Rheological Behavior of Trimeric Anionic Surfactant/Cationic Additive Mixed Systems

Surfactant structure is known to have a significant effect on the formation and properties of wormlike micelles. In the present study, a new trimeric anionic surfactant (sodium 2,2',2 ''-(benzene-1,3,5-triyltris(oxy)) tritetradecanoate, abbreviated as Ph-TrisC(14)Na) was synthesized from myristic acid and m-trihydroxybenzene. The viscoelastic properties of single component Ph-TrisC(14)Na and Ph-TrisC(14)Na/cationic additive systems were subsequently investigated by steady state and dynamic rheological measurements, using butyltrimethyl ammonium bromide (C(4)TAB), hexyltrimethyl ammonium bromide (C(8)TAB), and octyltrimethyl ammonium bromide (C(8)TAB) as the additives. The results show that the unique molecular structure of Ph-TrisC(14)Na enables the formation of wormlike micelles when this compound is the sole component of the solution, and generates solutions with significant viscoelasticity. The addition of cationic species further optimizes the molecular geometry of the Ph-TrisC(14)Na and promotes the rapid growth of wormlike micelles. Additives with longer hydrophobic chains have a marked effect on the viscoelasticity and the microstructure of the mixed solution systems. A 50 mmol.L-1 Ph-TrisC(14)Na solution exhibits a zero shear viscosity of 1535 Pa.s together with micelle lengths in the range of 4.0 to 7.5 mu m at a C(8)TAB to Ph-TrisC(14)Na molar ratio of 0.5. The present system shows the advantage of using an oligomeric surfactant in viscoelastic surfactant solutions. The information obtained from this work should be beneficial with regard to expanding the scope of highly viscoelastic anionic wormlike micellar systems.