Polymers viscoelastic behavior

Dynamic mechanical experiments yield both the elastic modulus of the material and its mechanical damping, or energy dissipation, characteristics. These properties can be determined as a function of frequency (time) and temperature. Application of the time-temperature equivalence principle [1-3] yields master curves like those in Fig. 23.2. The five regions described in the curve are typical of polymer viscoelastic behavior. 

Another mechanism is related to polymer viscoelastic behavior. The interfacial viscosity between polymer and oil is higher than that between oil and water. The shear stress is proportional to the interfacial viscosity. Because of polymer s viscoelastic properties, there is normal stress between oil and the polymer solution, in addition to shear stress. Thus, polymer exerts a larger pull force on oil droplets or oil films. Oil therefore can be pushed and pulled out of dead-end pores. Thus, residual oil saturation is decreased. This mechanism is detailed in Chapter 6. 

Polymer Viscoelastic Behavior and Its Effect on Field Facilities and Operations... 

This chapter discnsses this new concept. It first reviews some flnid viscoelastic properties. Then it presents the evidence of polymer viscoelastic behavior in the laboratory and in the field. In addition, this chapter discnsses the displacement mechanisms of polymer solntion and the effect of viscoelastic polymer solntion on held facilities and operations. 

This section presents the factors that affect polymer viscoelastic behavior. These factors include polymer concentration, salinity, surfactant, and temperature. The viscoelastic behavior in a typical Daqing solution is also presented. 

These equations are often used in terms of complex variables such as the complex dynamic modulus, E = E + E", where E is called the storage modulus and is related to the amount of energy stored by the viscoelastic sample. E" is termed the loss modulus, which is a measure of the energy dissipated because of the internal friction of the polymer chains, commonly as heat due to the sinusoidal stress or strain applied to the material. The ratio between E lE" is called tan 5 and is a measure of the damping of the material. The Maxwell mechanical model provides a useful representation of the expected behavior of a polymer however, because of the large distribution of molecular weights in the polymer chains, it is necessary to combine several Maxwell elements in parallel to obtain a representation that better approximates the true polymer viscoelastic behavior. Thus, the combination of Maxwell elements in parallel at a fixed strain will produce a time-dependent stress that is the sum of all the elements ... 

In Chapter 3, we used the Rouse model for a polymer chain to study the diffusion motion and the time-correlation function of the end-to-end vector. The Rouse model was first developed to describe polymer viscoelastic behavior in a dilute solution. In spite of its original intention, the theory successfully interprets the viscoelastic behavior of the entanglement-free poljuner melt or blend-solution system. The Rouse theory, developed on the Gaussian chain model, effectively simplifies the complexity associated with the large number of intra-molecular degrees of freedom and describes the slow dynamic viscoelastic behavior — slower than the motion of a single Rouse segment. 

Note that equation 17 is the general equation for the recoverable compliance regardless of the model. Figure 4 gives a simplified sense of what the various aspects of polymer viscoelastic behavior are, although the actual behavior is more complex. 

Table 1.2 Typical polymer viscoelastic behavior at room temperature (7a)...

It is quite a trivial statement that, owing to their viscoelastic character, the rheological and mechanical properties of polymers differ from those of other materials, and it is quite a common observation that the viscoelastic character of polymers is modified through the addition of foreign materials, e.g., mineral particles. The modification of the polymer viscoelastic behavior results from (at least) three type of parameters ... 

---