General characteristics of polymers

A general characteristic of polymers is that their hardnesses tend to be proportional to their elastic moduli, particularly their shear moduli (Flores et al., 2000). However, the shear modulus is often anisotropic so an average value may not be an appropriate measure of hardness. The modulus for the plane of shear should be a better indicator. 

We have described some of the general characteristics of polymers, and how they can be grouped according to structure, but we have not addressed any of the more quantitative aspects of polymer structures. For instance, we have stated that a polymer is made up of many monomer (repeat) units, but how many of these repeat units do we typically find in a polymer Do all polymer chains have the same number of repeat units These topics are addressed in this section on polymer molecular weight. Again, the kinetics of polymer formation are not discussed until Chapter 3—we merely assume here that the polymer chains have been formed and that we can count the number of repeat units in each chain. 

Inaccessible PV has been observed in all types of porous media for both polyacrylamides and biopolymers and is considered to be a general characteristic of polymer flow in porous media. The magnitude of the inaccessible PV can range from 1 % to 2% to as much as 25% to 30%, depending on the polymer and porous medium. Table 5.5 presents representative data on inaccessible PV for a xan-than and polyacrylamide in porous materials. A slight decrease in inaccessible PV with concentration is indicated by the polyacrylamide data, Several models have been offered to explain why inaccessible PV occurs,55 but none has gained universal acceptance. 

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