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    Small Is Ugly
    By Sascha Vongehr | October 8th 2012 12:59 AM | 8 comments | Print | E-mail | Track Comments
    About Sascha

    Dr. Sascha Vongehr [风洒沙] studied phil/math/chem/phys in Germany, obtained a BSc in theoretical physics (electro-mag) & MSc (stringtheory)...

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    A topic that should get more attention in science outreach is the weirdness of the small. And no – I do not mean the ad nauseam covered ‘quantum weirdness’, which is not* about small stuff anyway. The classical (non-quantum) behavior of the small is counterintuitive enough. Many misconceptions could be avoided with some awareness about how the surfaces of objects, even smooth looking metal surfaces, look like at small scales (think mountainous battle fields).


    Perhaps the best way to introduce the surprising world of nanometer** sized objects like molecules, is by talking about water. Whatever you are looking at, you are looking at water! The water molecule is not only small and thus likes to get stuck in the tiny crevices in between, for example, a metal’s crystals. The water molecule is also an electrical dipole, its oxygen being negative, its hydrogen positive. This induces fields near the molecule, thus water molecules stick well to almost any surface.



    When you succumb to thirst in the desert, rest assured that you actually rest on water. Every grain of sand is wrapped in water. That hot towel you take out of the dryer? Completely covered in water! This is a real pain in the behind when you want to achieve a clean vacuum in the laboratory:


    “Ultra-high vacuum (UHV) is the vacuum regime characterized by pressures lower than about 10-7 Pascal or 100 nanoPascals (10-9 mbar, ~10-9 torr). UHV requires the use of unusual materials in construction and by heating the entire system to 180°C for several hours ("baking") to remove water and other trace gases which adsorb on the surfaces of the chamber.” Wiki: Ultra-high vacuum


    Anybody should have heard this, and if just to undermine the misconception about molecules bumping around like billiard balls. They do not. If they hit against a surface, they mostly get stuck in a layer of water. All those pictures where gas molecules bang against a wall and come off like a light ray from a smooth mirror: Wrong not only because of surface roughness, but because particles get stuck as if in a swamp, then sometime later come loose again due to thermal vibrations.



    There are high impact journals publishing nonsense about novel effects that supposedly occur at temperatures around 100 to 200 degrees Celsius in nanosized metal layers. The experiment is often some sort of high voltage on some ultra thin metal layer fastened to a heater, all in a crappy vacuum chamber.


    Sure, tin melts at 232 °C and below 13.2 °C, tin becomes brittle, non-metallic alpha-tin, but generally speaking, especially with materials like iron in mind, 100 degree Celsius is not hot. Metals’ characteristic temperatures are around a thousand or even thousands of degrees (say Fermi temperature). There is little difference between room temperature and 200 degrees as far as most metals are concerned. However, something else happens at around 150 to 200 degrees: Adsorbed water starts coming off! (You might expect that those researchers thought about that, having them doctor titles and all. Think again. The ‘beauty’ of peer review is that one is reviewed by one’s peers.) In really dirty vacuum chambers, tempering colors occur due to the oxidation of the surface at these sorts of temperatures.

    ------------------------

    * Photons can have wave and coherence lengths of many kilometers. There is nothing “small” about quantum phenomena, but regurgitating such nonsense distinguishes people who write nonsense (like those Florians on the German ScienceBlogs) from those who understand science.

    ** 1 nm = 0.001 micrometer = 10-9m (No, I'm not gona translate this in fractions of a hair!)

    Comments

    UvaE
    The bonds between water and the metal surface are as strong as the hydrogen bonds between water molecules. From the bit I've read on the topic, it seems that the water-metal interaction actually enhances the  hydrogen bonding between water molecules themselves. Is this why the water only comes off at 150-200 oC?
    vongehr
    I do not know. Perhaps to do with the crystals of the metal surface and their defects that the last molecules hang on beyond 150 degrees? Perhaps Hydrogen bond dynamics at vapour–water and metal–water interfaces or refs. therein may help. Let me know if you find something interesting.
    M. Toney et al. Nature, 368 (1994), p. 444:
    ... Contrary to current models, however, we find that the first layer has a far greater density than that in bulk water. This implies that the hydrogen-bonding network is disrupted in this layer, and that the properties of the water in the layer are likely to be very different from those in the bulk.
     
    If everyone wants to see measurements relative to the thickness of a human hair, clearly the metric system is too hard, and we need a new unit system based on the width of a fraction of a hair.

    BTW, 1 nanometer = 10 microhirsutes, using the new hirsute (hairy) measurement system.

    There, I fixed that for you! :-)

    Very nice. I did not know about water and clean rooms.
    Thanks for the education.

    Now, I hesitate to contradict you. But thinking of the surface of metals as small valleys and mountains; isn't the attraction between water molecules and metal; kind of like the van der waals force of geckos' feet in your previous post which you described as due to quantum fluctuations.

    So yes the mountains and valleys of metal are classical but the attraction of water to that metal seems to be quantum similar to geckos feet.

    Not interested in argueing. Just looking for a good public education. thanks.

    vongehr
    I was more thinking in terms of cracks where water gets stuck rather than valleys. As Enrico above pointed out, the forces are comparable to hydrogen bonds, which are stronger than VdW. Of course they are all quantum, but that may not be too helpful here. Depending on the metal and the crystal surface (e.g. 111 versus 100 FCC), the water dissociates into OH and H (which is kind of the nature of the hydrogen bond of course). Palladium for example absorbs the H into the metal. So there is messy chemistry and materials science involved, most of which I have little knowledge about. Black holes are a lot easier.
    MikeCrow
    Palladium for example absorbs the H into the metal
    The space in the Pd lattice, is slightly smaller than what would be required to fit 2 hydrogen atoms.
    I had an explanation for "cold" fusion that relied on ion's flowing in the lattice and getting more than one H  trapped into a container that was "one size too small", Lubos pointed out that was about like 2 rubber duckies in an olympic swimming pool colliding hard enough to melt them into one blob (He didn't use duckies, but I like the image better).

    But I digress.......
    Never is a long time.
    vongehr
    The space in the Pd lattice, is slightly smaller than what would be required to fit 2 hydrogen atoms.
    Not sure whether there is a misunderstanding here, but my writing that Pd absorbs H is of course about a single, from the H2O dissociated proton entering the lattice, i.e. not even a single H atom enters.
    MikeCrow
    Actually this was something I was never sure of, I know Pt, Pd have an affinity to absorbing Hydrogen, and it's electrochemically active, I was never sure if the electron stayed in orbit or was lost in Pd's electron cloud.
    Never is a long time.

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