Morphological Transitions in Patchy Nanoparticles.

Nanoparticles (NPs) decorated with topographically or chemically distinct surface patches are an emerging class of colloidal building blocks of functional hierarchical materials. Surface segregation of polymer ligands into pinned micelles offers a strategy for the generation of patchy NPs with controlled spatial distribution and number of patches. The thermodynamic nature of this approach poses a question about the stability of multiple patches on the NP surface, as the lowest energy state is expected for NPs carrying a single patch. In the present work, for gold NPs end-grafted with thiol-terminated polymer molecules we show that the patchy surface morphology is preserved under conditions of strong grafting of the thiol groups to the NP surface (that is, up to a temperature of 40 C), although the patch shape changes over time. At higher temperatures (e.g., at 80 C), the number of patches per NP decreases, due to the increased lateral mobility and coalescence of the patches, as well as the ultimate loss of the polymer ligands due to desorption at enhanced solvent quality. The experimental results were rationalized theoretically, using a scaling approach. The results of this work offer insight into the surface science of patchy nanocolloids and specify the time and temperature ranges of the applications of patchy NPs.