electroless deposition technique. Tin, with its high wettability and electrical conductivity, acts as an intermediate layer between copper and the CNTs and provides a strong interaction between them. We also observed that by controlling the interfacial characteristics of CNTs and varying the composition of the electroless bath, the SnO2-Cu x O thin film morphology can be easily manipulated. Electrochemical characterizations show that CNT/SnO2-Cu x O nanocomposite possesses pseudocapacitive behavior that reaches a specific capacitance of 662 F g-1 and the retention is 94% after 5000 cycles, which outperforms any known copper and tin-based supercapacitors in the literature. This excellent performance is mainly attributed to high specific surface area, small particle size, the synergistic effect of Sn, and conductivity improvement by using CNTs. The combination of CNTs and metal oxides holds promise for supercapacitors with improved performance.Lloyds Register Foundation Londo

Effect of color on scratch and mar visibility of polymers

Polymer scratch mechanics has been widely studied. However, the physics behind scratch visibility is still not well understood. Scratch deformation mechanisms certainly affect visibility but also other material properties, such as roughness, color or gloss. This work relates to methods to quantitatively evaluate the effect of sample color on polymer scratch and mar induced visibility, aiming at linking scratch behavior with the underlying physics. A custom-built black box was utilized for the analysis of samples possessing different colors and surface finishing. Automatic image analysis was performed through a commercial software to quantify the onset of visibility in terms of a critical load above which the scratch becomes visible. Trained surveyors visually quantified said critical load. White color was shown to delay the onset of visibility by reducing the contrast between the damaged and undamaged area. For instance, the critical load for the onset of visibility for a white polycarbonate copolymer was nearly twice the value reported for its black variant. Consistent results were obtained for all tested samples. Similar findings were reported for the mar phenomenon, highlighting how white color can also mask a different type of damage. The usefulness of the present work and some future perspectives are discussed