Local surface pressure gradients observed during the transfer of mixed behenic acid pentadecanoic acid Langmuir films

Abstract

Fatty acids are good candidates for modelling biological membranes and the interactions occurring between lipids and proteins [1-2]. In particular, it is possible to form Langmuir films at the air/water interface when the hydrophobic chains are long enough to ensure a high water insolubility of the fatty acids. When transferred on a solid substrate by the Langmuir-Blodgett technique [3], the films can be studied by different spectroscopies, and by scanning force microscopy [1]. A problem of interest is to study the formation of lipid domains which may play a key role in biological processes [4]. It is possible to model this behaviour in Langmuir monolayers, by using at least two lipids [5-8], for example two fatty acids differing only by their chain length [9]. In this paper we report an initial study of Langmuir films constituted of two fatty acids, behenic acid and pentadecanoic acid. These first investigations led us to obtain original results, and in particular to observe a great rigidity of the mixed film. Scanning force microscopy confirmed the existence of microscopic domains stable for long times in these mixed films transferred on muscovite. The existence of pressure gradients in the film is discussed.