РОССИЙСКАЯ АКАДЕМИЯ НАУК

УРАЛЬСКОЕ ОТДЕЛЕНИЕ

ИНСТИТУТ ХИМИИ TBEPДОГО ТЕЛА
   
| | | | |
| | | |
 22.06.2009   Карта сайта     Language По-русски По-английски
Новые материалы
Экология
Электротехника и обработка материалов
Медицина
Статистика публикаци


22.06.2009


Nanoparticles make 'self-erasing' images



19 June 2009



Materials displaying 'self-erasing' colour images have been created by chemists in the US, who have studied how certain nanoparticles can assemble and disassemble themselves under different wavelengths of light.


The materials, which are printed with ultraviolet (UV) light and erased with visible light, could one day be used for self-expiring bus tickets or for carrying secret messages.


'Self-erasing papers are important for time-sensitive materials and secure communications,' said study leader Bartosz Grzybowski of Northwestern University in Evanston, Illinois. 'On the fundamental level, what we describe is also a very different way of looking at the concept of information storage. We're not using traditional coloured inks per se, but rather we "generate" or "elicit" colours only when particles in the film self-assemble.'











Top: The text in the films fades and is erased within 60 seconds by exposure to intense visible light. Bottom: Different colours are generated depending on how long each area is exposed to UV light.



© Angewandte Chemie



Grzybowski's group makes the materials by coating gold and silver nanoparticles with a single layer of azobenzene molecules, and then embedding the nanoparticles in thin, flexible 'organogel' films. When the films are exposed to UV light, the structural symmetry of the azobenzene molecules flips, and they acquire electric dipoles that make them attract. This attraction causes the nanoparticles to assemble, and thereby take on a new colour. However, in an absence of UV light - or even better, in strong visible light - the particles revert to their original symmetry, and the colour disappears over a period of time.


The exact colour of the exposed films depends on the amount of UV exposure they receive: the gold nanoparticles evolve from red to blue, while the silver nanoparticles evolve from yellow to violet. Moreover, by altering the surface coverage of the azobenzene molecules, the printing and erasing times can change from seconds to hours, and in this way the films can be programmed for different purposes.











When exposed to UV light, the trans-azobenzene groups coating the nanoparticles isomerize to cis-azobenzene with a large dipole moment



© Angewandte Chemie



Grzybowski told Chemistry World that he envisages applications from bus tickets that expire after a certain journey time to top-secret documents that are safe from prying eyes. 'Imagine Pentagon reports that after a meeting of their top brass would self-erase; there's no way to take the copy to the press,' he said. 'Better still, since these materials very rapidly self-erase when exposed to visible light, you cannot Xerox them.'


In fact, the Xerox printing corporation developed a type of self-erasing paper in 2006. It worked using a phenomenon known as photochromism, in which the ink itself changes structure and darkens upon exposure to a certain wavelength of light. The paper's image would last for 16-24 hours, but unlike the Northwestern group's films this time could not be programmed, and there was no option for colour.


Jon Cartwright


 


Interesting? Spread the word using the 'tools' menu on the left.



References


R Klajn et al, Angew. Chem. Int. Ed., 2009. DOI: 10.1002/anie.200901119


Дизайн и программирование N-Studio 
А Б В Г Д Е Ё Ж З И Й К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ъ Ы Ь Э Ю Я
  • Chen Wev .  honorary member of ISSC science council

  • Harton Vladislav Vadim  honorary member of ISSC science council

  • Lichtenstain Alexandr Iosif  honorary member of ISSC science council

  • Novikov Dimirtii Leonid  honorary member of ISSC science council

  • Yakushev Mikhail Vasilii  honorary member of ISSC science council

  • © 2004-2019 ИХТТ УрО РАН
    беременность, мода, красота, здоровье, диеты, женский журнал, здоровье детей, здоровье ребенка, красота и здоровье, жизнь и здоровье, секреты красоты, воспитание ребенка рождение ребенка,пол ребенка,воспитание ребенка,ребенок дошкольного возраста, дети дошкольного возраста,грудной ребенок,обучение ребенка,родить ребенка,загадки для детей,здоровье ребенка,зачатие ребенка,второй ребенок,определение пола ребенка,будущий ребенок медицина, клиники и больницы, болезни, врач, лечение, доктор, наркология, спид, вич, алкоголизм православные знакомства, православный сайт творчeства, православные рассказы, плохие мысли, православные психологи рождение ребенка,пол ребенка,воспитание ребенка,ребенок дошкольного возраста, дети дошкольного возраста,грудной ребенок,обучение ребенка,родить ребенка,загадки для детей,здоровье ребенка,зачатие ребенка,второй ребенок,определение пола ребенка,будущий ребенок