(60e) Polymer in Interstitial Space As Structure Director in Colloid Self-Assembly

The phase transition and associated structures of spherical colloids are important problems, as these hint at how nature determines the structure of many systems, often seemingly distant from each other. In the last few decades, the library of topologically close-packing structures (TCP) by the deformable spherical colloids has been documented and reasoned. However, the polymorphism of close-packed structures of equal spheres, which may appear more straightforward, has not been well explained. In this talk, I will describe a new strategy of using polymer chains residing in the interstitial space of close-packed spherical colloids to stabilize target polytypes, including hexagonal close-packed (HCP) and random stacking of two-dimensional hexagonal close-packed layers (RHCP). This strategy enables directed self-assembly of the interstitial sites to induce target self-assembled structures of colloids, not the lattice sites. The conformational entropy of polymer chains groups larger nearest interstitial sites together, which competes against the lattice entropy for the face-centered cubic (FCC) lattices forming smaller nearest site groups. Our toy calculation justifies that the same principle is applicable to other polytype crystal systems such as Laves phases.