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Besides the classical atom/ion/molecule based mechanism, nonclassical crystallization provides a nanoparticle-based crystallization pathway toward single crystals. However, there is a lack of experimentally established strategies for engineering a range of crystalline microstructures from common nanoparticles by nonclassical crystallization. We demonstrate that a commercial random copolymer polyelectrolyte poly(4-styrene sulfonate)-co-(maleic acid) (PSS-co-MA) considerably guides crystallization of calcium carbonate (CC) with a high versatility. The bioinspired nonclassical crystallization protocol yielded a series of calcite microstructures. Calcite single crystals obtained at low supersaturation show a pseudo-dodecahedral shape with curved faces, whereas increasing supersaturation generated calcite mesocrystals with pseudo-octahedral shapes and scalloped surfaces. Further increase of supersaturation induced the formation of polycrystalline multilayered and hollow spheres. In the initial growth stage of all these microstructures, amorphous CC nanoparticles formed as the early product. Remarkably, microparticles with minimal primitive (P)-surface were captured as the prominent intermediate indicative of liquidlike behavior. Moreover, nanogranular structures exist broadly in the as-synthesized crystals. These results demonstrate that the polyelectrolyte can effectively stabilize the amorphous CC nanoparticle precursors, impart control over the evolution from amorphous precursors via a liquid aggregate through P-surface intermediates to the final crystals, and thus allow the morphogenesis. Simple variation of calcium and polyeletrolyte concentrations enables a systematic control over the size and morphology of particles among pseudo-dodecahedra, pseudo-octahedra, multilayered spheres, and hollow spheres, which are expressed in a morphology diagram. A unifying nanoparticle aggregation formation mechanism was suggested to explain the morphogenesis by the combination of nonclassical crystallization and surface area minimization principles.
ACS Nano 2009 Jul 28
PMID:Polyelectrolyte-directed nanoparticle aggregation: systematic morphogenesis of calcium carbonate by nonclassical crystallization. 1957 17

In this work, we reported high performance OLED devices with transparent and conductive carbon nanotube anodes after modification. The modifications include IMRE proprietary PEDOT:PSS composite top coating (PS(C)), concentrated HNO(3) acid soaking, and polymer encapsulation. For PS(C)-modified nanotube thin film anode, we achieved maximum luminescence of approximately 9000 cd/m(2), close to ITO-based OLED device performance, and high efficiency of approximately 10 cd/A, similar with ITO-based OLED device. The performance is approximately 30 to 450 times better than that achieved for OLED devices using CNT anodes by others. In addition, we also investigate the mechanical property, work function, sheet resistance, and surface morphology of modified carbon nanotube thin-film anodes.
ACS Nano 2009 Aug 25
PMID:Surface-modified nanotube anodes for high performance organic light-emitting diode. 1958 7

The thermoelectric properties of carbon nanotube (CNT)-filled polymer composites can be enhanced by modifying junctions between CNTs using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), yielding high electrical conductivities (up to approximately 40000 S/m) without significantly altering thermopower (or Seebeck coefficient). This is because PEDOT:PSS particles are decorated on the surface of CNTs, electrically connecting junctions between CNTs. On the other hand, thermal transport remains comparable to typical polymeric materials due to the dissimilar bonding and vibrational spectra between CNT and PEDOT:PSS. This behavior is very different from that of typical semiconductors whose thermoelectric properties are strongly correlated. The decoupled thermoelectric properties, which is ideal for developing better thermoelectric materials, are believed to be due to thermally disconnected and electrically connected contact junctions between CNTs. Carrier transport at the junction is found to be strongly dependent on the type and concentration of stabilizers. The crucial role of stabilizers was revealed by characterizing transport characteristics of composites synthesized by electrically conducting PEDOT:PSS and insulating gum Arabic (GA) with 1:1-1:4 weight ratios of CNT to stabilizers. The influence of composite synthesis temperature and CNT-type and concentration on thermoelectric properties has also been studied. Single-walled (SW) CNT-filled composites dried at room temperature followed by 80 degrees C exhibited the best thermoelectric performance in this study. The highest thermoelectric figure of merit (ZT) in this study is estimated to be approximately 0.02 at room temperature, which is at least one order of magnitude higher than most polymers and higher than that of bulk Si. Further studies with various polymers and nanoparticles with high thermoelectric performance may result in economical, lightweight, and efficient polymer thermoelectric materials.
ACS Nano 2010 Jan 26
PMID:Improved thermoelectric behavior of nanotube-filled polymer composites with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate). 2004 30

