SAT OG 2018 Reading - Test 8 reading 3

Questions 22-31 are based on the following

This passage is adapted from Rachel Ehrenberg, “Salt Stretches in Nanoworld.” ©2009 by Society for Science & the Public. The “nanoworld” is the world observed on a scale one billionth that of ordinary human experience.

Inflexible old salt becomes a softy in the

nanoworld, stretching like taffy to more than twice

its length, researchers report. The findings may lead
to new approaches for making nanowires that could
5 end up in solar cells or electronic circuits. The work

also suggests that these ultra-tiny salt wires may

already exist in sea spray and large underground salt

“We think nanowires are special and go to great
10 lengths to make them,” says study coauthor

Nathan Moore of Sandia National Laboratories in

Albuquerque. “Maybe they are more common than

we think.”
Metals such as gold or lead, in which bonding
15 angles are loosey-goosey, can stretch out at

temperatures well below their melting points.

But scientists don’t expect this superplasticity in a

rigid, crystalline material like salt, Moore says.
This unusual behavior highlights that different
20 forces rule the nanoworld, says theoretical physicist

Krzysztof Kempa of Boston College. “Forget about

gravity. It plays no role,” he says. Surface tension and

electrostatic forces are much more important at this

25 Moore and his colleagues discovered salt’s

stretchiness accidently. They were investigating how

water sticks to a surface such as salt and created a

super-dry salt sample for testing. After cleaving a

chunk of salt about the size of a sugar cube with a
30 razor, the scientists guided a microscope that detects

forces toward the surface. When the tip was far away

there was no measured force, but within about seven

nanometers a very strong attraction rapidly

developed between the diamond tip of the
35 microscope and the salt. The salt actually stretched

out to glom on to the microscope tip. Using an

electron microscope to see what was happening, the

researchers observed the nanowires.
The initial attraction between the tip and salt
40 might be due to electrostatic forces, perhaps good old

van der Waals interactions,1 the researchers

speculate. Several mechanisms might lead to the

elasticity, including the excessive surface tension

found in the nanoworld (the same tension that allows
45 a water strider to skim the surface of a pond).
The surface tension is so strong that as the

microscope pulls away from the salt, the salt

stretches, Kempa says. “The inside has no choice but

to rearrange the atoms, rather than break,” he says.
50 This bizarre behavior is actually mirrored in the

macroworld, the researchers say. Huge underground

deposits of salt can bend like plastic, but water is

believed to play a role at these scales. Perhaps salty

nanowires are present in these deposits as well.
55 “Sodium chloride2 is everywhere—in the air, in

our bodies,” Moore says. “This may change our view

of things, of what’s happening at the nanoscale.”
The work also suggests new techniques for

making nanowires, which are often created through
60 nano-imprinting techniques, Kempa says. “We

invoke the intuition of the macroworld,” he says.

“Maybe instead of stamping [nanowires] we should

be nano-pulling them.”

Beginning of reading passage footnotes.

1 Attractive forces between nearby atoms

2 Common salt

Question 22 One central idea of the passage is that