What ancient Chinese scrolls can teach us about flexible electronics

Physicists from Taiwan have found a way to save scrolls from curling up after they're unrolled from storage -- a problem that's plagued artisans for thousands of years.

Qingming Festival with main gate.jpg
Posters, panoramic high school photos, ancient scrolls... they’re all plagued by the same problem. Curling edges. I usually just roll it up from the opposite side, but that leaves its own unsightly creases. 

Now, physicists from Taiwan have found a way to save paper from this unwelcomed warping. And they think their method could help with the development of flexible electronics.

Qi-Wa -- or the up-curl on the lengths of hand scrolls and hanging scrolls -- has troubled Chinese artisans and emperors since painting and calligraphy were invented. Rolling up scrolls for storage helps protect them, but in addition to aesthetic reasons, the curl often damages the fiber and ink.  

So, using some experiments, theoretical models, and molecular dynamics simulation, a team led by Tzay-Ming Hong from the National Tsing Hua University investigated the mechanics of the curvature incurred during paper storage. Specifically, they looked at deformation and strain distribution. 

In addition to cheap paper, the team also examined the curling of “Along the River During the Qingming Festival,” a 5-meter-long painting from the 12th-century (a portion is pictured above). They found that the biggest culprit is the flexible backing layer that the ornate top layer is mounted on, Science reports:

When a scroll is rolled, the backing layer stretches to accommodate bending while the decorated top layer compresses, creating a difference in elasticity over time. Once unfurled, the backing layer’s resting length is now longer than that of the top layer. Because the two layers are attached together, the bottom layer pushes outward while the top layer pulls inward, causing the scroll’s sides to deform and curl up.

With their findings, the team proposes modifications to traditional mounting techniques that could help mitigate Qi-Wa. New Scientist explains
  • The paper backing used to mount scrolls is often replaced as part of normal restoration. So, replace the backing on scrolls with paper that has fibers aligned with the long edges, increasing stiffness in that direction. Adding extra layers of paper to the sides has a similar effect.
  • Make tiny perforations along the entire backing sheet with a stiff brush. That should reduce the amount of stretch that converts into curling.

The team got similar results from experiments with polymer-based plastic films -- which suggests that the technique could be helpful for the development of flexible electronic paper displays , which also curl when unrolled.

This investigation all started after a visit with art conservationists at the National Palace Museum in Taipei. “Like the mounting masters before them, over the span of more than 2000 years, they did not think this problem was at all solvable," Hong tells New Scientist

The work was published in Physical Review Letters last week. 

PS. Happy Year of the Horse. 

Image: a portion of “Along the River During Qingming Festival” via Wikimedia

This post was originally published on Smartplanet.com