Fig. 1. Reflectance spectral changes of the blue-phase BPⅡ to BPⅠ phase transition process. （a） In situ POM images. 81.0~80.5 ℃ for BPⅡ， 80.0~77.5 ℃ for BPⅡ-BPⅠ， and 77.0~76.5 ℃ for BPⅠ. The lower left inset shows its Kossel diffraction pattern （430 nm filters）. （b） Reflectance spectral of the corresponding state in （a）. （c） Relationship between temperature and the reflection wavelengths of the BPⅡ and BPⅠ components in BP during the cooling process. （d） Relationship between temperature and the reflectance of the BPⅡ and BPⅠ components in BP during the cooling process.

Fig. 2. POM and its corresponding Kossel diffractogram （450 nm filter） of polymerized each stage of the BPⅡ to BPⅠ phase transition process.The five stages are （a） BPⅡ， （b） pre-BPⅡ-BPⅠ， （c） mid-BPⅡ-BPⅠ， （d） post-BPⅡ- BPⅠ， （e） BPⅠ.

Fig. 3. Morphological changes during the BPⅡ→BPⅠ phase transition under POM. （a~c） Single-domain phase transition process with a cooling rate of 0.05 ℃/min. （a） Stage Ⅰ： formation and development of BPⅡ grid； （b） Stage Ⅱ： BPⅠ nucleates from BPⅡ and terraces growth in the pre-BPⅡ-BPⅠ period； （c） Stage Ⅲ： reliefs growth in the post-BPⅡ-BPⅠ period and the formation of concentric rings texture on the BPⅠ surface； （d） Multi-domain phase transition process. （i~v） was gradually cooled down at a rate of 0.1 ℃/min.

Fig. 4. Lamellar structure of one-side bared multidomain BPⅡ under a low-pressure scanning electron microscopy. （a） POM of the polymerized one-side bared blue-phase film； （b~c） LV SEM images of blue multidomain regions in the center of the film. Observation condition： （b） 10.0k×， 0.5 kV； （c） 43.0k×， 0.3 kV.

Fig. 5. Schematic diagram of the BPⅡ to BPⅠ phase transition mechanism. （a） Generation of edge dislocations in BPⅡ （rectangular unit length in the thickness direction represents several cells）； （b） Nucleation of BPⅠ from the BPⅡ dislocation， and BPⅠ horizontal and vertical epitaxial growth； （c） Forming of BPⅠ relief textures and textures reconstruction.