In the summer of 2004, ChemMatCARS successfully commissioned a Langmuir Trough for use in liquid-vapor interface studies. The trough is designed to be used in conjunction with the x-ray liquid spectrometer available in ChemMatCARS station 15-ID-C, but also may be used as a stand-alone instrument in our chemistry lab (schedule permitting). The trough may be used to obtain information about interfacial structure at aqueous solution/vapor interfaces. Langmuir monolayers and thin films at such interfaces are also readily probed. The primary x-ray techniques which may be used with this instrument follow:

• Reflectivity provides information about film thickness, surface roughness and electron density profile normal to the interface.
• In-plane diffraction provides information about ordering within the plane of the interface.

Langmuir Trough mounted on the liquid surface spectrometer in station 15-ID-C.
X-rays go from right to left

The Langmuir Trough was custom built for the x-ray reflectivity and grazing incidence measurements described above. Other features include:

• Temperature control: a Lakeshore, Model 330 is used to control sample temperature, and has the capability for both heating and cooling. (Maximum temperature ~40°C)
• Sealing: near-hermetic sealing allows for the introduction of helium into the sample environment, thereby minimizing ozone production and x-ray absorption.
• Software: a widely used package from Nima Technology Inc. controls the barrier motion and Wilhelmy plate pressure sensor readout.
• Common operational modes: isothermal compressions and constant pressure monitoring.
• Compression: a compression ratio of 10:1 may be achieved without simultaneous x-ray measurement, and up to 5:1 for measurements with x-rays.