Anyone trying to build sandcastles on the beach will need some degree of skill and imagination, but not an instruction manual. The water content is actually relatively unimportant to the mechanical properties of the sand.
X-ray microtomography of a dense fluid cluster consisting of spherical glass beads (0.8 millimetres in diameter). Image: Max Planck Institute for Dynamics and Self-Organisation
This observation, which is borne out by precise measurements in the laboratory, puzzles researchers. Even with water content of just 3%, the fluid inside represents a highly-complex structure. The mechanical stiffness of the wet sand remains practically constant with moisture ranging from less than 1% to well over 10%, although the fluid structure changes enormously internally.
Researchers at the Max Planck Institute for Dynamics and Self-Organisation in Göttingen, the Australia National University in Canberra, the University of Erlangen, and the ESRF in Grenoble have studied the fluid structures in moist granules using x-ray microtomography to discover their laws (Nature Materials, online publication of February 10, 2008).
In medicine, x-ray microtomography is also known as computer tomography. Scientists x-ray an object from various angles to produce an outline image similar to a standard x-ray. A computer evaluates all of these images and determines which kind of three-dimensional structure the object must have to produce the outline images. When scientists use a bright x-ray source, such as the synchrotron source of radiation at the ESRF in Grenoble, computer tomography is produced with a resolution of thousandths of a millimetre. That is sufficient to resolve the tiny, highly-complex fluid structures that form in a moist granule, like inside a sandcastle for example.
What the research team saw was initially quite astonishing. The fluid did not fully push through the granulate structure and therefore did not force the air out of the interstitial space. More significantly, a filigree structure emerged in which the fluid, grains and air existed equally side by side. The reason for this is easy to understand. As the fluid moistens the grains (it would not otherwise be possible to get them into the granule), it tries to surround itself with as much "grain" as possible. This is best achieved at the points of contact where two grains touch. The "empty" space in between is relatively unattractive for the fluid and fills with air.
When the Göttingen scientists then carried out a more exact study of the geometry of these filigree fluid structures, they established that not only did they all have the same pressure, but that the pressure had to be independent of the fluid content. This explains the universal stiffness of the material. The equal pressure corresponds to an equal force inside and therefore results in the moist granules having the same mechanical properties. "These properties are not only significant to the building of sandcastles," said Stephan Herminghaus, the head of the study. "They are relevant to the pharmaceutical and food-production industries and help us to understand certain natural catastrophes, such as landslides. Wet granules are relevant in many fields and we now have a better understanding of their mechanical properties."
Dr. Bernd Wirsing | Max-Planck-Gesellschaft
Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern
20.07.2018 | Princeton University
Relax, just break it
20.07.2018 | DOE/Argonne National Laboratory
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences