Viscoelastic properties media

Static leak-off experiments with borate-crosslinked and zirconate-cross-Unked hydroxypropylguar fluids showed practically the same leak-off coefficients [1883]. An investigation of the stress-sensitive properties showed that zirconate filter-cakes have viscoelastic properties, but borate filter-cakes are merely elastic. Noncrosslinked fluids show no filter-cake-type behavior for a large range of core permeabilities, but rather a viscous flow dependent on porous medium characteristics. 

Ashby, R. D., Foglia, T. A., Solaiman, D. K. Y., Liu, C.-K., Nunez, A., and Eggink, G. 2000. Viscoelastic properties of linseed oil—based medium chain length poly(hydroxyalkanoate) films effects of epoxidation and curing. Int. J. Biol. Macromol., 27,355-361. 

The attenuation and velocity of acoustic energy in polymers are very different from those in other materials due to their unique viscoelastic properties. The use of ultrasonic techniques, such as acoustic spectroscopy, for the characterization of polymers has been demonstrated [47,48]. For AW devices, the propagation of an acoustic wave in a substrate causes an oscillating displacement of particles on the substrate surface. For a medium in intimate contact with the substrate, the horizontal component of this motion produces a shearing force. In such cases, there can be sufficient interaction between the acoustic wave and the adjacent medium to perturb the properties of the wave. For polymeric materials, attenuation and velocity of the acoustic wave will be affected by changes in the viscoelastic behavior of the polymer. 

Acoustic-wave devices are sensitive to a large number of physical and chemical measurands. These include such parameters as temperature, pressure, acceleration, stress, and the adjacent medium s density, viscoelastic properties, and electrical conductivity. Indeed, it is this wide range of measurand sensitivities that makes AW devices attractive for a wide variety of sensor applications. However, since one is interested in exploiting only one of these sensitivities for a particular application, all other responses become undesirable interferences. Thus, it is essential that the sensor environment be carefully controlled to eliminate the effects of sensor cross-sensitivities. 

The hierarchical structure model is generalized and applied to study the viscoelastic properties of a two-component inhomogeneous medium with chaotic, fractal structure. It is shown that just as the results obtained recently using the Hashin-Strikman model, the present model predicts the possibility of obtaining composites with an effective shear and dumping coefficient much higher than those characterizing the individual component phases. The viscoelastic properties of the fractal medium, however, differ qualitatively from the properties of the Hashin-Strikman medium. 

As an example of the viscoelastic properties of an actual medium, we consider the viscoelastic properties of a charged polymeric material. Percolation properties will be exhibited by the charged polymeric composite, if the stiffness of the agglomerates of particles is greater by some orders of magnitude than the stiffness of the unperturbed polymetric compound [49]. This can occur, for example, if the polymetric compound in the vicinity of a boundary (e.g., the surface of a particle) attains the superstrong state [171-173]. 

A dilute polymer solution is a system where polymer molecules are dispersed among solvent molecules. An assumption common to any existing theory for flow properties of polymer solutions is that the structure of solvent molecules is neglected and the solvent is assumed to be replaced by a continuous medium of a Newtonian nature. Thus, macroscopic hydrodynamics may be used to describe the motion of the solvent. Recently, some ordering or local structure of solvent molecules around a polymer chain has been postulated as an explanation of the stress-optical coefficient of swollen polymer networks (31,32) so that the assumption of a solvent continuum may not apply. The high frequency behavior shown in Chapter 4 could possibly due to such a microscopic structure of the solvent molecules. Anyway, the assumption of the continuum is employed in every current theory capable of explicit predictions of viscoelastic properties. In the theories of Kirkwood or... 

In the course of this work we realized that the available instruments are not suitable to carry out simultaneously mechanical and rheological measurements. For example, instruments which are suitable for determining polymer transitions operate at low-strain amplitudes and thus cannot be used to carry out fatigue experiments to rupture polymer specimens of normal and medium strength. In addition, most of the rheological instruments cannot measure the viscoelastic properties if the... 

What about the detection behavior of QCM if applied in solutions that is, does the deposited material have viscoelastic properties In 1981 Nomura and lijima first reported the QCM measurement in liquid medium. Since then much effort has been devoted to measuring QCM in solution. It appears that the frequency of quartz changes with the density, viscosity, conductivity, and dielectric constants of the solution studied. In addition the roughness of deposition materiaP and the nature of the electrode " used on the quartz s surface can affect the frequency of QCM. The Sauerbrey expression in (14.1) is therefore modified... 

The sensitivity of film viscoelastic properties to the ambient medium applies not only to the solvent but also to the electrolyte. This is illustrated for the case of poly[Os(bipy)2Cl(PVP)io] (where... 

