Effect of calcium zirconate nanofiller on Polyethylene productivity and properties

This work reports the preparation of ordered arrays of gold nanoparticles by sonochemically enhanced borohydride reduction of precursor lithium tetrachloroaurate (LiAuCl₄) incorporated into the core of polymeric micelles formed from amphiphilic copolymers of polystyrene (PS) and poly(ethylene oxide) (PEO). The copolymers were prepared with varying styrene block lengths from a PEO macroinitiator by atom transfer radical polymerization (ATRP). UV/visible spectroscopy was used to confirm the formation of elemental gold. The effect of sonication time on the appearance of the gold nanoparticles was determined and showed that the absorbance first increased as the nanoparticles formed but decreased at longer times, presumably as a result of a degree of agglomeration. Transmission electron microscopy revealed the morphology of the nanocomposites which confirmed that micellar polystyrene-block-polyethylene oxide is an excellent vehicle for the formation of well-defined films containing nanoparticulate gold. However, we report for the first time that care must be taken to optimize the preparation time to obtain the desired particle sizes because this parameter is very sensitive to the duration over which sonication is carried out.     

Frequency assignment problem in satellite communications using differential evolution

Satellite communications technology has a tremendous impact in refining our world. The frequency assignment problem is of a fundamental importance when it comes to providing high-quality transmissions in satellite communication systems. The NP-complete frequency assignment problem in satellite communications involves the rearrangement of frequencies of one set of carriers while keeping the other set fixed in order to minimize the largest and total interference among carriers. In this paper, we present a number of algorithms, based on differential evolution, to solve the frequency assignment problem. We investigate several schemes ranging from adaptive differential evolution to hybrid algorithms in which heuristic is embedded within differential evolution. The effectiveness and robustness of our proposed algorithms is demonstrated through solving a set of benchmark problems and comparing the results with a number of previously proposed techniques that solve the same problem. Experimental results show that our proposed algorithms, in general, and hybrid ones in particular, outperform the existing algorithms both in terms of the quality of the solutions and computational time.     

Preparation method and physical,mechanical, thermal characterization of poly(vinyl alcohol)/poly(acrylic acid) blends

A series of blends of poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) were prepared by solution mixing and casting. Glycerol was used as plasticizer. The blends were characterized for their physicochemical and thermo-mechanical properties. The FTIR results revealed the molecular level interaction between PVA and PAA at all blend ratios. The incorporation of PAA significantly reduced the storage modulus of PVA at a given temperature. PVA gradually lost its crystalline character with the increase of PAA and became fully amorphous when the PAA content in the blend exceeded 50 wt%. The kinetic parameters of the semi-crystalline blends were determined using the Avarami–Erofeev model, which showed excellent fitting with the experimental data from DSC. The loss in crystallinity of PVA also contributed to an increase in swelling of the blend when the PAA content is increased. The morphology study by FE-SEM demonstrated that there is no phase separation among the blend components at all blend ratios.     

Field-oriented test methods to evaluate structural build-up at rest of flowable mortar and concrete

Thixotropy of flowable mortar and concrete is an important property that affects stability and form pressure characteristics. The increase in thixotropy can reduce lateral pressure on formwork systems. On the other hand, low thixotropy or a continuous casting is required to eliminate the formation of weak interface between lifts in multilayer casting. Thixotropy can be assessed by determining the rate of structural build-up at rest, which necessitates the use of simple and robust test methods to be quantified. Five field-oriented test methods that can be used for the determination of structural build-up at rest of mortar and concrete are proposed in this paper in an attempt to select a reliable field-oriented test. This includes the inclined plane (IP), portable vane (PV), undisturbed slump spread (USS), cone penetration (CP), and K-slump test methods. The repeatability of these test methods was determined four times using two concrete-equivalent mortars and two self-consolidating concretes (SCC) of different thixotropy levels. The IP, PV, and USS tests showed relative error (RE) values of 0.5?C37?%. The CP test was successfully used to determine structural build-up of mortar; however, it was difficult to assess the thixotropy of concrete. The K-slump test exhibited a RE, less than 12?% for SCC mixtures with low thixotropy, but up to 76?% for highly thixotropic SCC. Good correlations were established among the various structural build-up indices determined from the proposed test methods and those determined by rheometric tests using various concrete.     

Dynamic Monte Carlo Simulation of Atom‐Transfer Radical Polymerization

Summary: A dynamic Monte Carlo model was developed to simulate atom‐transfer radical polymerization (ATRP). The algorithm used to describe the polymerization includes activation, deactivation, propagation, chain transfer, and termination by combination and disproportionation reactions. Model probabilities are calculated from polymerization kinetic parameters and reactor conditions. The model was used to predict monomer conversion, average molecular weight, polydispersity and the complete molecular weight distribution at any polymerization time or monomer conversion. The model was validated with experimental results for styrene polymerization and compared with simulation results from a mathematical model that uses population balances and the method of moments. The simulations agree well with experimental and theoretical results reported in the literature. We also investigated the control volume size and number of iterations to reduce computation time while keeping an acceptable noise level in the Monte Carlo results.

Comparison of the chain length distribution of polystyrene made with ATRP and conventional free radical (CFR) polymerization at 50% conversion. The initiator to monomer ratios are 1:100 (ATRP left peak), 1:500 (ATRP right peak), and 1:1000 (CFR).     

Influence of hydrolysed lecithin addition on protein adsorption and heat stability of a sterilised coffee cream simulant

Within an overall goal to enhance the stability of coffee cream, the influence of hydrolysed soybean lecithin addition was investigated. To avoid the seasonal variations in milk composition a model system was used containing 5% (w/w) soybean oil and 12% (w/w) skimmed milk powder with and without lecithin addition before a two-step high-pressure homogenisation. Addition of 20% (w/v) caesium chloride enabled a nearly complete recovery of the fat in the cream layer upon centrifugation of casein-stabilised emulsions. From the fat and protein content of this cream layer, it was concluded that lecithin addition did not significantly affect the protein content of the cream layer after emulsion preparation, but significantly reduced the additional milk protein adsorption at the oil/water interface upon sterilisation. The experimental data suggest that the enhanced heat stability of the lecithin-supplemented coffee cream simulant may be explained by the fact that hydrolysed lecithin largely reduces attractive protein–protein interactions during sterilisation.     

Concentration Dependence of Moisture Diffusivity in Aluminum Particle Filled Epoxy Adhesive in Salt Solutions

Moisture and aggressive ion ingress into bonded joints are primary causes of adhesive degradation. In this study, moisture diffusion behavior of aluminum-powder-filled epoxy adhesive was investigated through utilizing fluid immersion tests under complete immersion in salt solutions with varying NaCl concentrations. Aluminum powder is used in the adhesive for the purpose of improvement of its thermal properties, as demanded in a variety of industrial applications. Mass diffusivity for each specimen was determined by two methods, one using the diffusion data at early times (away from the saturation point) and the other using the data at large times (close to the saturation point). The results of the two methods were quite different, indicating that diffusivity is concentration dependent and a constant diffusivity assumption might lead to error in determining moisture diffusivity values in epoxy systems. Qualitatively, however, both methods indicated similar diffusion behavior. According to the results of both methods, the aluminum filler content did not affect the moisture diffusivity in the epoxy adhesive significantly but the effect of salt concentration was significant; the higher the salt content in the test solution, the higher the moisture diffusivity in the adhesive.