Physicochemical studies on ion-pair amphiphiles: Solution and interfacial behaviour of systems derived from sodium dodecylsulfate and n-alkyltrimethylammonium bromide homologues

Bulk and interfacial properties of ion-pair amphiphiles (IPA), formed between sodium dodecylsulfate (SDS) and n-alkyltrimethylammonium bromide homologues (C (n) TAB; n = 10, 12, 14, 16, and 18), have been investigated. Different phases and aggregated states, formed in the ternary combinations of C(n)TAB/SDS/H2O, have been identified and described. Equimolar mixture of IPAs in water yielded precipitates, in the form of coacervates. Aqueous solubility of isolated coacervates in presence and absence of additives like cholesterol and bile salts have been examined. The isolated coacervates have been characterized by H-1 NMR, FTIR, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarization microscopic measurements. The coacervates have appeared in the shape of needle and complex flower-like aggregates. Surface pressure (pi)-area (A) isotherm of the coacervates at the air/water interface have been constructed and compared with the lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Morphologies of the IPA monolayers at different surface pressures have been also examined by epifluorescence microscopy. The compressed interfacial monolayers have produced spherical (both regular and irregular) and fern-leaf like domains.