Reevaluation of Poly(ethylene- alt-propylene)- block-Polydimethylsiloxane Phase Behavior Uncovers Topological Close-Packing and Epitaxial Quasicrystal Growth

Aaron P Lindsay; Ashish Jayaraman; Austin J Peterson; Andreas J Mueller; Steven Weigand; Kristoffer Almdal; Mahesh K Mahanthappa; Timothy P Lodge; Frank S Bates

doi:10.1021/acsnano.1c02420

Reevaluation of Poly(ethylene- alt-propylene)- block-Polydimethylsiloxane Phase Behavior Uncovers Topological Close-Packing and Epitaxial Quasicrystal Growth

ACS Nano. 2021 Jun 22;15(6):9453-9468. doi: 10.1021/acsnano.1c02420. Epub 2021 Apr 22.

Authors

Aaron P Lindsay¹, Ashish Jayaraman¹, Austin J Peterson¹, Andreas J Mueller¹, Steven Weigand², Kristoffer Almdal³, Mahesh K Mahanthappa¹, Timothy P Lodge^{1

4}, Frank S Bates¹

Affiliations

¹ Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States.
² DND-CAT Synchrotron Research Center, Northwestern University, APS/ANL Building 432-A004, 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
³ Department of Chemistry, Technical University of Denmark, Kemitorvet 207, 2800 Kongens Lyngby, Denmark.
⁴ Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, United States.

PMID: 33886269
DOI: 10.1021/acsnano.1c02420

Abstract

Reanalysis of an asymmetric poly(ethylene-alt-propylene)-block-polydimethylsiloxane (PEP-PDMS) diblock copolymer first investigated in 1999 has revealed a rich phase behavior including a dodecagonal quasicrystal (DDQC), a Frank-Kasper σ phase, and a body-centered cubic (BCC) packing at high temperature adjacent to the disordered state. On subjecting the sample to large amplitude oscillatory shear well below the σ-BCC order-order transition temperature (T_OOT), small-angle X-ray scattering evidenced the emergence of a twinned BCC phase that, on heating, underwent a phase transition to an unusually anisotropic DDQC state. Surprisingly, we observe no evidence of this apparent epitaxy on heating or cooling through the equilibrium σ-BCC transition. We rationalize these results in terms of a shear-induced order-order transition and an apparent BCC-DDQC epitaxy favored by micelle translation-mediated ordering dynamics far below T_OOT.

Keywords: block copolymer; epitaxy; quasicrystal; self-assembly; shear orientation; topological close-packing.