We propose a new material for high power and high density supercapacitors with excellent cycle stability. Graphite oxide (PSS-GO) intercalated with poly(sodium 4-styrensulfonate) showed high performance of electric double layer capacitance (EDLC) compared to that of the pristine graphite oxide. Specific capacitance of the PSS-GO reached 190 F/g, and the energy density was much improved to 38 Wh/kg with a power density of 61 W/kg. Cycle test showed that the specific capacitance decreased by only 12% after 14860 cycles, providing excellent cyclic stability. The high EDLC performance of PSS-GO composite was attributed to the wide interlayer distance and simple pore structures accommodating fast ion kinetics.
ACS Nano 2010 Feb 23
PMID:Enhanced electric double layer capacitance of graphite oxide intercalated by poly(sodium 4-styrensulfonate) with high cycle stability. 2009 69

The percolation threshold of single-walled carbon nanotubes (SWCNTs) introduced into polystyrene (PS) via a latex-based route has been reduced by using conductive surfactants. The use of the conductive polymeric latex, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), in conjunction with SWCNTs leads to conductive composites with loadings of both constituents below their own individual percolation thresholds. The high concentration of PEDOT:PSS in the final composites raises the concern that the composite conductivity is a result of the presence of the PEDOT:PSS alone. To elucidate the cooperative nature of the two conductive components, the contribution of the SWCNTs to the overall composite conductivity is investigated by replacing the original high-quality SWCNTs with SWCNTs of a lower quality. Percolation thresholds recorded for systems utilizing the lower quality tubes stabilized with nonconductive surfactants were over 2 wt % SWCNTs (4 times that of previously reported systems). The introduction of PEDOT:PSS was, once again, found to lower the percolation threshold (to 0.3 wt %) and to increase the ultimate conductivity up to the level of a pure PEDOT:PSS/PS blend. In the PS/PEDOT:PSS-SWCNT systems, the role of the SWCNT network is proposed to be limited to the formation of a template or scaffold on which a (more or less) continuous PEDOT:PSS layer deposits. The ultimate conductivity is therefore determined by the PEDOT:PSS alone.
ACS Nano 2010 Apr 27
PMID:Probing the cooperative nature of the conductive components in polystyrene/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)-single-walled carbon nanotube composites. 2022 76

The generation and characterization of a robust thienylsilane molecular layer on indium tin oxide substrates was investigated. The molecular layer was found to reduce the oxidation potential required for the electrochemical polymerization of 3,4-ethylenedioxythiophene. The resulting electrochemically prepared poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) (ePEDOT:PSS) films were found to be more uniform in coverage with lower roughness and higher conductivity than analogous films fabricated with bare ITO. A relative improvement in the efficiency of 2,5-diyl-poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) bulk heterojunction solar cells was observed when devices were formed on thienylsilane-modified ITO electrodes, rather than unmodified ITO control electrodes.
ACS Appl Mater Interfaces 2009 Feb
PMID:Thienylsilane-modified indium tin oxide as an anodic interface in polymer/fullerene solar cells. 2035 15

An inverted-type organic bulk-heterojunction solar cell inserting zinc oxide (ZnO) as an electron collection electrode, fluorine-doped tin oxide (FTO)/ZnO/[6,6]-phenyl-C(61)-butyric acid methyl ester:regioregular poly(3-hexylthiophene) (PCBM:P3HT)/poly(3,4-ethylenedioxylenethiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS)/Au, was fabricated in air and characterized by an alternating current impedance spectroscopy (IS). In the IS measurement, we observed reproducibly the electric resistance and capacitance components originating from ZnO and organic active layers, and we found that the depletion layer functioning to take out the photocurrent to the external circuit was formed in both the ZnO and PCBM:P3HT layers at the ZnO/PCBM:P3HT interface. In this letter, we propose that this IS measurement is effective for evaluating the electric properties of several layers with capacitance components in organic thin-film solar cells.
ACS Appl Mater Interfaces 2009 Oct
PMID:Characterization of inverted-type organic solar cells with a ZnO layer as the electron collection electrode by ac impedance spectroscopy. 2035 41

