(Invited, Digital Presentation) Understanding the Self-Assembly of Polymer-Grafted Nanocrystals

Combination of inorganic nanocrystals (NCs) and polymeric materials is promising for the design of novel functional materials due to their complementary properties. For the preparation of such hybrid nanomaterials with tailored functionalities, it is important to precisely control their nanostructures since material properties of NCs strongly depend not only on the morphology of each NC building block, but also their assembled packing symmetries. In this talk, I will present precise control of polystyrene-grafted Au NC (Au@PS) superlattice symmetry, which shows non-conventional assembly behavior compared to short alkyl chain-coated NCs. Au@PS NCs were synthesized by ligand exchange using thiol-terminated PS with various molecular weights (M n). The Au@PS particles were self-assembled through liquid-air interface self-assembly process. Transmission electron microscopy images and grazing incidence small-angle X-ray scattering data indicated long-range ordered Au@PS superlattices. In particular, symmetry transitions from hexagonal close packing (hcp) to body centered cubic (bcc) symmetry were found as M n of PS increases or diameter of NCs decreases. We tried to understand the structural transitions by proposing “effective softness” model, which considers concentrated polymer brushes around NC surface as part of “hard core.” Finally, I will show how these polymer-grafted NCs can be self-assembled with block copolymers for the development of colloidal hybrid particles with stimuli-responsive photoluminescence behavior, which have great potential for the applications in smart material systems.