(653d) Crystallization-Driven Self-Assembly of Model Anisotropic Particles from Diblock Copolymers

Developing monodisperse anisotropic particles with tunable aspect ratio and flexibility is achieved by leveraging crystallization-driven self-assembly (CDSA) of PEO-PLLA diblock copolymers. Adjusting the solvent quality from a good solvent (THF) for both blocks to a solvent (D₂O) selective for PEO, the solution was held at a temperature so that PLLA crystallized, forming a core, surrounded by amorphous PEO corona. Crystallization of PLLA chains in the solution was confirmed by wide-angle X-ray scattering (WAXS). Crystallization under these conditions resulted in polydisperse rod-like particles. The effects of the solvent quality (THF/D₂O mixtures) on the single crystal formation as well as the overall crystalline properties of the rods were elucidated using small-angle X-ray scattering (SAXS)/WAXS.

The polydisperse rods were subjected to probe sonication to generate shorter nearly monodisperse rods. Altering the solvent quality and the sonication time allowed tuning the shape and size of the rod-like structures. This was verified using an assortment of scattering and imaging techniques. Under optimal conditions, a spatially homogeneous growth of the PLLA block from the solution onto its crystal growth front in the shorter rods allowed to develop fairly monodisperse rods with controlled aspect ratio depending on the diblock concentration. The purpose of the work is to develop a toolbox of particles with varying aspect ratio to answer the fundamental questions relevant to the flow behavior of soft materials under elevated shear rates or large pressures using slit capillary rheometry combined with neutron scattering.