Sci­en­tists de­velop re-writable pa­per

DNA Sunday (Mumbai) - - SCITE H - —PTI

Sci­en­tists have de­vel­oped an easy-to-make “rewritable” pa­per that can be drawn or printed on over and over again. Printed ma­te­ri­als of­ten get used once and are then dis­carded, cre­at­ing waste and po­ten­tial pol­lu­tion.

Re­searchers in­clud­ing those from the Fu­jian Nor­mal Univer­sity in China wanted to de­velop a sim­ple method for mak­ing long-last­ing re-writable pa­per that can be wiped clean sim­ply by chang­ing the tem­per­a­ture.

The mes­sages can last more than half a year, com­pared to other re-writable papers whose mes­sages fade af­ter a few days or a few months, ac­cord­ing to a study pub­lished in the jour­nal ACS Ap­plied Ma­te­ri­als & In­ter­faces. The idea for re-writable pa­per is not new, with sev­eral re­search groups pur­su­ing dif­fer­ent devel­op­ment strate­gies over the past few decades.

How­ever, many of these ap­proaches have draw­backs, such as com­plex fab­ri­ca­tion, the chem­istry that re­lies on ul­tra­vi­o­let light to erase the writ­ing or a con­stant need for en­ergy to main­tain the doc­u­ment. The new ma­te­rial con­sisted of three lay­ers in a sand­wich-like struc­ture. The re­searchers painted one side of a piece of pa­per with a blue dye that be­comes colour­less upon heat­ing, just like the T-shirts pop­u­lar in the 1990s that changed colour when they were touched with a warm hand.

Then, the other side of the pa­per was coated with a black toner layer that pro­duces heat upon ex­ci­ta­tion with light. Us­ing a “pen” that ap­plies heat, a ther­mal printer or a source of near-in­frared light, the team cre­ated im­ages and words that re­mained leg­i­ble for more than six months.

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