Polymorphism Driven by Concentration at the Solid–Liquid Interface

Self-assembly at the liquid–solid interface is controlled by concentration of solute in solvent. Trimesic acid (TMA) dissolved in fatty acids shows a polymorphism on HOPG surface tuned by its concentration at the solid–liquid interface via sonication of the solution. According to literature, TMA at long chain length fatty acids (C n–1H2n–1COOH)–HOPG interface, such as octanoic acid (n = 8) and nonanoic acid (n = 9) can only form low-packing density chicken-wire structure, whereas in short-chain length solutions (ranging from butyric acid (n = 4) to heptanoic acid (n = 7)), high-packing density flower structure is formed. Here we show that by adjusting the molecule concentration by sonication (using an ultrasonic bath), the different polymorphs can be deposited in a controlled manner, and it turns out that the observations previously made are valid only within a small window of low concentrations.