Featured Research

from universities, journals, and other organizations

Physicists Find Gyrations Of Tiny Rod-Like Viruses Induce Measurable Entropic Forces In Solution

Date:
August 10, 2001
Source:
University Of Pennsylvania
Summary:
In an experiment with exquisite sensitivity, physicists at the University of Pennsylvania have found that fluctuations as fleeting as the bending of rod-shaped viruses just 880 millionths of a millimeter in length can measurably increase the entropic forces between other particles in solution. The finding is reported in the journal Physical Review Letters.

PHILADELPHIA – In an experiment with exquisite sensitivity, physicists at the University of Pennsylvania have found that fluctuations as fleeting as the bending of rod-shaped viruses just 880 millionths of a millimeter in length can measurably increase the entropic forces between other particles in solution. The finding is reported in the journal Physical Review Letters.

Related Articles


Led by graduate student Keng-hui Lin, scientists in the laboratory of Penn physicist Arjun G. Yodh measured the entropic forces exerted by rod-like viruses on particles in water. Their research revealed anticipated entropic forces associated with shifts in position and rotation of the rigid nanorods; to their surprise, it also revealed tiny additional entropic effects of rod flexibility.

Entropy is a measure of the disorder of a system, with systems generally evolving to maximize entropy.

"Entropy in these systems is largely a function of the amount of space components have for moving about," said Yodh, a professor of physics. "It turns out that simply by bending, the rod-like virus can effectively occupy a little more space and thus entropically drive rearrangements of the system."

Yodh’s team captured these minuscule shifts in entropy using "laser tweezers" to manipulate inert, one-micron spheres floating in a microscopic tank full of rod-shaped viruses 880 nanometers long and 7 nanometers in diameter.

"The effects were quite subtle, but our experiments showed that the slight flexibility of the viruses strengthened the attraction between the spheres, driving them more strongly toward each other," Yodh said. "When the rods become a little more flexible, they occupy more space when they spin. The smidgen of additional space occupied by a bent virus compared to a straight virus was enough to increase the attractions between spheres that nearly touch one another."

In the mixture of rods and spheres, the rods seek to maximize their own freedom of motion, and therefore the mixture’s entropic energy, by avoiding the space between the spheres. The net effect of the rods’ preference not to be sandwiched between the spheres is manifested as a slight attraction between the larger particles.

Yodh and his colleagues measured the slight attractive force the viruses impart by partially immobilizing the spheres with laser tweezers. While trapped in the laser beam line trap, the spheres were able to move in only one dimension. By continuously photographing the positions of the spheres in a tank both with and without the rods, the team was able to discern these entropic attractions. The spheres’ attraction is accompanied by an overall increase in the system’s entropy.

The work of the Penn team tested detailed theoretical predictions by Portuguese theorist Carlos Marques and collaborators, demonstrating entropic forces associated with nanorod central position and rotation. These orientational degrees of freedom are, in fact, responsible for the rich variety of liquid crystalline phases exhibited by rods. The measured deviations from theory were due to rod flexibility.

Yodh and Lin were joined on the Physical Review Letters paper by John C. Crocker of the California Institute of Technology and Ana C. Zeri of the University of California, San Diego. Their work was funded by the National Science Foundation and NASA.


Story Source:

The above story is based on materials provided by University Of Pennsylvania. Note: Materials may be edited for content and length.


Cite This Page:

University Of Pennsylvania. "Physicists Find Gyrations Of Tiny Rod-Like Viruses Induce Measurable Entropic Forces In Solution." ScienceDaily. ScienceDaily, 10 August 2001. <www.sciencedaily.com/releases/2001/08/010810065304.htm>.
University Of Pennsylvania. (2001, August 10). Physicists Find Gyrations Of Tiny Rod-Like Viruses Induce Measurable Entropic Forces In Solution. ScienceDaily. Retrieved November 21, 2014 from www.sciencedaily.com/releases/2001/08/010810065304.htm
University Of Pennsylvania. "Physicists Find Gyrations Of Tiny Rod-Like Viruses Induce Measurable Entropic Forces In Solution." ScienceDaily. www.sciencedaily.com/releases/2001/08/010810065304.htm (accessed November 21, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Friday, November 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Baby Okapi Born at Houston Zoo

Raw: Baby Okapi Born at Houston Zoo

AP (Nov. 20, 2014) — The Houston Zoo released video of a male baby okapi. Okapis, also known as the "forest giraffe", are native to the Democratic Republic of the Congo in Central Africa. Video is mute from source. (Nov. 20) Video provided by AP
Powered by NewsLook.com
Your Complicated Job Might Keep Your Brain Young

Your Complicated Job Might Keep Your Brain Young

Newsy (Nov. 20, 2014) — Researchers at the University of Edinburgh found the more complex your job is, the sharper your cognitive skills will likely be as you age. Video provided by Newsy
Powered by NewsLook.com
Mysterious Glow Worms Found in the Amazon

Mysterious Glow Worms Found in the Amazon

Buzz60 (Nov. 20, 2014) — Wildlife photographer Jeff Cremer teamed up with entomologist Aaron Pomerantz and others to investigate a predatory glow worm found in the Amazon. Patrick Jones (@Patrick_E_Jones) explains. Video provided by Buzz60
Powered by NewsLook.com
Raw: Huge Snow Covers Buffalo Streets

Raw: Huge Snow Covers Buffalo Streets

AP (Nov. 20, 2014) — A new blast of lake-effect snow roared through western New York with thunder and lightning on Thursday, raising to nearly 6 feet the three-day total in parts of the Buffalo area. (Nov. 20) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins