Low-temperature thermal properties of the aqueous solutions of simple aminoalcohols: Finding of peculiarities in 1-amino-2-propanol solutions

摘要

Low-temperature heat capacity (C-p) and glass-transition temperature (T-g) values of the aqueous solutions of three simple aminoalcohols (hereafter abbreviated as AA); i.e., 2-aminoethanol (2AE), 3-amino-1-propanol (3A1P) and 1-amino-2-propanol (1A2P), were examined by differential scanning calorimetry (DSC). Both the 2AE and 3A1P aqueous solutions revealed gradual decrease of C-p values on cooling in an AA molar-fraction (x(AA)) in the range of 0.2-0.7, while displaying no crystallization. On the other hand, the 1A2P aqueous solutions revealed a C-p hump at the temperature slightly above T-g on both cooling and heating curves when the x(AA) approaches 0.19. The T-g values of the 1A2P solutions simultaneously displayed a maximum as a function of the x(AA), which suggests formation of an ordered aggregate structure with development of a certain hydrogen-bond network. We propose, as the origin of the anomalies, formation of a molecular-aggregate structure of nanometer-sized regions of two kinds; one region is composed of the hydrophilic groups of AA molecules and water molecules and the other of the hydrophobic groups of AA molecules. (C) 2015 Elsevier B.V. All rights reserved.