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Langmuir Film Balance

A langmuir film balance allows you to measure both the molecular area and surface pressure of surfactants spread at the air-water interface. This technique gives an experimentalist tremendous control of the packing environment of the monolayer. The behavior of lipids can be observed as they are compressed from a non-interacting gaseous phase to a tightly compressed gel. Below is a picture of a Langmuir trough. Click the trough to see a simple cartoon of this technique.

Langmuir Trough

Fluorescence Microscopy
The mixing phase behavior of lipid monolayers and bilayers can also be studied by including a trace amount of fluorescently tagged lipids into a multi-component monolayer or bilayer system. Miscible lipids provide a homogeneous environment for the fluorescently tagged probe to explore and as a result the image will appear uniformly bright. However, if the lipid mixture is immiscible the fluorescent probe will unevenly separate between the two phases. This uneven partitioning of fluorescent probe produces a contrast which can be observed and recorded with a CCD camera.

Fluorescence Microscopy
Click on the picture above to see a movie of a sterol/phospholipid phase transition.

Fluorescence Microscopy
Click on the picture above to see liquid-liquid coexistence at the air-water interface.

 

In addition to determining mixing properties fluorescence microscopy can also be used to identify liquid-liquid or liquid-solid coexisting phases. The image on the right illustrates solid-liquid coexistence in a pure DPPC monolayer. The image to the left illustrates liquid-liquid coexistence where line tension plays an important role. In both monolayers a trace amount of Texas Red has been added to provide contrast.