The specific mechanism that underlies monolayer evaporation resistance has been attributed to the physical barrier formed by the presence of these materials on the surface of the water (see figure). The extent to which a material can resist the evaporation of water is best treated on a case-by-case basis, however, a number of empirically derived formulas have been reported. Before the advent of surface spectroscopic techniques such as Brewster Angle Microscopy (BAM) and Glancing Incidence X-Ray reflectrometry (GIXD), it was thought that the intermolecular spacing between monolayer molecules was the largest determinant factor governing evaporation suppression. When the surface density of the monolayer was sufficiently small, water molecules were presumed to pass through the space between molecules. Scattering and imaging results, however, revealed that the intermolecular distance between monolayer molecules was essentially constant, and that evaporation was more likely at domain boundaries.
The factors governing the efficacy of an evaporation suppressing monolayer are the ability to remain tightly packed despite changes in surface pressure, the ability to adhere to the surface of water, and to neighbouring molecules.