FTIR STUDIES ON PHASE TRANSITIONS OF N-OCTADECANOYL-L-ALANINE AND ZINC OCTADECANOYL-L-ALANINATE LB FILMS

Abstract The phase transitions of N-octadecanoyl-L-alanine and zinc octadecanoyl-L-alaninate LB films have been investigated through variable temperature FTIR spectroscopy. Hydrogen-bonding interactions between the enantiomeric head-groups strengthens the interactions between the alkyl chains so that the transition temperature of the N-octadecanoyl-L-alanine LB film (Tc = 122 °C) is nearly twice as high as that of the same-chain-length stearic acid LB film (Tc = 65 °C). The intermolecular hydrogen-bonding interactions in the zinc octadecanoyl-L-alaninate LB film are greatly intensified in comparison to that in the N-octadecanoyl-L-alanine LB film; the relatively weak hydrogen-bonding interaction in the latter is easily disrupted around its transition temperature (Tc = 122 °C) together with an abrupt increase of va(CH2) stretching frequency, while the intensified intermolecular hydrogen-bonding interaction in the former weakens step by step with temperature along with a monotonic increase of va(CH2) stretc...

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