Scientific American - 09.2019

September 2019, ScientificAmerican.com 15

MARCUS DRYMON

Field Museum

MATERIALS SCIENCE

Cracked

Canvases

Microstructures in plastic

produce colorful portraits

For millennia humans have created art with

pigment-based paints, inks and dyes. Now

researchers have produced tiny plastic paint-

ings whose colors come from variations in

microscopic surface features instead.

Pigments are chemicals that absorb cer-

îDž³§žšîÿDþx§x³îšäD³lßx‹x`î ̧îšxßäî ̧

Çß ̧lø`xäÇx`ž‰`` ̧§ ̧ßäÍ

øîä ̧­x­Dîxߞ-

D§ääø`šDäîš ̧äx ̧³­ ̧ßǚ ̧UøîîxߋžxäÜ

iridescent blue wings and the striking feath-

ers of some hummingbirds—produce colors

based on the size and spacing of micro-

structures on their surfaces, which interact

ÿžîš§žšîÿDþx§x³îšä ̧…lž†xßx³î䞱xäÍ

Many plastics form minuscule cracks,

called crazes, when put under stress.

Typically these fractures occur randomly

îšß ̧øš ̧øîîšx­DîxߞD§Í

øî‰ßäîxĀÇ ̧䞳

some plastics to light beams can selective-

ly weaken them in places, where crazes

will appear when the plastic is stressed.

“You can actually control where the cracks

form,” says materials scientist and study

co-author Andrew Gibbons of Kyoto Uni-

versity in Japan. Depending on size and

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äîßø`îøßxäîšDîÇß ̧lø`xäÇx`ž‰`` ̧§ ̧ßäÍ

Gibbons and his colleagues shone pow-

erful LEDs on thin pieces of plastic and then

dunked them in acetic acid, generating

crazes in the places preweakened by light.

5šxäx`ßD`¦äž³žîžD§§āßx‹x`îîšxäD­xÿDþx-

length of light to which the section of plastic

ÿDäxĀÇ ̧äxljD`` ̧ßlž³î ̧îšxäîølājÿšž`š

was published in June in Nature.

…îšxǧDäîž`žää ̧D¦xl§ ̧³xß ̧ßxĀÇ ̧äxl

î ̧šžšîx­ÇxßDîøßxäjîšx`ßD`¦ä`D³xĀÇD³l

î ̧ßx‹x`î§ ̧³xßÿDþx§x³îšäÍ5šx䞱x ̧…

each region hit by light and the thickness of

îšxǧDäîž`D§ä ̧ž³‹øx³`xš ̧ÿ…Dßîšx`ßD`¦ä

xĀÇD³lÍ5 ̧îxäîîšxžß­xîš ̧ljîšxßxäxDß`š-

ers produced miniature renderings of classic

paintings and even a Queen album cover.

(The smallest was 0. 25 millimeter across.)

ÙîÜäD³ž³³ ̧þDîžþxîÿžäîjÚäDāäÇ ̧§ā­xß

scientist Christopher Soles of the National

Institute of Standards and Technology,

who was not involved in the study. “Usual-

ly crazing in materials is a very bad thing,”

Soles notes, “but here the crazes are use-

ful.” He was surprised the process worked

ÿžîšä ̧­D³ālž†xßx³îîāÇxä ̧…ǧDäîž`äj

including polystyrene, polycarbonate and

acrylic glass—used in food containers, CD

cases and bulletproof glass, respectively.

Gibbons says crazing could potentially

create a durable plastic coating for cur-

rency or high-end merchandise to dis-

courage counterfeiters. And the micro-

structures can produce more than pretty

pictures. Eventually he hopes the tech-

nique could be used to create devices that

store microscopic amounts of liquid for

medical analysis. — Jennifer Leman

FIELD BIOLOGY

A Migrating

Snack

For young sharks, land-based

birds can be easy targets

=šx³‰äšxߞxäbiologist James Drymon

noticed feathers in the vomit of a tiger shark,

šx‰ßäîDääø­xlîšxāUx§ ̧³xlî ̧ä ̧­x

unfortunate seabird: a gull, perhaps, or a

Çx§ž`D³Í

øîÿšx³šxD³lšžäîxD­x³xîž-

cally sequenced the feathers, the results sur-

prised them: the quills came from a land-

based songbird called a brown thrasher. So

ÿšDîÿDäžîl ̧ž³ž³DxßäšDߦÜääî ̧­D`š

ž³îšxø§… ̧…$xĀž` ̧Õ

Drymon, a researcher at Mississippi

3îDîx7³žþxßäžîāÜä ̧DäîD§2xäxDß`šD³l

Āîx³äž ̧³x³îxßjD³lšžä` ̧§§xDøxää ̧ßîxl

through the stomach contents of 105 juve-

nile tiger sharks between 2010 and 2018.

Nearly 40 percent had recently feasted on

birds that hail from dry land. In all, the scien-

tists counted 11 terrestrial bird species show-

ž³øÇ ̧³îšxäšDߦäÜ­x³øÍ5šxßxäø§îä

were published online in May in Ecology.

2xäxDß`šxßäšDþx¦³ ̧ÿ³䞳`xîšx¿ ́éćä

that sharks sometimes eat songbirds, “but

what was interesting to us was the preva-

lence” of the behavior, Drymon says. “This is

something that happens every year in a high

number” of sharks.

Every fall and spring, songbirds under-

take dramatic migrations across the Gulf of

$xĀž` ̧Í…UDlÿxDîšxß` ̧­xäD§ ̧³jîšxā

can be forced to land on the water—which is

x†x`îžþx§āDlxDîšäx³îx³`xÍÙ 5šxxäDîx

for the number of migrants that die because

of storm-related events is in the billions,”

Dr ymon says. He suspects that sharks have

long taken advantage of this twice-yearly

nutritional bounty raining down from the

skies, but scientists have only recently had

îšxx³xîž`î ̧ ̧§äî ̧` ̧³‰ß­äUāžlx³îž…ā-

ing partially digested feathers.

The results underscore how intercon-

nected marine and terrestrial ecosystems

can be, says University of Miami marine

ecologist Neil Hammerschlag, who was

not involved in the study: “It shows how

opportunistic and amazingly generalist

these sharks are.” — Jason G. Goldman

Girl with a Pearl Earring, by Johannes

Vermeer, re-created in polystyrene

ANDREW GIBBONS

Kyoto University

Songbird from

a tiger shark’s

stomach