화학공학소재연구정보센터
Journal of Chemical and Engineering Data, Vol.57, No.11, 3153-3163, 2012
Micellization and Catalytic Properties of Cationic Surfactants with Head Groups Functionalized with a Hydroxyalkyl Fragment
The catalytic activity of two homological series of cationic surfactants bearing a hydroxyalkyl fragment in the head groups R(CH3)(2)N+(CH2CH2OH)Br- and R(CH3)(2)N+(CH2CH2CH2OH)Br- toward the cleavage of the p-nitrophenyl esters of carbonic acids of different hydrophobicity (acetate, caprilate, caprinate, laurate, myristate) is shown to exceed that of typical cationic surfactants with the trimethylammonium (TMA) headgroup. The catalytic effect increases with the alkyl chain length of surfactants and nonmonotonous changes in the series: acetate < caprilate < myristate < laurate < caprinate, reaching 750 times. NMR and IR spectroscopy studies and the surface potential calculations revealed that the higher catalytic effect of hydroxyalkylated surfactants is not due to their higher surface potential and binding capacity toward substrates. This is in line with finding that binding constants for TMA series are higher than for their hydroxyalkylated analogues, which was demonstrated by the fitting of kinetic data in terms of the pseudophase model. The microenvironment factor rather than concentrating effect is responsible for the advanced catalytic properties of hydroxyalkylated surfactants in the micellar phase.