Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rethinking Brownian motion with the 'Emperor's New Clothes'

28.07.2009
In the classic fairy tale, "The Emperor's New Clothes," Hans Christian Andersen uses the eyes of a child to challenge conventional wisdom and help others to see more clearly.

In similar fashion, researchers at the University of Illinois have now revealed the naked truth about a classic bell-shaped curve used to describe the motion of a liquid as it diffuses through another material.

"The new findings raise fundamental questions concerning the statistical nature of the diffusion process," says Steve Granick, Founder Professor of Engineering, and professor of materials science and engineering, of chemistry, of chemical and biomolecular engineering, and of physics at the U. of I.

Diffusion is critical to processes such as drug delivery, water purification, and the normal operation of living cells. Key to the diffusion process is the manner in which the motion of one molecule affects the motion of another.

"In high school science classes, students are often assigned the task of using a microscope to watch a particle of dust sitting in a drop of water," Granick said. "The dust particle seems alive, moving back and forth, never in the same way. The motion of the dust particle is caused by the random 'kicks' of surrounding water molecules."

Called "Brownian motion" (after botanist Robert Brown, who noticed it in 1828), this phenomenon of fluids was described by Albert Einstein in 1905, when he published his statistical molecular theory of liquids.

According to Einstein, if the motions of many particles were watched, and the distance each moved in a certain time were recorded, the distribution would resemble the familiar Gaussian, bell-shaped curve used to assign grades in a science class.

Einstein had it right – almost.

"Like Einstein, we used to think we could describe Brownian motion with a standard bell-shaped curve," Granick said. "But now, with the ability to measure very small distances much more precisely than was possible 100 years ago, we have found that we can have extremes much farther than previously imagined."

In a paper to be published in the Proceedings of the National Academy of Sciences Online Early Edition next week, the U. of I. researchers show that Einstein's explanation, commonly cited in textbooks, fails in certain important cases.

The experiments were conducted by precisely tracking the motion of 100-nanometer colloidal beads using fluorescence microscopy.

In one series of experiments, the researchers watched as the beads moved up and down tiny tubes of lipid molecules by Brownian motion. In a second series of experiments, the researchers watched as the beads diffused through a porous membrane of entangled macromolecule filaments, again by Brownian motion.

In both sets of experiments, there were many features in full agreement with Einstein and the bell-shaped curve; but there were also features in significant disagreement. In those cases, the beads moved much farther than the common curve could predict. In those extreme displacements, diffusion behavior was not Gaussian, the researchers report. The behavior was exponential.

"These large displacements happen less often, but when they do occur, they are much bigger than we previously thought possible," Granick said.

The new findings "change the rules of the diffusion game," Granick said. "Like the emperor's new clothes, now that we know the bell-shaped curve isn't always the right way to think about a particular problem, process, or operation, we can begin to design around it, and maybe take advantage of it. And, we can correct the textbooks."

Granick is affiliated with the university's Beckman Institute, the department of bioengineering, and the Frederick Seitz Materials Research Laboratory.

With Granick, co-authors of the paper are graduate research assistant and lead author Bo Wang, graduate research assistant Stephen M. Anthony and research scientist Sung Chul Bae.

The U.S. Department of Energy funded the work.

James E. Kloeppel | EurekAlert!
Further information:
http://www.illinois.edu

More articles from Materials Sciences:

nachricht Molecular switch detects metals in the environment
15.08.2018 | Université de Genève

nachricht Breakthrough in nanoresearch - Quantum chains in graphene nanoribbons
09.08.2018 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

Unraveling the nature of 'whistlers' from space in the lab

15.08.2018 | Physics and Astronomy

Diving robots find Antarctic winter seas exhale surprising amounts of carbon dioxide

15.08.2018 | Earth Sciences

Early opaque universe linked to galaxy scarcity

15.08.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>