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Brewster Angle microscopy

O PT RE L GbR www.optrel.de

Monolayer at the air-water interface an* intercsting quasi-two-dimensional model systems for studying fumlamental internet ions. They are also a prectirsor film within tl»e LB fabrication process as illustrated in the following figurę:

The amphiphile is dissolved in au organie solvent and sub-sequently spread at the air-water interface. Tlie solvent evaporates and a monolayer of the amphipliile at the air-water interface is then produced. Tliese so callcd Lang-inuir monolayers can Im* further manipulated by ineans of a moveable barrier which allows us to control the area per inolecule. They possess a large numher of phases which may exhibit a different orient arion. tilt azinmth or rota-tional degrees of freedom of the inoleculcs. Tliese features can be visualized by means of Brewster Angle Microscopy (BAM). The typical domain sizes are in tlie order of 20-200 micrometers.

The existence of a Brewster angle is a peculiarity of p-polarized light. The rcflcctivity cocfficient r_p vanishes at the Brewster angle and hence no liglit is reflected therc. A monolayer at the air-water interface yields a certain amount of reflected light r_p = 10~⁶. which is sufficient to produce an image. This tedmique is superior to fluores-cence microscopy, sińce it does not recjuire any lal>el which could have an undeeired impact on tłie Systems.

The- following example shows tlie BAM image of domains of the glycerol ESD-16 recorded at t he air-water interface. Tlie domains are of circular shape and possess a sevenfold internal symmetry. The contrast between the segments is due to the different organization of tlie tilt azimutli within eacli segment. The picture on the riglit hand side shows the same domains at tlie oil-water interface. The circular shape is lost due to a reduction of the linę tension. (M. Harke. H. Motschmann. "On tlie Transition State between the Oil-Water and Air-Water Interfaces", Langmuir, 14, 313 (1998))

OPTREL GbR has established a succcssful collabo ration with tlie company RlBGLER&KlRSTEIN LTD. (www.rieglerkirstein.de). Tlie result is a custoin madę trough for the Multiskop which is displayed in this figurę.

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