- 作者: Fang-Fei Chou and Jeng-Shong Shih*
- 作者服務機構: Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan 116, R.O. C.
- 中文摘要: Fluorescence probe and nuclear magnetic resonance (NMR) methods were employed to investigate the micellation of prepared crown ether surfactants, e.g. decyl 15-crown-5 and decyl 18-crown-6. Pyrene was employed as the fluorescence probe to evaluate the critical micellar concentration (CMC) of these surfactants in aqueous solutions while spin lattice relaxation times (T1) and chemical shifts of H-1 NMR were applied in non-aqueous solutions. Decyl 15-crown-5 with lower CMC forms micelles much easier than decyl 18-crown-6 with higher CMC in aqueous solutions, whereas decyl 18-crown-6 forms micelles easier than decyl 15-crown-5 in nonaqueous solutions. Comparison of the CMC of crown ether surfactants and other polyoxyethylene surfactants such as decylhexaethylene glycol was made. Effects of salts and solvents on the micellar formation were also investigated. In general, additions of both alkali metal salts and polar organic solvents into the aqueous surfactant solutions increased in the CMC of these surfactants. The formation of micelles in organic solvents such as methanol and acetonitrile was successfully observed by the NMR method while it was difficult to study these surfactants in organic solutions by the pyrene fluorescence probe method. The NMR study revealed that the formation of micelles resulted in the decrease in all H-1 spin lattice relaxation times (T1) of hydrophobic groups, e.g. CH3 and CH2, and hydrophilic group OCH2 of these surfactants. However, upon the micellar formation, the H-1 chemical shifts (d) of these surfactant hydrophobic groups were found to shift to downfield (increased d) while the chemical shift of the hydrophilic group OCH2 moved to upfield. Comparison of the spin lattice relaxation time and H-1 chemical shift methods was also made and discussed.
- 英文摘要: --
- 中文關鍵字: Surfactant; Crown ethers; Crown ether surfactants; Micelles; Fluorescence probe; Spin lattice relaxation times.
- 英文關鍵字: Surfactant; Crown ethers; Crown ether surfactants; Micelles; Fluorescence probe; Spin lattice relaxation times.