I have a blue-sky invention, that I have been cherishing in the back of my mind for a decade or so, that is relevant to this discussion. It's a simple nanotech application -- actually within reach with present methods. I call it "black tape" because I imagine that is what it would look like. The tape would be coated with a substance, to be designed that would capture ambient water molecules and transport them preferentially in one direction (probably it would be marked with arrows every few centimeters to show the transport direction). When the tape was wetted anywhere, the downstream end would soon start to drip water. The transported water would be reasonably pure, because the surface coating would not be designed to transport, say, salt. One would dip one end in salt water, and the other end would soon start producing fresh water. Obviously the water transport requires energy. The tape would be black because the required energy would come from absorbed sunlight. "Wait a minute!" you cry. "What the heck is this magic water-transporting surface treatment?" Well, I'm not sure; I only know enough chemistry to guess that it might be possible. The image in my mind is that of a molecule that looks vaguely like a mousetrap, with two positions, "armed" and "released". It would be like a lever-arm, anchored to the substrate; at the outer end would be the "bucket" or water-carrying group, probably a C=C double bond that could be hydrated to CH-COH. In the armed position, the bucket would be a few nanometers upstream from its released position. These molecules would be arranged in a "bucket brigade", so that the released position of one molecule is in just the right place to pass the water molecule to the next molecule in the chain, provided that the next molecule is armed. When the bucket was hydrated, the geometry of the molecule would change in such a way as to snap the "mousetrap", causing the lever to whip over to the released position. Then an energy-neutral reaction would hydrate the next molecule in the chain, causing it also to snap over. A chain reaction could move the water molecule an arbitrary distance. After a while, solar action would restore the molecule to the armed position, ready to pick up another water molecule. How much water could such a tape transport? Let's imagine a meter-wide tape. If the bucket-brigade chains were spaced every nanometer (a water molecule is about a quarter of a nanometer across), then such a tape could carry 10^9 chains. I don't know how fast one could expect the carrier molecules to cycle, but at 10^9 Hz, a meter-wide tape would deliver 10^18 water molecules per second, about a millionth of a mole. This is clearly too slow for practical applications, so the invention as described is probably useless, but the general idea of sunlight-activated selective water transport seems promising. Any other ideas? On Wed, Apr 22, 2015 at 1:54 PM, Hans Havermann <gladhobo@teksavvy.com> wrote:
Here, from a few years ago, is a decent historical overview:
http://www.theatlantic.com/technology/archive/2011/08/the-many-failures-and-...
On Apr 22, 2015, at 11:43 AM, Henry Baker <hbaker1@pipeline.com> wrote:
One suggestion (Popular Mechanics??) from my childhood: towing an iceberg (assuming we can still find one) to San Diego/Long Beach/San Francisco harbor and harvest it into the water supply.
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