Maze Pattern at Nanometer-Scale in a Mixed Langmuir Monolayer of Fatty Acids

Abstract

We investigated the morphology of binary monolayers of palmitic acid and behenic acid using atomic force microscopic observations. The monolayers exhibited a phase-separated morphology composed of meandering domains with a width of nanometer order, which is probably due to fixation of the monolayer morphology at a stage on the way to phase separation.

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

“…It is, therefore, concluded from Figures – and previous results (C 16 /C 22 , C 16 /C 24 ) − that the molecular aggregation state, such as the molecular mixing or the phase separation of the mixed monolayer, depends on the difference in the number of methylene groups in the alkyl chain of a fatty acid molecule: the mixed system with a difference of four methylene groups was in a molecular mixing state and that of six and eight methylene groups were in a phase-separated state.…”

“…Previous morphological studies − for the (C 16 /C 22 ) and (C 16 /C 24 ) mixed monolayers (Figure S1 for C 16 /C 24 ) and Figure for the (C 16 /C 20 ) mixed monolayer showed that the molecular aggregation state of the mixed monolayer of fatty acids depended on the difference in the number of methylene groups (in other words, the difference in the cohesive energy of each alkyl chain): the molecularly mixed state was observed for the difference of four methylene groups, and the phase-separated state was observed for the difference of six and eight methylene groups. Next, the monolayer morphology was investigated using the different combinations (by fixing one fatty acid to C 24 ) of fatty acids.…”

“…Every monolayer was prepared at a surface pressure of 13.4 mN m –1 . This system has a difference of six methylene groups like the mixed system of C 16 and C 22 . The surface and thickness of the C 18 monolayer were considerably smooth with average surface roughness R a of ca.…”

“…The composition-ratio dependencies of surface area and specific pressures suggested that the (palmitic acid (C 16 )/arachidic acid (C 20 )) and (C 20 /lignoceric acid (C 24 )) mixed monolayers were in a molecularly mixed state, whereas the (C 16 /behenic acid (C 22 )), (stearic acid (C 18 )/C 24 ), and (C 16 /C 24 ) mixed monolayers were a phase-separated one. Of these combinations, the surfaces of the (C 16 /C 22 ) and (C 16 /C 24 ) − mixed monolayers have been observed using atomic force microscopy (AFM) to detect the height difference on a monolayer surface at the vertical and lateral resolutions of angstrom order. The (C 16 /C 22 ) and (C 16 /C 24 ) mixed monolayers were in a phase-separated state composed of domain and matrix regions at a height difference of ca.…”

Materials nanoarchitectonics in a two-dimensional world within a nanoscale distance from the liquid phase

“…4). 53 These structurally precise patterns are probably nanoarchitected through fixation of a two-dimensional morphology on the way to phase separation. Such delicate patterns would be useful in certain kinds of advanced applications such as nanoelectronics, nanophotonics, and nanosensing.…”