Featured Research

from universities, journals, and other organizations

Slick Research Says Fluids Slip On Solids, Depending On Speed

Date:
August 31, 2001
Source:
University Of Illinois At Urbana-Champaign
Summary:
When it comes to predicting boundary conditions of fluids flowing over solid surfaces, the textbooks are all wet, say researchers at the University of Illinois. How fluids behave on extremely smooth surfaces is important in such high-tech applications as moving materials through microfluidic devices and lubricating computer hard drives.

CHAMPAIGN, Ill. — When it comes to predicting boundary conditions of fluids flowing over solid surfaces, the textbooks are all wet, say researchers at the University of Illinois.

How fluids behave on extremely smooth surfaces is important in such high-tech applications as moving materials through microfluidic devices and lubricating computer hard drives.

“We found that if surfaces are smooth enough, and if the liquid is moving fast enough, the liquid will slip over the surface like ice skates gliding over ice,” said Steve Granick, a professor of materials science at the UI and a researcher at the Frederick Seitz Materials Research Laboratory on campus.

Liquids may be attracted poorly to a solid surface – like beads of water on a freshly waxed car – or they may be attracted strongly – like cooking oil on an old iron skillet. A basic tenet of textbook fluid dynamics – called the “no-slip” boundary condition – says that a layer of fluid molecules flowing across a solid surface will be stuck in place, regardless of the strength of attraction.

“When standing in a shower, for example, the no-slip boundary condition says that the water molecules closest to your skin will actually stick to you and come to rest,” Granick said. “Molecules one layer away will move a little, those a little farther away will move a little faster, and so on, until the water is running freely off your body. This also explains why large dust particles can be blown off dirty eyeglasses, but smaller bits must be wiped off – a thin layer of air next to the lens doesn’t move.”

To explore the no-slip boundary condition, Granick and doctoral student Yingxi (Elaine) Zhu placed drops of liquid between molecularly smooth mica surfaces within a modified surface forces apparatus. Surface spacing was measured using optical interferometry and dynamic forces were measured using piezoelectric methods. The team’s findings were reported in the Aug. 27 issue of Physical Review Letters.

By first coating the mica with a smooth monolayer of octadecyltriethoxysiloxane, the researchers studied the behavior of two dissimilar fluids – tetradecane (an oil) and water. Each drop was squeezed until the fluid was only a few layers thick. Not only did none of the layers in either fluid “stick” to the surface (as textbooks claim they should), the amount of slip depended on the velocity of the fluid.

The researchers also saw the same effect when, instead of first modifying the solid surface, they added soap-like molecules to the flowing liquid. “The surfactant migrated to the surface where it formed a smooth coating that lessened the attraction of the liquid for that surface,” Granick said. “This means we can achieve the same lubrication goal without going through the complicated protocols of producing a perfect surface.”

This could be an easy and inexpensive way to save energy when transporting fluids through pipelines, and for reducing friction in engines and machinery, Granick said. “There will be many other applications down the road, when we know more about manipulating the no-slip boundary condition.”

The National Science Foundation and the U.S. Department of Energy supported the research.


Story Source:

The above story is based on materials provided by University Of Illinois At Urbana-Champaign. Note: Materials may be edited for content and length.


Cite This Page:

University Of Illinois At Urbana-Champaign. "Slick Research Says Fluids Slip On Solids, Depending On Speed." ScienceDaily. ScienceDaily, 31 August 2001. <www.sciencedaily.com/releases/2001/08/010831080908.htm>.
University Of Illinois At Urbana-Champaign. (2001, August 31). Slick Research Says Fluids Slip On Solids, Depending On Speed. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2001/08/010831080908.htm
University Of Illinois At Urbana-Champaign. "Slick Research Says Fluids Slip On Solids, Depending On Speed." ScienceDaily. www.sciencedaily.com/releases/2001/08/010831080908.htm (accessed July 29, 2014).

Share This




More Matter & Energy News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Baluchistan Mining Eyes an Uncertain Future

Baluchistan Mining Eyes an Uncertain Future

AFP (July 29, 2014) Coal mining is one of the major industries in Baluchistan but a lack of infrastructure and frequent accidents mean that the area has yet to hit its potential. Duration: 01:58 Video provided by AFP
Powered by NewsLook.com
Easier Nuclear Construction Promises Fall Short

Easier Nuclear Construction Promises Fall Short

AP (July 29, 2014) The U.S. nuclear industry started building its first new plants using prefabricated Lego-like blocks meant to save time and prevent the cost overruns that crippled the sector decades ago. So far, it's not working. (July 29) Video provided by AP
Powered by NewsLook.com
Lithium Battery 'Holy Grail' Could Provide 4 Times The Power

Lithium Battery 'Holy Grail' Could Provide 4 Times The Power

Newsy (July 28, 2014) Stanford University published its findings for a "pure" lithium ion battery that could have our everyday devices and electric cars running longer. Video provided by Newsy
Powered by NewsLook.com
The Carbon Trap: US Exports Global Warming

The Carbon Trap: US Exports Global Warming

AP (July 28, 2014) AP Investigation: As the Obama administration weans the country off dirty fuels, energy companies are ramping-up overseas coal exports at a heavy price. (July 28) 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:
from the past week

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