不对称Gemini表面活性剂在气/液界面的吸附动力学

合成出由1个亚甲基联接羟基和季铵基头基, 且带两根不同长度烷烃链的不对称Gemini表面活性剂CmH2m+1OCH2CH(OH)CH2N+(CH3)2C8H17Br(记为CmOhpNC8, m=10, 12, 14). 用最大泡压法研究了浓度低于临界胶团浓度时, CmOhpNC8在气/液界面上的吸附动力学. 结果表明, CmOhpNC8表现出很明显的吸附动力学效应. CmOhpNC8向新鲜气/液界面吸附时由扩散过程控制; 当界面上已具有一定吸附量时, 显示出吸附能垒Ea. 随着烷烃链的增长而明显降低, 表明长烷烃链的分子到达亚层后更容易插入表面层,这被归结为分子烷烃链间的疏水相互作用随着链增长而增强所致.

Adsorption Kinetics of Asymmetric Gemini Surfactants at Air/Water Interface

Asymmetric Gemini surfactants CmH2m 1OCH2CH(OH)CH2N (CH3)2C8H17Br,referred to as CmOhpNC8(m=10,12 and 14),were synthesized.This type of surfactant molecule has a head region(a hydroxyl and a quaternary ammonium linked by one methylene group)with a small size and two alkyl chains with different lengths.The maximum bubble pressure technique was used to investigate the adsorption kinetics of CmOhpNC8 aqueous solution below their critical micelle concentrations at the air/water interface.The results showed an obvious kinetic process for the adsorption of CmOhpNC8.When CmOhpNC8 were adsorbed on the freshly formed interface,the adsorption process was pure diffusion controlled.When some molecules existed at the interface,the adsorption barrier(Ea)appeared,which reduced with increasing m.This indicated that those molecules with long alkyl chain migrated more easily from the subsurface into the surface,which was attributed to enhanced hydrophobic interaction between the alkyl chains with increasingm.