Friday, October 31, 2008

Water - That's Different

While it is not something I use every day, this site is extremely useful and well referenced with technical literature. It is the site to get good information on water and why it is so different from any other solvent in some many ways, some that you are not aware of.

P.S., "That's different" is a common phrase in the Minnesotan language, used to express doubt about something without being overtly critical. An example:

Lena: "Say Sven, what do you tink about dose new electic hybrid cars?"
Sven: "That's different"

Certainly not the meaning I take here.

Monday, October 27, 2008

So when are they going to ban Scotch Tape?

Triboluminescence is nothing new - it's been known for decades that if you quickly pull some tape off a roll, you can see sparks. (HINT: if you are trying this a home, do it in a dark room with you eyes adjusted to the darkness.) But now some researchers have found that you can even generate x-rays from this simple act.

Since they correlated it to the stick-slip phenomenon, this would predict that masking tape (tan, not blue) and even duct tape would be a stronger source. (Stick-slip is an uneveness in the peeling. As you pull on the tape, it doesn't peel until a critical amount of energy is stored in the system and then it lets go suddenly, starting the cycle all over again. This also produces noise. Noisy tapes have lots of stick-slip.)

Monday, October 13, 2008

Another Unusual Water Soluble LCST System

A family of block copolymers known as poloxomers (or by the BASF tradename Pluronics) can also act "funny". These polymers are made of two blocks of polyethylene oxide (which is readily water soluble at all temperatures) and a mid-block of polypropylene oxide (which isn't water soluble). You can get the blocks in varying lengths and the relative amounts, so it really is a family of copolymers. There's even a scheme to numbering and lettering the various grades, but I've never worried about it too much. In water, the PPG blocks try to isolate themselves from teh water by hooking up with other PPG blocks from other molecules. As a result, weak crosslinks form.

F127 is a great example of some of the unusual behavior you can find. A 20 wt% solution makes a great get at room temperature, but cool it down just a few degrees and it thins down to a very thin liquid. (You can also get the same viscosity if you heat it up to about 80 oC. Note that this is an example of LCST or UCST as the polymer is soluble in all cases. It is instead a matter of balancing the interaction energies of the two blocks and the water.

Friday, October 10, 2008

A polymer that has is all backwards

Poly(N-isopropylacrylamide), often abreviated as PNIPAM or similarly, is a water soluble polymer that doesn't act the way most polymers do. As backed up by your everyday experiences, solubility generally increases as the temperature increases. That is not so with PNIPAM. It is readily soluble at room temperature, but increase the mix to about 33 oC will cause the polymer to settle out. This is called a lower solution critical temperature (LCST). I suppose that having a name for this implies that it is something that is not so uncommon, or at least something that could be theorized. And yes, upper solution critical temperatures exist. They are very common, as that is the lowest temperature at which a material is soluble in a solvent.

Polymer solutions are not very useful in that state. You can remove the solvent (in this case water) and work with the dried polymer, but to do so would leave you without that neat LCST. So the way to have your polymer solution and play with it too is to crosslink the polymer. When this is done, the PNIPAM soaks up water like a sponge. Or at least until the temperature is raised. Once it hits the LCST, the water is expelled.

This is more a lab curiosity than anything important.

Magnets and Mileage

I'm undecided about this one. It's a modern upgrade of the "cow magnets on your gas line can dive you 200 mpg!" hype. On the up side, the researchers are from a reputable research institution (Temple University), but on the down side, the information provided is quite sparse and unclear. It also seems to have more than a few errors. Is is right that a Mercedes 300D engine is only producing 0.4 +/- 0.04 hp? Equation 1 is for a suspension, but it doesn't appear that anything is being suspended in the fuel.

Perhaps a patent is being filed, which could explain the lack of detail. Good luck in enforcing such a patent in the aftermarket. It would be an easy retrofit for existing cars, and only enforceable on new production.