Transient rheological properties

Meissner, J. Modification of the Weissenberg rheogoniometer for measurement of transient rheological properties of molten polyethylene under shear. Comparison with tensile data. J. Appl. Polymer Sci. 16, 2877-2899 (1972). 

Bretas, R.E.S. and Powell, R.L. (1985) Dynamic and transient rheological properties of glass-filled polymer melts, Rheol. Acta, 24,69-74. 

A review of rheo-optical techniques by Sherman et al. (1996) notes that there has been an increase in the use of rheo-optic set-ups both for FT-IR dichroism and for dynamic IR dichroism spectroscopies for polymer melts and polymer blends. Skytt et al. (1996) highlight the use of simultaneous measurement of the transient or steady-state rheological properties and IR dichroism to characterize orientation in polymer melts. However, there is little reference to dual spectroscopic-rheological techniques for reactive polymer systems in the literature. 

The above references mainly describe rheological behavior of graphite fiber (length 0.5-16 cm) in poly-ether-ketone-ketone (PEKK) at 370°C. Anthors conclnde that the transient and steady-state rheological properties of these materials are different from the unfilled melt. 

The two main rheological properties of a suspension are the yield stress and the viscosity. Yield stress determines when the system becomes a fluid state and when is in a solid state, whereas viscosity determines the ability to flow. In this section, we start with the viscosity measurement. Although one can extract the yield stress from the complete viscosity-shear rate curve, it is helpful to measure the yield stress directly as well. The dynamic and transient measurements are also important for concentrated suspensions. However, because these two types of measurements can be blended into the measurements of the two main rheological properties with some modifications to the measuring instrument, we refer to their measurements only briefly when it is relevant to the discussion. 

Sepehr, M., Ausias, G., and Carreau, P. J., Rheological properties of short fiber filled polypropylene in transient shear flow, J. Non-Newtonian Fluid Mech., 123,19-32 (2004). 

The morphology may affect the rheological properties under shear and extension in different manners. If the dispersed phase is rigid but deformable, it more effectively contributes to the rheological properhes of the blend. In Section 8.3.2, the transient extensional viscosity was measured at a lower temperature than the melting temperature of the dispersed phase. Rigid fibrils enhance extensional viscosity even with a small amount of the dispersed phase (1 wt%). Nevertheless, the morphological effect under shear flow is not... 

An interdisciplinary team of leading experts from around the world discuss recent concepts in the physics and chemistry of various well-studied interfaces of rigid and deformable particles in homo- and hetero-aggregate dispersed systems, including emulsions, dispersoids, foams, fluosols, polymer membranes, and biocolloids. The contributors clearly elucidate the hydrodynamic, electrodynamic, and thermodynamic instabilities that occur at interfaces, as well as the rheological properties of interfacial layers responsible for droplets, particles, and droplet-particle-film structures in finely dispersed systems. The book examines structure and dynamics from various angles, such as relativistic and non-relativistic theories, molecular orbital methods, and transient state theories. 

Although the binder plays a transient role in the overall fabrication route, careful selection of a binder is vital to the success of the injection molding operation. The binder must provide the desired rheological properties to the feed material so that the powder can be formed into the desired shape and then must be removed completely from the shaped article prior to firing, without the disruption of the particle packing or any chemical reaction with the powder. A good binder must... 

It is demonstrated that MCT generalized in the integration through transient framework provides a full description of the flow curves as well as the viscoelastic behavior of concentrated suspensions with a single set of well-defined parameters, (see Figure 24). The theoretical approach describing nonlinear rheological properties of such dense colloidal suspensions was recently discussed by Fuchs. ... 

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