Dynamic shear

It has also been suggested that steady state low shear dynamic measurements in the melt could be a convenient method for the study of particle dispersion in relation to flller properties, which might also correlate with mechanical properties of the composite [48,49]. 

Figure 4.15. Time evolution of the shear dynamic modulus during curing at two temperatures 23°C (curves 1 - 3) and 61°C (curves 4 to 6) and different frequencies 3 s 1 (curves 1 and 4) 12 s 1 (curves 2 and 5) and 25 s 1 (curves 3 and

Measurements of creep in torsion can be made very accurately. The reason is that deformation can be measured by measuring the large deflections of a light beam. A convenient way to simultaneously obtain shear dynamic and transient data is to combine both types of measurements in the same equipment (4). Usually this requires only small modifications of the experimental device. For example, the cross bar in a torsion pendulum can be removed and replaced by weights and pulleys to apply a constant torque to the upper clamp. In this way, a torsion creep apparatus is obtained (Fig. 7.8). The... 

Polymorphism and kinetics of crystallization of TAG and fat under static conditions (e.g., in differential scanning calorimetry [DSC] apparatus) have been studied for a long time and are summarized in many reviews (2-6). Yet, these conditions are far-removed from industrial applications, where crystallization is usually achieved under shear (dynamic). Shearing has a major effect on crystallization kinetics it induces a faster and more homogeneous crystallization, often in the stable form and with a refined grain size. Yet, its effect is far from being fully understood. Recently, several studies of dynamic crystallization of lipids have been reported (7-12). 

LDPE, and with polypropylene, PP, was studied In steady state shear, dynamic shear and uniaxial extenslonal fields. Interrelations between diverse rheological functions are discussed In terms of the linear viscoelastic behavior and Its modification by phase separation Into complex morphology. One of the more Important observations Is the difference In elongational flow behavior of LLDPE/PP blends from that of the other blends the strain hardening (Important for e.g. fllm blowing and wire coating) occurs In the latter ones but not In the former. 

Shear rheology itself can be further subdivided into cases of steady shear, dynamic shear and transient shear. 

Chemoviscosity profiles may also be correlated to chemical rate parameters. Simultaneous acquisition of the NIR spectrum and low-shear dynamic rheology may also be undertaken from prior to gelation to beyond vitrification for various epoxy-resin systems for selected isothermal profiles to provide network information from rheological power-law indices, fractal dimensions and network rheological structure parameters. 

Section 4.2.1) gives a good description of the steady-shear-dynamic-shear relationship. They found that the following general relationship is a good representation of the chemo-viscosity profile ... 

Three types of flow are mainly used in the rheological measurements steady state shearing, dynamic shearing, and elongation. The three can be classified according to the strain, y, vorticity, as well as uniformity of stress, a, and strain within the measuring space (see Table 7.1). 

To verify this postulate, two CPNC specimens were prepared, one sheared dynamically between parallel plates (disks) at >= 100 rad/s and y = 40% for 15 min, and another just inserted into the rheometer, melted, but not sheared. To determine the clay orientation, the specimens were microtomed close to the disk border (maximum shear strain) in the planar and perpendicular directions and then observed under the high-resolution transmission electron microscope [Perrin, 2002]. In the first specimen the well-dispersed clay platelets (see Figure 16.8) were found to be oriented perpendicular to the stress direction, while in the second, unsheared specimen, the exfoliated, often bent platelets were randomly oriented. 

Laboratory tests can be classified into two groups (1) shipboard testing including Torvane, laboratory miniature vane shear (ASTM D4648), pocket penetrometer, and fall cone penetrometer and (2) shore-based tests, which includes the above as well as triaxial tests (ASTM D4767) direct simple shear, dynamic, and cyclic tests, consolidation tests (ASTM D4186, ASTM D2435) and the usual array of index property tests, and special tests appropriate... 

Figure 5 (a) Elastic and viscous moduli as functions of shear stress obtained from oscillatory shear dynamic rheometry (see text and Ref 80 for details) performed at the oil-water interfece. The system consisted of 40 ml of water on to which 35 ml of an oil phase was layered, consisting of 0.75% (w/v) B6 asphaltenes dissolved in 50% (v/v) toluene in heptane. The asphaltenes were allowed to adsorb for 8 h at which point the rheometrical measurements were performed. The frequency of oscillation of the biconical hob was 1 rad/s. (b) Elastic and viscous moduh as functions of frequency. The same system and experiment as described for Fig. 5a were used with the exception that the shear stress was fixed at 1 mPa and the frequency was varied. Asphaltenes were allowed to adsorb for a period of 8 h. 

