The counterion releasing effect and the partition coefficient of branched alkanols in ionic micellar solution

Abstract.

In the micellar solution of SDS, the partition coefficient (K _x) of following branched alkanols at infinite dilution was determined by applying a differential conductivity method: the alkanols used were i-C _m H_{2 m +1}OH (m=4–9, i=1–5) in which the position of OH group (i) shifts from an end to the center of a hydrocarbon chain. The method provides two significant quantities, dα/dX _am and dC _sf/dC _af in addition to K _x. The following results have been obtained. (1) The dependence of K _x on i indicates that the hydrophobicity of alkanol is weakened with increasing i, whereas the increase in m strengthens the hydrophobicity. (2) The degree of counterion disossiation of micelles (α) is accelerated by the solubilized alkanols in micelles (mole fraction: X _am) and the acceleration rate, dα/dX _am (=0.17), depends on neither m nor i. (3) In the bulk water, the monomerically dissolved alkanols (concentration: C _af) depresses the concentration of free monomer surfactant (C _sf), and the depressing rate, dC _sf/dC _af, in micellar solution is identical with the corresponding quantity, (ΔCMC/ΔC _a)_o at CMC.