Self-assembly and aggregation of melamine and melamine-uric/cyanuric acid investigated by STM and AFM on solid surfaces

The self-assembly and aggregation of melamine (M), and a mixture of melamine with uric/cyanuric acid (UA/CA) are investigated by performing scanning tunneling microscopy (STM) and atomic force microscopy (AFM) on graphite and mica surfaces at room temperature. Two-dimensional (2D) porous molecular networks and disordered adlayers are found, respectively, in the M and UA-M assembly on graphite. Uniformly dispersed nanoparticles of M and UA-M are found at various concentrations by AFM. Owing to complementary NH center dot center dot center dot O and NH center dot center dot center dot N hydrogen bonds, the CA-M mixture forms 2D densely packed adlayers and nanoscale crystals on graphite and aggregates into three-dimensional (3D) clusters on the surfaces. The size of the cluster is dependent on the molecular concentration. The results provide important information for the self-assembly of triazine compounds and are significant in the study of kidney disease related to melamine.