Water assisted biomimetic synergistic process and its application in water-jet rewritable paper

Abstract

The colour of water-jet rewritable paper (WJRP) is difficult to be expanded via single hydrochromic molecule, especially black. Here, inspired by the amazing phenomenon of bound-water in cells enabling various biological transformations via facilitating synergistic inter-/intra-molecular proton transfer, we present a simple strategy toward WJRP based on binary systems containing less-sensitive acidochromic dyes and mild proton donors (or developers). With such a binary system containing commercial black dye as the colouring agent, benzyl 4-hydroxybenzoate as the developer, and biomimetic bound-water as proton-transferring medium, we successfully achieve the long-awaited black WJRP. Printed images on such WJRP have excellent performances and long retaining time (>1 month). In addition, the robustness, durability and reversibility of WJRP could be increased distinctly by using polyethylene terephthalate as substrate. This strategy significantly expands hydrochromic colours to entire visible range in an eco-friendly way, which opens an avenue of smart materials for practical needs and industrialization.

Fig. 1

Schematic illustration of different mechanism for water-jet rewritable paper (WJRP) between this work and our previous work. Mechanism of WJRP showing colour based on the hydrochromic single molecule in our previous work and the binary system in this work after addition of water

Fig. 2

Structure and basic performances of WJRP. a The preliminary structure of WJRP and the composition of this hydrochromic system in the imaging layer of WJRP (black dashed line: H-bonding). b The reflective UV-vis spectra of the WJRP before and after addition of water as well as drying the WJRP. c Plots of the reflectivity at 460 nm (red dots) and 586 nm (blue dots), respectively versus the number of cycles as the WJRP is cycled through water spraying (write) and water removal (erase) by means of heating at 80 °C. d Time-dependent reflection variations of black WJRP at 586 nm during exposure to a water droplet (red arrow: the point of adding water). e The reflective UV–vis spectra of WJRP after exposure to different volume of water

Fig. 3

Function of each component in WJRP and the hydrochromic mechanism of WJRP. Variation of reflectance (R%) at 586 nm of WJRP integrated with ODB-2/developers (n/n 1/4) including a carboxylic acid derivatives and polyhydroxyls phenol derivatives and b developers with different logP before (blue dots) and after addition of water (red dots). c UV–vis reflection spectra of the mixture of ODB-2 and B4H on the glass before and after introduction of PEG and the mixture with PEG after adding water. d UV–vis reflection spectra of the mixture of ODB-2 and B4H on filter paper before and after addition of water. e UV–vis reflection spectra of ODB-2 alone dispersed on filter paper before and after addition of water as well as adding acid. f Schematic representation of WJRP based on the binary system writing with water and the erasing process (blue dashed line: supramolecular interaction, black dashed line: H-bonding)

Fig. 4

Repeatability, resolution, colour intensity and retaining time of water-jet prints. a Schematic illustrations of a printing-erasing cycle of WJRP printed with water-jet printer, scale bar = 1 cm. b Photographs of patterns printed on WJRP after 10 consecutive writing-erasing cycles (scale bar = 1 cm). c L*, a*, b* measured by spectrodensitometer and photographs of water-jet prints and ink-jet prints, respectively. d Microscopic images of WJRP before and after addition of water, scale bar = 200 µm. e Photographs of WJRP maintaining in ambient air after printing as time passed by, scale bar = 5 mm. f WJRP based on PET substrate before and after printed with water, scale bar = 2 cm

Fig. 5

Other colours for WJRPs based on binary systems. a The structures of a series of acidochromic dyes. b Multicolours obtained by various acidochromic dyes in solution after treating with acid and c on solid state treated with B4H after addition of water and d corresponding UV-vis reflection spectra of the solid state. e Plots of corresponding positions of six kinds of WJRPs after adding water in the CIE 1931 colour space