Relevance of π-stacking in tuning the neighboring structural pattern of soft nano-aggregates

Abstract

Smart wormlike micellar blends can be readily formed from surfactant micelles in presence of counterion, salt or under varying conditions of pH, concentration, salinity driven by cation-π interaction whereas the role of π-π interaction in the same remains less explored. In this investigation the impact of π-π interaction on nanoaggregates of cationic amphiphile viz., cetylpyridinium bromide (CPB) in contrast with the cation-π interaction in cetyltrimethylammonium bromide (CTAB) in the presence of surface-active aromatic π conjugated hydroxy aromatic derivatives of naphthalene viz., 1 Naphthol, 2 Naphthol and 2,3 Dihydroxynaphthalene is reported. The presence of π-π interaction in CPB enables stronger synergism between the hydroxynaphthalenes compared to the non-aromatic analogue CTAB while face-to-face stacking interaction in CPB-hydroxynaphthalene systems lead to formation of worm like micelle (WLM) with relatively short entanglement lengths as compared to that in CTAB. The modification of surface parameters and molecular interactions of the systems are studied via tensiometry, 1H nuclear magnetic resonance (NMR), 2D-Nuclear Overhauser effect spectroscopy (NOESY) and small angle neutron study (SANS). The non-Newtonian behavior of the complex fluids comprising the cationic amphiphiles and hydroxyaromatic derivatives are studied using static and dynamic rheometry.