Visco-elastic properties

See literature on visco-elasticity, for example J.D. Ferry, The Visco-elastic Properties of Polymers, 3rd Ed, Wiley, New York, 1980. 

Silicone oils have very desirable visco-elastic properties, and are very stable. They have been used for many years for breast implants, as a cosmetic to improve appearance. There are many lawsuits charging that silicone oil can leak out of the containing sacks and cause adverse physiological reactions. The current customers either abandon the breast implant or use salt water implants, which do not have the same desirable viscoelastic properties. 

Yamamoto M. The visco-elastic properties of network structure. 1. General formalism. J Phys Soc Jpn 1956 11 413-421. 

A more detailed discussion of the visco-elastic properties of rubber-like elastomers for composite propellants was recently given in a paper by Landel and T. L. Smith [8]. 

In general these factors determine cost, mechanical and visco-elastic properties, resistance to degrading environments and influences, processing characteristics of the compound, and special requirements such as flame resistance, oil resistance, low temperature flexibility, chemical resistance wear and abrasion resistance and non-toxicity requirements for application in contact with foodstuff, etc. 

We will discuss some preliminary results, which have been performed recently l01). In Fig. 39a the results for polymer No. 2d of Table 10 are shown, which were obtained by torsional vibration experiments. At low temperatures the step in the G (T) curve and the maximum in the G"(T) curve indicate a p-relaxation process at about 120-130 K. Accordingly the glass transition is detected at about 260 K. At 277 K the nematic elastomer becomes isotropic. This phase transformation can be seen only by a very small step in G and G" in the tail of glass transition region, which is shown in more detail in Fig. 39 b. From these measurements we can conclude, that the visco-elastic properties are largely dominated by the properties of the polymer backbone the change of the mesogenic side chains from isotropic to liquid crystalline acts only as a small disturbance and in principle the visco-elastic behavior of the elastomer... 

The ratio of elastic constants Ku, calculated for the S-effect according to the equation (4) appeared to be (Kn (polymer XIV)/Kn (polymer XIII)) x 1 100 and (Ku (polymer XVI)/Kn (polymer XV)) x 1 36. Yet, as we have just indicated, taking into account molecular masses of the LC polymers and reducing k, values for various polymers to equal values of DP one may come to substantially different values for ratios of constants presented. It is necessary to note that up to date no quantitative data on the determination of elastic constants of LC polymers has been published (excluding the preliminary results on Leslie viscosity coefficients for LC comb-like polymer127)). Thus, one of the important tasks today is the investigation of elastic and visco-elastic properties of LC polymers and their quantitative description. 

Bulk processes of carbonization can be "stopped" at an appropriate stage and mesophase separated from the remaining pitch by solvent extraction. Spheres of mesophase can then be isolated. However, from the viewpoint of specialised industrial usage, e.g. spinning /moulding (not traditional coke-making) such mesophase can be said to be "overcooked". It is not readily soluble in generally available solvents it does not represent a minimum in its visco-elastic properties. 

The stabilising action of the adsorption layers from high molecular substances (protective colloids) is related to the decrease in the forces of molecular attraction. Hence, films from aqueous solution of polyvinyl alcohol obtained between drops of cyclohexane have thickness of 80 nm and respectively, a very low attraction force, in contrast to black films [513]. Along with that the adsorption layers from such compounds possess visco-elasticity properties with modulus of elasticity 104 N m"2, impeding the film thinning and drop coalescence [503]. 

At this voliime fraction, the viscosity diverges because the shear stress is now given by the particle-particle contact in the tightly packed structure. As a result, we obtain a fluid with visco-elastic properties similar to polymeric solids. In ceramic processing, we extrude and press these pastes into green shapes. As a result, the rheology of ceramic pastes is of importance. The rheology of very concentrated suspensions is not particularly well developed, with the exception of model systems of monodisperse spheres. This section first discusses visco-elastic fluids and second the visco-elastic properties of ceramic pastes of monodisperse spheres. The material on visco-elastic fluids draws heavily from the book Colloidal Dispersions by Russel, Saville, and Schowalter [31]. 

