Particle ordering

All particles ordering the machine must have the opportunity to be floated. 

The phenomenon of adsorbed particle ordering and the change in the rates of the surface processes in ordered systems the relation of the characteristics of these processes to data on low-energy electron diffraction. 

The self assemblies are difficult to obtain and, up to now, the patterns extend to only a few hundred of nanometers in diameter. Therefore, the use of structured substrate has been proposed as a way to obtain long distances particle ordering. As an example, lithography patterning [49, 50] allowed to obtain FePt nanoparticles arrays on Si wafer, with juqHc = 1.2 T after annealing. 

Figure 15.3 indicates that for the silica microspheres, the potential and viscosity both follow the expected behavior predicted by the classical DLVO theory. On the other hand, the nanosize fnmed silica exhibits a discrepancy between the expectation of DLVO theory and the experimental results that is, as the of the nanosize fumed silica increases, viscosity sharply increases. Hence factors such as particle crowding, particle ordering, and electroviscous effects will also impact viscosity, in addition to aggregate or network formation. 

Many food systems exhibit complex flow behavior and are thixotropic, that is their viscosity decreases as their molecules shear. This depends upon the spherical nature of the particles in the suspension. Initially they are randomly orientated but begin to line up in one direction as shear/stress is applied. Sonication results in reduced viscosity probably due to the particles ordering themselves uniformly in the path of the ultrasound. 

We have already used at several places in this chapter, the notion of nucleation and growth. We discuss this extremely important concept in some more detail here. When a melt - which for simplicity is of a single component glass-forming material - is cooled below its melting point slowly, it crystallizes at an undercooling equal to T -Tct) T. The crystallization involves two processes - one, the nucleation and the other, the growth of the crystals. Nucleation is the step in which, by virtue of thermal fluctuations alone the constituent particles order spontaneously into a tiny units called embryo. These embryos redissolve spontaneously... 

Figure 1. Hydrophoretic separation principle, (a) Schematic showing a hydrophoretic device with anisotropic microfluidic obstacles, (b and c) Simulated streamlines in the device. The slanted groove patterns on the channel generate rotational flows by using a steady axial pressure gradient, (d) Different particle ordering according to particle size by steric hindrance mechanism. (Reproduced with permission from Ref [20] Copyright 2009, American Chemical Society.)...

S. Choi and J.-K. Park, Optically coated mirror-embedded microchannel to measure hydrophoretic particle ordering in three dimensions. Small, 5, 2205-2211 (2009). 

Fig. 5 Shown is a plot in g]/g2 sPace for git=g2, for v2=v, for ]v 1 =%1921 and for V]=0. The resulting regions of one-dimensional two-particle ordering are shown. Note that the boundary for g2<0 for which the Bogoliubov trans formation is valid is displaced to the right, and there is no region where the SS response is the only divergent one. We may speculate, however, that in the region for gj<0 to the left of this boundary and to the right of the (dotted) boundary in the absence of v2 and v/, that the SS response is the only divergent response.

Diffusion through media containing impermeable particles (ordered on the left and random on the right). 

Another technique is to assemble the particles under the influence of a liquid flow field, as achieved by filtering the dispersion. A membrane with pore sizes smaller than the particle diameter is used while continuously drawing the dispersion through a funnel, and the colloidal particles are retained at the membrane surface and accumulate [30,52]. Simultaneous application of an oscillating shear field during the filtration process improves the quality of particle ordering [53]. 

The microstructural changes occurring upon con-sohdation were studied for the cases of uniaxial compression in odometer and for the cases of tri-axial isotropic compression in stabilometer on the model systems, i.e., kaolinite and montmorillon-ite powder moistened above the liquid limit and thoroughly mixed up. Samples were compacted according to a standard technique up to the load of 1 MPa. After the end of consohdation, samples were collected for microstructural analyses, and the anisotropy of sample properties was investigated. Simultaneously, the rate of clay-particles order was studied by X-ray method. 

Juhue and Lang investigated the effect of surfactant post-added to surfactant-free poly(butyl methacrylate) latex dispersions on film formation. The particle ordering and packing was determined by SFM, which allowed these authors to determine the optimal surfactant concentration corresponding to fully covered latex particles (198). 

Computer simulation of the compression of nanolayers is a powerful tool to gain a better insight into the structure formation and particle ordering in two dimensions [37, 38]. It is also applicable to confirm model assumptions, or to assess the error of the oversimplified calculations concerning the layer properties or the interparticle energies. 

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