Mechanism of Contact-Induced Heterogeneous Nucleation

Understanding and controlling nucleation is a long-standing issue in the field of crystallization and solid state chemistry. Herein, we use gold–thiol self-assembled monolayers (SAMs) as heterosurfaces in combination with contact force to induce nucleation. Our approach elucidates the mechanism of contact-induced heterogeneous nucleation and has clear technological implications in that it reduces induction time and controls polymorphism of pharmaceutical crystals. The combination of SAMs and contact force can immediately induce nucleation under conditions that do not otherwise promote fast crystallization. The chance of nucleation is enhanced by SAMs that interact strongly with solute molecules. These observations and analyses of obtained crystals led us to conclude that contact-induced heterogeneous nucleation follows a similar path as undisturbed heterogeneous nucleation in the early stage, but departs from it at the later stage due to the interruption by contact force. In contrast to undisturbed heterogeneous nucleation, crystals are not attached to and do not chemically interact with SAMs in contact-induced heterogeneous nucleation