T. M. Bohanon

X‐ray diffraction study of heneicosanol monolayers on the surface of water

We have studied Langmuir monolayers of CH3(CH2)20OH (heneicosanol) using x‐ray diffraction. Over the temperature range 7–55 °C, the monolayer isotherms show only one discontinuity, which may be either a ‘‘flat section’’ or a ‘‘kink;’’ we find that these are transitions between tilted and untilted phases. There are several untilted phases, with hexagonal and distorted‐hexagonal structures, as in monolayers of the corresponding (heneicosanoic) acid. However, in contrast to the acid, when the pressure is lowered the molecules tilt only towards a next‐nearest neighbor. The dependence of the lattice spacings on pressure and temperature indicate that the monolayer does not form a ‘‘tilted hexagonal’’ phase, even at temperatures where the untilted phase is hexagonal (rotator‐II).

Fiber‐optic detection system for capillary waves: An apparatus for studying liquid surfaces and spread monolayers

Generating capillary waves with an alternating electric field gradient is a noncontact way to study the mechanical properties of monolayers. By studying capillary waves the surface tension can be calculated. In addition, the surface elasticity can be deduced and film inhomogeneity can be determined. We have incorporated a fiber‐optic detection system into a capillary wave apparatus. This makes the apparatus more compact, movable, versatile, and easier to use than detection systems currently in use.

Apparatus with an elastic barrier for radial compression of liquid supported monolayers

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.

X-Ray Diffraction Studies of Fatty Acid Monolayers on the Surface of Water

We review the current status of X-ray diffraction studies of Langmuir films. The structures of most known fatty acid monolayer phases have now been determined (and found to be different from what had historically been assumed); and various previously unexplained observations have now been given a microscopic basis.