The effect of structural variation of alcohols on water solubilization in nonionic microemulsions - 2. Branched alcohols as solubilization modifiers: Results and interpretation

In this second part of a paper dealing with the effect of branched alcohols on solubilization, an attempt has been made to provide explanations of experimental data related mostly to the system Brij 97/branched alcohol + dodecane = 1:1 (by weight)/water at 27 +/- 0.2 degrees C. Applying the Hou-Shah mechanism it was shown that for many C-4-C-6 branched alcohol isomers having one methyl branch, solubilization behavior is readily interpreted by assuming control of the critical radius, R-c. Two parameters, both included in the definition of the branching factor, F-b (which was treated in the first part of the paper), were also used to analyze solubilization data. The first, l(i), is defined as the distance from the free end of the alcohol molecule to the methyl branch. The second, d, is virtually N-A, the chain length of the alcohol. When l(i) > 3, the solubilization becomes dominated by the natural radius Of Curvature, R-0. Also, we have suggested that for R-c-control, solubilization will be enhanced in direct proportion to the distance d-l(i), whereas for R-0-control, solubilization will increase with decreasing d-l(i). The validity of our assumptions was demonstrated in many cases. Some examples of the more complicated case of double branching (two methyl groups along the alcohol chain) were also analyzed. (c) 2005 Elsevier Inc. All rights reserved.