Interparticle termination

In SI-ATRP involving nanoparticles, there are two possible modes for termination between two surface radicals interparticle and intraparticle termination. Intraparticle termination is basically similar to termination between two surface radicals observed on flat substrates, with the additional limitation of a curvature effect. On the other hand, interparticle termination occurs between chains that are... 

Equations 3 to 7 indicate the method by which terminal velocity may be calculated. Erom a hydrodynamic force balance that considers gravity, buoyancy, and drag, but neglects interparticle forces, the single particle terminal velocity is... 

The question these correlations ask is why does the entrainment rate decrease for smaller particles for some systems whereas in other systems, the entrainment rate correlates with the particle terminal velocity or particle drag. Baeyens infers that particles may be clnstering due to an interparticle adhesion force that becomes dominant at some critical particle diameter. However, no evidence of particle clnsters was reported. Baeyens assnmption was based on fitting their data. Therefore, the role of particle clnstering on entrainment rates was difficult to establish from first principles. 

In that publication a dependence of the shape of the rate-time function on such parameters as initial monomer concentration, emulsifier concentration, and dose rate was shown for the methyl acrylate system. The behavior of this system tentatively was explained by assuming a strong gel effect even at low conversions, of prolonged particle formation, and some kind of interparticle radical termination—all factors which are included neither in the Harkins view nor in the classical Smith-Ewart theory. 

Consider the collision of particles due to wake attraction, as shown in Fig. E3.1. It is assumed that (a) the motion of the leading particle is not affected by the approach of the trailing particle (b) particles are equal-sized, rigid, and spherical and (c) initially, the particles move nearly at their terminal velocities with a very small velocity difference and are separated by a characteristic distance Zo- An empirical relation can be used to describe the effects of the interparticle distance Z and particle Reynolds number Rep on the drag force of the trailing particle as... 

The EPDM particles were found to either initiate crazes or to terminate them, depending on the interfacial bonding, the particle size, concentration and the interparticle distances. The variation of notched Izod impact strength of PPBC blends with different EPDM concentrations is shown in Figure 12.16. The fracture surface of a blend with 10 wt% EPDM, as examined under SEM, is shown in Figure 12.20. The hemispherical embeddings and hollows (representing the removed... 

The FCC reactor is an upflow pipe (riser reactor). The designers of this entrained bed system soon discovered that fine powders do not seem to obey Stokes law (Avidan and Shinnar, 1990). Even at velocities several times higher than the single particle terminal velocity in free fall (approximately 0.1 ms, see Example 6.7.2), entrainment is not reached. The particles behave as clusters with an effectively higher terminal velocity due to interparticle forces. 

Fig. 6 Interparticle and intraparticle termination modes between two surface radicals in SI-ATRP on nanoparticles...

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