Self-Assembled Shape-Anisotropic Diblock Copolymer Particles from Evaporative Emulsions: Experiment and Theory*

We report the systematic design of shape-anisotropic diblock copolymer (dBCP) particles based on a new theoretical model that embodies entropic penalty associated with bending of the cylindrical and lamellar dBCP chains upon deformation of the particles. First, we produced the convex-lens shaped (oblate) and football-shaped (prolate) PS-b-PDMS particles, where the aspect ratios (AR) were tunable over a broad range from 1 to 10. Of note, the AR of oblate particle increased almost linearly up to 10 as the particle size increased, whereas the increase of AR for the prolate particle was limited to 2.0. To understand this discrepancy, we developed the theoretical model that includes the bulk elastic and bending energies of dBCP cylinders and lamellae, and the surface energy between the particle/ surrounding medium. For oblate particles, the high excessive bending energy of the curved cylinders at the periphery of particle can be released by increasing the AR of particle. However, the relatively low excessive bending energy of curved lamellae of prolate particles prevents the particles from having a high AR.