INTERFACIAL-TENSION AND INTERACTION PARAMETERS

In view of various contradictory theoretical equations relating the in terfacial tension sigma between phase-separated polymer solutions to t he Flory-Huggins interaction parameter of the system, the idea that si gma should depend on the extent of the 'hump' in the concentration dep endence of the Gibbs energy of mixing was studied. This investigation is based on 12 series of sigma(T) measurements reported in the literat ure and on additional experiments for the system cyclohexane/polystyre ne. To quantify the extent of the 'hump', a reduced 'hump energy' epsi lon was introduced and its value calculated for different temperatures from the measured critical data of the systems. The analysis of the e ntire experimental material yields a scaling law of the form sigma = E epsilon(F) where F is close to 0.5 for all systems, in contrast to E which varies within a larger interval. Furthermore, epsilon is related to tau, the relative distance to the critical temperature, by epsilon = A tau(B); B is approximately 2.4, again relatively independent of t he system, in contrast to A. In case of trustworthy values of the scal ing parameters, the above relations offer an interesting possibility t o estimate sigma(T) from the sole knowledge of the critical temperatur e of the system.