2003 年 52 巻 8 号 p. 421-428
By spin probe ESR, examination was made of the effects of temperature on aggregate properties of quaternary ammonium salt cationic surfactant solution with sodium salicylate (NaSal) as a function of 1) alkyl chain length and 2) number of 2-hydroxyethyl groups. For detailed study of rod-like micelle fluidity, measurement was made of the ESR spectra of 5NS, 12NS and 16NS incorporated in micelles in aqueous solution of [NaSal]/[HMODA]. The order parameter (S33) for 5NS considerably exceeded that of 16NS. Fluidity about the spin probe 5NS was much less. The hydrophilic layer of rod-like micelles in aqueous solution of [NaSal]/[HMODA] was more rigid compared to the hydrophobic core. The order parameter of 5NS decreased remarkably at 45-55°C but showed no significant change for 12NS and 16NS spin probes. The hyperfine splitting constant of 5NS (aN′), which reflects polarity about a spin probe, decreased remarkably at 45-55°C. Dehydration of 2-hydroxyethyl groups in [HMODA] took place with increase in temperature, with resultant reduction in the hydrophilicity of [HMODA]. For rod-like aggregates in aqueous solution of [NaSal]/[HMODA], a clear transition temperature was noted, which increased with alkyl chain length and the number of 2-hydroxyethyl groups in cationic surfactants.
