Properties of binary mixtures of surfactants containing symmetric hydrophobic tails and ammonium/phosphonium head groups as studied by tensiometry and 1H NMR

Tensiometric and NMR techniques have been utilized to study binary mixtures of tetradecyltriphenylphosphonium bromide (TTPB) with a series of gemini surfactants, viz. butanediyl-1,4-bis(dimethyltetradecylarnmonium bromide) (14-4-14, 2Br(-)), pentanediyl-1,5-bis(dimethyltetradecylammonium bromide) (14-5-14, 2Br(-)), hexanediyl-1,6-bis(dimethyltetradecylammonium bromide) (14-6-14, 2Br(-)), and a conventional surfactant tetradecyltrimethylammonium bromide (TTAB) in aqueous medium at 303 K The results obtained from tensiometric measurements have been analyzed by considering theoretical models of Clint, Rubingh and Rosen. The mixed surfactant systems show lower critical micelle concentration values than those of the individual components and that predicted by ideal mixing and strong synergism are observed in the systems. Throughout the entire bulk phase compositions of the components, the fractions of TTPB within the micelles and monolayers remain almost same. The H-1 NMR studies reveal that 14-4-14, 2Br(-) is more de-shielded than the other geminis elucidating that these micelles are crowded with more N-methyl protons. (C) 2014 Published by Elsevier B.V.