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 –1 H 2 n –1 COOH)–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 (1) are valid only within a small window of low concentrations.