Two-dimensional films of discotic molecules at an air-water interface

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Abstract
The possibility of forming Langmuir monolayers with disc-like molecules of benzene-hexa-alkanoates has been investigated for the first time. Surface pressure measurements show that these monolayers behave in many respects as the well-known films of fatty acids. The benzene ring plays the role of the polar head group while the alkanoates chains are the long aliphatic tails. Molecular dimensions can be derived from the surface pressure-concentration isotherms. The results indicate that the benzene rings lie flat at the interface. The projection of the molecular diameter onto the interface is practically identical to the lattice spacing measured in the liquid-crystalline columnar mesophases formed by benzene-hexa-alkanoates in bulk. These experiments allow to refute the interpretation of the liquid expanded-liquid condensed transition in terms of a second order isotropic → nematic phase transition, as recently proposed by several theoretical groups

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