Interparticle domain sizes

The microstructures of Fig. 4.34 also show that the size of the domains can be altered through manipulation of the interparticle forces. The size of the domains increases for higher double-layer repulsion. Furthermore, the efficiency of the packing of the domains increases, leading to high packing density in the consolidated colloid (Fig. 4.34C). As the repulsion decreases (or equivalently, as the attraction increases), the domain size decreases and the interdomain pore size increases. The interdomain porosity is therefore the main cause of the low packing density of flocculated colloids. 

The overall amount of energy required and then the degree of toughness enhancement of the PER materials will be certainly dependent on factors such as volume fraction, particle size, interparticle distance, interface structure and adhesion between dispersed domains and matrix. 

In this group of disperse systems we will focus on particles, which could be solid, liquid or gaseous, dispersed in a liquid medium. The particle size may be a few nanometres up to a few micrometres. Above this size the chemical nature of the particles rapidly becomes unimportant and the hydrodynamic interactions, particle shape and geometry dominate the flow. This is also our starting point for particles within the colloidal domain although we will see that interparticle forces are of great importance. 

In order to obtain a finely sized dispersed phase in the PET matrix, the use of reactive compatibilization has been found to be important. Small dispersed rubber particles and a small interparticle distance are necessary to induce high toughness. For effective rubber toughening of PET, it is important that the rubber domains be less than 3 im in diameter (and preferably less than 1 xm) and that the interparticle distance be between 50-300 nm. 

For most of the samples studied, the size of the particles (around 10 nm) is well below the single domain particle size (340 nm for the Fe5oPt5o phase [33]). The coercivity is found to depend critically on the layer thickness, on the annealing temperature and on the additives-content, parameters which determine the particle size and the interparticles separation. 

Table I shows that the size is constant ( 0.26 /x) for all three samples, and a2 decreases from 1.05 to 0.78 as the graft rubber content increases from 25 to 50%. The same rubber latex was used for all three samples. Therefore the smaller dimension a is attributed to the size of the filler domain. The large dimension a2 varies inversely with the filler content and hence is considered as an interparticle separation distance.

Indeed the radius in front of the crack tip is not zero and inelastic deformation mechanisms, such as local plasticity or crazes, can be initiated at the crack tip. This is particularly true in heterogeneous polymers such as those investigated here, in which very small size inclusions initiate local plasticity in interparticle domains, even when the external stress applied is well below the yield stress of the neat matrix. 

Previous work (3, 6) has suggested that the spacing between the rubber domains is the critical parameter which correlates the DBTT with rubber content and particle-size. Work to date, however, appears to have calculated this interparticle spacing from the measured particle-size distribution and the known volume fraction of rubber added to the blend, rather than from a direct stereological analysis of electron micrographs. The former method assumes that there is no occlusion of the nylon continuous phase within the rubber particles during mixing. 

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