Heat capacity studies of formation of micelle-like structure in aqueous solutions of some alkane polyols.
Some polyols show micellar behavior in aqueous solutions at concentrations greater than the critical micellar concentration (cmc). The 1,2-alkanediols (C(n)H(2n+2)O2 with n=5,6,7), the 1,2,3-alkanetriols (C(n)H(2n+2)O3 with n=7,8,9), and the geminated alkanetriols (C(n)H(2n+2)O3 with n=8 and 9) are investigated by microcalorimetric techniques. Only the 1,2-hexanediol (n=6), the 1,2,3-octanetriol (n=8), and the 2,2-dihydroxymethyl 1-heptanol (n=9) possess, in aqueous solutions, an organized structure above the critical micellar concentration (cmc). The 1,2-pentanediol (n=5) and the 1,2,3-heptanetriol (n=7) would form weak associations, whereas the 2,2-dihydroxymethyl 1-hexanol (n=8) does not form any associations even at large concentration. The 1,2-heptanediol (n=7), being only very slightly soluble even at a temperature of 30 degrees C, could not be studied. The 1,2,3-nonanetriol (n=9) is not soluble at temperatures between 20 and 35 degrees C. The critical micellar concentrations are determined by specific heat capacity methods. The passage from the dispersed environment to the organized environment gives a constant quantity of specific heat capacities (about 50 JK(-1)mol(-1)) only for the 1,2-hexanediol (n=6), the 1,2,3-octanetriol (n=8) and the 2,2-dihydroxymethyl 1-heptanol (n=9), which form true micelles. Structural effects of these systems are discussed.
Hajji
M Said
MS
Ecole Normale Supérieure, Laboratoire de Chimie Organique et d'Etudes Physico-Chimiques, B.P. 5118, Av. Oued Akreuch, Takaddoum, Rabat, Morocco. hajji-ms@yahoo.fr