Gained from Studies of the Exchange Process

Information Gained from Studies of the Exchange Process 

The linear part of the variation of Ihi with C, close to the cmc, has been used to obtain the values of the rate constants k+ and k for the association and dissociation of one surfactant to/from a micelle and of the distribution width 0 (see Equation 3.9), using known or estimated values of the mean micelle aggregation N. Many values of k and k have been reported.2 2 2 ° Table 3.1 lists values for representative anionic, cationic (including dimeric), nonionic and zwitterionic surfactants. Note that the values listed in Table 3.1 have been obtained from an analysis of the 1/Xi vs. C data using Equation 3.9 or Equation 3.16, which is more correct for the ionic surfactants considered here. The two t5q)es of analysis 3ueld data than can differ by much more than the experimental error, as noted in several studies. Also the errors involved in the different methods used for measuring can be very different. The main conclusions are as follows  

For all the listed surfactants, except the entries 38 0 that refer to long-chain dimeric surfactants discussed below, the values of k+ fall, say, between 2 

The dynamics of the surfactant exchange is little affected upon increasing the ionic strength of the solution. Thus k+ is slightly increased and k is slightly decreased in the presence of a salt having the same counterion as the surfactant. -  

The substitution of H2O by D2O has little effect on the surfactant exchange. For instance, for STS, N decreased from 44 to 31, the cmc decreased from 2.21 to 1.94 mM, and k decreased from 7x10 to 5.76 X10 s in going from H2O to 02 . The rate constant 

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B. Information Gained from Studies of the Exchange Process... 

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