Calorimetric study of micellar solutions of pentaethylene glycol monooctyland monodecyl ethers

The enthalpy of micelle formation of C8ES and C10E5 were obtained at seven temperatures from 283.15 to 313.15 K by measuring the enthalpies of mixing of C8E5 in water and of aqueous solution of C10E5 in water, respectively. A ppropriate thermodynamic treatment of the enthalpy of mixing for the latter case was derived and checked. The enthalpies of micelle formation of C8E5 and C10E5 are positive and decrease with increasing temperature. The increa se of enthalpy of C8E5 accompanied by micelle formation is superior to that of C10E5 at higher temperature than 283.15 K, while the gap of heat capaci ty of C10E5 between monomeric and micellar states is larger than that of C8 E5, These results might be due to the differences of the hydration of hydro carbon in monomer state and of the molecular packing in micellar state betw een C8E5 and C10E5. The two kinds of compensation temperatures were propose d.