Processing Effects on the Self-Assembly of Brush Block Polymer Photonic Crystals

The self-assembly of poly(dimethylsiloxane)-b-poly(trimethylene carbonate) (PDMS-b-PTMC) bottlebrush block polymers was investigated under different processing conditions. Small-angle X-ray scattering (SAXS) and UV/Visible spectroscopy provided insight into the self-assembly and structure in response to heating and applied pressure. In the absence of applied pressure (i.e., before annealing), the PDMS-b-PTMC bottlebrush block polymers are white solids and adopt small, randomly oriented lamellar grains. Heating the materials to 140 °C in the absence of applied pressure appears to "lock in" the isotropic, short-range-ordered state, preventing the formation of the long-range-ordered lamellar structure responsible for photonic properties. Applying modest anisotropic pressure (3 psi) between parallel plates at ambient temperature orients the short-range lamellar grains; however, applied pressure alone does not produce long-range order. Only when the bottlebrush block polymers were heated (>100 °C) under modest pressure (3 psi) were long-range-ordered photonic crystals formed. Analysis of the SAXS data motivated analogies to liquid crystals and revealed the potential self-assembly pathway. These results provide insight into the structure and self-assembly of bottlebrush block polymers with low glass transition temperature side chains in response to different processing conditions. ; © 2021 American Chemical Society. Received: September 9, 2021; Accepted: November 4, 2021; Published: November 11, 2021. This work was supported by the Department of Energy under Award Number DE-AR0000683 (ARPA-E Program) and by the National Science Foundation under Award Number CHE-1502616. A.L.L.-M. thanks the Resnick Sustainability Institute at Caltech for fellowship support and Chapman University for funding. A.B.C. thanks the U.S. Department of Defense for support through the NDSEG Fellowship. Henry Hallam is thanked for assistance measuring the force applied by binder clips. This research used resources of the Advanced Photon ...