Viscoelasticity particulate fillers

Reinforcement by particulate fillers is primarily a phenomenon of the rubbery state of viscoelastic response. Fillers which produce dramatic increases in the strength of a polymer 100° C above Tg, often give little or no reinforcement below Tg. 

The influence of particulate fillers mixed with a polymer on the linear viscoelastic properties in the transition zone have been discussed briefly in Section C4 of Chapter 12. We now discuss briefly their effects in the plateau and terminal zones and at equilibrium, including nonlinear behavior. 

Then, for a particulate composite, consisting of a polymeric matrix and an elastic filler, it is possible by the previously described method to evaluate the mechanical and thermal properties, as well as the volume fraction of the mesophase. The mesophase is also expected to exhibit a viscoelastic behaviour. The composite consists, therefore, of three phases, out of which one is elastic and two viscoelastic. 

We have shown in the preceding section that the rheological properties of particulate-filled molten thermoplastics and elastomers depend on many factors (1) particle size (t/p), (2) particle shape (a), (3) volume fraction of filler (f)), and (4) applied shear rate (y) or shear stress a). The situation becomes more complicated when interactions exist between the particulates and polymer matrix. There is a long history for the development of a theory to predict the rheological properties of dilute suspensions, concentrated suspensions, and particulate-filled viscoelastic polymeric fluids. As early as 1906, before viscoelastic polymeric fluids were known to the scientific community, Einstein (1906,1911) developed a theory predicting the viscosity of a dilute suspension of rigid spheres and obtained the following expression for the bulk (effective) viscosity of a suspension ... 

This chapter will deal with how the mucus reacts to particles and particulate loads, thereby altering its rate of clearance. Particles can stimulate secretion and modulate ciliary function, either by mechanical factors or irritation, or by the ehemicals they contain or are capable of releasing. Particles have a direct effect on the physical properties of mucus, even when acting as a neutral filler, for whieh their contribution to viscoelasticity is a simple function of their volume fraction. Beyond this, particles may interact with the mucous gel network, and add multiple cross-link points. 

The effect of cellular debris, and other particulate matter, on the mechanical properties of mucus depends on the strength of the interaction. It has generally been assumed that cells act as a neutral filler, adding relatively little to the viscoelastic properties of mucus in comparison with other sources of variation in mucous gel viscoelasticity. 

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