In this chapter, we described the fundamentals of suspension iheol-ogy from dilute suspensions to concentrated suspensions. Attention has been paid to interparticle forces and the structure of the suspension because these things drastically influence suspension iheology. In addition, visco-elastic properties of concentrated suspensions including ceramic pastes have been discussed. Finally, the mechanical properties of dry ceramic powders have been discussed in terms of the dJoulomb yield criterion, which gives the stress necessary for flow (or deformation) of the powder. These mechanical prc rties will be used in the next chapter to predict the ease with vdiich dry powders, pastes, and suspensions can be made into green bodies by various techniques. 

Texture modifications occur mainly during the first step of drying (the constant rate period) and are related to the visco-elastic properties of the gel network [6]. During the second step of drying (the falling rate period), liquid water leaves the capillaries and the pore walls can be damaged by forces linked to the existence of liquid-gas meniscus [6, 7],... 

Ludema KC, Tabor D (1966) The friction and visco-elastic properties of polymeric solids. Wear 9 329-348... 

Puvanenthiran, A., Williams, R.P.W., and Augustin, M.A. (2002). Structure and visco-elastic properties of set yoghurt with altered casein to whey protein ratios. Int. Dairy J. 12, 383-391. 

Viability time courses, collected at NCGRP for a large number of samples for more than 30 years, provide a rich source of informafion on the nature and kinetics of seed deterioration. Time courses follow a sigmoidal pattern, where a period of minor loss in viabilify precedes a cataclysmic phase where severe reductions in viability are observed. Recently, Avrami kinetics, which describe cooperative reactions based on visco-elastic properties (Avrami, 1941), have been used to describe the pattern of seed aging (Walters et al., 2004 Walters et al., 2005) ... 

Auer, P. L. Thc visco-elastic properties of solutions of rod-like macromolecules. J. Chem. Phys. 19,281-283 (1951). 

For the transport of heavy ions to a solid surface coated with an adherent water film, like aluminium oxide, the visco-elastic properties of electric field forces and the concentration of heavy ions may be important for the rate of adsorption. For this reason we need information not only on relaxations restricted to a surface of an extended liquid, but also on the adherent water layer at the adsorbents. The last issue may be a bridge to the thermodynamics and flow properties of thin liquid films have been studied by some excellent research groups. 

We want to emphasize that a logarithmic time dependence of d and w, and the corresponding decrease of V, are not expected for a Newtonian liquid [42]. Moreover, our results cover times shorter than the longest relaxation time in equilibrated bulk samples (i.e., the reptation time). Thus, the visco-elastic properties of PS certainly affect our dewetting experiments. Thus, a detailed theoretical model has been developed that takes into account residual stresses, interfacial friction (i.e., slippage), and visco-elasticity [42,44,46],... 

Above results clearly demonstrate that dewetting can be considered as a nanorheology experiment that gives insight into the structure and properties of out-of-equiUbrium PS thin films. We may thus consider dewetting as a rheological probe for the study of the visco-elastic properties of nanoscopic polymer films. 

Shiraki, Y. and Komaki, T., 1955, Smdies on clay-water system. (1-12) Visco-elastic properties of clay paste. Journal of the Ceramic Association of Japan, 63(708), 194—197. 

The evolution of visco-elastic properties in non-Newtonian fluids exhibiting time-dependent rheological changes is a matter of wide scientific interest, particiflarly so in systems undergoing gelation. The gel-point, where a three-dimensional network structure is established, may be identified rheologically by the establishment of a eharacteristic frequency dependence of the dynamic moduli, and an associated frequency independent loss tangent [Winter and Chambon, 1986]. 

The teelmique, iiutially developed to measure visco-elastic properties in the curing of polymers [Malkin etal., 1984], has been applied to gels (In and Prud homme, 1993) and model visco-elastic fluids [Davies and Jones, 1994]. In a variation of the teehnique, dynamic mechanical properties are determined using the Fourier transform of pulsed deformations [Vratsanos and Farris, 1988]. 

Inevitably, the conjunction of frequency-dependent visco-elastic properties and wave propagation leads to consideration of visco-elastic wave dispersion and its influence on conventional wave-based measurements, such as those involving resonance phenomena and pulse propagation techniques. 

Resonance phenomena provide a simple method of characterizing visco-elastic properties which does not require absolute determination of force, or precise setting of shearing gaps. Many high frequency devices based on resonance have been reported [Waterman, et al., 1979 Hausler et al., 1996 Stoimenova et al., 1996],... 

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