Evolution of CTAB/NaSal Micelles: Structural Analysis by SANS

Surfactants self-assemble into micelles in aqueous solution and exhibit structural polymorphism. Under certain conditions, long and flexible structures referred to as wormlike micelles (WLMs) can develop and entangle to form a transient network, leading to spectacular viscoelastic properties. The salt concentration–in particular, the molar ratio of salt (C_s) to surfactant (C_d), C_s/C_d–has been shown to have a significant influence on the viscoelastic properties of WLMs. Salicylate (Sal^-) has a strong affinity for the cationic surfactant cetyltrimethylammonium bromide (CTAB) and can promote the growth of WLMs even at very dilute surfactant concentration. We investigate the structure of CTAB/NaSal micelles at relatively low concentration over a wide range of C_s/C_d. Using small-angle neutron scattering and the most advanced scattering function for WLMs, we characterize the development and structural evolution of wormlike micelles both qualitatively and quantitatively, culminating in an understanding of the phase behavior of CTAB/NaSal within this region of phase space.