An interplay between spacer nature and alkyl chain length on aqueous micellar properties of cationic Gemini surfactants: A multi-technique approach

Micellar parameters (critical micelle concentration (cmc), degree of micellar ionization (alpha), Krafft temperature (T-k), micro-polarity, aggregation number (N-agg) and dielectric constant (epsilon(a))) of aqueous cationic geminis (denoted as m-s-m; where, m = 12 or 14 and s = polymethylene, diester, diamido or diester isosorbate) have been studied by multi-technique approach (conductometry, fluorescence and H-1 NMR) and compared with alkyltrimethylammonium bromide (C(m)TAB). Geminis show lower cmc and T-k than C(m)TAB. Among the geminis, hydrophilic spacer containing geminis show even lower cmc and T-k than the polymethylene spacer geminis. Temperature dependence of cmc shows a decrease, constancy followed by an increase (U-shaped behaviour) as s or m changes. Thermodynamic parameters have been obtained by temperature dependence of cmc. Intramicellar monomeric arrangement and micellar size information have been acquired by 2D NOESY/COSY H-1 NMR and dynamic light scattering (DLS), respectively. Data suggest that the hydrophilic spacer based geminis produce compact micelles with higher polarity compared to polymethylene spacer geminis (or C(m)TAB). The approach might be employed to tune the micellar interior environment/size, by changing the nature of the spacer or m. (C) 2019 Elsevier B.V. All rights reserved.