Effects of sodium halide on the interaction between polyvinylpyrrolidone and sodium oleate : Surface tension and oscillating barrier studies

Abstract The effects of sodium halide (NaX: X = Cl, I) on the interaction between polyvinylpyrrolidone (PVP) and sodium oleate (C 17 H 33 COONa) were studied via surface tension and oscillating barrier methods. The results of surface tension measurement indicate that there is an interaction between C 17 H 33 COONa and PVP. Both critical micelle concentration (CMC) of C 17 H 33 COONa and the saturation concentration of C 17 H 33 COONa on PVP ( T 2 ) decrease in the presence of NaX. It is found that the binding amount of C 17 H 33 COONa on PVP is enhanced after NaX is added. NaCl is more efficient than NaI in promoting the association of C 17 H 33 COONa with PVP. The results obtained from the oscillating barrier at low dilational frequencies (0.01–0.1 Hz) reveal that the dilational modulus passes through a maximum value with increasing C 17 H 33 COONa concentration. Addition of PVP to C 17 H 33 COONa solutions makes the maximum value occur at much lower concentration while addition of NaX to C 17 H 33 COONa/PVP mixed systems further enhances this effect.