Langmuir monolayers and Langmuir–Blodgett films of 1-acyl-1,2,4-triazoles

New 1-acyl-1,2,4-triazoles (ATs) with different n-alkyl chain lengths from C2 to C18 were synthesized. ATs with long n-alkyl chains (C12 and larger) are non-charged amphiphilic molecules with a polar triazole head group. The Langmuir isotherms of ATs at the air–water interface with 12 (DoT-C12), 14 (MyT-C14), 16 (PaT-C16) and 18 (StT-C18) carbon atoms in their n-alkyl chains were studied using surface pressure-mean molecular area (π-mmA) measurements. Characteristic for the Langmuir isotherms of PaT-C16 and StT-C-18 was the first sharp increase of the surface pressure at a mmA value of ∼20 Å2 marking a transition of the ATs from the gaseous state with n-alkyl chains already oriented perpendicular to the water surface to a condensed state. The collapse of the monolayers occurred between 20 and 36 mN m−1 with a typical ‘spike’ in the isotherms of MyT-C14, PaT-C16 and StT-C18 which can be assigned to the buckling and subsequent folding of the monolayer. After the collapse point a pseudo-plateau region of slightly increasing surface pressure appeared for all ATs from C12 to C18 indicating a trilayer formation by the roll-over mechanism for MyT-C14, PaT-C16 and StT-C18. Upon further compression the final collapse occurred at π values between 59 and 67 mN m−1. From reversibility studies it was found that the Langmuir isotherms of the ATs were irreversible. The morphology of Langmuir–Blodgett films of ATs transferred onto silicon wafers was studied by atomic force microscopy.

Compression isotherm of StT-C18 and respective morphology images of transferred LB films.Figure optionsDownload as PowerPoint slide