Abstract
A drop of liquid, when deposited on a subphase of another immiscible liquid ideally exhibits two types of spreading behavior: it may either spread completely to a thin film on the underlying fluid, or it may reach an equilibrium shape of a static lens. The equilibrium spreading coefficient, which depends on the three interfacial tensions, subphase-air, drop-subphase and drop-air, determines this. In some cases, we notice a static lens even though a positive spreading coefficient predicts complete spreading. Also, we always observe a surface tension change at considerable distances outside the lens boundary. Surfactant solutions and surfactants alike show this behavior. This thesis investigates this abnormal behavior and we deduce that surfactants move across the contact line of a lens in the form of a monolayer and reduce the surface tension. This explains why the lens resists spreading on the monolayer thereby leading to autophobing.
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