Tunable morphology and surface wettability of an amphiphilic azobenzene derivative and its melamine-induced self-assembly

Herein, a series of novel hydrogen-bonded complexes derived from 4-[[(dodecyloxy)benz-4-yl]azo]benzoic acid (DBA) and melamine are reported. The morphology and surface wettability of the resulting self-assembled supramolecular architectures can be easily modulated not only by varying the molar ratios of DBA and melamine, but also by external UV irradiation. Based on the results of atomic force microscope, X-ray diffractometer and contact angle measurements, orientation of the coassembled units with different molar ratios of DBA and melamine could be clearly confirmed. Moreover, the effect of photo-isomerisation of the azobenzene units on the wettability of the assemblies has been investigated in detail. As we know, the films derived from the cis-azobenzene derivative usually exhibit a more hydrophilic property than that from the trans-azobenzene derivative. However, the opposite results were obtained for the samples derived from the cis isomers of DBA-melamine (3:1) complexes or DBA. An explanation, based on the surfaces topography, has been proposed.