Physical Chemistry under pressure

Our research interests in this field are (mainly for polymer containing systems): - Rheological measurements under pressure - pressure influence on the viscosity We also describe both the obtained data and literature data theoretical (for example using Sanchez-Lacombe or Flory-Huggins)

Equipment

For the rheological measurements under pressure we have two instruments: These are a rolling ball apparatus for low viscosities and a high pressure rheometer. The later one posesses the advantage that measurements in dependence of the shear rate can be done.

Rheometer

Fig. 1. High pressure rheometer

High pressure cell

Fig. 2. High pressure cell

We also have a Kratky apparatus for determing the density.

Examples of scientific topics

An example for rheological measurements is at our rheology-page. The following diagram depicts the cloud points of the system ethylene / PIB 1.4 (Polyisobutylene). The determination took place visual by reducing the pressur starting from the homogenious region until reaching the two-phase region. By increasing the temperature the pressure has also to be increased to take the system into the homogenious region.

Phase diagram Ethylene/PIB

Fig. 3. Phase diagram for the system Etylene / PIB 1.4 (Polyisobutylene)

Using the Kratky apparatus pvT data of both, the pure polymers and the mixtures can be obtained. The following graphs gives an example for the system CO2 / PDMS 42:

pVT data CO2/PDMS

Fig. 4. pvT data for the system CO2 / PDMS 42.

Theoretical calculations

We use different theories for measured and for literature data.
critical points TD/PS

Fig. 5. Interrelation of critical composition and pressure in the system trans-decaline / poly(styrene) for different molecular weights.

Cloud points for sloutions of polystyrene of different molar masses in trans-decalin as a function of pressure: (open symbols) measurements, (full triangles) extrapolation to infinite molar amss; (full lines) calculated isopleths; (broken lines) calculated critical curves. The volume fractions of the polymer are the critical ones at atmospheric pressure. Since the critical composition changes with pressure according to theory, the calculated critical curves (broken lines) differ from the isopleths (full lines). The pressures of optimum solvent quality are indicated by full circles. The two-phases area is indicated by hatching. The experimental data have been reported in the literature.

Publications concerning pressure