Synthesis and characterization of novel photoactive polyamide derived from substituted fluorene by copper (I) catalyst

A novel polyamide has been successfully prepared through the reaction of 2,7‐dibromo‐9,9‐dioctylfluorene with 2,5‐dipiperazinedione in the presence of CuI, N,N′‐dimethylethylene diamine (DMEDA) and K₂CO₃ as base mixture and as catalyst. The structures of the monomer and the resulting model compound, as well as the structure, solution viscosity, solubility, molecular weights, thermal behavior, thermal stability, and light absorption and emission spectra of the resulting polyamide were characterized by means of FTIR, elemental analysis, ¹H‐NMR, ¹³C‐NMR, DSC, TGA, GPC and UV–visible absorption, and fluorescence emission spectrophotometers. The polyamide possesses excellent solubility in organic solvents such as tetrahydrofuran (THF), N‐methyl‐2‐pyrrolidone (NMP), N,N‐dimethylacetamide (DMAc), N,N‐dimethylformamide (DMF), ethylacetate, acetone, ethanol, pyridine, chloroform, and toluene at room temperature. The polyamide had inherent viscosity of 0.65 dL/g, and molecular weights of M_n= 4.25 × 10⁴ and M_w= 5.99 × 10⁴ g/mol. The polyamide had glass transition temperature (T_g) of 138°C, and 10% weight loss at 350°C in nitrogen. The polyamide showed strong UV absorption and blue emission in solution and in solid state. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Experimental investigation of turbulent heat transfer and flow characteristics of SiO2/water nanofluid within helically corrugated tubes

Experiments were conducted to investigate the effect of nanofluid on turbulent heat transfer and pressure drop inside concentric tubes. Water and SiO₂ with mean diameter of 30 nm were chosen as base fluid and nano-particles, respectively. Experiments were performed for plain tube and five roughened tube with various heights and pitches of corrugations. Results show that adding the nano-particles in tube with high height and small pitch of corrugations augments the heat transfer significantly with negligible pressure drop penalty. It is discussed on relative Nusselt number and thermal performance of heat exchanger.     

Microstructure and castability of lead‐free silicon brass alloys

Development of lead free brass alloys is an important subject due to the environmental demands and new regulations and standards that restrict lead contamination to decrease the toxicity. Pb‐free Si brasses are interesting alloys for this application, due to economical aspects and promising properties. In this work four Pb‐free brasses prepared with 1, 2, 3 and 4 wt% Si, based on Cu60/Zn40 alloy, are characterized. Their microstructure is examined and phases formed are identified. Castabilty indicated by fluidity and porosity is studied and correlated with the phases formed and their volume fraction.     

Year-round comparative study of three types of solar desalination units

Simulations of three different types of solar stills were performed to compare their productivity using typical meteorological year data of a remote location (Marmul) in Oman. These are the regenerative, conventional, and still with double-glass-cover cooling. Several system parameters were also investigated with respect to their effect on the productivity, namely, water with and without dye in the lower basin, basin heat loss coefficient, mass of water in the basins, and mass flow rate into the double-glass cover. The regenerative still had more than 70% higher productivity in comparison with the conventional still. If the stills are appropriately insulated, the conventional still had higher productivity than the double-glass-cover cooling. Increasing the water in the lower basin moderately reduced the productivity of the three stills. Increasing the water film thickness on top of the lower glass had no effect on the productivity of the still with double-glass-cover cooling, but slightly lowered the productivity of the regenerative still.     

Synthesis and characterization of novel aromatic polyamides bearing CF3, quinoxaline‐anthraquinone pendants: Study of photophysical and electrochemical properties by using nanocomposite electrode paste

A new aromatic diamine, 2,3‐bis(4‐(4‐amino‐2‐(trifluoromethyl) phenoxy)phenyl)naphtho[2,3‐f]quinoxaline‐7,12‐dione, was synthesized and fully characterized by using FTIR, ¹H and ¹³C NMR, DEPT technique, and elemental analysis. A series of novel fluorescent anthraquinone‐quinoxaline containing polyamides (PAs) with inherent viscosities of 0.39–0.62 dL/g was prepared by direct polycondensation of the diamine with various dicarboxylic acids. These PAs were readily soluble in many polar aprotic organic solvents and could be solution‐cast into tough and flexible films. The PAs exhibited glass transition temperatures (T_g)s between 230 and 323°C, and 10% weight loss temperatures in the range of 362–433°C in N₂. All of the PAs have fluorescence emission in solution and in solid state with maxima around 452–510 nm and with the quantum yields in the range of 6–17%. Also, cyclic voltammetry (CV) method was used to study the electrochemical oxidation behavior of these polymers at the surface of a modified multiwalled carbon nanotube (MWCNT)s glassy electrode. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Oxidative coupling of various aromatic phenols and anilines in water using a laccase from Trametes villosa and insights into the ‘PEG effect’

