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Figure 4. Mechanochromic photonic film containing a non-close-packed 3D-PC array. (A) Scheme of the photonic film consisting of silica particle as building block and elastomer as medium; Photographs of photonic film taken under (B) reflection condition and (C) transmission condition; (D) Cross-sectional Scanning electron microscope (SEM) image and related fast Fourier transform image; A photonic film under three different strains recorded in (E) reflection mode and (F) transmission mode. Reproduced with the permission of Ref.^[85] Copyright 2017, ACS Publications. 3D: Three-dimensional; PCs: Photonic crystals.