Solution properties of double-tailed cationic surfactants having ferrocenyl groups in their hydrophobic moieties

Solution properties of novel double-tailed cationic surfactants with two ferrocenyl groups introduced to the end of each alkyl chain ({Fc(CH2)(n)}N-2(+)(CH3Br- (n-BFDMA; n = 5, 11)) have been investigated by light scattering, relative conductivity, and polarized optical microscope measurements. The aggregation form of n-BFDMA is fairly dependent on its concentration. Scattered light intensity from a diluted (<10(-3) mol/L) 5-BFDMA solution shows a continuous increase at concentrations above 3 x 10(-5) mol/L (critical micelle concentration; cmc), suggesting the formation of micelles. On the other hand, the temporary decrease of the scattered light intensity from the diluted 11-BFDMA solution was observed at concentrations between 4 x 10(-6) and 6 x 10(-6) mol/L, which is more than 1 order higher than its cmc (1 x 10(-7) mol/L). The vesicles are found to be formed spontaneously above this concentration range. Vesicle formation may be attributed to a rod-like structure of the 11-BFDMA molecule by introducing the ferrocenyl groups at the end of the hydrophobic moiety. Furthermore, observation of concentrated (>10(-3) mol/L) solutions of 5- and 11-BFDMA by polarized optical microscopy shows the formation of liquid crystals dispersed in water and liquid crystals with high viscosity, respectively.