Monolayer Characteristics of an N-Acylated Ethanolamine at the Air/Water Interface

• Published in: Journal of physical chemistry. C 2011-04, Vol.115 (16), p.8206-8213
• Main Authors: Brezesinski, G, Dobner, B, Stefaniu, C, Vollhardt, D
• Format: Article
• Language: English
• Subjects: C: Surfaces, Interfaces, Catalysis
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp200847c

The main characteristics, such as surface pressure−area (π−A) isotherms, morphology of the condensed phase domains, lattice structure of the condensed phase, and the existence of hydrogen bonds (NH···OC) of the monolayers of a highly purified N-acylated ethanolamine (C13H27CONHC2H4OH, TDAHA), are determined. At temperatures measured between 10 and 36 °C, the characteristics of the surface pressure−area (π−A) isotherms, which indicate the main first-order phase transition from the fluid phase to the condensed phase, are similar to those of usual amphiphiles. However, at temperatures of ≤10 °C, a second inflection point whose transition pressure increases strongly with increasing temperature proves the existence of a second first-order phase transition between two condensed phases. The entropy change of this second transition is small with only 10% of that observed for the main phase transitions at the same temperature. The fractal-like shaped condensed phase domains have a limited tendency to branching and are characterized by the absence of an inner texture in the homogeneously reflecting domains. The characteristic features of the two-dimensional lattice structure are obtained by GIXD studies. An oblique lattice is formed after the main phase transition with a cross-sectional area of 19.3 Å2, whereas after the second phase transition an orthorhombic L2′ phase arises accompanied by a drastic decrease of the molecular tilt angle. The IRRAS experiments confirm the existence of an extended hydrogen bonding network (NH···OC) in the TDAHA monolayers by the positions of the amide bands and the transition from an oblique into an orthorhombic phase by the split of the CH2 deformation band.