High viscosities of cationic and anionic micellar solutions in the presence of added salts

Abstract

Viscosities of micelles of cetyltrimethylammonium salts (CTAX, X = tosylate (TOS-), Cl-, Br-, NO3 -) in the presence of Cl-, Br-, NO3 -, benzene sulfonate (BS-), and TOS-, of cetylpyridinium chloride (CpyC) in the presence of Cl-, Br-, and NO3 -, and of sodium dodecyl sulfate (SDS) in the presence of Na+ and H+ counterions have been measured at 25 ± 0.01 °C. Viscosities were determined using a conventional Ubbelöhde viscometer connected to a wide U-Shaped tube containing water, which allowed measurement of the viscosities under different pressure and, consequently, at different flow rates; the viscosities reported here correspond to the values extrapolated to zero rate of flow because the solutions were highly non-Newtonian. The viscosity values exhibit the order TOS- > NO3 - > Br- > Cl- in CTAX and Na+ > H+ in SDS micellar solutions; i.e., the more strongly bound counterions produce the more viscous solution. The high viscosities observed in these systems are interpreted in terms of a