AW: [RASMB] FW: viscosity

Tue Mar 31 03:52:35 PDT 2009

Hi Antje, Helmut and everyone

You are right, Antje, it is certainly the dynamic viscosity of the solvent
which should be used - the full expression for the correction of s values to
s(20,w) already contains a term which takes into account the effect of the
density of the solvent.

However, there is an interesting little point arises, which has only
occasionally been commented on. That is - if one is reporting s(c) values,
should one report the dynamic s value or the kinematic s value? The
difference is that the former includes a term correcting for the density of
the solution, not merely that of the solvent. Unlike the case of intrinsic
viscosity, where the 'Tanford correction' is applicable, the dynamic s value
and the kinematic s value become identical at infinite dilution: but that
still leaves the dilemma - which s(c) value ought one to report? I think
that in 99.9% of cases it is the kinematic value which gets reported.

For anything with a large frictional ratio, whether from extension or from
swelling, the difference between the two types of s value is numerically
negligible. However for compact, 'globular' solutes that is not the case.
For PSL spheres, Cheng & Schachman long ago (1955) showed that the s-c
dependence coefficient ks(dynamic) = 4.06 ml/g, whilst the kinematic
coefficient is ~5 ml/g, all in accordance with expectation based on theory.
In general,

ks (dynamic) = ks (kinematic) - vbar

It probably does not matter too much that unspecified s(c) values get
reported, since they will almost always be kinematic s(c) values. And it is
easy enough to convert the two types of s(c) value if one wants to. But the
issue becomes more important if you are doing conformation analysis, say via
conformation zoning (Pavlov et al 1997), or by getting the Wales-Van Holde
ratio (ks/[eta]) and using the formula for that ratio (Rowe 1977). Here is
is important to have both dynamic ks and dynamic [eta] values if one is to
get meaningful estimates.

Arthur

P Y Cheng & H K Schachman (1955) J Polymer Sci 16: 19
A J Rowe (1977) Biopolymers 16 2595
Georges M Pavlov, Arthur J Rowe & Stephen E Harding (1997)  "Conformation
zoning of large molecules using the analytical ultracentrifuge"  Trends in
Analytical Chemistry, 16: 401-405

-- 
*************************
Arthur Rowe
Lab at Sutton Bonington
tel: +44 115 951 6156
fax: +44 115 951 6157
*************************

Dear Helmut and colleagues,

I took the dynamic viskosity, because it is in good agreement with the
literature values. 

Checking the units, I found that kinematic viscosity is in m2/s and dynamic
viscosity is in kg/(m·s) which is Pas and 10 Poise.

Best regards to upstairs :)

and everywhere 

Antje 

Von: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] Im
Auftrag von Helmut Coelfen
Gesendet: Dienstag, 31. März 2009 00:12
An: rasmb at rasmb.bbri.org
Betreff: [RASMB] FW: vsicosity

From: Helmut Coelfen
Sent: Dienstag, 31. März 2009 00:09
To: 'rasmb at rasmb.bbri.edu'
Subject: vsicosity 

Dear colleagues, 

When correcting sedimentation coefficients from a given temperature to
s20,w; which viscosity is needed ? Dynamic or kinematic ?

Thanks for any insight

Helmut 

________________________________________________________________

PD Dr. habil. Helmut Cölfen

Max-Planck-Institute of Colloids and Interfaces

Colloid Chemistry 

Am Mühlenberg, D-14476 Golm, Germany

Tel: --49 331 567-9513

Fax: --49 331 567-9502

http://www.mpikg-golm.mpg.de/kolloidchemie/arbGruppen/trennmethoden/index.ht
ml 

http://www.mpikg-golm.mpg.de/kolloidchemie/arbGruppen/trennmethoden/Mitarbei
terInnen/Helmut_C__lfen/index.html

 _______________________________________________________________

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<http://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Dr.+Helmut+Coelfe
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