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 (pi-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 approximately 20A(2) 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 36mNm(-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 pi values between 59 and 67mNm(-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.
Department of Chemistry, Martin Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany.
Sascha
S
Reuter
Karsten
K
Busse
Ute
U
Radics
Hans-Joachim
HJ
Niclas
Jörg
J
Kressler