Thickening behavior

Repulsive interparticle forces cause the suspension to manifest non-Newtonian behavior. Detailed calculations reveal that the primary normal stress coefficient [cf. Eq. (8.7)] decreases like y 1. In contrast, the suspension viscosity displays shear-thickening behavior. This feature is again attributed to the enhanced formation of clusters at higher shear rates. 

Time-dependent shear-thickening behavior was also seen with autoclaved 2.0% dispersions of unmodified waxy maize starch in 0.2A KOH (Dintzis and Bagley, 1995). Two hysteresis loops were seen in the first shear cycle one loop, at shear rates <200s , was anticlockwise indicating time-dependent shear-thickening, and the... 

Hard sphere systems are characterized by viscous flow and for low solids loading (less than 5%) they can be described as Newtonian fluid. At higher loadings, cluster formation takes place and the fluid cau acquire shear thinning or thickening behavior. The viscosity and solids loading are correlated with the... 

When the shear rate increases up to a critical value, the layers begin to disrupt, and the two-dimensional layering is disturbed. With further increase in shear rate, a three-dimensional random arrangement is obtained. Thus, the viscosity begins to increase with the shear rate, (i.e., shear-thickening behavior) (6, 9). 

Concentrated suspensions can also behave as Newtonian, but more commonly these suspensions show shear thinning or shear thickening behavior. 

To control the surface properties of silica (reduced filler-filler interactions, advanced filler-polymer interactions, minimized moisture uptake of the silica), it is necessary to modify the silica surface with silanes. Thickening behavior of silica, for example, is related to structure and surface properties of the silica. 

Thermotropic LCPs have high melt elasticity, but exhibit little extrudate swell. The latter has been attributed to a yield stress and to long relaxation times (60). The relaxation times for LCPs are normally much longer than for conventional polymers. Anomalous behavior such as negative first normal stress differences, shear-thickening behavior and time-dependent effects have also been observed in the. rheology of LCPs (56). Several of these phenomena are discussed for poly(benzylglutamate) solutions in the chapter by Moldenaers et al. 

In this chapter, we focus on the first stage of clogging and investigate the impaction of non-Newtonian power-law fluids on thin fibers. We aim to obtain the threshold radius of impacting droplets in different impact velocities. Effect of shear-thinning and shear-thickening behavior of droplets is evaluated and compared with corresponding Newtonian fluids. For this purpose, volume of fluid method is used and open source OpenFOAM software is applied for simulations. 

Thus, the characteristics of a silica surface that affect the energy of particle-particle versus particle-liquid contacts, as well as the particle size and degree of dispersion, determine the potential of that silica to thicken. The thickening behavior of a silica can be altered by modification of its surface, such as by the partial attachment of hydrophobic groups. 

Shear Thickening and Discontinuity Behaviors. Although continuous shear thinning behavior is commonly observed, shear thickening behavior can also be observed for concentrated suspensions of nonaggregating solid particles when subjected to the appropriate conditions (141). 

Metzner and Whitlock (142) were probably the first to observe the shear thickening behavior of suspensions. The systematic studies on this subject have been conducted by Hoffman (68,143,144), Strivens (145), Wagstaff and Chaffey (124), Woodcock (146), Laun (147), Boersma et al. (148,149), Yilmazer and Kalyon (150), and Laun et al. (151). However, a better understanding of the shear thickening behavior is needed to predict the conditions for which shear thickening would occur. 

Figure 22. Shear thickening behavior of suspensions of monodisperse and bidisperse polyvinyl chloride particles in dioctyl phthalate (68, 149).

Hoffman (68) attributed the shear thickening behavior to some order-disorder transition of particle microstructure, which was also observed by Ackerson and Pusey (153) and Wagner and Russel (71). This model was continued by Boersma et al. (148). They assumed that the shear thickening occurs when the shear forces overcome the interparticle forces. Hence, a dimensionless group, Nd, the ratio of the viscous to the repulsive forces, may be used to describe the transition ... 

Shear thickening behavior appears almost like a jump in the steady shear viscosity versus shear rate, fi versus 7, or ix versus Pe plots, especially for more concentrated suspensions. Time dependence is thus expected to occur. Boersma et al. (149) demonstrated that strong time dependence can be observed when a steady shear is applied near the critical point for which the shear thickening occurs. 

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