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Tuning the Color of Photonic Glass Pigments by Thermal Annealing.

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Thermal or solvent annealing is commonly employed to enhance phase separation and remove defects in block copolymer (BCP) films, leading to well-resolved nanostructures. Annealing is of particular importance for photonic BCP materials, where large, well-ordered lamellar domains are required to generate strong reflections at visible wavelengths. However, such strategies have not been considered for porous BCP systems, such as inverse photonic glasses, where the structure (and thus the optical response) is no longer defined solely by the chemical compatibility of the blocks, but by the size and arrangement of voids within the BCP matrix. In this study, a demonstration of how the concept of "thermal annealing" can be applied to bottlebrush block copolymer (BBCP) microparticles with a photonic glass architecture is presented, enabling their coloration to be tuned from blue to red. By comparing biocompatible BBCPs with similar composition, but different thermal behavior, it is shown that this process is driven by both a temperature-induced softening of the BBCP matrix (i.e., polymer mobility) and the absence of microphase separation (enabling diffusion-induced swelling of the pores). Last, this concept is applied toward the production of a thermochromic patterned hydrogel, exemplifying the potential of such responsive biocompatible photonic-glass pigments toward smart labeling or anticounterfeiting applications.



block copolymers, confinement, inverse photonic glasses, structural color, thermal annealing

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Adv Mater

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BBSRC (BB/V00364X/1)
European Research Council (790518)
European Commission Horizon 2020 (H2020) Marie Sk?odowska-Curie actions (893136)
European Research Council (639088)
Engineering and Physical Sciences Research Council (EP/R511675/1)
Engineering and Physical Sciences Research Council (EP/N016920/1)
Royal Society (IE160420)
Biotechnology and Biological Sciences Research Council (BB/K014617/1)
This work was supported by: 1] The European Research Council [ERC-2014-STG H2020639088; ERC-2017-POC 790518] 2] The Biotechnology and Biological Science Research Council [BBSRC David Phillips Fellowship BB/K014617/1; BB/V00364X/1] 3] The Engineering and Physical Sciences Research Council [EPSRC EP/N016920/1; EP/R511675/1] 4] The Royal Society [IE160420] 5] The European Union Horizon 2020 Research and Innovation Program (Marie Skłodowska-Curie Actions Grant No. 893136) 6] The Emil Aaltonen Foundation 7] CSC Cambridge Scholarship 8] Croucher Cambridge International Scholarship.
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