Physical properties viscoelastic frequency dependence

FIGURE 13.27 Frequency dependences of G (co) and G"(co) for a typical polymer melt. (From Graessley, W.W., Viscoelasticity and flow in polymer melts and concentrated solutions in Physical Properties of Polymers, 3rd ed., Cambridge University Press, 2004, Chap. 3. With permission.)... 

Tr = 150 °C. The master curve clearly displays the five different characteristic viscoelastic regions or physical states noted in Fig. 5.2, with respect to the time or frequency axis. The superposition process underscores the fact that the viscoelastic properties of polymers depend more strongly on temperature than time, with changes in modulus and other properties over several orders of magnitude occurring over a modest temperature range (in this case -40 °C). 

Abstract Grease lubrication is a complex mixture of science and engineering, requires an interdisciplinary approach, and is applied to the majority of bearings worldwide. Grease can be more than a lubricant it is often expected to perform as a seal, corrosion inhibitor, shock absorber and a noise suppressant. It is a viscoelastic plastic solid, therefore, a liquid or solid, dependent upon the applied physical conditions of stress and/or temperature, with a yield value, ao- It has a coarse structure of filaments within a matrix. The suitability of flow properties of a grease for an application is best determined using a controlled stress rheometer for the frequency response of parameters such as yield, a, complex shear modulus, G phase angle, 5, and the complex viscosity, rj. ... 

From the rheokinetic curves the dependencies of the reaction time corresponding to the break points on the initiator concentration have been plotted (Fig. 73). Roman nmnerals denote the same regions of the IPN as in Fig. 72b. To judge the physical state of the system imder consideration (initial PU and IPN) the viscoelastic properties have been studied for all the time regions. The dependencies of the real part G and of the imaginary part G" of the complex shear modulus on frequency obey the scaling laws G = af and G" co. Here the exponents a and p at logo) < 0.5 are equal corre-... 

---