Tough, Freestanding, and Colorless Photonic Paper Using Water as Ink

Abstract

Structural colors arising from interactions of light with submicron scale periodic structures have been found in nature. Inspired by photonic materials, rewritable paper using water as ink is fabricated via entrapping amorphous colloids crystals film into hydrogel. This photonic paper is tough, free‐standing, transparent, and colorless in dry state, just like plastic sheet. Marks display using water as ink to write on the paper and disappear with the evaporation of water. The color of the marks similar to that of the initial PS colloids film and could be tuned by changing the size of the colloids. The photonic paper possesses high durability and can be rewritten over 70 cycles without significant color fading. Besides, the retention time of the written marks could be well controlled from minutes to weeks by using glycerol/water as ink. It is worth noting that long‐range order is not the necessary condition for the formation of photonic paper, which makes the preparation easy to achieve. More interesting, the wet hydrogel film is sensitive to strain, and has the potential to be mechanical sensor.

Stimuli‐responsive photofunctional materials for green and security printing

“…The color of oxazolidine, oxazine, and spiropyran can be reversibly converted by the isomerization of ring-open and ring-close forms. 29,97 NCs and photonic crystals can undergo color conversion through expansion and contraction of the matrix. 98 To date, they have been successfully used for water-soluble color humidity sensors, [99][100][101][102][103][104][105][106][107][108] sweat hole mapping systems, [109][110][111][112][113] water detection in organic solvents, [114][115][116][117] and rewritable paper.…”

“…98 To date, they have been successfully used for water-soluble color humidity sensors, [99][100][101][102][103][104][105][106][107][108] sweat hole mapping systems, [109][110][111][112][113] water detection in organic solvents, [114][115][116][117] and rewritable paper. 44,46,54,97,98,111,[118][119][120][121] Particularly, hydrochromic materials are very popular in the design of water-jet printing rewritable papers. This is because water is clean, low cost, convenient, and compatible with current inkjet printers.…”

Mechanochromism of Structural‐Colored Materials

“…Therefore, increasing efforts have been made to fabricate mechanochromic sensor based on the angle‐independent photonic glass. [ 12,35,37,38 ] The fabrication and mechanochromic mechanism are similar to those of opal photonic crystals. As for the fabrication, elastomer precursor is infiltrated into the as‐assembled photonic glass, followed by polymerization to prepare the final mechanochromic photonic glass.…”

“…Emerging structural‐colored materials can be divided into three main categories according to their nanoscale architectures: photonic crystals (PCs), [ 10 ] liquid crystals (LCs), [ 11 ] and photonic glass. [ 12 ] Due to their ability to modulate visible light, the structural‐colored materials have been applied in diverse domains such as optical waveguides, [ 13–16 ] luminescence enhancement, [ 17–19 ] photoelectric devices, [ 20,21 ] photocatalysts, [ 22,23 ] anti‐counterfeiting technologies, [ 24–26 ] and chemical and biological sensing. [ 27–29 ]…”

“…With ingenious designs of nanostructures, a variety of responsiveness has been obtained on the structural‐colored materials, corresponding to varying stimuli such as temperature, [ 30–32 ] solvent, [ 27 ] gases, [ 28 ] magnetic fields, [ 33 ] and external forces. [ 10–12 ] Among them, the mechanical responsive structural colors are able to visualize invisible stress in the materials, providing effective indicators for mechanical stimuli such as stretching, compression, or bending. Such mechanochromism can be directly achieved by the deformation‐induced changes in periodic lattice constants of the structural‐colored materials.…”