From: Arthur Rowe IMAP <arthur.rowe@nottingham.ac.uk>
  To  : Helmut C=?ISO-8859-1?B?9g==?=lfen <coelfen@MPIKG-GOLM.MPG.DE>
  Date: Fri, 05 Oct 2001 12:08:27 +0000

Re: charge effect on sedimentation

Hi Helmut !

When charged particles sediment, their differential migration with respect
to small ions present gives rise to an electric field, which retards
particle motion. That is classically known as the 'primary charge effect',
and is what you will have with your charged spheres. A so-called 'secondary
charge effect' can also arise, but only if co-/counter- ions with a
significant sedimentation rate are present - not the case I presume with
your spheres.

Migration of charged particles producing an electric field is related to the
electrophoretic retardation phenomenon, in which charged particles moving in
an electrical field are retarded as the result of a similarly induced field.
This phenomenon has long been known, numerical solutions which are probably
adequate have been computed and they fit experimental data:

Wiersema, P.H., Loeb, A.L. & Overbeek, J.Th.G. J Colloid Interface Sci. 22,
78 (1966)

Alas, as you have found, we hydrodynamics people have been less active than
our colloid science brethren - so far as I know, Pedersen's work probably
*is* the 'state of the art' !  It would of course be really nice if a quick
s upon (c, ionic strength, whatever) gave one serious charge information,
but I don't think it can be done, and I fear that the Zeta-Sizer still has
some mileage left in it.

But - guess what ? I see that next week, at the American Association for
Aerosol Research 20th Annual Conference October 15-19, 2001,in Portland,
Oregon (and we'll all be there . . . ) there is a paper being presented:

Effect of Charge on the Mobility of Singly and Multiply Charged Clusters and
Macromolecules, SVEN UDE, Yale Univ, Manuel Gamero-Castano, Yale University,
Juan Fernandez de la Mora, Yale University

A renaissance, perhaps ?

All best to you and to the RASMB fraternity

Arthur

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Arthur J Rowe
Professor of Biomolecular Technology
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University of Nottingham
School of Biosciences
Sutton Bonington
Leicestershire LE12 5RD   UK

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> From: Helmut Cölfen <coelfen@MPIKG-GOLM.MPG.DE>
> Date: Thu, 04 Oct 2001 23:14:11 +0200
> To: rasmb@bbri.harvard.edu
> 
> Hi my friends out there,
> 
> I seem to have a quite trivial problem but nevertheless seek your advivice if
> you are aware of more recent theories.
> 
> I  have a close look at strongly charged colloids - all of them are more or
> less the ideal of a
> monodisperse solid hard sphere. The sedimentation behaviour of their
> uncharged counterparts is precicisely
> known as all of you will aggree. OK, I know the VBAR, the molar mass from
> their diameter from
> dynamic light scattering, Field flow fractionation and transmission
> electron microscopy.
> The world should be fine to describe everything so far.
> But as you can imagine, there are strong charge influences on sedimentation
> and I wonder
> if this "ideal" case has not yet been treated in dependence of particle
> charge.
> 
> Now the charge comes into play. I have started reading the classical AUC
> textbooks and
> surprisingly, I found the best answer in Svedberg/Pedersens classical book.
> But this is almost
> 70 years old so  I guess there are more recent theories of charge influence
> on sedimentation
> underway. OK, there are many papers treating the sedimentation of
> polyelectrolytes but the thing
> I look for is: Can I determine the average particle charge QUANTITATIVELY
> once I know
> the VBAR and particle dimension ???
> 
> I have the feeling that the answer is trivial but nevertheless, I believe
> that there must be a more
> recent treatment than that of Svedberg in 1940's.
> 
> Any hints towards more recent theories for SOLID CHARGED SPHERES are highly
> appreciated.
> 
> Thanx a lot
> 
> Helmut
> 
> 
> 
> 
> 
> 
> 
> 
> _______________________________________________________________
> Dr. Helmut Cölfen
> Max-Planck-Institute of Colloids and Interfaces
> Colloid Chemistry
> Am Mühlenberg 2
> 14424 Potsdam
> Germany
> 
> Tel: --49 331 567-9513
> Fax: --49 331 567-9502
> http://www.mpikg-golm.mpg.de/kc/coelfen/
> _______________________________________________________________
> 
>