Insights into MWCNTs/polyimide nanocomposites: from synthesis to application as free-standing flexible electrodes in low-cost micro-supercapacitors

In the pursuit to enlarge the library of polyimide materials for energy applications, new polyimide/MWCNTs composite films have been developed by MWCNTs-assisted polycondensation reaction of a hydroxyl and triphenylmethane-containing diamine with benzophenone tetracarboxylic dianhydride targeting to highlight their electrical storage capability as flexible electrodes in micro-supercapacitors (mSCs). The Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance, UV–vis, fluorescence, and Raman spectroscopies were used to demonstrate the evolution of interfacial interactions between MWCNTs and the precursors (diamine monomer and intermediate polyamidic acid) and polyimide matrix that proved to be the origin of MWCNTs homogeneous dispersion. Thus, composite films incorporating 1, 3, 5, and 10 w.t.% MWCNTs were obtained and thoroughly investigated with regard to their morphology, mechanical behavior, thermal stability, and electrical conductivity. The electrochemical performance of these composites was first analyzed in a classical three-electrode cell by cyclic voltammetry and galvanostatic charge-discharge in both aqueous and organic electrolyte systems. By far, the best electrical storage capacity was obtained with the composite polyimide film containing 10% MWCNTs that was further used as both active material and current collector in a flexible symmetric mSC realized by a straightforward and low-cost procedure. In the attempt to better exploit the advantages of this composite film, it was layered with a graphite-containing paint and tested as an electrode in a flexible mSC, which provided satisfactory results. To our knowledge, this is the first report on the electrical charge storage capability of a polyimide/MWCNTs free-standing film as a flexible electrode in mSCs, which do not require time- and resource-consuming processing steps.     

Highly diastereoselective multicomponent synthesis of polysubstituted 2-hydroxy-2-trifluoromethylpiperidineswith four and five stereogenic centers

The Michael–Mannich cascade cyclization of cyano olefins, ethyl 4,4,4-trifluoro-3-oxobutanoate, aromatic aldehydes and ammonium acetate provides convenient stereoselective formation of ethyl 5,5-dicyano-4,6-diaryl-2-hydroxy-2-(trifluoromethyl)piperidine-3-carboxylates with fourstereogenic centers and dialkyl 4,6-diaryl-5-cyano-2-hydroxy-2-(trifluoromethyl)piperidine-3,5-dicarboxylates with five stereogenic centers. Ammonium acetate plays dual role, acting as a base and as a nitrogen source.     

Rh(III)-Catalyzed One-Step Synthesis of ortho-Alkynylated Perylene Imide Dyes: Optical and Electrochemical Properties of New Derivatives

A one-step Rh-catalyzed site-selective ortho-C−H alkynylation of perylene as well as naphthalene mono- and diimides is reported. A single step regioselective access to ortho-C−H alkynylated derivatives of these ryleneimides not only increases the step economy of the ortho-functionalization on these dyes but also provides a quick access route towards highly functionalized dyes that have potential optoelectronic applications. Increased solubility of tetra(triisopropylsilyl)acetylenyl PDIs in organic solvents greatly enhances their utility for further derivatization.     

Viscoelastic properties of ultrathin polycarbonate films by liquid dewetting

A liquid dewetting method for the determination of the viscoelastic properties of ultrathin polymer films has been extended to study thickness effects on the properties of ultrathin polycarbonate (PC) films. PC films with film thicknesses ranging from 4 to 299 nm were placed on glycerol at temperatures from below the macroscopic glass transition temperature (T_g) to above it with the dewetting responses being monitored. It is found that the isothermal creep results for films of the same thickness, but dewetted at different temperatures can be superposed into one master curve, which is consistent with the fact of PC being a thermorheologically simple material. Furthermore, the results show that the T_g of PC thin films is thickness dependent, but the dependence is weaker than the results for freely standing films and similar to literature data for PC films supported on rigid substrates. It was also found that the rubbery plateau region for the PC films stiffens dramatically, but still less than what has been observed for freely standing polycarbonate films. The rubbery stiffening is discussed in terms of a recently reported model that relates macroscopic segmental dynamics with the stiffening. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1559–1566     