The basis of the majority of specific liquid crystal electrooptical effects is found in the reorientation of the director (the axis of preferred orientation of the molecules) in the macroscopic volume of the material under the influence of an externally applied field or the fiow of the liquid. Anisotropy of the electrical properties of the medium (of the dielectric susceptibility and the electrical conductivity) is the origin for reorientation, whereas the dynamics of the process also depend on the viscoelastic properties and the initial orientation of the director of the mesophase relative to the field. The optical properties of the medium, its local optical anisotropy, are changed as a result of this reorientation of the director (either occurring locally or throughout the whole of the sample) and underlies all the known electrooptical effects. 

Besides the adsorbed or deposited mass, roughness, and the viscoelastic properties of the adjacent medium, the shift of the resonance... 

Fig. 40 Experimental apparatus developed by Murayama and Silverman [44] for measuring viscoelastic properties of a polymer in a liquid medium. The letter A denotes a thermoregulator B, a temperature controller C, clamps and T, transducers.

The theory of fluid flow, together with the theory of elasticity, makes up the field of continuum mechanics, which is the study of the mechanics of continuously distributed materials. Such materials may be either soKd or fluid, or may have intermediate viscoelastic properties. Since the concept of a continuous medium, or continuum, does not take into consideration the molecular structure of matter, it is inherently an idealization. However, as long as the smallest length scale in any problem under consideration is very much larger than the size of the molecules making up the medium and the mean free path within the medium, for mechanical purposes all mass may safely be assumed to be continuously distributed in space. As a result, the density of materials can be considered to be a continuous function of spatial position and time. 

Chapter 4 investigates the rheological and the dynamic mechanical properties of rubber nanocomposites filled with spherical nanoparticles, like POSS, titanium dioxide, and nanosilica. Here also the crucial parameter of interfacial interaction in nanocomposite systems under dynamic-mechanical conditions is discussed. After discussing about filled mono-matrix medium in the first three chapters, the next chapter gives information about the nonlinear viscoelastic behavior of rubber-rubber blend composites and nanocomposites with fillers of different particle size. Here in Chap. 5 we can observe a wide discussion about the influence of filler geometry, distribution, size, and filler loading on the dynamic viscoelastic behavior. These specific surface area and the surface structural features of the fillers influence the Payne effect as well. The authors explain the addition of spherical or near-spherical filler particles always increase the level of both the linear and the nonlinear viscoelastic properties whereas the addition of high-aspect-ratio, fiberlike fillers increase the elasticity as well as the viscosity. 

M.C. Bonferoni, S. Rossi, F. Ferrari, M. Bertoni, C. Caramella, Influence of medium on dissolution-erosion behaviour of Na carboxymethylcellulose and on viscoelastic properties of gels, Int J Pharm, 117 41-48,1995. 

Reorientation of director L (or the optical axis) of the macroscopic volume of a liquid crystal under the effect of a field or flow of a liquid is Ae basis of most of the Imown electro- and magneto-optical effects. The anisotropy of the electrical and magnetic properties of the medium (dielectric constant Ae, diamagnetic susceptibility A%, electrical conductivity Aa) is the direct cause of orientation. The rearrangement processes are a function of the initial mientation of the molecules of the liquid crystal and its viscoelastic properties. The change in the c tical properties as a result of reorientation is the consequence of the optical anisotropy of liquid crystals. 

The quartz crystal microbalance (QCM) consists of a quartz crystal that is electrically driven into oscillation. The resonance frequency of the crystal is monitored. This frequency is highly dependent on any mass added to the crystal surface. Hence the mass dependence of the QCM resonance frequency can be, in air, used to weigh minute amounts of material with a sensitivity of the order of 1 ng/cm. QCM can also be coupled with electrochemistry here, the quartz crystal surface is coated with an appropriate electrode material, for example, thin film gold. This electrochemical QCM (EQCM) configuration can be used to monitor electrochemically triggered surface processes associated with the deposition (or loss) of material at the working electrode surface. However, in liquid medium the frequency shift of the QCM crystal is not solely sensitive to added mass but is also influenced by changes in the local property of the medium associated with the surface electrochemical process of interest. For example, density or viscosity variation of the medium in the electrode vicinity, in addition to variation in the viscoelastic properties of the deposited layer, can cause shifts in the resonant frequency of QCM. 

Some features of the phase structure, which follow from IPN viscoelastic properties, can be pointed out. The continuous medium for samples 2-6 is the phase enriched in PU network, which is evidenced by a plateau on the elastic-... 

Here, the asymptotic value AqP//2kt can be used to estimate trap stiffness. This method does not require high detection bandwidth and allows mapping of the linear range of the trap where kt is constant. Recently, Tolic-Norrelykke et al. [329] used a combination of sinusoidal drag force and power spectrum to obtain both distance and force calibration without the need of independent information on the hydrodynamic drag coefficient. A similar approach has been introduced to allow calibration in viscoelastic media such as the cytoplasm, where the viscoelastic properties of the medium are not known a priori [330]. 

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