From Gibbs- To Langmuir-Type Adsorbed Layers: Alkylated Azacrown Ethers At Liquid-Liquid Interfaces

摘要

Adsorption properties of three alkylated diazacrown ether derivatives in a toluene—water system are described. The three derivatives share the same hydrophilic diaza-18-crown-6 moiety, substituted at both nitrogen atoms with decyl (ACE-10), hexadecyl (ACE-16), or tetracosane (ACE-24) alkyl chains. Dynamic interfacial tension measurements at the toluene—water interface revealed a nondiffusional mechanism of adsorption for all three ACEs. The interfacial tension isotherms obtained from the drop-shape analysis were fitted with a reorientation model (for ACE-10 and ACE-16) and Langmuir model (ACE-24), pointing to different structures of the respective spontaneously adsorbed layers: loose (Gibbs-like) for the short-chain derivatives and dense (Langmuir-like) for the long-chain. These results are in full agreement with previous neutron and X-ray reflectivity studies. Despite an apparent cmc, the ACE molecules probably do not form reverse micelles in highly concentrated solutions in nonpolar solvents.