Bimodal Particle Size Distribution (bimodal + particle_size_distribution)

Distribution by Scientific Domains


Selected Abstracts


Measurement based modeling and control of bimodal particle size distribution in batch emulsion polymerization

AICHE JOURNAL, Issue 8 2010
Mazen Alamir
Abstract In this article, a novel modeling approach is proposed for bimodal Particle Size Distribution (PSD) control in batch emulsion polymerization. The modeling approach is based on a behavioral model structure that captures the dynamics of PSD. The parameters of the resulting model can be easily identified using a limited number of experiments. The resulting model can then be incorporated in a simple learning scheme to produce a desired bimodal PSD while compensating for model mismatch and/or physical parameters variations using very simple updating rules. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]


MEL-type Pure-Silica Zeolite Nanocrystals Prepared by an Evaporation-Assisted Two-Stage Synthesis Method as Ultra-Low- k Materials,

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2008
Yan Liu
Abstract A MEL-type pure-silica zeolite (PSZ), prepared by spin-on of nanoparticle suspensions, has been shown to be a promising ultra-low-dielectric-constant (k) material because of its high mechanical strength, hydrophobicity, and chemical stability. In our previous works, a two-stage synthesis method was used to synthesize a MEL-zeolite nanoparticle suspension, in which both nanocrystal yield and particle size of the zeolite suspension increased with increasing synthesis time. For instance, at a crystal yield of 63%, the particle size is 80,nm, which has proved to be too large because it introduces a number of problems for the spin-on films, including large surface roughness, surface striations, and large mesopores. In the current study, the two-stage synthesis method is modified into an evaporation-assisted two-stage method by adding a solvent-evaporation process between the two thermal-treatment steps. The modified method can yield much smaller particle sizes (e.g., 14,vs. 80,nm) while maintaining the same nanocrystal yields as the two-stage synthesis. Furthermore, the nanoparticle suspensions from the evaporation-assisted two-stage synthesis show a bimodal particle size distribution. The primary nanoparticles are around 14,nm in size and are stable in the final suspension with 60% solvent evaporation. The factors that affect nanocrystal synthesis are discussed, including the concentration, pH value, and viscosity. Spin-on films prepared by using suspensions synthesized this way have no striations and improved elastic modulus (9.67,±,1.48,GPa vs. 7.82,±,1.30,GPa), as well as a similar k value (1.91,±,0.09 vs. 1.89,±,0.08) to the previous two-stage synthesized films. [source]


Investigation of the effect of delayed reflux on PVC grain properties produced by suspension polymerization

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010
N. Etesami
Abstract The effects of the condenser operation on properties of polyvinyl chloride (PVC) particles produced by suspension polymerization process were investigated in a pilot scale reactor. It was observed that delaying reflux operation increased the cold plasticizer absorption of the final resin. Both bulk density and K-value of the PVC powder decreased by increasing time delay in the reflux operation. It was also found that commencement of refluxing before 20% conversion resulted in bimodal particle size distribution (PSD), while monomodal PSD was obtained for longer delays in refluxing. SEM micrographs showed that surface of produced particles were rough and smooth when reflux started before and after 20% conversion, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


Effect of an organic dicarboxylic acid salt on fractionated crystallization of polypropylene droplets

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007
Y. Jin
Abstract The effect of a particulate nucleating agent on fractionated crystallization of polypropylene (PP) was studied. A novel method utilizing breakup of PP nanolayers was used to obtain a dispersion of PP droplets in a polystyrene (PS) matrix. An assembly with hundreds of PP nanolayers alternating with thicker PS layers was fabricated by layer-multiplying coextusion. The concentration of an organic dicarboxylic acid salt (HPN) nucleating agent in the coextruded PP nanolayers was varied up to 2 wt %. When the assembly was heated into the melt, interfacial driven breakup of the thin PP layers produced a dispersion of PP particles in a PS matrix. Analysis of optical microscope images and atomic force microscope images indicated that layer breakup produced a bimodal particle size distribution of submicron particles and large, micron-sized particles. Almost entirely submicron particles were obtained from breakup of 12 nm PP layers. The fraction of PP as submicron particles dropped dramatically as the PP nanolayer thickness increased to 40 nm. Only large, micron-sized particles were obtained from 200 nm PP nanolayers. The crystallization behavior of the particle dispersions was characterized by thermal analysis and wide angle X-ray diffraction. Only part of the PP was nucleated by HPN. It was found that HPN was not effective in nucleating the population of submicron particles. The particulate HPN was too large to be accommodated in the submicron PP particles. On the other hand, the amount of nucleated crystallization qualitatively paralleled the fraction of PP in the form of large, micron-sized particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source]


Measurement based modeling and control of bimodal particle size distribution in batch emulsion polymerization

AICHE JOURNAL, Issue 8 2010
Mazen Alamir
Abstract In this article, a novel modeling approach is proposed for bimodal Particle Size Distribution (PSD) control in batch emulsion polymerization. The modeling approach is based on a behavioral model structure that captures the dynamics of PSD. The parameters of the resulting model can be easily identified using a limited number of experiments. The resulting model can then be incorporated in a simple learning scheme to produce a desired bimodal PSD while compensating for model mismatch and/or physical parameters variations using very simple updating rules. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]


The Concept of a Low-Temperature Synthesis for Superparamagnetic BaFe12O19 Particles

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010
Miha Drofenik
Superparamagnetic Ba-hexaferrite, BaFe12O19, nanoparticles were prepared by reacting tetrahydroxoferrates (III), [Fe(OH)4],(aq), and barium ions, Ba2+(aq), in an autoclave in the presence of a high concentration of hydroxide ions OH,. The synthesis temperature was between 80° and 140°C. The size and the morphology of the synthesized nanoparticles were confirmed by transmission electron microscopy. The crystal structure of the nanoparticles was characterized by X-ray diffraction. The powders synthesized above 120°C exhibited a bimodal particle size distribution, while those synthesized below 120°C showed a monomodal particle size distribution. The field-cooled/zero-field-cooled magnetization measurements showed typical superparamagnetic behavior. The superparamagnetic nanoparticles synthesized below 100°C exhibited a disk-like shape, on average <10 nm wide and 3 nm thick, with a room-temperature magnetization of approximately 3 emu/g at 1 T. [source]


On the evolution of the rate of polymerization, number and size distribution of particles in styrene emulsion polymerization above CMC

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2010
Shirley Carro
Abstract This work is an extension of a communication reported by two of the authors [Carro and Herrera-Ordoñez, Macromol Rapid Commun 2006, 27, 274], where bimodal particle size distributions (PSD), obtained by asymmetric flow-field flow fractionation (AFFF, AF4), were taken as evidence of certain degree of stability of primary particles. Now, emulsion polymerizations of styrene were performed under conditions employed before by other researchers, intending to examine if the behavior observed is general. The number of particles (N) and PSD were studied by means of dynamic light scattering and AF4. By the later, bimodal PSDs were detected in all cases, where the population corresponding to primary particles (diameter <20 nm) depends on reaction conditions. Regarding N, AF4 results show that it is constant during interval II, in contrast to DLS results. Primary particle coagulation was evidenced as minimums in N evolution and the rate of polymerization curves, monitored by calorimetry and gravimetry, which are enhanced when higher particle number is generated and/or the ionic strength is increased. These results suggest that particle coagulation is not as extensive as it would be expected according to the coagulative theory. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3152,3160, 2010 [source]