Interfacial tension between polymer-containing liquids - Predictability and influences of additives

The first part of the contribution deals with the interfacial tension, sigm a, of phase-separated polymer solutions in single or mixed solvents and of binary polymer blends as a function of the relative distance to the critica l temperature of the system, special attention being paid to the possibilit ies of theoretical prediction. Two methods are discussed in more detail. On e is based on a realistic description of the Gibbs energy of mixing as a fu nction of composition, the second correlates sigma with the length of the m easured tie line. The second part is devoted to another aspect, namely the effects of additives on the interfacial tension between the coexisting phas es of demixed polymer solutions and between highly incompatible polymers. I n the former case, it is demonstrated that an addition of a thermodynamical ly good solvent is normally associated with a reduction in sigma; however, adding a high-molecular-weight compound which is incompatible with the diss olved polymer leads to an increase in sigma. The interfacial tension betwee n incompatible homopolymers is efficiently reduced by block copolymers cons isting of monomeric units which are either identical with or different from those of the homopolymers; in contrast to theoretical expectation, the mol ecular architecture of the additives seems to be of minor importance only. Random copolymers which are insoluble in the homopolymers can also efficien tly reduce the interfacial tension.