Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Atomic force microscopy reveals liquids adjust viscosity when confined, shaken

02.05.2008
Getting ketchup out of the bottle isn’t always easy. However, shaking the bottle before trying to pour allows the thick, gooey ketchup to flow more freely because it becomes more fluid when agitated. The opposite is not typically true – a liquid such as water does not become a gel when shaken.

However, new research published in the March 14 issue of the journal Physical Review Letters shows that when fluids like water and silicon oil are confined to a nanometer-sized space, they behave more like ketchup or toothpaste. Then, if these confined liquids are shaken, they become fluidic and exhibit the same structural and mechanical properties as those in thicker layers.

The study – the first to use an atomic force microscope to measure the viscosity of confined fluids – revealed that these liquids can respond and modify their viscosity based on environmental changes.

“Knowing this could be very important,” said Elisa Riedo, an assistant professor in the Georgia Tech School of Physics. “If a lubricant used in a piece of machinery becomes thick and gelatinous when squeezed between two solid surfaces, serious problems could occur. However, if the machine vibrated, the liquid could become fluidized.”

With funding from the National Science Foundation and the U.S. Department of Energy, Riedo and graduate student Tai-De Li used atomic force microscopy (AFM) to measure the behavior of thin and thick layers of liquids while they were vibrated. A nanometer-size spherical silicon tip was used to approach a mica surface immersed in water or silicon oil, while small lateral oscillations were applied to the cantilever support.

“Some researchers have measured the force it takes to squeeze out a fluid, but we took a different approach,” explained Riedo. “We are the first group to use AFM to study the viscosity of confined fluids from direct high-resolution lateral force measurements.”

The normal and lateral forces acting on the tip were measured directly and simultaneously as a function of the liquid film thickness. The ratio of stress to strain under vibratory conditions, called the viscoelastic modulus, was also measured at different frequencies and strains.

Riedo and Li measured the relaxation times of two wetting liquids: water and silicone oil (octamethylcylotetrasiloxane), which is primarily used as a lubricant or hydraulic fluid, and is the main ingredient in Silly Putty®.

“The relaxation time describes how active the molecules are. A longer relaxation time means it takes longer for the molecules to rearrange themselves back into their original shape after shaking them,” said Li. “Liquids have very short relaxation times – as soon as one stops shaking a bottle of water, it reverts to its original configuration.”

Experimental results showed that the relaxation time became orders of magnitude longer in water and silicone oil when they were confined, meaning they behaved more like gels or glass. The researchers also showed that the relaxation times depended on the shaking speed when the liquids were confined. However, in thick layers that were not confined, the molecules showed no dependence on the shaking speed and always relaxed very quickly, meaning they behaved like a “normal” liquid.

Longer relaxation times were observed when the water film was less than one nanometer thick, composed of about three molecules of water stacked on top of each other. Otherwise, its properties were the same as in a bottle of water. For silicone oil, a thickness of four nanometers was required before the properties were like those of a glassy material.

“We observed a nonlinear viscoelastic behavior remarkably similar to that widely observed in metastable complex fluids, such as gels or supercooled liquids,” noted Riedo. “Because we observed these phenomena in both water and silicone oil, we believe they are very general phenomena and may apply to all wetting liquids.”

Since the behavior of confined water observed in these experiments is similar to the behavior of supercooled water at -98.15 degrees Celsius, the researchers are currently examining whether confinement defines a lower effective temperature in the confined liquid.

Abby Vogel | EurekAlert!
Further information:
http://www.gatech.edu

More articles from Physics and Astronomy:

nachricht Columbia engineers create artificial graphene in a nanofabricated semiconductor structure
13.12.2017 | Columbia University School of Engineering and Applied Science

nachricht Long-lived storage of a photonic qubit for worldwide teleportation
12.12.2017 | Max-Planck-Institut für Quantenoptik

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Gecko adhesion technology moves closer to industrial uses

13.12.2017 | Information Technology

Columbia engineers create artificial graphene in a nanofabricated semiconductor structure

13.12.2017 | Physics and Astronomy

Research reveals how diabetes in pregnancy affects baby's heart

13.12.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>