Self-assembly and micellar transition in CTAB solutions triggered by 1-Octanol

Abstract

This study exploits higher-order micellar transition ranging from ellipsoidal to rodlike to wormlike induced by 1-octanol (C$_8$OH) in an aqueous solution of cetyltrimethylammonium bromide (CTAB), characterizing phase behavior, rheology, and small-angle neutron scattering (SANS). The phase diagram for the ternary system CTAB–C$_8$OH–water was constructed, which depicted the varied solution behavior. Such performance was further inferred from the rheology study (oscillatory-shear frequency sweep (ω) and viscosity (η)) that displayed an interesting solution behavior of CTAB solutions as a function of C$_8$OH. It was observed that at low C$_8$OH concentrations, the solutions appeared viscous/viscoelastic fluids that changed to an elastic gel with an infinite relaxation time at higher concentrations of C8OH, thereby confirming the existence of distinct micelle morphologies. Small-angle neutron scattering (SANS) provided various micellar parameters such as aggregation numbers ($N_{agg}$) and micellar size/shape. The experimental results were further validated with a computational simulation approach. The molecular dynamic (MD) study offered an insight into the molecular interactions and aggregation behavior through different analyses, including radial distribution function (RDF), radius of gyration (R$_g$), and solvent-accessible surface area (SASA).