6533b862fe1ef96bd12c6079

RESEARCH PRODUCT

Über die möglichkeiten zur bestimmung von mischungsenthalpien und -volumina aus der molekulargewichtsabhängigkeit der kritischen entmischungstemperaturen und -drücke am beispiel des systems trans-decahydronaphthalin/polystyrol

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description

Cloud-point curves and critical curves (Tc = f(p)) have been measured for the system trans-decahydronaphthalene/polystyrene and three different molecular weights of the polystyrene component (2,5 · 106; 3,9 · 105; 1,1 · 105). It turned out that by variation of the pressure the metastable region can be investigated up to the spinodal curve. A comparison of the theta-temperatures and the enthalpy contributions χH (to the Flory-Huggins interaction parameter χ) resulting from the measured critical temperatures according to Shultz-Flory, with the corresponding directly obtained literature data, demonstrates that, although the extrapolation of Tc to infinite molecular weight is feasible, χH obtained in this way is greater by a factor of approximately three, due to the concentration dependence of χ. The same is true for the determination of χV (the contribution of the work in change of volume to χ) from the molecular weight dependence of the critical pressure. The determination of χV from the slope of the critical curves and known χH is, however, possible; the results are in good agreement with direct measurements. The shape of the critical curves calculated theoretically according to Prigogine and Patterson, turns out to be very sensitive to the precise values chosen for the mechanical data of the pure components. By adjustment of the system-specific parameters the measured critical curves can be well represented analytically.