A Monte Carlo simulation was used to estimate the particle size distribution in the synthesis of nanoparticles using microemulsions. When two microemulsions each containing reactants were mixed together, continuous collisions of the droplets lead to a particle-forming reaction through a repeated coalescence and breakup process. The particle formation in this process typically was limited by the droplet collision, because the mixing and reaction of the reactants were fast once two droplets coalesced. The present simulation indicates that a significant number of fine particles is generated making a broad hump in the particle size distribution on the small particle side. However, the volume fraction of the fine particles is insignificant, and the particle size distribution may be considered to be a narrow one if the fine particles are neglected. This prediction appears to be consistent with experimental observations, although only a limited number of experimental data is available.

The interfacial structure of physisorbed homopolymers is studied by means of Monte Carlo simulations. The focus is on relatively long chains in an effort to reach the "power law regime" inside the intermediate portion of the solid-polymer interface. The chain lengths required exceed substantially those of polymers typically used for colloid stabilization. Our findings confirm the correctness of the generic −4/3 exponent for long chains. Furthermore, they quantify the difference between mean-field predictions and Monte Carlo data, which is exaggerated for long chains. Finally, these findings illustrate that resolution of the finer trends of interfacial structure requires even longer chain lengths than those studied in this article.

No abstract

The effective medium approximation (EMA) has been applied for the prediction of the permeability of packed beds filled with polydisperse spheres. The EMA assumes a model system in which a packing particle is surrounded by a fluid envelope and an effective medium beyond the envelope. This model provides an analytical expression for the permeability of the packed bed as a function of the packing size distribution and the porosity. Unlike the present model, most existing models utilize an average packing size for the permeability prediction as they are not capable of fully incorporating the packing size distribution. The permeability prediction of the present model has been compared with those of recent numerical calculations, the semiempirical Kozeny−Carman correlation, and experimental data that are available. The Kozeny−Carman correlation, which is widely accepted in industrial applications, uses a mean particle size to account for the packing size distribution. Both the present model and the Kozeny−Carman correlation show a good agreement with the numerical results for packed beds of monodisperse particles and experimental data for packed beds of bidisperse particles. While the prediction of the present model agrees well with the Kozeny−Carman correlation when the packing size distribution is narrow, a significant deviation is noted as the size distribution becomes broader.

Objects with spatially varying properties are often desirable for some applications such as the functionally gradient materials (FGMs) in the field of powder metallurgy and ceramics or the graded-index plastic optical fibers (GI-POFs) for communications. In the case of FGMs, the material composition of the composite materials may vary spatially, whereas the refractive index varies continuously in the radial direction in the case of GI-POFs. Because of the peculiar property of such objects, they can have very specialized functions. When an optical fiber has a specific refractive index profile, it is capable of transmitting more optical signals per unit time, corresponding to higher bandwidth communications. While the concept of the objects with spatially varying properties has a great potential for various applications, the major obstacle has been limited availability of fabrication techniques. Although there are some methods available, such as the “centrifugal casting” for FGMs and the “interfacial-gel polymerization technique” for GI-POFs, their capabilities are still limited, requiring further development. In this paper, a new fabrication method for cylindrical objects with radially varying properties is introduced with an experimental confirmation. While this method is shown to be capable of producing GI-POFs, its applicability may not be limited to GI-POFs.