Elastic and viscoelastic properties

The elastic and viscoelastic properties of materials are less familiar in chemistry than many other physical properties hence it is necessary to spend a fair amount of time describing the experiments and the observed response of the polymer. There are a large number of possible modes of deformation that might be considered We shall consider only elongation and shear. For each of these we consider the stress associated with a unit strain and the strain associated with a unit stress the former is called the modulus, the latter the compliance. Experiments can be time independent (equilibrium), time dependent (transient), or periodic (dynamic). Just to define and describe these basic combinations takes us into a fair amount of detail and affords some possibilities for confusion. Pay close attention to the definitions of terms and symbols. 

Equation (52) allows us to estimate the impact of viscoelastic braking on the capillary flow rate. As an example, we will consider that the liquid is tricresyl phosphate (TCP, 7 = 50 mN-m t = 0.07 Pa-s). The viscoelastic material is assumed to have elastic and viscoelastic properties similar to RTV 615 (General Electric, silicone rubber), i.e., a shear modulus of 0.7 MPa (E = 2.1 MPa), a cutoff length of 20 nm, and a characteristic speed, Uo, of 0.8 mm-s [30]. TCP has a contact angle at equilibrium of 47° on this rubber. 

This document gives definitions of terms related to the non-ultimate mechanical behaviour or mechanical behaviour prior to failure of polymeric materials, in particular of bulk polymers and concentrated solutions and their elastic and viscoelastic properties. 

Effect of Crosslink Density on Elastic and Viscoelastic Properties... 

The effect (or lack of effect) of crosslinks on basic physical properties of thermosetting polymers is discussed in Chapter 10, while the effect on elastic and viscoelastic properties is analyzed in Chapter 11. Yielding and fracture of neat and modified thermosetting polymers are discussed in Chapters 12 and 13. Finally, the very important problem of the durability of polymer networks is presented in Chapter 14. 

Pad Hardness Hardness, measured in relative units based on the type and mode of the indentation, is generally a measure of the ability of the pad to maintain its shape, and thus it is linked to elastic and viscoelastic properties. Harder pads are expected to provide better planarity. Softer pads, on the other hand, may provide better (defect-free) surfaces. Whereas it is difficult to measure the hardness of the pads, the viscoelastic behaviors can be measured to provide the necessary information. 

As stated earlier, this chapter has concentrated on the elastic and viscoelastic properties of compact cortical bone and the elastic properties of trabecular bone. At present there is considerable research activity on the fracture properties of the bone. Professor William Bonheld and his associates at Queen Mary and Westfield College, University of London and Professor Dwight Davy and his colleagues at Case Western Reserve University are among those who publish regularly in this area. Review of the literature is necessary in order to become acquainted with the state of bone fracture mechanics. 

Zanna JJ, Stein P, Marty JD, Mauzac M, Martinoty P. 2002. Influence of molecular parameters on the elastic and viscoelastic properties of side chain liquid crystalline elastomers. Macromolecules 35 5459 5465. 

The elastic and viscoelastic properties of blends of PP and ethylene-propylene (EP) were investigated with the force modulation technique by Nysten and co-workers (250,251). In addition to a mapping of the distribution of the rubbery nodules of EP at the surface, the subsurface distribution of these nodules could be estimated. While the FMM data yielded qualitative data, more recent indentation mapping based on f-d curves allowed Nysten and co-workers to obtain quantitative information of the surface elastic modulus (252). 

Tribological properties of polymers are strongly influenced by adhesion and elastic, and viscoelastic properties as well as by surface forces. K. L. Johnson reviews progress in... 

Aiello MA, Leone M, Aniskevich AN, Starkova OA (2006) Moisture effects on elastic and viscoelastic properties of CFRP rebars and vinylester binder. J Mater Civ Eng 18(5) 686-691... 

Corti organ depiction, 5-5 Cortical areas inhuman, 5-13 visual pathways to, 4-4 Cortical bone, 47-16 cortical bone screws, in long bone repair, 45-4 elastic and viscoelastic properties of, 47-1-47-17... 

The relationship between macroscopic properties and molecular properties is a major area of interest, since it is through manipulation of the molecular structure of me-sogens, that the macroscopic liquid crystal properties can be adjusted towards paricu-lar values which optimize performance in applications. The theoretical connection between the tensor properties of molecules and the macroscopic tensor properties of liquid crystal phases provides a considerable challenge to statistical mechanics. A key factor is of course the molecular orientational order, but interactions between molecules are also important especially for elastic and viscoelastic properties. It is possible to divide properties into two categories, those for which molecular contributions are approximately additive (i.e. they are proportional to the number density), and those properties such as elasticity, viscosity, thermal conductivity etc. for which intermolecular forces are responsible, and so have a much more complex dependence on number density. For the former it is possible to develop a fairly simple theory using single particle orientational order parameters. 

One of the most common methods utilized to characterize the phase behavior of polymer blends employs low amplitude cyclic deformation studies to obtain the elastic and viscoelastic properties. This method, termed dynamic mechanical characterization, yields high resolution of polymer transitions including secondary relaxation processes, crystalline melting transitions and of primary importance, the glass transition. This method maps the data over a broad temperature range to ascertain the phase behavior. 

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