The One About the DLS
Oct. 14th, 2011 08:36 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
tanarillDynamic light scattering is a method of detecting the size of particles in solution by using them to scatter light. If you hit the solution with a beam of plane polarized light (like from a laser), some amount of it will be scattered an no longer be plane or polarized. The light detector is therefore not behind the sample where it'd pick up the light that didn't scatter, but ninety degrees to the side, so it picks up the light that did.
How much light is scattered is related to whether or not there happens to be a particle in front of the beam at any given time. Water hardly scatters at these distances, while proteins scatter lots. So you can detect if something is there. You can also detect how big the there-thing is, by a bit of logic. Molecules cannot occupy the same space at the same time. Therefore, for a molecule to move out of the beam, any other molecules that were in its path also have to move, leaving space. Since big things need more space, more room needs to made, which takes longer. Therefore, after a big particle starts scattering, how long it takes it to move out of the beam and stop scattering again has to do with how big it is. The caveat is that it's a log scale. It's possible to detect two differently sized things in solution only if one is at least a hundred times larger than the other. So we have several solutions that we're pretty sure contain two different things, and we even know what one probably is, but the other is a mystery.
That's my Science! life.
In other news, paper cranes have mysteriously appeared overnight hanging from the bike path underpasses. The bike paths get their own underpasses, so as not to disturb road traffic. They have a window between the lanes in either direction, and the cranes are taped to this. Anyway, it is totally a Random Thing but I liked it.
Delicious sweet-sour meatballs tomorrow.
How much light is scattered is related to whether or not there happens to be a particle in front of the beam at any given time. Water hardly scatters at these distances, while proteins scatter lots. So you can detect if something is there. You can also detect how big the there-thing is, by a bit of logic. Molecules cannot occupy the same space at the same time. Therefore, for a molecule to move out of the beam, any other molecules that were in its path also have to move, leaving space. Since big things need more space, more room needs to made, which takes longer. Therefore, after a big particle starts scattering, how long it takes it to move out of the beam and stop scattering again has to do with how big it is. The caveat is that it's a log scale. It's possible to detect two differently sized things in solution only if one is at least a hundred times larger than the other. So we have several solutions that we're pretty sure contain two different things, and we even know what one probably is, but the other is a mystery.
That's my Science! life.
In other news, paper cranes have mysteriously appeared overnight hanging from the bike path underpasses. The bike paths get their own underpasses, so as not to disturb road traffic. They have a window between the lanes in either direction, and the cranes are taped to this. Anyway, it is totally a Random Thing but I liked it.
Delicious sweet-sour meatballs tomorrow.
