Composition-programmable inverse opal toroidal photonic microobjects with a broad thermochromic response window

Thermoresponsive photonic hydrogels translate polymer hydration changes into structural-color variations, but many systems still constrain their optical response within a narrow temperature region. Herein, composition-programmable P(OEGMA-co-MEO 2 MA) hydrogel-based inverse opal toroidal photonic microobjects (IO-TPMs) are developed to realize broad and reversible thermochromic responses. Monodisperse SiO 2 colloids were assembled into toroidal opal templates, followed by precursor infiltration, UV polymerization, and wet template removal to generate ordered macroporous IO-TPMs. By varying the OEGMA/MEO 2 MA feed ratios, the hydrogel hydration states were systematically regulated, producing composition-dependent swelling, broad dehydration, dimensional contraction, and continuous Bragg peak blue shifts. The characteristic optical response temperature ( T o p t ), defined from the maximum of the apparent optical response rate ( R a p p ), shifted from 44.5 to 83.2 °C with increasing OEGMA content. The same composition-dependent ordering was reproduced by the error-function and Boltzmann fits, supporting the robustness of the extracted trend. DSC and derivative DSC provided auxiliary thermal evidence for broad dehydration-associated transitions and followed the same composition-dependent trend. Under the same thermal stimulus, the tested IO-TPMs showed faster normalized macroscopic dimensional relaxation than the IO-PMs; because the specimens were not size-matched, this difference is described as geometry-associated rather than topology-specific. This work establishes a composition-dehydration-photonic response relationship for hydrogel-based IO-TPMs and provides a colloidal-assembly route to programmable, reversible structural-color materials.