Influence of isopropanol on the rheological behavior of wormlike micelles

Abstract The influence of replacing water with isopropanol (IP) on the rheological properties of aqueous solutions containing wormlike micelles (WLMs) prepared by mixing cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) at 25 °C was investigated. Viscosity of CTAB aqueous solutions exhibits two maxima and one minimum with increasing amounts of NaSal, consisting of entangled WLMs. When water is replaced by increasing amount of IP, the viscosity maxima and the minimum changes drastically. The elastic plateau modulus G° of these solutions remains almost the same with increasing IP contents (up to ∼5 wt%), whereas their relaxation time changes drastically. Critical micelle concentration (CMC) of CTAB has increased with further IP addition, indicating an increase in the micellar hydrophilicity. For WLMs at minimum viscosity, increasing addition of IP (>5.0 %) to WLMs at maximum and minimum viscosities, leads to a drastic decrease in the elastic modulus G°, indicating the formation of smaller micellar aggregates. The influence of IP as a co-solvent on the WLMs rheological properties is also compared to that of glycerol and 1,3 butanediol (1,3 BD) for the same NaSal/CTAB viscoelastic system.