We fabricated photopatternable and conductive polymer/multiwalled carbon nanotube (MWNT) composites by dispersing MWNTs with poly(4-styrenesulfonic acid) (PSS) and poly(acrylic acid) (PAA) in water. PAA enables photo-cross-linking in the composite by adding ammonium dichromate, and PSS assists the dispersion of MWNTs in the composites, leading to higher conductivity. Composite films of PAA/PSS-MWNTs were characterized by conductivities of 1.4-210 S/cm and a work function of 4.46 eV, which could be increased to 4.76 eV during UV photo-cross-linking. By using PAA/PSS-MWNT composites as source/drain electrodes, 6,13-bis(triisopropylsilylethynyl)pentacene field-effect transistors (FET) exhibited a field-effect mobility of 0.101 +/- 0.034 cm(2)/(V s), which is 9 times higher than that of FETs fabricated with gold as source/drain electrodes (0.012 +/- 0.003 cm(2)/(V s)).
ACS Appl Mater Interfaces 2009 Oct
PMID:Photopatternable source/drain electrodes using multiwalled carbon nanotube/polymer nanocomposites for organic field-effect transistors. 2035 70

Metal-mediated coordination polyelectrolyte multilayers with a bisterpyridine ligand (Bisterpy) have been self-assembled at air-water interfaces via coordination reactions of the bidentate ligand Bisterpy with inorganic salts in the subphases. To avoid dissolution of the viologen-like coordination polyelectrolyte monolayers, anionic poly(styrenesulfonic acid-o-maleic) (PSS) acid was added in the subphases as a supporting layer. The average molecular area of the ligand Bisterpy could reach 1.2-1.5 nm(2) on the surfaces of the subphases containing mixtures of inorganic salts (M) and PSS, although the ligand was unable to form a stable monolayer on the pure water surface. The Langmuir-Blodgett (LB) method was used to deposit the Bisterpy/PSS and M-Bisterpy/PSS hybrid multilayers on the substrate surfaces, which were characterized by using absorption and fluorescence spectroscopy as well as electrochemical analysis. Quasi-reversible redox waves were recorded and centered at about -0.68 and -0.92 V (vs Ag/AgCl), respectively, corresponding to the two-electron process of the ligand, Bisterpy2+ <--> Bisterpy(*+) <--> Bisterpy(0), which were slightly shifted to lower potentials in the LB films of metal-mediated coordination polymers. The film compositions were determined by using X-ray photoelectron spectroscopy. The as-prepared LB films showed strong stability and good electrochromic response upon the applied potential of -1.1 V vs Ag/AgCl and thus could act as potential materials in the development of redox-based molecular switches and display devices.
ACS Appl Mater Interfaces 2009 Jun
PMID:Interfacial self-assembly of metal-mediated viologen-like coordination polyelectrolyte hybrids of the bisterpyridine ligand and their optical, electrochemical, and electrochromic properties. 2035 20

Effective cell design variables having a large impact on the fill factor (FF) of organic photovoltaic cells (OPVCs) were systematically identified using a general device structure of ITO/PEDOT:PSS/P3HT + PCBM/LiF/Al. The results show that the characteristic properties of the organic layer, such as morphology and thickness, the regioregularity of the conjugated polymer, and the two interfaces between the electrodes and the blend layer have a large influence on the FF by affecting the series resistance (R(s)) and the shunt resistance (R(sh)). The systematic investigation described in this contribution provides a comprehensive understanding of the correlation between the device variables and R(s) and R(sh) and a way to control FF, which is critically important to achieving a high-performance OPVC.
ACS Appl Mater Interfaces 2009 Jun
PMID:Effective variables to control the fill factor of organic photovoltaic cells. 2035 22


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