Effect of atom transfer radical polymerization macroinitiator on properties of poly(meth)acrylate-based pentablock type of thermoplastic elastomers

We report well controlled synthesis of novel tri-component [polyisobutylene (PIB), poly(n-butyl acrylate) (PnBA) and poly(methyl methacrylate) (PMMA)] pentablock copolymers (PMMA-b-PnBA-b-PIB-b-PnBA-b-PMMA) by Atom Transfer Radical Polymerization (ATRP) using PIB as a macroinitiator. The surface properties (hydrophobicity, in vitro oxidative stability and cellular interaction) and the bulk properties (phase separation and mechanical properties) of the PIB-containing pentablock copolymers were compared with PMMA-b-PnBA-b-PDMS-b-PnBA-b-PMMA (where PDMS = polydimethylsiloxane) and conventional PMMA-b-PnBA-b-PMMA copolymers synthesized by PDMS and PnBA macroinitiators respectively. It is revealed that type of ATRP macroinitiator (with low glass transition temperature) influences the properties of resultant pentablock copolymers in terms of phase separation, mechanical properties in vitro oxidative stability, cytocompatibility and cell proliferation. Pentablock copolymers synthesized by PIB macroinitiator exhibited superior overall properties compared to pentablock copolymers synthesized by PDMS macroinitiator and neat triblock copolymer synthesized by PnBA macroinitiator. Among the copolymers tested, one with composition PIB:PnBA:PMMA = 10:64:26 (w/w) exhibited best mechanical property, oxidative stability and cytocompatibility. The newly designed PIB-containing pentablock copolymer may be useful where softness, flexibility, processability and biostability/cytocompatibility are desired.     

Tribological and Microstructure Examination of Environmental Waste (Marble Dust) Filled Silicon Bronze Alloy for Wear Resistant Applications

In the present work, marble dust particulate filled silicon bronze (SiBr) alloy composites were fabricated in five different weight percentages (0 wt.%, 2.5 wt.%, 5 wt.%, 7.5 wt.% and 10 wt.% of MD). The main focus of this work was to study their physical and dry sliding wear behavior for rolling elements. The void contents of the particulate filled alloy composites decreased with the increase in marble dust content in the composites up to 7.5 wt.% of marble dust (MD). Similarly, the hardness of the filled composites showed an increasing trend with the increase in hard marble dust content in the alloy composites i.e. 119.25 Hv to 181.5 Hv for 0 wt.% to 7.5 wt.% addition of MD particulates. However, both the void content and hardness showed inferior properties in higher weight percentages of marble dust content. The Taguchi design of experimental (L ₂₅ orthogonal array) technique was implemented to find out the dry specific wear rate of the unfilled and marble dust filled SiBr alloy composites. A scanning electron microscopy (SEM) study was performed to study the wear mechanism of the worn composites along with atomic force microscopic (AFM) analysis to predict the surface profile of the worn particulate filled alloy composites.     

p-Chloroacetophenone: A study of enolization kinetics

The reaction rate of enolization of p-chloroacetophenone has been studied in the presence of amino acids, namely, β-alanine, DL-alanine, L-alanine, and glycine. Maximum reaction rate was observed in the case of β-alanine at 22M concentration. The effects of parameters such as effect of ketone concentration, effect of dielectric constant, effect of catalysts, etc., have been found to exert a significant effect on the reaction rate. The effect of temperature was studied in the range of 313–328?K, and several thermodynamic parameters such as entropy (ΔS^≠), enthalpy (ΔH^≠), energy of activation (ΔE_a), and Gibbs free energy (ΔF^≠) were found to be ?10.32?e.u., 17.87?cal?mol^?1, 19.24?kcal?mol^?1, and 21.20?cal?mol^?1, respectively. The reaction rate increased from 1.9 to 5.8?min^?1 on increasing the percentage of dimethylformamide from 10 to 50% (v/v).     

Nanobiocatalysts for Carbon Capture, Sequestration and Valorisation

Extensive efforts are being made to use biocatalysts for addressing an important millennium development goal i.e. global warming/climate change with recourse to CO₂ capture valorisation and storage (CCVS). New advanced enzyme-based catalysts with significantly improved catalytic properties and stability have been discussed in detail with specific reference to carbonic anhydrase for biomimetic CO₂ sequestration.     

