Electron microscopic studies of monolayers at the air/water interface

Abstract

The question of artifact formation associated with electron microscopic examination of the structure of monomolecular films was investigated. The effects of mode of film compression, surface energy of solid substrate, and surface roughness of solid substrate onto which fatty acid and phospholipid monolayers were transferred by the Langmuir-Blodgett technique from the air/water interface were systematically examined. Aberrations in monolayer structure can occur when low-energy solid surfaces such as Formvar and collodion are used for monolayer transfer below some specific surface pressure which is slightly different for each solid substrate. The observed structures bear similarity to the observations reported in other studies. However, when the monolayers are transferred onto mica substrates, the artifacts previously observed by electron microscopy appear to be eliminated and surface films existing in the liquid-expanded and liquid-condensed states exhibit a structure indicative of single-phase behavior, i.e., they are smooth, continuous, and homogeneous in agreement with current theories on monolayer structure. These results are discussed and compared with those of earlier microscopic studies.