Optimal Particle Shape and Size

The problem of the optimal particle shape and size is crucial for packed bed reactor design. Generally, the larger the particle diameter, the cheaper the catalyst. This is not usually a significant factor in process design - more important are the internal and external diffusion effects, the pressure drop, the heat transfer to the reactor walls and a uniform fluid flow. 

The LEC structure that involves the addition of ionic dopants and surfactants to the printable inks enables the ability to print a top electrode without restriction by the work function of the metal. Silver, nickel, or carbon particle-based pastes are generally the preferred printable electron injecting electrodes however, the shape and size of the particles combined with the softening properties of the solvent can create electrical shorts throughout the device when printed over a thin polymer layer that is only several hundred nanometers thick. For optimal performance, the commercially available pastes must be optimized for printing onto soluble thin films to make a fully screen-printed polymer EL display. 

Of critical importance in the development of DPI products is the evaluation, optimization, and control of flow and dispersion (deaggregation) characteristics of the formulation. These typically consist of drug blended with a carrier (e.g., lactose). The properties of these blends are a function of the principal adhesive forces that exist between particles, including van der Waals forces, electrostatic forces, and the surface tension of adsorbed liquid layers [7], These forces are influenced by several fundamental physicochemical properties, including particle density and size distribution, particle morphology (shape, habit, surface texture), and surface composition (including adsorbed moisture) [8]. In addition,... 

Deposition rate of the metal is a crucial parameter for the shape and size of the islands low rates give the best enhancement. Optimal film thickness for maximum enhancement depends on the deposition rate. Control of the substrate temperature during deposition permitted the growth of a film with a highly homogeneous distribution of particle shapes. 

Besides the composition and textural properties, the shape and size of HDT catalysts are other characteristics that must be carefully selected according to the type of feed and reactor technology for optimal performance. Conventional catalyst shapes such as spheres and pellets are well suited for distillate HDT. For heavy feeds, such shapes are inadequate because large molecules do not have access to the interior of the particle as a result of diffusional limitations. Therefore, it is necessary to... 

Recent studies have shown that the hemodynamics within cancer lesions constitutes another type of barrier to particle localization [21]. Delivery vehicles of different shapes and sizes can offer a dramatic increase in therapeutic index, by optimizing their properties of margination, extravasation, firm adhesion to the vascular endothelium and control of phagocytic uptake. 

Due to their high surface-to-volume ratio and size-dependent electronic properties nanostructured materials like NPs are good as catalysts. NPs of different sizes and structures can show significantly different catalytic activities and thus provides an opportunity to understand the structure-function relationship. NPs prepared usually in ensembles of NPs immobilized on an electrode. Thus the electrocatalytic property result of the average properties of the ensemble. Optimization of the catalyst requires increasing the number of sites available for the reaction to occur, shape and size effect of NP and composition of particles (in case of mixed metal... 

At the outset of the development of the synthesis of particles from solution there is an integrated approach which may be taken to optimize the production of particles with the desired features for a particular application. An understanding of how thermodynamic equilibrium is approached leads to an understanding of the phase stability of the desired solid phase. Fundamental principles of solution and colloid chemistry provide guidelines for control of particle size, particle shape and agglomeration. To complement the application of these fundamental principles, there are a number of computer programs that ease the trauma associated with predictions of phase stability, ionic equilibria, and predictions of agglomeration tendency. 

Several parameters must be optimized in order to achieve successful extraction efficiency, such as supercritical fluid nature, working temperature and pressure, extraction time, shape and size of the extraction cell, sample particle size, moisture content of the matrix and the analyte collection system. Due to the high number of parameters affecting the overall performance, the optimization in SEE is often tedious and difiBcult, which has avoided a wider applicability of the technique. Other disadvantages of the SEE technique include limited sample size and high cost of the equipment. 

In any catalyst selection procedure the first step will be the search for an active phase, be it a. solid or complexes in a. solution. For heterogeneous catalysis the. second step is also deeisive for the success of process development the choice of the optimal particle morphology. The choice of catalyst morphology (size, shape, porous texture, activity distribution, etc.) depends on intrinsic reaction kinetics as well as on diffusion rates of reactants and products. The catalyst cannot be cho.sen independently of the reactor type, because different reactor types place different demands on the catalyst. For instance, fixed-bed reactors require relatively large particles to minimize the pressure drop, while in fluidized-bed reactors relatively small particles must be used. However, an optimal choice is possible within the limits set by the reactor type. 

Moreover, particle size can significantly affect the material properties of the nanoparticles and is important for their interaction with the biological enviromnent (e.g., as concerns their ability to pass fine capillaries or to leave the vascular compartment via fenestrations after intravenous administration). Particle sizing results are thus crucial parameters in the development and optimization of preparation processes as well as in the evaluation of dispersion stability. Particle sizing, however, has also been employed for other purposes for example, to evaluate the size dependence of the nanoparticle matrix properties [1] or to obtain additional information on the particle shape [2,3]. 

Controlled optimal particle size and size distribution ensures superior flow properties of coprocessed excipients and reduced reliance on addition of glidants. The volumetric flow properties of SMCC were studied in comparison with those of the physical mixture of its parent excipients (42). The particle size range of the two test samples was found to be similar, but the flow of coprocessed excipient was better than that of the physical mixture. A comparison of the flow properties of Cellactose with its parent excipients was also performed (5) by measuring the angle of repose and Hausner ratio, and Cellactose was found to have better flow characteristics than lactose or a physical mixture of cellulose and lactose. The spray-dried coprocessed product had a spherical shape and even surfaces, which resulted in improved flow properties. On similar terms, mechanically coating the 2% CSD over microfine cellulose powder resulted in improving its flow properties (43). 

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