One and a half layers? Mixed Langmuir monolayer of 10,12-pentacosadiynoic acid and a semifluorinated tetracosane

The different mixed Langmuir monolayers of 10,12-pentacosadiynoic acid (PDA ) and semifluorinated tetracosane (CF3(CF2)(7)(CH2)(15)CH3, as F8H16 below) were studied by surface pressure-area isotherm, W-Vis spectroscopy, and Br ewster angle microscopy (BAM). The surface pressure-area isotherms of the m ixed PDA/F8H16 monolayers show reduced limiting molecular areas, which indi cate miscible films with strong interactions. A minimum limiting area was f ound for the monolayer of PDA/F8H16 mixed at 1:2 molar ratio. The UV-Vis sp ectra show that the PDA in the mixtures can be polymerized upon UV irradiat ion up to the molar ratio of 1:2 (PDA/F8H16). The BAM images of the mixture s show that at higher ratio of F8H16 the condensed domains of PDA disappear . The above evidence suggests that the fluorinated moiety of F8H16 may stay on top of PDA to form an extra half layer at high surface pressures.