Fig 1

(a) The method for preparing cholesteric liquid crystals (CLCs), (b) schematic illustration to show the capillary microfluidic devices and (c) tunable helical superstructures and applications of the CLC microdroplets as 3D photonic crystals."

Table 1

Different microfluidic devices for fabricating various CLC microdroplets."

Fig 2

Schematic illustration for glass-capillary microfluidic devices for fabricating (a) single-, (b) double-, and (c) triple-CLC microdroplets."

Fig 3

Schematic illustration to show the capillary microfluidic device with double channels for fabricating CLC microdroplets with different structural colours. The red and blue CLC mixtures were respectively injected in the device at various flow rates to tune the concentration of the chiral dopant 36. Adapted with permission from Ref. 36, Copyright 2018 American Chemical Society."

Fig 4

Schematic illustrations to show mechanisms of temperature-responsive CLCs. (a) Sm-Ch transition, (b) temperature-responsive helical twisting power (β) 65. (c) Tuning reflection wavelengths of the cholesteric microdroplets by combining the handedness of incident circularly polarized light and temperature. QWP, LP and CPL represent quarter-wave plate, linear polarizer, and circularly polarized light respectively 54. (c) Adapted with permission from Ref. 54, Copyright 2017 John Wiley and Sons."

Fig 5

(a) Schematic illustration to show the tunable reflection wavelengths in the cholesteric microdroplets based on swelling; (b) The diameters and reflection wavelengths of the CLC microdroplets in pyridine/water mixture change with the water content, where pyridine and water are good and poor solvents 41. Adapted with permission from Ref. 41, Copyright 2017 Royal Society of Chemistry."

Fig 6

(a) Chemical structure of the light-driven chiral molecular switch; (b) A flower patter composed with eight monodisperse photoresponsive CLC microdroplets, and the color of each petal changes with different exposure times 31; (c) Chemical structures of light-driven chiral molecular switch Azo4 and photoinsensitive chiral dopant R5011, and the mechanism of light-driven handedness inversion; (d) POM images to show optical textures in the CLC microdroplets change with different exposure times 32. (b) Adapted with permission from Ref. 31, Copyright 2015 John Wiley and Sons; (c, d) Adapted with permission from Ref. 32, Copyright 2017 Royal Society of Chemistry."

Fig 7

(a) Schematic illustration to show the photonic-communication between CLC microdroplets, where i, ii, and iii represent the normal reflection, double reflection and triple reflection, respectively; (b) POM images to show the photonic-communication in single- and double-emulsion CLC microdroplets, the insets to show the area of internal reflection occurred at 45°; (c) Schematic illustration and POM images to show photonic-communication between double-emulsion CLC microdroplets with different reflection wavelengths 43; (d) POM image of annular pattern in a double-emulsion CLC microdroplet, of which the shell is very thin at the top and thick at the bottom. The inset shows the reflection behavior 44; (e) Schematic illustration and POM images of reflection behaviours in different microbowls 46. (d) Adapted with permission from Ref. 44, Copyright 2018 John Wiley and Sons; (e) Adapted with permission from Ref. 46, Copyright 2020 John Wiley and Sons."

Fig 8

(a) Schematic illustration to show the Bragg onion optical microcavity; (b) SEM image to show the cholesteric microdroplets with parallel surface anchoring; (c) Lasing and reflection spectra of the single cholesteric microdroplets 84."

Fig 9

(a) Schematic illustration to show the triple-emulsion CLC microdroplets with different laser modes; The schematic illustration of the pumping laser with different diameters irradiated on the CLC microdroplets (b), and the corresponding emission spectra (c) 55. Adapted with permission from Ref. 55, Copyright 2019 Royal Society of Chemistry."

Fig 10

(a) Schematic illustration and POM images to show the fabrication of the CLC microdroplets with five layers by liquid-liquid phase separation; (b) Schematic illustration to show the lasing at two different wavelengths from the outermost and inner shells of the CLC microdroplets; (c) Emission and reflection spectra of the CLC microdroplets 59. Adapted with permission from Ref. 59, Copyright 2020 John Wiley and Sons."

Fig 11

Emission and reflection spectra of the CLC microdroplets change with temperature in the range of 18 to 21.5 ℃ (a), and range of 22 to 34 ℃ (b); (c) OM images of the CLC microdroplet lasers confined in the different polygonal holes 57."

Fig 12

(a) Chemical structure of the light-driven chiral molecular switch, which is used to tune the reflection wavelengths of the CLC microdroplet lasers; (b) Variation of laser emission in the photoresponsive CLC microdroplet lasers after pumping different times 51. Adapted with permission from Ref. 51, Copyright 2014 John Wiley and Sons."

Fig 13

Schematic illustration to show the structure of the triple emulsion encapsulated by silicone rubber, and the photograph of the flexible photonic film fabricated by the triple emulsions 58; (b) Schematic illustration to show positioning cholesteric microshells by a magnetic pen and POM images of the microshells arranged into English letters 52; (c) POM images of the "KRICT" illuminated by non-, left- and right-handed circularly-polarized light 33; (d) Schematic illustration to show cholesteric microdroplets with structural color under white light and fluorescent color upon UV irradiation, and photographs to show the geminate label with reflective "Christmas tree" and fluorescent QR code created by the microdroplets 34; (e) Schematic illustration and POM images to show the magnetic field-induced reorientation of a single Janus droplets. Right photographs to show the Janus droplets for data encryption, which exhibits "8" at initial state and switches to "5" when the magnetic field is applied. M in the schemes denotes the magnetic field-responsive Janus droplets 60. (a) Adapted with permission from Ref. 58, Copyright 2015 John Wiley and Sons; (c) Adapted with permission from Ref. 33, Copyright 2017 Royal Society of Chemistry; (e) Adapted with permission from Ref. 60, Copyright 2022 John Wiley and Sons."

Fig 14

(a) Chemical structures of the CLC composed of three cholesterol-based mesogens; (b) OM images to show structural colors of the CLC microdroplets change with temperatures 40. Adapted with permission from Ref. 40, Copyright 2022 John Wiley and Sons."

Fig 15

(a) Schematic illustration to show the configuration transition in the CLC microdroplets from homeotropic to planar, which is triggered by bile acid; (b) POM images in reflection mode to show the transition in CLC microdroplets after adding acid 35."