Synthesis and characterization of VO–vanillin complex immobilized on MCM-41 and its facile catalytic application in the sulfoxidation reaction,and synthesis of 2,3-dihydroquinazolin-4(1H)-ones and disulfides in green media

In this work, a vanillin complex is immobilized onto MCM-41 and characterized by FT-IR, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, and BET techniques. This supported Schiff base complex was found to be an efficient and recoverable catalyst for the chemoselective oxidation of sulfides into sulfoxides and thiols into their corresponding disulfides (using hydrogen peroxide as a green oxidant) and also a suitable catalyst for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives in water at 90°C. Using this protocol, we show that a variety of disulfides, sulfoxides, and 2,3-dihydroquinazolin-4(1H)-one derivatives can be synthesized in green conditions. The catalyst can be recovered and recycled for further reactions without appreciable loss of catalytic performance.     

Simultaneous enhancement of the efficiency and stability of organic solar cells using PEDOT:PSS grafted with a PEGME buffer layer

We report a simple processing method to simultaneously improve the efficiency and stability of organic solar cells (OSCs). Poly(4-styrene sulfonate)-doped poly(3,4-ethylenedioxy-thiophene (PEDOT:PSS), widely used as hole transport layer (HTL) in OSCs, tends to accelerate the degradation of devices because of its hygroscopic and acidic properties. In this regard, we have modified PEDOT:PSS to reduce its hygroscopic and acidic properties through a condensation reaction between PEDOT:PSS and poly(ethylene glycol) methyl ether (PEGME) in order to improve the efficiency and stability of OSCs. As a result, the power conversion efficiency (PCE) increased by 21%, from 2.57% up to 3.11%. A better energy level alignment by the reduced work function of the modified PEDOT:PSS with a highest occupied molecular orbital (HOMO) level of poly(3-hexylthiophene-2,5-diyl) (P3HT) is considered the origin of the improved the efficiency. The half-life of OSCs with PEDOT:PSS modified with PEGME buffer layer also increased up to 3.5 times compared to that of devices with pristine PEDOT:PSS buffer layer.     

Deposition,opto-electronic and structural characterization of polymorphous silicon thin films to be applied in a solar cell structure

In this study we analyze the optoelectronic properties and structural characterization of hydrogenated polymorphous silicon thin films as a function of the deposition parameters. The films were grown by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of argon (Ar), hydrogen (H₂) and dichlorosilane (SiH₂Cl₂). High-resolution transmission electron microscopy images and Raman measurements confirmed the existence of very different internal structures (crystalline fractions from 12% to 54%) depending on the growth parameters. Variations of as much as one order of magnitude were observed in both the photoconductivity and effective absorption coefficient between the samples deposited with different dichlorosilane/hydrogen flow rate ratios. The optical and transport properties of these films depend strongly on their structural characteristics, in particular the average size and densities of silicon nanocrystals embedded in the amorphous silicon matrix. From these results we propose an intrinsic polymorphous silicon bandgap grading thin film to be applied in a p–i–n junction solar cell structure. The different parts of the solar cell structure were proposed based on the experimental optoelectronic properties of the pm-Si:H thin films studied in this work.     

Structural and optical properties of CdTe-nanocrystals thin films grown by chemical synthesis

By mans of a chemical synthesis technique stoichiometric CdTe-nanocrystals thin films were prepared on glass substrates at 70 °C. First, Cd(OH)₂ films were deposited on glass substrates, then these films were immersed in a growing solution prepared by dissolution of Te in hydroxymethane sulfinic acid to obtain CdTe. The structural analysis indicates that CdTe thin films have a zinc-blende structure. The average nanocrystal size was 19.4 nm and the thickness of the films 170 nm. The Raman characterization shows the presence of the longitudinal optical mode and their second order mode, which indicates a good crystalline quality. The optical transmittance was less than 5% in the visible region (400–700 nm). The compositional characterization indicates that CdTe films grew with Te excess.