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!
Argon is not the 'dope' for metallic hydrogen
24.03.2017 | Carnegie Institution for Science
Researchers make flexible glass for tiny medical devices
24.03.2017 | Brigham Young University
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy