Photoinitiating capabilities of vinyl polyperoxides and metamorphosis of block-into-block copolymer

This article describes the first comprehensive study on the use of a vinyl polyperoxide, namely poly(styrene peroxide) (PSP), an equimolar alternating copolymer of oxygen and styrene, as a photoinitiator for free radical polymerization of vinyl monomers like styrene. The molecular weight, yield, structure and thermal stability of polystyrene (PS) thus obtained are compared with PS made using a simple peroxide like di-t-butyl peroxide. Interestingly, the PS prepared using PSP contained PSP segments attached to its backbone preferably at the chain ends. This PSP-PS-PSP was further used as a thermal macroinitiator for the preparation of another block copolymer PS-b-PMMA by reacting PSP-PS-PSP with methyl methacrylate (MMA). The mechanism of block copolymerization has been discussed. (C) 1996 John Wiley & Sons, Inc.

Mesoporous MnO2 synthesized by using a tri-block copolymer for electrochemical supercapacitor studies

Mesoporous MnO2 is prepared from KMnO4 by using a tri-block copolymer, namely, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEG-PPG-PEG) as a reducing as well as a structure-directing agent. The as synthesized MnO2 samples are poorly crystalline with mesoporosity having pore diameter between 8 and 40 nm. BET surface area as high as 273 m(2) g(-1) is obtained. By heating, the poorly crystalline MnO2 turns into a well crystalline form at 400 degrees C with nanorod morphology. However, the surface area decreases for the heated samples. Samples of MnO2 prepared by varying the ratio of KMnO4 and the copolymer, and also the heated samples are subjected to electrochemical characterization for supercapacitor studies. High specific capacitance values on mass basis are obtained for the as prepared mesoporous MnO2 samples. (C) 2011 Elsevier Inc. All rights reserved.

Hexagonally ordered arrays of metallic nanodots from thin films of functional block copolymers

We demonstrate a new and simple route to fabricate highly dense arrays of hexagonally close packed inorganic nanodots using functional diblock copolymer (PS-b-P4VP) thin films. The deposition of pre-synthesized inorganic nanoparticles selectively into the P4VP domains of PS-b-P4VP thin films, followed by removal of the polymer, led to highly ordered metallic patterns identical to the order of the starting thin film. Examples of Au, Pt and Pd nanodot arrays are presented. The affinity of the different metal nanoparticles towards P4VP chains is also understood by extending this approach to PS-b-P4VP micellar thin films. The procedure used here is simple, eco-friendly, and compatible with the existing silicon-based technology. Also the method could be applied to various other block copolymer morphologies for generating 1-dimensional (1D) and 2-dimensional (2D) structures. (c) 2010 Elsevier Ltd. All rights reserved.

Co-assembly of a Nafion-Mesoporous Zirconium Phosphate Composite Membrane for PEM Fuel Cells

Synthesis of mesoporous zirconium phosphate (MZP) by co-assembly of a tri-block copolymer, namely pluronic-F127, as a structure-directing agent, and a mixture of zirconium butoxide and phosphorous trichloride as inorganic precursors is reported. MZP with a specific surface area of 84 m(2) g(-1) average pore diameter of about 17 nm and pore volume of 0.35 cm(3) g(-1) has been prepared, and characterised by X-ray diffraction (XRD) and transmission electron microscopy. Nafion-MZP composite membrane is obtained by employing MZP as a surface-functionalised solid-super-acid-proton-conducting medium as well as all inorganic filler with high affinity to absorb water and fast proton-transport across the electrolyte membrane even under low relative humidity (RH) conditions. The composite membranes have been evaluated in H-2/O-2 polymer electrolyte fuel cells (PEFCs) at varying RH values between 18 and 100%; a peak power density of 355 mW cm(-2) at a load current density of 1,100 mA cm(-2) is achieved with the PEFC employing Nafion-MZP composite membrane while operating at optimum temperature (70 degrees C) under 18% RH and ambient pressure. On operating the PEFC employing Nafion-MZP membrane electrolyte with hydrogen and air feeds at ambient pressure and a RH value of 18%, a peak power density of 285 mW cm(-2) at the optimum temperature (60 degrees C) is achieved. In contrast, operating under identical conditions, a peak power density of only similar to 170 mW cm(-2) is achieved with the PEFC employing Nafion-1135 membrane electrolyte.

Photoluminescence spectroscopy and lifetime measurements from self-assembled semiconductor-metal nanoparticle hybrid arrays

We present results of photoluminescence spectroscopy and lifetime measurements on thin film hybrid arrays of semiconductor quantum dots and metal nanoparticles embedded in a block copolymer template. The intensity of emission as well as the measured lifetime would be controlled by varying the volume fraction and location of gold nanoparticles in the matrix. We demonstrate the ability to both enhance and quench the luminescence in the hybrids as compared to the quantum dot array films while simultaneously engineering large reduction in luminescence lifetime with incorporation of gold nanoparticles. (C) 2010 American Institute of Physics. [doi:10.1063/1.3483162].

Controlled photoluminescence from self-assembled semiconductor-metal quantum dot hybrid array films

Thin films of hybrid arrays of cadmium selenide quantum dots and polymer grafted gold nanoparticles have been prepared using a BCP template. Controlling the dispersion and location of the respective nanoparticles allows us to tune the exciton-plasmon interaction in such hybrid arrays and hence control their optical properties. The observed photoluminescence of the hybrid array films is interpreted in terms of the dispersion and location of the gold nanoparticles and quantum dots in the block copolymer matrix.

Rapid sonochemical synthesis of mesoporous MnO2 for supercapacitor applications

Mesoporous MnO2 samples with average pore-size in the range of 2-20 nm are synthesized in sonochemical method from KMnO4 by using a tri-block copolymer, namely, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as a soft template as well as a reducing agent. The MnO2 samples are found to be poorly crystalline. On increasing the amplitude of sonication, a change in the morphology of MnO2 from nanoparticles to nanorods and also change in porosity are observed. A high BET surface area of 245 m(2) g(-1) is achieved for MnO2 sample. The MnO2 samples are subjected to electrochemical capacitance studies by cyclic voltammetry (CV) and galvanostatic charge-discharge cycling in 0.1 M aqueous Ca(NO3)(2) electrolyte. A maximum specific capacitance (SC) of 265 Fg(-1) is obtained for the MnO2 sample synthesized in sonochemical method using an amplitude of 30 mu m. The MnO2 samples also possess good electrochemical stability due to their favourable porous structure and high surface area. (C) 2012 Elsevier B.V. All rights reserved.

Mesoporous MnO2 synthesized by hydrothermal route for electrochemical supercapacitor studies

Poorly crystalline mesoporous MnO2, which is suitable for supercapacitor studies, is synthesized from neutral KMnO4 aqueous solution by hydrothermal route. But it requires a high temperature (180 A degrees C) and also a long reaction time (24 h). Addition of a tri-block copolymer, namely, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123), which is generally used as a soft template for the synthesis of nano-structured porous materials, reduces the hydrothermal temperature to 140 A degrees C and also reaction time to 2 h. When the reaction time is increased, the product morphology changes from nanoparticles to nanorods with a concomitant decrease in BET surface area. Also, the product tends to attain crystallinity. The electrochemical capacitance properties of MnO2 synthesized under varied hydrothermal conditions are studied in 0.1 M Na2SO4 electrolyte. A specific capacitance of 193 F g(-1) is obtained for the mesoporous MnO2 sample consisting of nanoparticle and nanorod mixed morphology synthesized in 6 h using P123 at 140 A degrees C.

Mesoporous bioactive glass and glass-ceramics: Influence of the local structure on in vitro bioactivity

Mesoporous quaternary bioactive glasses and glass-ceramic with alkali-alkaline-earth oxide were successfully synthesized by using non-ionic block copolymer P123 and evaporation induced self assembly (EISA) process followed by acid treatment assisted sal-gel method. As prepared samples has been characterized for the structural, morphological and textural properties with the various analytical techniques. Glass dissolution/ion release rate in simulated body fluid (SBF) was monitored by inductively coupled plasma (ICP) emission spectroscopy, whereas the formation of apatite phase and its crystallization at the glass and glass-ceramic surface was examined by structural, textural and microscopic probes. The influence of alkaline-earth oxide content on the glass structure followed by textural property has become more evident. The pristine glass samples exhibit a wormhole-like mesoporous structure, whereas the glass-ceramic composition is found to be in three different phases, namely crystalline hydroxyapatite, wollastonite and a residual glassy phase as observed in Cerabone (R) A/W. The existence of calcium orthophosphate phase is closely associated with the pore walls comprising nanometric-sized ``inclusions''. The observed high surface area in conjunction with the structural features provides the possible explanation for experimentally observed enhanced bioactivity through the easy access of ions to the fluid. On the other hand, presence of multiple phases in glass-ceramic sample inhibits or delays the kinetics of apatite formation. (C) 2013 Elsevier Inc. All rights reserved.

Anomalous structural and dynamical phase transitions of soft colloidal binary mixtures

We report microscopic structural and dynamical measurements on binary mixtures of homopolymers and polymer grafted nanoparticles at high densities in good solvent. We find strong and unexpected anomalies in the structure and dynamics of these binary mixtures, including appearance of spontaneous orientational alignment, as a function of added homopolymers of different molecular weights. Our experiments point to the possibility of exploiting the phase space in density and homopolymer size, of such hybrid systems, to create new materials with novel structural and physical properties.

Anomalous phase transitions in soft colloid-polymer binary mixtures

We have shown earlier [1] that these PGNPs resemble star polymers or spherical brushes in terms of their morphology in the melt. However, these particles show dynamics in melt which is quite different from other soft colloidal particles. Since most of the work on soft colloidal particles have been performed in solutions we have now explored the phase behavior of the PGNPs in good solvent using microscopic structural and dynamical measurements on binary mixtures of homopolymers and soft colloids consisting of polymer grafted nanoparticles. We observe anomalous structural and dynamical phase transitions of these binary mixtures, including appearance of spontaneous orientational alignment and logarithmic structural relaxations, as a function of added homopolymers of different molecular weights. Our experiments points to the possibility of exploiting the phase space in density and homopolymer size, of such hybrid systems, to create new materials with unique properties.

Swelling behaviour of soil-bentonite mixtures

Studies on the swelling behaviour of mixtures of bentonite clay and nonswelling coarser fractions of different sizes and shapes reveal that observed swelling occurs only after the voids of the nonswelling particles are filled up with swollen clay particles. The magnitude of the swell within the voids, called intervoid swelling is large when the size and percentage of the nonswelling coarser fraction is large. The observable swell, after intervoid swelling, is called primary swelling and follows a rectangular hyperbolic relationship with time. The total swell per gram of the clay decreases with an increase in the size of the nonswelling fraction and with a decrease in the percentage of swelling clay. Time-swell relationships show that swelling continues to occur for a long time after the primary swelling, and this is called secondary swelling.

Solid fuel block as an alternate fuel for cooking and barbecuing: Preliminary result

A large part of the rural people of developing countries use traditional biomass stoves to meet their cooking and heating energy demands. These stoves possess very low thermal efficiency; besides, most of them cannot handle agricultural wastes. Thus, there is a need to develop an alternate cooking contrivance which is simple, efficient and can handle a range of biomass including agricultural wastes. In this reported work, a highly densified solid fuel block using a range of low cost agro residues has been developed to meet the cooking and heating needs. A strategy was adopted to determine the best suitable raw materials, which was optimized in terms of cost and performance. Several experiments were conducted using solid fuel block which was manufactured using various raw materials in different proportions; it was found that fuel block composed of 40% biomass, 40% charcoal powder, 15% binder and 5% oxidizer fulfilled the requirement. Based on this finding, fuel blocks of two different configurations viz. cylindrical shape with single and multi-holes (3, 6, 9 and 13) were constructed and its performance was evaluated. For instance, the 13 hole solid fuel block met the requirement of domestic cooking; the mean thermal power was 1.6 kWth with a burn time of 1.5 h. Furthermore, the maximum thermal efficiency recorded for this particular design was 58%. Whereas, the power level of single hole solid fuel block was found to be lower but adequate for barbecue cooking application.

Index properties of illite-bentonite mixtures in electrolyte solutions

Bentonite, commonly used for liner constructions in waste containment systems, possesses many limitations. Illite or illite containing bentonite has been proposed as an alternative material for liner construction. Their properties in different types of pore fluids are important to assess the long-term performance of the liner. Further, the illite-bentonite interaction occurs and changes their properties. The effect of these interactions is known when the pore fluid is only water. How their properties are modified in electrolyte solutions has been brought out in this paper. The index properties have been studied since they give an indication of their engineering properties. Due to reduction in the thickness of the diffused double layer and consequent particle aggregation in bentonite, the effect of clay-clay interaction reduces in electrolyte solutions. In electrolyte solutions, the liquid limit, the plasticity index, and free swell index of bentonite are lower than illite. The plasticity index of bentonite is further reduced in KCI solution. Clays with a higher plasticity index perform better to retain pollutants and reduce permeability. Hence, the presence of both illite and bentonite ensures better performance of the liner in different fluids.

Electron Mean Energy, Secondary Ionization Coefficients And (E/P)Crit In Binary-Mixtures Of Sf6-N2 And Ccl2f2-N2

Measurements of the ratio of diffusion coefficient to mobility (D/ mu ) of electrons in SF6-N2 and CCl2F2-N2 mixtures over the range 80mixtures and 5.12 for CCl2F2 mixtures. In the present study, it has been possible to show that beta is indeed to a factor of synergism. Estimated gamma values (secondary ionisation coefficients) did not show any significant variation with F for F<50.