Langmuir-Blodgett monolayers and multilayers of stearic acid and stearyl amine

Abstract

For mixed monolayers it has long been shown that the addition of stearic acid facilitates the transfer of Langmuir-Blodgett monolayers and multilayers otherwise difficult to transfer. Mixed monolayers of stearic acid (SA) and stearyl amine (SAM) have been studied with the aim both of obtaining monolayers appropriate for transfer and of defining the parameters relevant to the latter. The spreading isotherms of SA and SAm in several molar ratios on a subphase at pH 5.5 and T = 20°C allowed determination of the complete miscibility of the two components. Moreover the comparison of the transfer ratios between the mixtures and the pure components proves that the mixtures, and in particular the equimolecular mixture, show an improved transferability. The hysteresis isotherms show that the improved transferability can be attributed to improved surface rheological properties of SAm monolayer to which SA had been added. The Fourier transform IR spectra of transferred multilayers and the spectra of the monolayer of each component and of their mixtures in equimolecular ratio obtained by electron spectroscopy for chemical analysis show that, beyond the favourable disposition of the hydrophobic chains, interactions between the carboxilic and aminic functional groups are responsible for the improved transferability.