Tensiometric investigation of the interaction and phase separation in a polymer mixture-ionic surfactant ternary system

Abstract

The interaction and phase separation in a ternary mixture composed of hydroxypropyl methyl cellulose (HPMC), sodium carboxymethyl cellulose (NaCMC), and sodium dodecylsulfate (SDS) were investigated by tensiometry. Surface tension measurements of binary mixtures (0.7 % HPMC and 0.00-2.00 % SDS) and of ternary mixtures (0.7 % HPMC, 0.3 % NaCMC, and 0.00-2.00 % SDS) were performed. The measurements indicated interaction between HPMC and SDS, which resulted in HPMC-SDS complex formation. The critical association concentration, CAC, and polymer saturation point, PSP, were determined. Phase separation of ternary HPMC/SDS/NaCMC mixtures occurs at SDS concentration > CAC, i.e., when the HPMC-SDS complex is formed. The volume of the coacervate increases with increasing SDS concentration, and at SDS concentrations > 1.00 %, the coacervate vanishes. The surface tensions (σ) of ternary HPMC/SDS/NaCMC mixtures in the pre-coacervation region and at the onset of the coacervation region are similar to the σ of the corresponding binary HPMC-SDS mixtures, while in the coacervation and post coacervation region, they are close to the σ of the corresponding SDS solutions.