Effect of subphase temperature on the phase-separated structures of mixed Langmuir and Langmuir–Blodgett films of fatty acids and hybrid carboxylic acids

We examined the phase-separated structures of the mixed Langmuir–Blodgett (LB) films of CkH2k+1COOH (HkA: k = 17, 21) and CmF2m+1C10H20COOH (FmH10A: m = 6, 8) fabricated isothermally or after isobaric thermal treatments. Under isothermal fabrication conditions, disks and wire-type domains formed in the H17A/F6H10A LB films at high and low fabrication temperatures, respectively, because the line tension and dipole–dipole interaction were comparable with each other. The thermodynamically stable phases of H21A/F6H10A LB films at high and low fabrication temperatures were disks and polygonal domains, respectively. Isobaric thermal treatments of the Langmuir films affected the domain size and not the domain shape when the transfer temperature was the same. Isobaric thermal treatments were effective in controlling the domain size. The thermodynamically stable phases of both H17A/F8H10A LB films and H21A/F8H10A LB films were nanowires in the range of the fabrication temperatures studied. Isobaric thermal treatments of the Langmuir films did not affect the domain shape significantly and affected the domain size in both the LB films studied. The change in the value m of FmH10A was more effective in controlling the phase-separated structures of the mixed LB films than the value of k of HkA.

Graphical abstractThe line tension and dipole-dipole interaction are comparable in the H17A/F6H10A LB films, resulting in the formation of micrometer- and nanometer-phase-separated structures at higher and lower temperature, respectively.Figure optionsDownload full-size imageDownload high-quality image (49 K)Download as PowerPoint slideHighlights► Phase-separated structures of mixed LB films were examined. ► Fatty acids and hybrid carboxylic acids were used as film-forming molecules. ► Disks and nanowires formed in the LB films at high and low temperatures. ► Isobaric thermal treatments of the Langmuir films had notable effects on the domain size.