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.
Highlights
The colour of water-jet rewritable paper (WJRP) is difficult to be expanded via single hydrochromic molecule, especially black
Certain periodically ordered photonic crystals embedded in hydrogels or polymer matrices[18,19,20], which vary reflectance wavelengths depending on water content, and hydrochromic dyes, which can change their configuration and structure responding to water[2,21,22,23,24,25], are both potentially applicable in water-jet rewritable paper (WJRP)
With reference to our previous work[22], the black WJRP was constructed by a threelayer structure: a substrate at the bottom, a polyethylene glycol (PEG) layer in the middle and an imaging layer on the top (Fig. 2a)
Summary
The colour of water-jet rewritable paper (WJRP) is difficult to be expanded via single hydrochromic molecule, especially black. 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 protontransferring medium, we successfully achieve the long-awaited black WJRP. This will avoid traditional complicated synthesis/preparations and dramatically reduce related industrialization cost, and make extension of ideal colour for the WJRP much easier, especially the black WJRP
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