PHASE-EQUILIBRIA AND INTERFACIAL-TENSION BETWEEN COEXISTING PHASES FOR THE SYSTEM WATER 2-PROPANOL POLY(ACRYLIC ACID)

The cloud point curve, tie-lines and interfacial tensions were measured for solutions of 50 mol-% neutralized (counter-ion Na-circle plus) poly(arylic acid) (mass-average molar mass (M) over bar(w) = 9 700 g/mol; polydispersity index (M) over bar(w)/(M) over bar(w) = 2,0) in the mixed solvent water/2-propanol at 30 degrees C. Due to the non-uniformity of the polymer, the end-points of the tie-lines are not situated on the cloud-point curve. The interfacial tension sigma - determined by means of the spinning drop method - increases in sigmoidal manner with R(t1), the length of the tie-line, expressed in terms of weight fractions. An evaluation of these data in a double-logarithmic plot of sigma.M(-0,5) versus R(t1) yields a critical exponent of 4,23 as compared with 3,85 in the case of binary systems. The dependence of a on w(w), the over-all weight fraction of water in the mixture, can also be expressed as a power-law choosing (w(cw)-w(w))/w(cw) as the concentration variable (w(cw): critical weight fraction of water); for the present system the exponent of the resulting equation amounts to 2,33 as compared with 2,0 for toluene/polyisobutylene/poly(dimethylsiloxane).