Figure 8 Elastic modulus as a function of frequency obtained from oscillatory shear dynamic rheometry (see text) performed at the oil-water interface. The proportions of oleic and aqueous phase are the same as described for Fig. 5. Concentrations of 0.25, 0.75, and 1.5% (w/v) B6 asphaltenes were dissolved in the oleic phase (50% yh toluene in heptane) before adsorption. Samples were aged for 8 or 24 h. Shear stress was held constant at 1 mPa.

First, we focus on the relaxation inside a single domain of finite size to get the dynamical behavior of the whole heterogeneous network one needs then to average over all of the domains in the system. The shear dynamic modulus G (a)) (and, correspondingly, the relaxation modulus G(f)) of polymer networks and gels often shows a power law behavior (especially at the sol-gel transition), see [101,102,152-154] and also Sect. 6. Therefore, we consider here a class of GGS-domains for which the relaxation modulus G(Nu t) obeys this power law behavior in the region of internal, intra-domain relaxation ... 

Material functions must however be considered with respect to the mode of deformation and whether the applied strain is constant or not in time. Two simple modes of deformation can be considered simple shear and uniaxial extension. When the applied strain (or strain rate) is constant, then one considers steady material functions, e.g. q(y,T) or ri (e,T), respectively the shear and extensional viscosity functions. When the strain (purposely) varies with time, the only material functions that can realistically be considered from an experimental point of view are the so-called dynamic functions, e.g. G ((D,y,T) and ri (a), y,T) or E (o),y,T) and qg(o),y, T) where the complex modulus G (and its associated complex viscosity T] ) specifically refers to shear deformation, whilst E and stand for tensile deformation. It is worth noting here that shear and tensile dynamic deformations can be applied to solid systems with currently available instruments, whUst in the case of molten or fluid systems, only shear dynamic deformation can practically be experimented. There are indeed experimental and instrumental contingencies that severely limit the study of polymer materials in the conditions of nonlinear viscoelasticity, relevant to processing. 

Stress relaxation for step squeezing of polystyrene at 180°C. (a) Stress versus time for increasing strain steps. Stress increases at short times, 2-10 ms because the plates take a finite time to close. The horizontal stress response signifies transducer overload. The rapid drop for strains e > 1 indicates loss of lubricant, (b) Stress relaxation data plotted as relaxation modulis. Solid line is the linear viscoelastic relaxation modulus calculated from shear dynamic data. Adapted from Soskey and Winter (1985). 

Toshchevikov VP, Gotlib YY (2009) Shear dynamic modulus of nematic elastomers modified Rouse model. Macromolecules 42 3417-3429... 

Sanchez-Reyes, J., Archer, LA. Step shear dynamics of entangled polymer liquids. Mflcromo/. (2002) 35, pp. 5194-5202... 

Recently, Starnes and Zaikov have reported that thiol esters such as 2-ethylhexyl 3-mercaptobenzoate function as efhcient stabilizers both by displacement of labile chloride and addition to polyene sequences. In this case, good performance was noted with high-shear dynamic stability testing, using 3 phr of thiol plasticizer/stabilizer. Although it is difficult to visualize such a system being competitive with low-cost tin stabilizers used at levels as low as 0.3 phr, it will, nevertheless, be of interest to follow commercialization of this approach. 

Hre butterfly patterns were observed at various tempera-mres and concentrations and for various solvents such as DOP, tydohexane, and diethyl malonate, which are theta solvents for PS at 35°C, as wdl as dibutyl phthalate and tricresyl phosphate, which are good solvents for PS. The patterns were also observed for semidilute solutions of polyethylene with paraflin as the solvent (athermal solution) and for sheared colloidal srrspensions. They are thus quite general for sheared dynamically asymmetric systems. The butterfly pattern was also formd for PS/PVME mixtures by Mani et and Gerard et and for other polymer mixtures. ... 

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