CMC for SDS?

Wed Feb 23 10:47:28 EST 1994

As noted in the most recent post, SDS is very sensitive to the polarity of 
the medium.  The CMC (critical micellar concentration) drops as the ionic
strength is increased.  Concomitantly, the micelle size increases as the 
CMC decreases.  A book I have found quite useful in this regard over the 
years is Charles Tanford's "Hydrophophic Effect" (2nd edition, Wiley and 
Sons, publisher).  On p. 67 (Fig 7-2) a plot is shown of the CMC of SDS as 
a function of [NaCl].  The trend is as follows (and may answer the original
question fairly closely):
            CMC (mM)     [NaCl] (M)    Micelle Size (number)
            ___________  ____________  _____________________
                8             0                60
                1.4           0.1              90
                0.9           0.2             110
                0.6           0.4             130

If you dig into the literature on this, you'll find a bit of scatter in the 
numbers, but the ones in the table are pretty good.  Hope this helps.
Cheers,  Shaun
  = Shaun D. Black, PhD     | Internet:  shaun%jason.decnet at = 
  = Dept. of Biochemistry   | University of Texas Health Center, at Tyler = 

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