Spontaneous Formation of Micelles and Vesicles in Langmuir Monolayers of Heneicosanoic Acid

In Langmuir monolayers of heneicosanoic acid (C21H42O2), at low temperature, in the L′2 and CS crystalline phases, a blinking phenomenon occurs at the same positions of the monolayer, which is called localized oscillations (LO), but its origin has not been clarified. In this study, the LO phenomenon was correlated with the ejection of material out of the monolayer which was analyzed to understand this phenomenon. The techniques used for this purpose were pressure-area isotherms on a Langmuir balance and simultaneous observation of the monolayer by Brewster angle microscopy (BAM). Subsequently, using the Langmuir-Blodgett technique, the monolayers were transferred using freshly cleaved mica substrates for analysis by atomic force microscopy (AFM). Our results showed that the origin of the LO is related to a spontaneous formation of micelles and vesicles, since in AFM images these structures were observed in a size range from 4 to 16 nm. In addition, the AFM images showed that the difference between the heights of the L′2 and CS crystalline phases ranges from 13 to 15 Å.

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