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kslusar science forum beginner
Joined: 08 May 2006
Posts: 2

Posted: Mon May 08, 2006 1:41 pm Post subject:
Stokes diameter of phenol particle



Hi,
I'm working on electrokinetic phenomena model in VHDLAMS, which is a
part of my PhD thesis (in microelectronics), and in one of my models
I'd like to implement an equation describing the electrophoretic
mobility (or velocity) as a charge to size ratio. I've got some
experimental results taken during capillary electrophoresis experiment,
therefore I can easily estimate a Stokes diameter of phenol by myself,
but I'd like to know what the size of phenol particle really is. I
couldn't find such an information anywhere. If a phenol particle size
is a problem, at least a benzen particle size is desired.
I know, it's not a problem for guys of the world of analytical
chemistry, so I'm looking forward for an answer.
Krzysztof Slusarczyk 

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Marvin science forum Guru Wannabe
Joined: 24 Mar 2005
Posts: 224

Posted: Mon May 08, 2006 4:24 pm Post subject:
Re: Stokes diameter of phenol particle



kslusar wrote:
Quote:  Hi,
I'm working on electrokinetic phenomena model in VHDLAMS, which is a
part of my PhD thesis (in microelectronics), and in one of my models
I'd like to implement an equation describing the electrophoretic
mobility (or velocity) as a charge to size ratio. I've got some
experimental results taken during capillary electrophoresis experiment,
therefore I can easily estimate a Stokes diameter of phenol by myself,
but I'd like to know what the size of phenol particle really is. I
couldn't find such an information anywhere. If a phenol particle size
is a problem, at least a benzen particle size is desired.
I know, it's not a problem for guys of the world of analytical
chemistry, so I'm looking forward for an answer.
Krzysztof Slusarczyk

A better name than particle for the smallest unit of phenol
is "molecule". A molecule in solution isn't quite like a
molecule in a gas. Its effective size in electrophoresis
will depend on what other molecules are loosely bound to it,
and move with it in the electric field.
It isn't the simple answer you seemed to be looking for, but
the reality of solutions isn't simple. 

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kslusar science forum beginner
Joined: 08 May 2006
Posts: 2

Posted: Mon May 08, 2006 7:21 pm Post subject:
Re: Stokes diameter of phenol particle



Correct me if I'm wrong, but phenol is a small particle (molecule, if
it's more precise), Stokes diameter of which is much smaller than Debye
length, therefore its electrophoretic mobility can be easily calculated
from an equation:
mu = q/(3*pi*nu*d)
where:
mu  electrophoretic mobility [m^2/Vs],
q  total charge of a molecule [C],
nu  dynamic fluid viscosity [Pa*s],
d  Stokes diameter of a molecule [m].
Because modeling is simpifying the reality, I'd like to know the order
of magnitude (the closer the better, naturally) of the diameter; is it
5E9 m or 1E8 m, I'm not interested in very precise answer like
5.00001E9 m or 5.00002E9 m.
The model is going to be the very first attempt while desinging a
system, accuracy of a few percent is fine, when computing a final
parameter (like migration time for a microfluid system), therefore
there is no sence in defining parameters of a huge precision. 

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David Stone science forum beginner
Joined: 27 Mar 2006
Posts: 14

Posted: Tue May 09, 2006 11:36 am Post subject:
Re: Stokes diameter of phenol particle



In article <1147116068.750255.287800@j73g2000cwa.googlegroups.com>,
"kslusar" <kslusar@dmcs.pl> wrote:
Quote:  Correct me if I'm wrong, but phenol is a small particle (molecule, if
it's more precise), Stokes diameter of which is much smaller than Debye

Molecule is the correct term. Particle, in this context, is too vague.
Quote:  length, therefore its electrophoretic mobility can be easily calculated
from an equation:
mu = q/(3*pi*nu*d)
where:
mu  electrophoretic mobility [m^2/Vs],
q  total charge of a molecule [C],
nu  dynamic fluid viscosity [Pa*s],
d  Stokes diameter of a molecule [m].

As the previous responder pointed out, it all depends...
Quote:  Because modeling is simpifying the reality, I'd like to know the order
of magnitude (the closer the better, naturally) of the diameter; is it
5E9 m or 1E8 m, I'm not interested in very precise answer like
5.00001E9 m or 5.00002E9 m.
The model is going to be the very first attempt while desinging a
system, accuracy of a few percent is fine, when computing a final
parameter (like migration time for a microfluid system), therefore
there is no sence in defining parameters of a huge precision.

You can use something like a molecular mechanics program to
figure out the "size" of a phenol molecule. The issue is, to
what extent are there going to be other molecules (e.g.) water
associated with it? This will especially be the case for the
phenolate anion.
A speaker once pointed out that, although we can predict electrophoretic
mobilities from Stokes radii, these are frequently derived from
specific conductivity measuerments. If you think about that for
a moment, you'll see there's a potential problem there (pardon the
pun!) It does, however, give you some means of accessing estimates
for the Stokes radius from other data sources. 

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Marvin science forum Guru Wannabe
Joined: 24 Mar 2005
Posts: 224

Posted: Tue May 09, 2006 3:38 pm Post subject:
Re: Stokes diameter of phenol particle



kslusar wrote:
Quote:  Because modeling is simpifying the reality, I'd like to know the order
of magnitude (the closer the better, naturally) of the diameter; is it
5E9 m or 1E8 m, I'm not interested in very precise answer like
5.00001E9 m or 5.00002E9 m.
The model is going to be the very first attempt while desinging a
system, accuracy of a few percent is fine, when computing a final
parameter (like migration time for a microfluid system), therefore
there is no sence in defining parameters of a huge precision.
The size of a small molecule is in the range of several 
nanometers. Most basic chemistry texts wll discuss this,
but the best reference, IMHO, is still Linus Pauling's "The
Nature of the Chemical Bond", which is still in print if you
can't borrow it from a library. 

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