THIS MONTH'S FEATURE ARTICLE
Studying Movement Against A Current
November 2019
Going upstream, and against a current, involves a front-first downward tilt and then moving along a surface, shows new research by a team of scientists, which created “nano-motors” to uncover this effective means of locomotion under such conditions. Its findings and the creation of these tiny motors offer new insights into the nature of movement in fluids and have implications for engineering.
Nano-motors of micron-meter size, made of platinum and gold, propel themselves against a flow (big arrows on channel walls) that contains hydrogen peroxide. Random thermal jiggling from the fluid molecules disturbs the motors' motion, but the long-gold motors (pullers) still maintains a relatively straight trajectory because its steeper tilt helps it align more easily against the flow and hence move upstream. Illustration by Dr. Yan-Peng Liu.
“These nano-motors not only helped us better understand the nature of moving against flows at the tiny scales we can’t easily see, but also could be the first step in developing smart material and robotic systems in the microscopic world,” says Jun Zhang, a professor of physics and mathematics at New York University (NYU) and a co-author of the paper, which appears in the journal Physical Review Letters.
“While this effect of movement has long been known, our work offers a comprehensive explanation for it, which enhances our understanding of this widespread dynamic,” adds co-author Michael Shelley, a professor at NYU’s Courant Institute of Mathematical Sciences.
According to information, the researchers focused on a previously discovered phenomenon, rheotaxis—movement involving a change of direction to head upstream or into a current.
However, detailed explanations for rheotaxis had been lacking. To fully understand this process, the scientists created nano-motors composed of two metals—platinum and gold (Pt/Au). Shelley, Zhang, also a professor at NYU Shanghai, and their colleagues had previously created a more basic version of these nano-motors, which are less than the width of a human hair.
Fabricated in the Molecular Design Institute in NYU’s Department of Chemistry, the motors described in the Physical Review Letters paper were more advanced; the researchers varied the proportions of these metals in order to vary their movement—in some models, the composition was evenly split while others had a 3:1 gold-to-platinum ratio or a 3:1 platinum-to-gold make-up.
Fueled chemically by a hydrogen peroxide dilution when placed in water, the nano-motors could swim—with the platinum end always serving as the head. However, these motors had different “tilts,” which differed depending on their make-up. Those composed primarily of gold were labeled “pullers” while those largely made up of platinum were called “pushers.” The pullers tended to move with their tails up (a pronounced tilt) while the pushers remained relatively flat.
This difference was significant when it came to moving against currents.
When the tilt is large (pullers), the tail is more exposed to an oncoming flow, which catches the tail and turns the motor around—similar to the way wind turns a weather vane. Consequently, the motor’s front faces the flow, after which the motor continues forward, now moving against the current. By contrast, if the motor is not tilted (pushers), a current cannot catch its tail and spin it around to move against this flow—and, as a result, it is unlikely to respond to an oncoming flow.
This work was supported by the MRSEC Program of the National Science Foundation (NSF) and also by additional NSF grants.
Feature Articles
Below are listed the 12 most recent Feature Articles.
To see the entire list of Feature Articles, visit the Feature Article Archive.
To be alerted to new Feature Articles, subscribe to The Virginia Engineer Newsfeed: RSS / Atom
Studying Movement Against A Current
November 2019
Going upstream, and against a current, involves a front-first downward tilt and then moving along a surface, shows new research…
October 2019
The Operations and Systems Engineering Extreme Event Research (OSEEER) network will advance basic science and engineering while also improving societal well-being.
September 2019
Robots are the size of the world’s smallest ant.
August 2019
Research at Washington University in St. Louis has shown however, that in conjunction with certain other chemicals, naturally occurring manganese can lead to big changes in…
July 2019
This year, exceptionally high spring rainfall and streamflow is transporting nitrogen to tidal waters in amounts above the long-term average…
June 2019
The Materials Explorers ™ STEM outreach program recently launched its newest classroom activities for high school students through…
May 2019
When you flush the toilet, you probably don’t think about the traces of the medicine and personal care products in your body that are winding up in…
April 2019
Although glass, ceramics, and metal forms have been around for ages, researchers don’t yet know key details about how materials crumble, dissolve, or otherwise come undone.
March 2019
Milos Manic, Ph.D., professor of computer science and director of VCU’s Cybersecurity Center, along with colleagues at the Idaho National Laboratory (INL), has developed a protection system that…
February 2019
Webb’s exquisite angular resolution will allow it to pick up the tiniest details.
January 2019
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes – while significantly reducing your electric bill and carbon footprint?
December 2018
Virginia Tech is making a historic commitment to build a revolutionary 1 million-square-foot, technology-focused campus in Alexandria…
