Synthetic Bilayers on Mica from Self-Assembly of Hydrogen-Bonded Triazines

• Published in: Langmuir 2020-11, Vol.36 (44), p.13301-13311
• Main Authors: Yao, Yin, Aldilla, Vina R, Bhadbhade, Mohan, Bhattacharyya, Saroj, Gong, Bin, Kumar, Naresh, Rich, Anne M, Sando, Daniel, Cheong, Soshan, Tilley, Richard, Yin, Songyan, Marjo, Christopher E
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.0c02377

This study describes organic thin films prepared under a range of conditions from a model series of bis-N-alkyl chloro-triazines functionalized with short alkyl chains from ethyl to hexyl. The pure films were characterized using atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). When cast on mica, these compounds assemble as crystalline sheets made up of a synthetic bilayer along the crystallographic ab-plane with an internal hydrogen-bonded domain between external alkyl chains. These micron-scale surfaces stack along the c-axis, and increasing the alkyl chain length results in changes to the crystal morphology from needles to nanoscale plates. Thicker films produce nanoscale, pyramidal stacks of bilayers. Compared to atomically flat mica, a rougher, unetched silicon substrate produced irregular domains in the secondary bilayer. Films of mixtures comprising the ethyl derivative with butyl, pentyl, or hexyl derivative were imaged using time-of-flight secondary-ion mass spectrometry (ToF-SIMS) that indicated a trend toward a constant stoichiometry with increasing alkyl chain length. AFM of mixed films on mica showed single bilayers of height