I was reading in New Scientist (November 10th, 2012 page 5) of the discovery of a red star identical, it appears, to the star Superman’s home planet, Krypton. Red dwarf LHS2520, discovered by astronomer Neil deGrasse Tyson (Yes! What a name!), is 27 light years from earth and the right, size, color, and distance to fit in with the Superman legend. This got me to thinking, as I stared into the heavens that weekend, as to how tiny we are in relation to the size of the universe. Yes, I guess we all have these profound moments from time-to-time….
And then I got to thinking how much bigger we are than the nanoparticles that we measure in our Zetasizer ZS. Then I recalled Galileo’s comment “If you can’t measure it, then how can you control it?” He apparently made this comment much earlier than the accreditation to Lord Rayleigh (pronounced Rawl-ee, by the way). And one of Galielo’s students said to him – “Why look at the stars? They all look the same”, but that’s digressing…
This thought process took me full circle to ask the question, “Well, if you can’t see it, then how can you measure it?” completing the link to the Zetasizer ZS. I guess we all know that the Dynamic Light Scattering (DLS) technique that the Zetasizer ZS uses relies on a phenomenon called Brownian motion named after a scientist who was trying to account for the rapid movement of pollen grains in water. Now you may think that if the motion was truly random and a particle was hit in a random manner from all sides by the surrounding solvent molecules then the effect would cancel out and the particle wouldn’t or couldn’t move… This sort of thought keeps me awake at night…. This tells you that the bombardment isn’t strictly random but temporary voids form in the liquid due to the random movement of the liquid molecules and the particle is moved into these voids. This moves the particle along in a manner called random walk.
But we’re back to voids again and the empty space between us and the stars – and there’s roughly only 10km of atmosphere protecting us from the ravages of space. A frightening thought showing how fragile we are in the entire spectrum of things… And as my friend Gerry Colvin wrote, “And man is just a speck of dust in the giant Dyson in the sky; everything on earth has so much worth than you or I”….
Now we, correlate these Brownian motion movements over small periods of time (tens of nanoseconds and upwards) to obtain what is termed a diffusion coefficient – we can do the same for twinkling stars to remove the random atmospheric thermal effects typically over seconds or tens of seconds. Larger particles (like me) move more slowly than smaller particles like a child on E numbers. This allows an equation called the Stokes-Einstein equation (SEE) to be used that translates the diffusion coefficient into the size of an equivalent diffusing sphere. And Einstein’s reason for deriving that SEE equation was for another estimate of Avogadro’s Number – the Boltzmann constant in the Stokes-Einstein equation is R/N where R is the Gas Constant and N is Avogadro’s number.
And what is time according to Einstein? Simply Nature’s way of ensuring that everything doesn’t happen at once…..
So, you don’t have to have Superman’s X-ray vision to measure the size of small particles although small-angle X-ray scattering, as well as DLS, will help – see September 22nd 2011 “The NIST Au colloid nanomaterial, RM 8011: a DLS and SAXS comparative study of the particle size distribution”
This SAXS technique has been pioneered by our sister company in Spectris, PANalytical.
You WILL need to be Superman if you want to travel back to your home planet of Krypton…..