Langmuir films of nitro substituted N-benzylidene hexadecylamine Schiff bases at air/water interface—Phase transitions and molecular dynamics simulation

Interfacial Behaviors of Giant Amphiphilic Molecules Composed of Hydrophobic Isobutyl POSS and Hydrophilic POSS Bearing Carboxylic Acid Groups at the Air–Water Interface

“…Additionally, Frank et al, who use poly(benzyl ether) monodendrons with linear oligo(ethylene glycol) tail molecular systems, also find the same cusp phenomenon. 39 However, in this research, the π−A isotherms of giant molecules present an obvious cusp, while they do not show the long plateau region after the cusp.…”

“…The similar cusp phenomenon in the π−A isotherms was also observed previously in various molecular systems, such as nitro-substituted n-benzylidene hexadecylamine Schiff bases, 40 oxyethylenated nonionic surfactants, 41 diethylene glycol monon-octadecyl ether, 42 and trisilanolcyclohexyl-POSS. 29,39,43 The π−A isotherms of these studied molecules showed a cusp point and followed a long plateau region, which indicates the phase transition of a monolayer from a liquid expanded phase to a density liquid condensed phase. 40−43 However, most of cusp phenomena of π−A isotherms do not show the small peak shape but have more like a turning point.…”

“…Davies and Rideal described that the monolayer is in the liquid expanded (LE) state when 12.5 < C s −1 < 50 mN/m, in the liquid condensed (LC) state when 50 < C s −1 < 250 mN/m, and in the solid state for 1000 < C s −1 < 2000 mN/m to define the different phase behaviors of long-chain fatty acids. 25,39 However, due to the different molecular structures, the monolayer phase behavior of giant molecules is significantly different. There are three main features in the figures.…”

“…The first increment of C s −1 indicates a phase transition of the monolayer, and the second increase in C s −1 represents the tightest arrangement of molecules. 39 Second, because of the cusp phenomenon, the isotherms of (BPOSS) n -ACPOSS (n = 2−5) show decreases in the surface compression modulus which are caused by the transition from monolayer to multilayer (Figure 3). Finally, the maximum surface compression modulus increases gradually as the size of BPOSS blocks increases, indicating the denser stacking of molecules.…”

“…The hydrophobicity of the molecules can affect the stability of the monolayer. 39 However, the main chain giant molecules do not show the cusp phenomenon (Figure S2). The main chain giant molecules with rigid molecular structure limit the rearrangement of monolayer structure.…”