Dominance of long-chain N,O-diacylated ethanolamine in mixed amphiphilic acid amide monolayers

The main characteristics of Langmuir monolayers of acid amide amphiphiles with one and two alkyl chains are fundamentally different. This is demonstrated by comparison of surface pressure–area (π–A) isotherms, the mesoscopic morphology, and the two-dimensional lattice structure of the condensed phases in the case of the single-chain acid amides with N-myristoyl ethanolamine (TDAHA) and 3-hydroxy-N-tridecyl propanoic acid amide (HTPA) as well as in the case of the double-chain acid amide with N,O-dimyristoyl ethanolamine (TAOAE). The studies of the binary mixtures TDAHA/TAOAE, HTPA/TDAHA, HTPA/TAOAE (1:1) and ternary mixtures TAOAE/TDAHA/HTPA (1:1:1) performed at 5 °C and 25 °C allow the comparison with the single components. The results indicate convincingly that all binary 1:1 monolayers and the ternary 1:1:1 monolayer exist as homogeneously mixed systems. The dominance of the double-chain TAOAE in the binary and ternary monolayers mixed with single-chain acid amide amphiphiles TDAHA and HTPA in mesoscopic and molecular scale can be unequivocally concluded from the GIXD and BAM measurements. The probability for the presence of N,O-diacylated ethanolamine, such as TAOAE, as impurity in N-acylated ethanolamine, e.g. TDAHA, is high so that in such systems the most important interfacial characteristics are dominated by the impurity.