Improved thermal stability of Langmuir-Blodgett films through an intermolecular hydrogen bond and metal complex

Langmuir-Blodgett (LB) films of N-octadecanoyl-L-alanine and its silver and zinc complexes have been investigated by variable-temperature Fourier transform infrared transmission spectroscopy. The thermal stability of LB films is improved through an intermolecular hydrogen bond and metal complex. The intermolecular hydrogen-bonding interaction between hydrophilic head groups in the same monolayers and the metal complex between one head group and another in the neighboring monolayers considerably increase the interaction between the corresponding hydrophobic alkyl chains. It is shown that the transformation of the triclinic subcell packing of the molecules in the LB films prior to and after the silver complex into hexagonal packing occurs before the phase transition accompanied with a change in molecular orientation. The phase transition behavior of the LB films is varied from a small temperature interval to large one depending on the hydrogen bond and metal complex.