Three-dimensional self-assembly of rodcoil copolymer nanostructures

We have used electron tomography to characterize the self-assembly of nanostructures formed by rodcoil copolymers. The rodcoil copolymers used contained a perfectly monodisperse rod segment prepared by stepwise synthesis. The chemical compound rod segment is, in turn, covalently linked at one terminus to an end-functionalized polyisoprene segment prepared by living polymerization. We found that rodcoil molecules with rod volume fraction equal to 0.36 self-assemble into long strips with a nanoscale cross section. At lower rod volume fractions, the rodcoil molecules self-assemble into supramolecular aggregates with nanoscale x,y,z dimensions. Interestingly, the nanostructures organize into discrete layers of uniform thickness, containing in some cases a hexagonal 2D superlattice of rodcoil aggregates. Furthermore, nanostructures were found to self-assemble in all cases with three-dimensional order across the layers. The unique three-dimensional order observed in multilayers of the nanostructures must originate in the anisotropic aggregation of rod segments and the consequent space filling requirements as well as coil entropic penalties.