Z Khattari, U Langer, S Aliaskarisohi and Th M Fischer
Keywords: Langmuir monolayers, line tension, optical tweezers
Abstract: The line tension of a liquid expanded (LE)/gas (G)-phase boundary of methyl octadecanoate Langmuir monolayer (LM) at the air/water interface is investigated upon adsorption of protein or surfactant dissolved at different concentrations in the aqueous subphase. Optical tweezers experiments coupled with fluorescence microscopy were used to achieve this goal. We combined different theoretical models which view LMs as a 2d-fluid coupled with a 3d-subphase viscose barrier for better understanding of the LM properties such as viscosity and line tension. In particular, the line tension of the LE/G boundary has been investigated at nano-molar subphase concentrations and an increase in the line tension was observed. This result suggests that the presence of the aqueous subphase may affect the viscosity and the line tension of the monolayer and provides a direct test for the validity of existing theoretical models.
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