BACKGROUND: Studies with peroxidases (EC 1.11.1.7) have demonstrated extended lifetimes for conversion of phenolics into insoluble polymers in the presence of polyethylene glycol (PEG). Yet the mechanism of this ‘PEG effect’ has eluded investigators. The effectiveness of a laccase (EC 1.10.3.2) with PEGs of various average molar masses on the conversion of phenol, o‐, m‐, p‐cresols, aniline, o‐, m‐, and p‐toluidines was investigated. This structure‐activity comparison, with and without the additive, could provide further insight into the ‘PEG effect’. RESULTS: The ‘PEG effect’ was observed only with the cresols and only with PEGs of average molar mass ≥ 1450. Other additives capable of H‐bonding, such as polyvinylpyrrolidone, had similar results. When a ‘PEG effect’ was observed there was a linear relationship between the amount of additive used and the amount incorporated into the precipitate, suggesting a strong interaction between products and PEG, which was confirmed by nuclear magnetic resonance spectroscopy. Optimum pH was not affected by the quantity or molar mass of the PEG added. CONCLUSION: PEG only enhances the laccase‐catalyzed oxidative coupling of certain substrates implying a product‐additive relationship that may be related to the functionality and substituent positioning of the substrate. Copyright © 2011 Society of Chemical Industry     

Textile applications of photochromic dyes. Part 5: application of commercial photochromic dyes to polyester fabric by a solvent‐based dyeing method

A series of commercial photochromic dyes was applied to polyester by a solvent dyeing process followed by thermal fixation using dichloromethane as the solvent. The process was optimised in terms of solvent/fabric ratio, dye concentration and the conditions of thermal fixation. The dyed fabrics showed reversible photochromism, developing colour on ultraviolet exposure and fading after removal of the ultraviolet source. The degree of photocoloration, background colours, fading characteristics, fatigue resistance and storage stability of the dyes were evaluated and comparisons made with the outcomes of a traditional aqueous disperse dyeing method. A study of the visible spectra of concentrated solutions of the dyes in a range of solvents provided evidence for the origin of the permanent background colours on the fabric when applied from solvents. Relationships were established between the magnitudes of the visible absorption in solution and the background colours developed, in relation to the nature of the solvents. The results suggest that toluene and ethyl acetate may offer certain advantages as solvents for the application of these dyes.     

Characteristics of a high brightness gaseous field ion source employing tungsten-carbon doped NiAl needles

We report on the characterization of a high brightness gaseous field ion source using an emitter made of a NiAl needle containing tiny spherical tungsten-carbon precipitates. By field evaporation of such a multiphase alloy, a surface protrusion is formed out of a precipitate, which can act as a small source size field ion emitter. The emission current-voltage characteristics of this emitter were recorded for a variety of parameters. The results obtained suggest that its application as a stable ion source is possible even on long term operation.     

Peak-Average-Power Ratio Techniques for 5G Waveforms Using D-SLM and D-PTS

Multicarrier Waveform (MCW) has several advantages and plays a very important role in cellular systems. Fifth generation (5G) MCW such as Non-Orthogonal Multiple Access (NOMA) and Filter Bank Multicarrier (FBMC) are thought to be important in 5G implementation. High Peak to Average Power Ratio (PAPR) is seen as a serious concern in MCW since it reduces the efficiency of amplifier use in the user devices. The paper presents a novel Divergence Selective Mapping (DSLM) and Divergence Partial Transmission Sequence (D-PTS) for 5G waveforms. It is seen that the proposed D-SLM and PTS lower PAPR with low computational complexity. The work highlighted a combination of multi-data block partial transmit schemes along with tone reservation. In this, an overlapping factor is used to determine the number of data blocks for every group. Here, considering only those data blocks that have minimum signal power, the use of DSLM and DPTS are required to eliminate the segment’s peaks. Simulation results reveal that the suggested hybrid technique proves to be better than the conventional PTS scheme. Furthermore, the power saving performance of FBMC and NOMA is compared with the Orthogonal Frequency Division Multiplexing (OFDM) waveform.