Wyatt Microbatch Zimm Plot
Convert your scattering data obtained on polystyrene sulfonate into a Zimm plot. SOME guidance
can be found from the general method in the “HowTo” guide for our Phoenix (rotating arm)
Instrument. Here some of the relevant differences:
1. Your scattering volume does not follow a simple V~ sin-1() relationship.
2. You used about 10 detectors, none of which has the same sensitivity.
3. The first two factors lead to a “normalization” step not needed on a properly working rotating
arm instrument.
4. It is easy to measure the Rayleigh reference factor on the Wyatt, but it is disruptive. You have
to flush the flow cell with various solvents and wind up pumping in toluene. So….we did not do
that step. The appropriate “instrument constant” will be given to you by Dr. Cueto. This factor
connects an experimentally measured voltage in Channel 11 (90 degrees angle) with the Rayleigh
factor for toluene. It is assumed that this factor has not changed since Dr. Cueto last calibrated it.
5. You can consult the Wyatt manual!
You can do the problem in Excel, although the HowTo is wrapped around a program called
GuiDe (also known as NonZimm). You can use the dn/dc value you obtained earlier. You may
have to make an assumption or two to get your concentrations in the required units (g/cm3).
Other stuff you need: The Wyatt uses a Helium-Neon gas laser at o = 632.8. We think the
optics are set so that m=1 in the equation regarding how volume should compare from Rayleigh
standard (toluene) to the solutions (in water). The refractive index of toluene is about 1.495 and
that of water 1.33. Other things can be found on the website
(http://macro.lsu.edu/HowTo/guide/guide.doc ) especially the appendix and, within that, the
section entitled Mechanics of Gathering Data. Once you get Excel to make the plot, you may
very well find it easiest to just draw the rest graphically.
a) Specify what concentrations you prepared (by weight).
b) Specify your concentrations as g/mL and list any approximations required to make the
conversion.
c) Specify how you got your dn/dc value (in most cases, using the CN Wood differential
refractometer).
d) Specify the value you obtained, being sure to include a ± uncertainty term.
e) Specify what angles you measured.
f) Show the normalization plot: intensity above water baseline for all angles during the
normalization run.
g) Show your Zimm plot as just bare points.
h) Draw the c = 0 and  = 0 extrapolation lines.
i) Determine Mw, A2 and Rg, if possible. Each one needs a ± estimate.
Grading Rubric: 50 points total
27 points: 3 points for each of the items above)
10 points: evidence for critical thought and reflection about what went wrong or right during
measurements, integrated with the information above).
13 points: quality of the results (full credit for publication-quality work)