Nav: Home

How to tie microscopic knots

September 26, 2019

Physicists at the University of Colorado Boulder have gone to creative lengths to earn their scouting merit badges for knot-tying.

In a study that will appear Sept. 22 in the journal Science, a team of researchers discovered a new way to tie microscopic knots within a solution of liquid crystals. This type of material is found in a wide range of electronics from high-definition TVs to cellphone screens.

And while the tiny knots won't help you to secure a rowboat or pitch a tent, they are a feat of control, said Jung-Shen (Benny) Tai, lead author of the new research. Once tied, these molecular pretzels won't untie, and they can come together to form large, three-dimensional crystals.

"By changing the voltage we apply to the liquid crystal with our knots, we can make them expand or shrink and even form the CU Boulder logo when manipulated using lasers," said Tai, a graduate student in the Department of Physics.

Co-author Ivan Smalyukh believes that the team's liquid crystal knots will have other uses, too.

Physicists, he explained, have long been interested in how knots might form in a wide range of physical fields, such as those emerging from magnets. The problem is that these phenomena aren't easy to observe or manipulate using conventional tools.

"Scientists have proposed knots like these in cosmology, nuclear physics, particle physics, everywhere," said Smalyukh, a professor of physics. "But what is beautiful about liquid crystals is that you can see and study them under a microscope."

He added that the study builds on humanity's long-running obsession with knots. Such shapes have played a central role in the artwork of Celtic, Norse, Tibetan and Chinese cultures, to name a few.

"Humankind has been fascinated by knots for millennia," Smalyukh said.

Scientists are no exception. In the 19th century, for example, famed physicists William Thomson and James Clerk Maxwell proposed that atoms themselves might be made up of tiny knots of energy. This model was eventually debunked, but it helped to inspire a current area of research called mathematical knot theory.

And it pushed a lot of scientists to look for knots in other physical phenomena. For their part, Smalyukh and Tai turned to liquid crystals.

These types of materials are useful because they behave a little like solids and a little like liquids.

In the new study, the researchers experimented with a type of liquid crystal molecule that is shaped like a helix, or a small screw. Because those screws don't fit together well, they tend to twist, Smalyukh said. As a result, if you mix them under just the right conditions, small kinks will begin to appear in the solution. Through a microscope, those kinks look a bit like grains of sand floating in a glass of water.

But they're not grains. They're knots.

"We're seeing a huge number of molecules that know how to tie knots," Smalyukh said.

Put another way, the molecules within the tiny kinks point in different directions than those around them. And if you measure their collective orientations in different locations, they trace the line of a knot.

Tai added that the team has seen several different kinds of knots appear in their liquid crystal solutions. The most basic is the trefoil knot, which crosses over itself three times and was a popular motif in Celtic artwork.

"We also had more complicated ones like cinquefoil knots, or knots with five crossings, and even ones with seven crossings," he said.

Like the best knots, these creations won't snap unless the researchers disturb the surrounding medium--the equivalent of using a scissors to snip them. As a result, the team was able to use lasers to move the knots around, nudging them together to form much bigger structures.

"With liquid crystals, we can easily image and analyze these knots and compare them to actual mathematical knots," Tai said. "So this provides a very nice platform to test knot theory."

Smalyukh agreed and said that it's also just exciting to find a new way to play with knots.

"We know that there is a beautiful history of people being fascinated by the possibility of knots in fields," he said. "But it was quite unexpected to see them in this embodiment right in front of our eyes."

University of Colorado at Boulder

Related Physics Articles:

Challenges and opportunities for women in physics
Women in the United States hold fewer than 25% of bachelor's degrees, 20% of doctoral degrees and 19% of faculty positions in physics.
Indeterminist physics for an open world
Classical physics is characterized by the equations describing the world.
Leptons help in tracking new physics
Electrons with 'colleagues' -- other leptons - are one of many products of collisions observed in the LHCb experiment at the Large Hadron Collider.
Has physics ever been deterministic?
Researchers from the Austrian Academy of Sciences, the University of Vienna and the University of Geneva, have proposed a new interpretation of classical physics without real numbers.
Twisted physics
A new study in the journal Nature shows that superconductivity in bilayer graphene can be turned on or off with a small voltage change, increasing its usefulness for electronic devices.
Physics vs. asthma
A research team from the MIPT Center for Molecular Mechanisms of Aging and Age-Related Diseases has collaborated with colleagues from the U.S., Canada, France, and Germany to determine the spatial structure of the CysLT1 receptor.
2D topological physics from shaking a 1D wire
Published in Physical Review X, this new study propose a realistic scheme to observe a 'cold-atomic quantum Hall effect.'
Helping physics teachers who don't know physics
A shortage of high school physics teachers has led to teachers with little-to-no training taking over physics classrooms, reports show.
Physics at the edge
In 2005, condensed matter physicists Charles Kane and Eugene Mele considered the fate of graphene at low temperatures.
Using physics to print living tissue
3D printers can be used to make a variety of useful objects by building up a shape, layer by layer.
More Physics News and Physics Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

There's so much we've yet to explore–from outer space to the deep ocean to our own brains. This hour, Manoush goes on a journey through those uncharted places, led by TED Science Curator David Biello.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Dispatch 1: Numbers
In a recent Radiolab group huddle, with coronavirus unraveling around us, the team found themselves grappling with all the numbers connected to COVID-19. Our new found 6 foot bubbles of personal space. Three percent mortality rate (or 1, or 2, or 4). 7,000 cases (now, much much more). So in the wake of that meeting, we reflect on the onslaught of numbers - what they reveal, and what they hide.  Support Radiolab today at