A molecular simulations study of the miscibility in binary mixtures of polymers and low molecular weight molecules

The miscibility behavior of binary mixtures of polymeric and low molecular weight molecules was studied using a combination of modified Flory-Huggins theory and molecular simulation techniques. Three different atomistic approaches were used to investigate the phase behavior and χ parameters of binary mixtures consisting of polymethyl methacrylate (PMMA) and 4-n-pentyl-4′-cyanobiphenyl (5CB). Binary mixtures of methyl methacrylate monomer/5CB and methyl methacrylate oligomer/5CB were also studied. As a first approach, a fast method that calculates the local interaction between a fragment of the polymer and the organic molecule and then extends it to determine the energy of mixing using an estimated coordination number was used. By using modified coordination numbers, we were able to extend this method to include cases where the polymer segment and the small molecules are slightly dissimilar in size. More detailed studies which take into account bulk effects were also carried out where the cohesive energies of the pure compounds were derived from molecular dynamics simulations and the interaction parameters were determined from the differences in the cohesive energies. The concentration and temperature dependence of the χ parameters was evaluated by calculating the energy of mixing from the differences in the cohesive energy densities of the mixed and demixed systems. The present study provides a detailed understanding of the miscibility of PMMA and 5CB as PMMA polymerizes from its monomer, and the results indicate that although methyl methacrylate and 5CB are completely miscible, 5CB is not miscible in PMMA even in small quantities.     

Selective drying of hygroscopic materials wetted with binary mixtures

ABSTRACT

Drying experiments were carried out in a laboratory apparatus with differently hygroscopic materials wetted with binary mixtures. Composition curves were determined under variation of the drying conditions, the sample thickness, and the drying method. The results obtained are presented and compared with those of non-hygroscopic materials.

In particular, the interactions between moisture and solid when using strongly hygroscopic products influence the composition curve from the very beginning of the drying process, contrary to weakly hygroscopic materials, where the selectivity is controlled by the sorption equilibrium only at the end of the drying process.

A method to calculate the selectivity in knowledge of the binary adsorption equilibrium is given. For this purpose, it is necessary to split the total moisture into a free and a bounded share.     

Equilibrium liquidus temperatures of binary mixtures from differential scanning calorimetry

The measurements of solid-liquid phase diagrams for a binary mixture using a differential scanning calorimeter are revisited in this paper. A new method employing the DSC curves and a theoretical model to detect solid-liquid equilibrium temperature of the initial mixture before freezing is proposed. The liquidus temperatures for different compositions are found to be in good agreement with the available literature data.     

Dynamic characteristics of binary mixtures in a two-jet fluidized bed

Aiming to understand biomass-related pyrolysis and gasification processes, which have received particular interests recently due to increasing concerns over fossil fuels and carbon emissions, this work conducts a detailed experimental study of the fluidization characteristics and jet dynamics of biomass mixtures in a fluidized bed. Both single jet and two jets dynamics are investigated, and a parametric study of the influence of particle properties and operational conditions on the dynamic performance of the bed, especially on the jet penetration depth and jet frequency of the binary mixtures, is conducted. Detailed frame-by-frame image analysis coupled with physical parameters reveals many interesting phenomena, which includes multistage flow pattern development and a stochastic nature of jet dynamics, as well as a strong dependence of the jet penetration depth and jet frequency on the bed materials.     

Artificial Neural Network approach to segregation characteristic of binary homogeneous mixtures in promoted gas-solid fluidized beds

Binary mixtures of size-different dolomites are fluidized in a bed where co-axial promoters are introduced. The segregation characteristic of jetsam particles has been determined for different mixtures in terms of the segregation distance by empirically correlating the results with the various system parameters viz. initial static bed height, height of a layer of particles above the bottom grid, superficial gas velocity and average particle size of the mixture with dimensional analysis for both the un-promoted and the promoted beds. Correlations have also been developed with the above system parameters from an Artificial Neural Network approach. Segregation distances for the promoted and un-promoted beds have been compared. The results through the correlations thus developed with the above system parameters from the ANN-approach and the findings with respect to the dimensional analysis approach have been compared.     

Formation of nanometric hard materials by cold milling

The fabrication of nanosized, single crystal TiC or TiN powders from ilmenite or TiO₂ within a single low temperature stage is reported in this paper. The titaniferous powders were ball milled for 100 h in a laboratory scale mill with magnesium powder and either graphite or nitrogen. The resultant powders were then subjected to an annealing step at 1200°C. Differential thermal analysis and X-ray diffraction showed that the phases formed within the milling step and underwent grain growth on annealing. Acid leaching of the powders selectively removed the unwanted product phases leaving only the hard material. The final particle size and Scherrer XRD crystallite size were similar after annealing, implying that the particles produced were single crystal.     

Development of a multi-fluid model for poly-disperse dense gas-solid fluidised beds, Part II: Segregation in binary particle mixtures

Particle mixing and segregation rates in a bi-disperse freely bubbling fluidised bed have been studied with a new multi-fluid model (MFM) based on the kinetic theory of granular flow for multi-component systems (see Part I). The MFM simulation results have been compared with digital image analysis experiments obtained by Goldschmidt et al. [2003. Digital image analysis of bed expansion in dense gas-fluidised beds. Powder Technology 138, 135-159] for bi-disperse mixtures of glass beads. In strong contrast to MFMs previously described in the literature, that strongly overestimate the segregation rates, the new MFM seems to underestimate the segregation rates at longer times. This underprediction of the segregation rate is probably related to the neglect of frictional stresses associated with long-term multiple-particle contacts resulting in an overestimation of the mobility of the emulsion phase, which is corroborated by discrete particle simulations without friction between the particles and the particles and the wall. The level of the granular temperature of the segregating system, as computed with the new MFM, compares reasonably well with the granular temperatures found in the DPM simulation.     

Experimental study of the mixing kinetics of binary pharmaceutical powder mixtures in a laboratory hoop mixer

As increasingly commented by the literature during the last 5 years, estimating the homogeneity of a powder mixture and following powder mixing processes is not a simple task. In this paper, we present the development and statistical validation of a sampling methodology for defining the number of samples required to provide a reasonable estimation of the homogeneity attained in a laboratory scale tumbler mixer. This method is then used to follow the mixing kinetics of a dilute binary powder mixture in a hoop mixer. Special attention is paid to the statistical meaning of the values obtained and the influence of the physical characteristics such as particle size and shape. The role of the particle shape of the majority powder is particularly emphasised and it is quantitatively demonstrated that spherical particles are harder to mix and more ready to segregate than particles with irregular shapes. The different mixing mechanisms at play are identified; the practical limits of use of such tumbler mixers with pharmaceutical powders are discussed.     

Pyrolysis kinetics of olive residue/plastic mixtures by non-isothermal thermogravimetry

The TGA studies of a pyrolytic decomposition of mixtures of olive residue/plastic were carried out. The investigation was made at the temperature ranging from 300 to 1273 K) in the nitrogen atmosphere at four heating rates β = 2, 10, 20 and 50 K min^− 1. High density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and polystyrene (PS) were selected as plastic samples. Based on the results obtained, three thermal stages were identified during the thermal degradation. The first two were dominated by the olive residue pyrolysis, while the third was linked to the plastics pyrolysis, which occurred at much higher temperatures. Discrepancies between the experimental and calculated TG/DTG profiles were considered as a measurement of the extent of interactions occurring on pyrolysis olive residue/plastic mixtures. The maximum degradation temperatures of each component in the mixture were higher than those of the individual components. These experimental results indicate a significant synergistic effect during olive residue and plastic co-pyrolysis at the high temperature region. In addition, a kinetic analysis was performed to fit thermogravimetric data. A reasonable fit to the experimental data was obtained for all materials and their mixtures.     

