Research Fields

Thermodynamic behavior

The reports collected under the title "Thermodynamic 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.

  • A molecular approach for the modeling of polymer-containing systems: It separates the dilution process into two separable steps, (i) the insertion of a solvent molecule between two contacting polymer segments and (ii) the subsequent re-arrangement of the polymer chain into the equilibrium state. It uses a maximum of three adjustable parameters and correctly describes all experimentally observed phenomena, like islands of miscibility or immiscibility or three phase equilibria.

  • A simple phenomenological approach for the modeling of polymer-containing systems: It modifies the original Flory-Huggins theory by using weight fractions instead of volume fractions and accounts for ternary contacts; moreover it multiplies the logarithmic term by a freely selectable factor. The number of adjustable parameters is three again. The big advantage of this approach consists in its applicability to all kinds of high molecular weight compounds, including for instance globular proteins.

  • Flow effects on phase separation: The key for the understanding of such influences lies in the energy the systems are able to stow in the stationary state. Extending the Gibbs energy of mixing by this term enables the modeling of shear induced mixing and shear induced demixing likewise.

  • Prediction of interfacial tensions: The calculation of the area defined by the composition dependence of the Gibbs energy of mixing on one side and the double tangent to it (indicating the extension of the two-phase region) yields reliable access to this quantity.

  • Measuring Flory-Huggins interaction parameters: One of the easiest ways to obtain such data consists in the combination of head space sampling and gas chromatography. To cover the complete range of composition, this method should be complimented by light scattering or osmometry.

  • 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".