From: Richard M Thomas <rthomas@ifp.mat.ethz.ch>
  To  : rasmb@bbri.harvard.edu
  Date: Fri, 06 Apr 2001 11:29:14 +0200

Re: centrepieces again

Dear Joel,
I've got one and, like you, I find it useful for high speed equilibrium 
runs. The centrepiece you are describing is Kel-F not epon. The upper
speed 
at which these centrepieces can be used is  'the maximum speed of the 
rotor'  (according to Beckman). The last reference I can find to the
exact 
part number is in a catalogue that must be at least 15 years old and I 
suspect that they have been discontinued since then . Kel-F centrepieces 
are also good with aggressive solvents although they become slightly 
distorted with prolonged use. I've never found this a problem, although I 
suppose there's a chance of  inducing convection in the sample or leakage.
Hope this helps - if you can find a means of supply, I'd be interested too.
All the best
Richard
Dr Richard M Thomas
Inst. für Polymere
ETH-Zentrum
CH-8092 Zürich
Switzerland
(tel) +41 1 632 5540
(fax) +41 1 632 1073