Water molecules queue into nanotubes
Researchers have, for the first time, demonstrated that
water can enter ultrathin carbon nanotubes ‑ tubes with a wall consisting of a
single layer of carbon atoms and a diameter down to half of a billionth of a
meter (0.548 nanometer) ‑ thin enough to prevent water molecules from passing
each other inside the tube. This first experimental proof of such single‑file
transport of water occurring in nanotubes holds promise for the design of
ultraselective filter membranes and, eventually, nanofluidic devices where
water or other fluids would be transported and manipulated at the molecular
scale in a "first‑in‑first‑out" manner.
While intuitively unexpected because of the highly water‑repellent carbon
surface of the tubes, transport of water through carbon nanotubes has been the
subject of many theoretical studies. In the present work, the researchers
caused nanotubes of specific diameters and structures to vibrate, using a wide
range of lasers of different wavelengths (colors). They could distinguish
water‑filled and empty nanotubes, as these vibrate at different frequencies ‑
in much the same way as a water‑filled glass resonates at a higher pitch than
an empty glass.
The team found water‑filling in extremely thin tubes ‑ thinner than generally
predicted by theory ‑ and the results even indicate that the water molecules
are forced to adopt specific orientations and arrangements depending on the
exact nanotube structure.
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EL10710
Solving the mystery of raindrop formation
We have experimentally discovered a new physical mechanism for the formation of local small-scale concentrations of inertial particles (e.g. droplets) suspended in turbulent nonisorthermal flow. The mechanism of rain formation is not yet sufficiently understood and remains an outstanding problem in atmospheric physics. Calculations based on the assumption of uniform spatial distribution of droplets yield unrealistically long times for rain formation. One of the most important mechanisms of rain formation is associated with appearance of small-scale clusters of droplets ("inch" clouds) due to cloud turbulence. All previous studies of inertial particle clustering were performed for isothermal turbulence, while temperature distribution in clouds is inhomogeneous. The new effect of small-scale clustering in the presence of non-uniform mean temperature distribution is much stronger than inertial clustering in isothermal turbulence and leads to formation of small-scale concentrations even of very fine droplets. This effect elucidates the mechanism of rain formation in turbulent clouds and can be also significant in various industrial multi-phase turbulent flows (e.g. internal combustion engines).