Densities,ultrasonic speeds,refractive indices,and COSMO analysis for binary mixtures of dichloromethane with acetone and dimethylsulfoxide at T = (298.15, 303.15, and 308.15) K

Experimental densities (ρ), ultrasonic speeds (u), and refractive indices (n_D) of binary mixtures of dichloromethane (DCM) with acetone (ACT) and dimethylsulfoxide (DMSO) were measured over the whole composition range at T?=?298.15, 303.15, and 308.15?K. From the experimental data, excess molar volume (V^E), deviations in isentropic compressibility (Δk_s), deviations in intermolecular free length (ΔL_f), deviations in refractive index (Δn_D), and deviations in ultrasonic speed (Δu) were calculated. Moreover, the Benson–Kiyohara theory was applied to the binary mixtures to obtain the theoretical Δk_s values. The COSMO calculations depending on density functional theory were utilized to estimate the σ-profiles for the DCM, ACT, and DMSO. The interpreted σ-profile trends were found supportive with the experimental findings. Applicability of different empirical and semi-empirical relations of refractive index data were tested against the measured results, and good agreement has been obtained. The possible results of intermolecular molecular interactions among mixture components were interpreted.     

Effect of processing parameters on the formation process of nano-sized ZrB2 powders by the high energy ball milling

ABSTRACT

Nano-sized ZrB₂ powders were synthesised using the high energy ball milling with ZrO₂ and B₂O₃ as raw materials and Mg as the reducing agent. The resulting powders were characterised by X-ray diffraction, scanning electron microscopy, laser particle size analysis, transmission electron microscopy, energy dispersive spectrometry, and X-ray photoelectron spectroscopy. The influence of the synthesis parameters, including the ratios of ZrO₂ to B₂O₃, milling medium, and reaction time, on the synthetic course of the ZrB₂ nanopowders were studied systematically. The mechanisms by which these parameters influence the synthetic course of and the resulting product quality are determined. Ultimately, the diameter of the resulting particles is about 200–400?nm, which are an agglomeration composed of many individual small particles with an average diameter of ～50?nm. In addition, the oxidation of ZrB₂ powders has also been studied.     

Minimization of Pb content in a ceramic glaze by reformulation the composition with secondary raw materials

In this study a commercial ceramic glaze composed by both olivine (magnesium iron silicate, (Mg,Fe)₂SiO₄) and commercial frits, rich in lead (about 30 wt%), was reformulated by using secondary raw materials (CRT cone glass and municipal solid incinerator post-treatment bottom ashes before and after vitrification). The waste-based products were characterized and, compared to the standard glaze, showed better acid resistance, comparable aesthetic characteristics and slightly lower stainless resistance. Environmental benefits were obtained by saving natural raw material (olivine), by reducing lead percentage in the proposed formulations (from around 30 to 5 wt%), by energy saving (for the avoided use of commercial frits) and by reducing lead content in the new compositions.     

Effect of S53P4 bioactive glass content on structural and in-vitro behavior of hydroxyapatite/bioactive glass mixtures prepared by mechanical milling

This work presents silicon-substituted hydroxyapatite preparation through planetary ball milling using biogenic hydroxyapatite and different wt% of S53P4 bioactive glass (5, 10, 15, and 20 wt%) sources for the first time. The prepared mixtures showed a BHAp lattice contraction with SiO₄^4? incorporation; rich- and poor-Si phases were subsequently identified. Furthermore, two types of interaction among the functional groups in the S53P4 and BHAp mixtures are proposed. First, the 95-5 (wt.%) sample displayed a BHAp lattice with SiO₄^4?, CO₃^2?, and OH^? ions substitution. In samples with S53P4 BG content higher than 95-5, the lattice substitution was related to SiO₄^4?, PO₄^3?, and CO₃^2? ions, and a dehydroxylation process occurred in the BHAp. Finally, the bioactive behavior of the samples was studied by immersion in Hank's solution for 7, 14, and 28 days. The results showed that the mixtures formed a bone-like apatite layer with a dune-like morphology that increased in size and quantity with increasing S53P4 content in the mixtures.