Particle size and shell composition as effective parameters on MFFT for acrylic core–shell particles prepared via seeded emulsion polymerization

In this study, acrylic-based copolymer particles were prepared with core–shell morphology and the effect of T_g of the shell, particle size and their bimodal size distribution on minimum film formation temperature (MFFT) were investigated. The main goal was to optimize conditions to obtain latexes with low MFFT and appropriate mechanical properties. These will develop the applicability of such water-borne binders as paints and coatings at ambient conditions. A series of latexes with core–shell morphology with variable T_g of the shell from −56 to 30 °C were prepared and the MFFT, hardness and thermal behavior of the obtained films were studied. Then a series of latexes with particle sizes ranging from 46 to 960 nm were prepared and the effect of particle size on MFFT was studied too. By inducing the formation of secondary nucleation during emulsion polymerization, latexes with bimodal size distribution were obtained and the effect of presence of such particles on film formation was investigated. Results indicate that latexes with appropriate composition and bimodal particle size distribution lead to optimized performance in both mechanical and film formation properties as a proper choice for water-borne coatings.     

Two-phase flow hydrodynamic study in micro-packed beds – Effect of bed geometry and particle size

Microscopic visualizations nearby the wall region of micro-fixed beds and hydrodynamic measurements during gas–liquid two-phase flows were carried out with an aim to investigate the effect of particle size and capillary tube shape on the bed pressure drop, flow regime transition, hysteresis and bed transient response to flow-rate step perturbations. Visualizations through inverted microscopy revealed that a decrease in particle size leads to early inception of a high interaction flow regime whereas changing capillary shape from circular to square had no effect on flow regime changeover. The effect of particle size on the wetting pattern hysteresis in square micro-packed beds was also investigated in both imbibition and drainage paths. It was found that wetting pattern hysteresis decreases with a decrease in particle size. Finally, the transient behavior of micro-fixed beds of circular and square geometries packed with particles of two different sizes were studied by monitoring the bed pressure drop variations upon step changes in liquid flow rate at iso-G conditions. Larger particle sizes and square geometry showed shorter transient times as compared to smaller particle sizes and circular geometry.     

Optimal Ru particle size for selective CO oxidation in H2 over Ru/κ-Al2O3

Ru/κ-Al₂O₃ catalysts with different Ru dispersions were prepared by controlling the pretreatment conditions, and were applied to selective CO oxidation in H₂. The prepared catalysts were characterized by N₂ physisorption, transmission electron microscopy, temperature-programmed oxidation, CO chemisorption, and O₂ chemisorption. The Ru dispersion decreased with increasing reduction and oxidation temperature of Ru/κ-Al₂O₃. The turnover frequency for CO oxidation in H₂ increased as the Ru particle size increased from 2.2 to 3.6 nm, whereas the apparent activation energy decreased as the Ru particle size increased from 2.2 to 3.4 nm for 1% Ru/κ-Al₂O₃. However, larger Ru particles were not always favorable for the selective CO oxidation in H₂ because H₂ oxidation was also promoted by these catalysts. In the case of the 1 wt% Ru/κ-Al₂O₃ catalyst, Ru nanoparticles of approximately 3 nm appeared to be optimal for the selective CO oxidation in H₂ on the basis that they provided the widest temperature window, resulting in complete removal of CO even in the presence of H₂O and CO₂.     

Simulation study on the relationship between a high resolution αs-plot and the pore size distribution for activated carbon

The effects of the micropore structure of activated carbons on the high resolution α_s-plot for nitrogen adsorption isotherms were examined with the grand canonical Monte Carlo simulation. Adsorption isotherms of nitrogen were simulated in graphitic slit pores at 77 K as a function of the slit width (w). As no pore effect was observed below P/P₀=0.6 for w=3.5 nm, α_s-plots for the simulated adsorption isotherms were constructed using the standard isotherm simulated for w=3.5 nm. The simulated α_s-plots had filling and cooperative swings which were experimentally shown in the previous works, and the shape of the simulated α_s-plot varied with the micropore structure. As the subtracting pore effect (SPE) method for the specific surface area (SSA) determination using the α_s-plot was proposed in the previous experimental works, the theoretical ground for the SPE method was discussed. The best evaluation method of SSA using the α_s-plot was shown, almost agreeing with the SPE method. This simulation study showed clearly that the SPE method is available for pore systems of w≥0.7 nm, whereas even the SPE method underestimates the SSA of the pores of w≤0.6 nm. The observed swings of the α_s-plot were simulated using the different micropore size distribution. The bimodal micropore size distribution lead to both of filling and cooperative swings, while a single pore size distribution <0.9 nm gave only the filling swing. Thus, four representative types of the α_s-plot for activated carbons were proposed and it was shown how to understand the micropore size distribution through the α_s-plot.