Arrays of particles

In filters etc. the particles become largely static in a bed or cake and in such cases the fluid therefore passes through a fixed array of particles or a porous solid and experiences drag as it does so (Figure 2.9). The particles resist the flow, reduce the velocity and give rise to an enhanced pressure drop compared with that in open channel flow. 

The production of fatty acid-capped silver nanoparticles by a heating method has been reported [115]. Heating of the silver salts of fatty acids (tetradecanoic, stearic, and oleic) under a nitrogen atmosphere at 250°C resulted in the formation of 5-20-nm-diameter silver particles. Monolayers of the capped particles were spread from toluene and transferred onto TEM grids. An ordered two-dimensional array of particles was observed. The oleic acid-capped particle arrays had some void regions not present for the other two fatty acids. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

If we calculate the mass concentration, cp, which would correspond to a cubic array of particles with a center-center distance of L, Eq. (29) can be written in terms of concentration to yield... 

Thus, within the context of the Newtonian force atom and the caloric theory of heat, solids, liqitids, and gases were all viewed as organized arrays of particles produced by a static equilibrium between the attractive interparticle forces, on the one hand, and the repulsive intercaloric forces, on the other. The sole difference was that the position of eqitilibriitm became greater as one passed from the solid to the liqitid to the gas, due to the increasing size of the caloric envelopes siuToittrding the component atoms (Figures 5 and 6). 

The increasing importance of the surface area as the linear dimensions of particles decrease is stated concisely in a quantity known as the specific surface area Asp of a substance. This quantity is determined as the ratio of the area divided by the mass of an array of particles. If the particles are uniform spheres, as we have assumed throughout this section, this ratio equals... 

FIGURE 20-30 Rosettes. The outside surface of the plant plasma membrane in a freeze-fractured sample, viewed here with electron microscopy, contains many hexagonal arrays of particles about 10 nm in diameter, believed to be composed of cellulose synthase molecules and associated enzymes. 

Idealization of particulate fluidization provides the essential concept towards a basic understanding of fluid-particle systems in terms of the most significant factors, L/S in particular and G/S after appropriate corrections. The nature of fluid-particle motion cannot be properly understood, e.g., the preferential arrays of particles, L/S versus G/S, without supplementary studies of the basic mechanisms. Of immediate interest from a practical point of view is how to adapt the relatively simple relations derived for ideal fluidization to G/S systems, as already exemplified for fast fluidization. For polydisperse systems, the problem was oversimplified to the binary case, and... 

One method of communication between cells is by passage of chemical substances through special junctions which, because of their appearance in electron micrographs of thin sections (Fig. 1-15, G) are known as gap junctions. T45,146 Q p junctions may cover substantial areas of the cell interface. In cross section, a thin 3-4 nm gap between the adjacent cell membranes is bridged by a lattice-like structure, which may appear in freeze-fractured surfaces as a hexagonal array of particles (Fig. 1-15, F, lower junction). These particles or connexons are each thought to be composed of six protein subunits. A central channel in the connexon is able to pass molecules of molecular mass up to about 500 Small molecules may be able to pass... 

Finally, with EBL it is possible to prepare well-defined arrays of particles on the TEM membranes with both well-defined particle sizes and interparticle separation (both short- and long-range ordering). In Fig. 4.8, this is illustrated by an array of 50-nm wide and 15-nm thick Cu nanoparticles on Si02. There are three interparticle distances, 100, 200, and 500 nm, respectively. 

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