Statistical model for self-assembly of trimesic acid molecules into homologous series of flower phases.

The statistical three-state model is proposed to describe the ordering of triangular TMA molecules into flower phases. The model is solved on a rescaled triangular lattice, assuming following intermolecular interactions: exclusion of any molecules on nearest neighbor sites, triangular trio H-bonding interactions for molecules of the same orientation on next-nearest neighbor sites, and dimeric H-bonding interactions for molecules of different ("tip-to-tip") orientations on third-nearest neighbor sites. The model allows us to obtain the analytical solution for the ground state phase diagram with all homologous series of flower phases included, starting with the honeycomb phase (n=1) and ending with the superflower structure (n=∞). Monte Carlo simulations are used to obtain the thermodynamical properties of this model. It is found that phase transitions from disordered to any of the flower phases (except n=1) undergo via intermediate correlated triangular domains structure. The transition from the disordered phase to the intermediate phase is, most likely, of the first order, while the transition from the intermediate to the flower phase is definitely first order phase transition. The phase diagrams including low-temperature flower phases are obtained. The origin of the intermediate phase, phase separation, and metastable structures are discussed.