Research Fields

Rheological behavior

The reports collected under the title "Rheological behavior" are incomplete by nature. Additional information can also be found in the sections "Interrelation of thermodynamic and flow effects" and in "Continuous polymer fractionation". For that reason, and because of the fact that the number of investigations is in some areas (like in the field of kinetics) not numerous enough to justify a separate chapter, we propose to search the homepage for the topic you are interested in.

Some of the findings and approaches described in the present section might be helpful in research areas that differ widely from the ones we have investigated. They are specified below.

  • Modeling the viscosity over the full range of composition: A phenomenological equation describes the viscosities from the pure solvent up to the polymer melt by means of a maximum number of three parameters, where one of them can in many cases be set zero. It enables the unequivocal determination of intrinsic viscosities of polyelectrolytes in pure water and allows the determination of a new parameter, the intrinsic bulkiness of the polymer.

  • Subdivision of the viscosity in an entanglement and a frictional term: Numerous cases exist for which the influences of shear rate on the viscosities of solutions cannot be modeled adequately by entanglement theories. This deficiency can be easily eliminated by introducing a frictional term, independent of shear rate. The importance of this contribution rises as the solvent becomes poorer.

  • Extrapolation of viscosities to zero shear: An analytical expression, models the dependence of the viscosities on shear rate quantitatively. It enables a reliable extrapolation to zero shear in cases, also in cases in which direct measurements are impossible. Moreover, the approach introduces two helpful system-specific parameters.

  • Morphology: We have studied the structure development of liquid two-phase systems upon changes in the rate of shear (studying subdivision or coalescence of droplets). These results may contribute to a more comprehensive understanding of such mixtures.

  • Anomalous p and T dependencies : Activation volumes and activation energies normally vary smoothly with composition. However, extra effects need to be taken into account for thermodynamically poor solvents.

  • Polymer clusters: A clear distinction between clusters formed under equilibrium conditions and clusters established under stationary flow conditions is mandatory for the understanding of polymer containing systems, as discussed in the section "Interrelation of thermodynamic and flow effects".