Showing papers by "Mingliang Sun published in 2013"

Preparation and electrochemical properties of poly-2,5-dihydroxyaniline/activated carbon composite electrode in organic electrolyte

Abstract: Poly-2,5-dimethoxyaniline coating has been fabricated on active carbon (AC) substrates by cyclic voltammetry (CV) in organic system. The resulted coating is hydrolyzed to produce poly-2,5-dihydroxyaniline (PDHA) to enhance the capacitance of the composite electrode. Scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectra, CV, electrochemical impedance spectroscopy, and galvanostatic charge/discharge test are used to investigate the properties of these electrodes. In organic electrolyte, due to the introduced hydroquinone units, high value of capacitance up to 975 F g−1 of the PDHA/AC has been obtained at a current density of 0.37 A g−1 at a potential window of 0–1.5 V. An asymmetric capacitor has been assembled with the PDHA/AC positive and pure AC negative electrodes, which is able to obtain a specific energy as high as 178 Whkg−1 in the potential range of 0–2.0 V at a current density of 0.93 A g−1. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The structural and optical properties of a single ZnO comb and an individual nail-like tooth

Abstract: A systematic investigation of the light emission properties on a single ZnO microcomb structure and an individual tooth has not been carried out so far. Through a catalyst-free thermal evaporation method, we successfully synthesized large quantities of well-crystallized ZnO comb-like structures on an Si substrate. Each ZnO comb is composed of a ribbon stem and well-aligned nanotooth arrays that are evenly decorated along one side of the stem. A structural characterization reveals that the stem and the nail-like teeth, which grow respectively along the [2-1-10] and the [0001] directions, are single crystalline with a wurtzite (WZ) structure. Cathodoluminescence (CL) measurements over a single ZnO comb and a tooth were conducted to reveal a correlation between the optical properties and structural size. The results indicate an inhomogeneous light emission throughout the entire comb, and the back and tips contribute more towards the near band-edge (NBE) emission and deep level (DL) emissions than the other regions of the comb. We also observed an alteration of the relative intensity of the NBE and the DL emissions along the length of a single tooth. The middle region of the tooth, where it has the smallest diameter, shows a relatively stronger DL emission than the NBE emission. The opposite was observed at the two ends of the tooth where the diameters are larger.

An electrochemically prepared sky-blue light emitting ether functionalized polyfluorene as chemosensor for metal ions

Abstract: Synthesis and electrochemical polymerization of 9,9-bis(2-(2-(2-methoxy ethoxy)ethoxy)ethyl)-fluorene (EO-F) into poly[9,9-bis(2-(2-(2-methoxy ethoxy)ethoxy)ethyl)-fluorene] (EO-PF) films are reported. The boron trifluoride diethyl etherate electrolyte enables facile preparation of EO-PF films at lower potential compared to LiClO4/MeCN and the electrochemical polymerizations are discussed. The EO-PF shows good electrochemical behavior and can be dissolved in solvents such as DMSO and THF. The solubility of EO-PF in THF is 2 mg·mL−1 and the number average molecular weight is 35300 with a polydispersity index of 1.65. The side chains on C9 position of the monomer maintain unchanged after electrooxidation into corresponding polymer. The EO-PF dissolved in THF under 365 nm ultraviolet light is sky blue light emitting with the Commission Internationale de L’Eclairage-CIE coordinates of (0.19, 0.15). The electropolymerized EO-PF is used for the first time in chemosensing metal ions, demonstrating fluorescence quenching for Mn2+ and Fe3+ while fluorescence enhancement for Cr6+ ions.

β-Phase transformation and energy transfer induced photoluminescence modulation of fluorene based coploymer mono-dispersive nanoparticles

Abstract: 9,9-Dioctylfluorene (DOF) copolymer nanoparticles (NPs) aqueous suspensions were prepared by a simple reprecipitation method. The copolymer comprises 99% 9,9-dioctylfluorene (DOF) and 1% 2,3-dimethyl-5,8-dithien-2-yl-quinoxalines (DDQ) in the polymer backbone. Transmission electron microscopy (TEM) images of NPs show mono-dispersive size distribution of 1–3 nm, among the smallest fluorescent polymer NPs reported in literature. Several NPs aqueous suspension samples are prepared by controlling polymer concentrations in the reprecipitation method. The photophysical properties of NPs were studied by UV-vis absorption spectroscopy and photoluminescence (PL) spectroscopy. The UV-vis absorption peaks at 402 and 435 nm indicate formation of the β-phase in the PFO while the 390 nm peak is attributed to the disordered PFO glassy phase. PL spectra of the NPs, as determined by the energy transfer between glassy phase PFO, β-phase PFO and narrow band gap DDQ segments, can be controllably tuned from blue to white by controlling the initial concentration of the copolymer solution.

Furan-Based Narrow-Band-Gap Copolymers for Red Light-Emitting Diodes and Bulk Heterojunction Photovoltaic Cells

Abstract: A series of conjugated copolymers (PFO-DFQ) derived from 2,3-dimethyl-5,8-difuran-2-yl-quinoxalines (DFQ) and 9,9-dioctylfluorene (DOF) were prepared by the palladium-catalyzed Suzuki coupling reaction with molar feed ratios of DFQ around 1%, 5%, 15% 30% and 50% respectively. The obtained polymers were readily soluble in common organic solvents. The absorption spectra of the copolymers ranged from 300 nm to 560 nm, with two absorption peaks at around 390 nm and 480 nm, both in solution and thin film. The photoluminescence (PL) emission peaks were in the region from 465 nm to 611 nm in thin solid films. The electroluminescence (EL) emission peaks were from 550 nm to 712 nm, depending on the DFQ content. Bulk heterojunction photovoltaic cells fabricated from composite films of PFO-DFQ copolymers and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as electron donor and electron acceptor respectively, showed power conversion efficiencies 0.13% with open-circuit voltage (Voc) of 0.60V and short-circuit current density (Jsc) of 0.68 mA/cm2 under AM1.5 solar simulator (100 mW/cm2).