Mixing Behavior of the Binary Monolayers of Fatty Acids Based on Their Cohesive Energy Differences.

The morphology involving the height difference and the surface roughness of the binary monolayers of saturated fatty acids were evaluated using atomic force microscopy (AFM) to investigate the mixing behavior of their monolayers. AFM observations revealed that the mixed monolayers of (palmitic acid/arachidic acid) and (arachidic acid/lignoceric acid), which had four methylene group differences between fatty acids, were in a molecularly mixed state. Further, the mixed monolayer of (stearic acid/lignoceric acid), which had six methylene group differences, was in a phase-separated state.