We have constructed an apparatus that radially compresses monolayers on the surface of water. This mode of compression prevents the anisotropy that is sometimes observed in films that are compressed uniaxially. The area is changed using an elastic band stretched around 12 fingers which move synchronously. The ratio of maximum to minimum diameter of the elastic barrier is ∼7:1, so that the compression ratio is ∼50:1. The apparatus can accommodate dishes of various sizes up to 8 in. in diameter. The temperature is controlled by circulating water under the dish. Isotherms obtained using this apparatus illustrate the difference between uniaxial compression and radial compression for a fatty acid monolayer.
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