Anomalous Rheology

As already noted, the measured nonlinear shear relaxation modulus, for linear molecules with little polydispersity, is in excellent agreement with the Doi-Edwards model at long times. However, for melts or concentrated solutions of very high molecular weight (e.g., j M 10 for polystyrene, where 0 is the polymer volume fraction), the measuredfiamping function, h(y), is drastically lower than the Doi-Edwards prediction (Einaga et al. 1971 Vrentas and Graessley 1982 Larson etal. 1988 Morrison and Larson 1992). This anomalous 

A somewhat Hifferent, though related, mechanism of slip in polymers of high molecular 

Theories for material instabilities or slip in highly entangled melts and solutions are still under active development. 

---

Much of the knowledge in this area is either derived from practical experience or anecdotal. Theoretical predictions of the viscosity of elastomer blends [46f, g] are of limited use since (1) the inhomogeneous phase morphology of an elastomer blend changes easily in response to applied stress, and (2) the nonuniform distribution of fillers and plasticizers in the phases responds to flow. These structural changes in elastomer blends under shear lead to anomalous rheological properties quite different from the expected average of pure components. 

The influence of electron beam irradiation on rheological properties and morphology of polypropylene and polypropylene/ethylene-propylene rubber blends was studied. Electron beam irradiation of isotactic PP causes pronounced chain scission (degradation) at dosis < 100 kGy. Melt viscosity can be controlled easily up to this dose for pure PP. For the blende however, an anomalous rheological behaviour is observed. 

Radiation crosslinking of the dispersed EPDM phase and a simultaneous grafting of PP onto EPDM is proposed to be the explanation for both the anomalous rheological and an enhanced morphology fixation. This idea is supported by gelfraction measurements. 

M.E. Mackay. Anomalous rheology of polymer-nanoparticle suspensions. XVth International Congress on Rheology, Monterey, CA, August 3-8, 2008. Paper KL.ll. 

As rheological research into complex substances of industrial importance advanced, anomalous flow behavior near solid walls was noted and the concept of wall-slip or wall effect was bom. Highly heterogeneous materials, such as foods, detergents,... 

The concept that friction between filler particles and breakdown of filler network is heat generating is applied to an understanding of the fusion behaviour of PVC. It is shown that the treatment of a PVC melt as a filler-containing polymer provides information on the anomalous effects observed in the rheological properties of PVC and that differences in the fusion behaviour of PVC compounds containing different impact modifiers and lubricants can be explained with the aid of this approach. 17 refs. 

FIG. 155. Types of rheological behaviour (a) Newtonian liquid (b) anomalous (pseudoplastic) liquid (c) Bingham body (d) real plastic body (e) thixotropic body (f) dilatant body. The viscosity is given by the tangent of the indicated angle. 

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. 

The effect of NaOH concentration on the ion transport and rheological properties of the Nafion ion exchange membranes may be attributable to some variation in the ionic domain structure in the presence of NaOH. Therefore, it is extremely Important to understand the ionic domain structure under these conditions. The anomalous behavior of Na" " ion transport as a function of NaOH concentration is seen more frequently in bilayer Nafion membranes in which one layer is treated with diamine and also in perfluorinated carboxylic ion exchange membranes. Several mechanisms have been proposed to explain their ion transport results including water absorption, transport of hydroxide ion tunneling, ion pairing mechanisms, etc. (54-56). As the ion transport properties are beyond the scope of this review, no detailed discussion will be presented. 

Significant replacement of monovalent metal cations on layer silicate clay surfaces by protons can occur if the electrolyte concentration is very low. The long-term result, beyond hydrolytic exchange, is acidic decomposition of the clay structure in part, and release of structural AP or Mg + to solution. These multivalent cations may then readsorb onto exchange sites, influencing the rheological properties of clays in very dilute salts. Some of the anomalous behavior of Na -smectites suspended in... 

Under one-dimensional shear, many Theologically stable fluids of complex structure (whose rheological characteristics are time-independent) have a flow curve other than Newtonian. If the flow curve is curvilinear but still passes through the origin in the plane 7, r, then the corresponding fluids are said to be nonlinearly viscous (often they are said to be purely viscous, anomalously viscous, or sometimes non-Newtonian). 

In other cases, including those involving considerable deformation of macromolecules (conformational changes) in the flow, an inverse phenomenon constituting an increase in viscosity with increasing flow rate may also take place. This phenomenon can not be described in terms of the simplest rheological models with constant parameters. Systems in which viscosity is dependent on the strain rate are referred to as anomalous, or non-Newtonian fluids. In sufficiently dilute systems, i.e. in the absence of interactions between particles, changes in viscosity due to the orientation and deformation of dispersed particles are usually rather small. 

This paper, the third in a rheotechnics series, reports on rheological studies performed at y higher than 10 1 sec-1. In two-phase polymer systems, Rosen and Rodriquez (3) hypothesized anomalous behavior (yield shear stress) at y = 10 1. Recently, Zosel (9) verified this hypothesis experimentally for ABS systems. A study of the rheological behavior of ABS resins at very low y is now in progress at our laboratories. The correlation between rheological behavior and moldability will be discussed in detail in a subsequent paper. 

Abstract A united mathematical model for the rheological and transport properties of saturated clays is proposed. The foundation of the model is the unification of filtration s consolidation theory and the theory of the stability of lyophobic colloids, which is based on the conception of disjoining pressure as a surplus in relation to hydraulic pressure. This pressure is caused by surface capacities and exists in water films between clay particles. In this work it is shown that the problem of the shrinkage of a clay layer can be reduced to the well known problem. We obtained the approximate solution for pressing the water out of a clay layer. The solution that we obtained requires introduction of a concept for the limit shear stress for clays. We investigated the model, and explained some characteristic features of transfer processes in clays (the existence of anomalous high pressures in clays, the flocculation at diffusion in clays, etc.). It is shown that solutions which we received are in harmony with results of experiments. 

Watase M, Nambu M, Nishinari K (1983) Rheological properties of an anomalous poly (vinyl alcohol) gel. Polym Commun 24 52-54... 

The electrical conductivity results discussed in section 1 have shown that the macroemulsions seem to exsit as W/o type below 1.8% NaCl and as 0/W type above 1.8% NaCl for all aqueous to oil phase ratios. This result together with the pressure drop data thus suggest that pressure drop associated with the flow of macroemulsions increase with the increase in the amount of the dispersed phase irrespective of whether it is oil or aqueous phase. It is suggested that the anomalous behavior at 2% NaCl could only be attributed to optimal salinity effects. Rheological data for this composition and for those compositions in the transition region... 

Mallette J G, Quej L M, Marquez A and Manero O (2001) Carbon black-filled PET/HDPE blends Effect of the CB structure on rheological and electric properties, J Appl Polym Sci 81 562-569. Xu X B, Li Z M, Dai K and Yang M B (2006) Anomalous attenuation of the positive temperature coefficient of resistivity in a carbon-black-filled poljoner composite with electrically conductive in situ microfibrils, Appl Phys Lett 89 032105. 

These types of phenomena can t be described in terms of simple rheological models with constant parameters. Systems that reveal the dependence of the viscosity on the flow rate are referred to as anomalous or non-Newtonian. In dilute suspensions, changes in the viscosity associated with the orientation and deformafion of the particles in the absence of particle-partide interactions are typically not too large. 

---