The specific heat capacities of aqueous solutions of diethylene glycol n-pentyl ether (C5E2) with molalities m(2) <= 1.8232 mol kg(-1) were measured within the temperature range 273.15-338.15 K by DSC. Changes in the specific, apparent and partial molar heat capacities of the aqueous system investigated were analyzed and considered as an effect of structural transformations in order to determine the boundary between the region, within which the molecules of amphiphile occur in the form of monomers, and the area, in which the first large aggregates or micelles appear. For each solution, the temperature dependence of differential heat flow was analyzed in order to determine the temperature of phase transition and the boundary between mono- and diphase systems. (C) 2012 Elsevier B.V. All rights reserved.