Improved graphitization and electrical conductivity of suspended carbon nanofibers derived from carbon nanotube/polyacrylonitrile composites by directed electrospinning

Single suspended carbon nanofibers on carbon micro-structures were fabricated by directed electrospinning and subsequent pyrolysis at 900 °C of carbon nanotube/polyacrylonitrile (CNT/PAN) composite material. The electrical conductivity of the nanofibers was measured at different weight fractions of CNTs. It was found that the conductivity increased almost two orders of magnitude upon adding 0.5 wt.% CNTs. The correlation between the extent of graphitization and electrical properties of the composite nanofiber was examined by various structural characterization techniques, and the presence of graphitic regions in pyrolyzed CNT/PAN nanofibers was observed that were not present in pure PAN-derived carbon. The influence of fabrication technique on the ordering of carbon sheets in electrospun nanofibers was examined and a templating effect by CNTs that leads to enhanced graphitization is suggested.     

Low percolation threshold in polycarbonate/multiwalled carbon nanotubes nanocomposites through melt blending with poly(butylene terephthalate)

Here, we demonstrate an easy method for the preparation of highly electrically conductive polycarbonate (PC)/multiwalled carbon nanotubes (MWCNTs) nanocomposites in the presence of poly(butylene terephthalate) (PBT). In the presence of MWCNTs, PC and PBT formed a miscible blend, and the MWCNTs in the PC matrix were uniformly and homogeneously dispersed after the melt mixing of the PC and PBT–MWCNT mixture. Finally, when the proportion of the PC and PBT–MWCNT mixture in the blend/MWCNT nanocomposites was changed, an electrical conductivity of 6.87 × 10^?7 S/cm was obtained in the PC/PBT–MWCNT nanocomposites at an MWCNT loading as low as about 0.35 wt %. Transmission electron microscopy revealed a regular and homogeneous dispersion and distribution of the MWCNTs and formed a continuous conductive network pathway of MWCNTs throughout the matrix phase. The storage modulus and thermal stability of the PC were also enhanced by the presence of a small amount of MWCNTs in the nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal deactivation studies of coconut shell pyrolysis

The kinetics of pyrolysis of predried coconut shell sample has been investigated in the temperature range of 523 K to 1023 K in an inert atmosphere by captive sample technique. A kinetic scheme has been proposed where two parallel reactions are given for the production of volatiles and char. The reaction rate constants are found to decrease with high temperatures above 673 K due to chemical and physical changes of the reactant during devolatilisation reaction. Several deactivation models have been proposed to give good agreement with the experimental data.     

Constructing dependable Web services

The majority of today's millions of Web sites offer read-only access to relatively small amounts of infrequently changing information. The load on these sites is usually small, and services can often be hosted as background tasks on general-purpose workstations. Concern for the quality of service (QoS) presented to users at these sites is generally not primary. Conversely, a much smaller number of sites are very popular; they support heavy loads and must meet user expectations regarding QoS to maintain their popularity. We discuss issues involved in supporting high-volume, high-reliability Web services. We begin by surveying the diverse technical challenges and constraints posed in this environment, followed by currently used hardware and network based approaches to meeting the scalability requirements and software-implemented techniques to addressing fault tolerance. However, these approaches do not scale well, so we discuss possible alternatives     

Low-Loss Slow Light Transmission in Photonic Crystal Waveguides Comprising of Liquid Crystal Infiltration

A low loss photonic crystal(PhC) waveguide having rectangular air holes in Si core is proposed having an average group index of 55 in the bandwidth of 1.2 THz.The possible propagation losses due to inefficient coupling are also investigated for proposed structure.It is found that high transmission is obtained for a broad bandwidth from the output of the finally designed heterogeneous waveguide consisting of a slow liquid crystal infiltrated PhC waveguide surrounded by fast PhC waveguides on both sides.     

Effects of slip on unsteady mixed convective flow and heat transfer past a porous stretching surface

This paper investigates the unsteady mixed convective boundary layer flow and heat transfer over a porous stretching vertical surface in presence of slip. Similarity solutions for the transformed governing equations are obtained and the reduced equations are then solved numerically. With increasing values of the unsteadiness parameter, fluid velocity and the temperature are found to decrease in both the presence and absence of slip at the boundary. Fluid velocity decreases due to increasing values of the velocity slip parameter resulting an increase in the temperature field. Skin-friction decreases with the velocity slip parameter whereas it increases with unsteadiness parameter. The rate of heat transfer decreases with the velocity slip parameter while increases with unsteadiness parameter. Same feature is also noticed for thermal slip parameter. Effects of increasing mixed convection parameter on the velocity boundary layer is to increase the velocity field and the temperature decreases in this case.