Surface thermodynamics of aqueous solutions of alkylethanolamines
Introduction
This is a continuation of our collection of physical properties of pure and aqueous mixtures of alkylalkanolamines. Bulk properties of pure liquid alkylalkanolamines: heat capacities [1], thermal conductivity [2], densities and viscosities [3] and of binary aqueous mixtures, excess molar properties of (monoethanolamine, MEA+H2O), (monomethylethanolamine, MMEA+H2O) and (dimethylethanolamine, DMEA+H2O) mixtures at 298.15 K [4], the volumetric properties of (MEA+H2O), (diethanolamine, DEA+H2O) and (triethanolamine, TEA+H2O) mixtures at 298.15–353.15 K [5], of (methyldiethanolamine, MDEA+H2O) and (ethyldiethanolamine, EDEA+H2O) mixtures at 298.15–353.15 K [6], and of (dimethylethanolamine, DMEA+H2O) and (diethylethanolamine, DEEA+H2O) mixtures at 293.15–313.15 K [7], thermodynamic properties such as densities, apparent molar volume have been reported. Isobaric specific heat capacities of (MEA+H2O) mixtures [8], transport properties of (DEA+H2O) and (MDEA+H2O) mixtures at 298.15–353.15 K [9], excess molar enthalpies of (MEA+H2O), (MMEA+H2O) and (DMEA+H2O) mixtures at 298.15 K [4] of (DEA+H2O), (MDEA+H2O) and (TEA+H2O) mixtures at 298.15 K [10], of (monoethylethanolamine, MEEA+H2O), (diethylethanolamine, DEEA+H2O) and (n-propylethanolamine, n-PEA+H2O) and (2-amino-2-methyl-1-propanol, AMP+H2O) mixtures at 298.15 K [11] and the excess molar enthalpies of (diethanolamine, DEA+H2O), (methyldiethanolamine, MDEA+H2O), (ethyldiethanolamine, EDEA+HO) and (n-butyldiethanolamine, n-BDEA+H2O) mixtures [12] were reported at 298.15–338.15 K.
The surface properties of (MEA+H2O) and 2-amino-2-methyl-1-propanol, (AMP+H2O) mixtures and ternary mixtures of water with these ethanolamines at 298.15–323.15 K [13], and of (DEA+H2O) and (TEA+H2O) mixtures at 298.15–323.15 K [14] and of (MDEA+H2O) and ternary mixtures of water with these ethanolamines at 298.15–323.15 K [15] were studied. In this report, we are interested in the surface properties of (methyldiethanolamine, MDEA+H2O) and (dimethylethanolamine, DMEA+H2O) mixtures.
Section snippets
Materials
Dimethylethanolamine [(CH3)2NCH2CH2OH, DMEA, 99%] and methyldiethanolamine [CH3N(CH2CH2OH)2, MDEA, 99%] were both obtained from Aldrich Chemicals. These compounds were used as received, after confirmatory analysis by titration with standard hydrochloric acid. Mixtures of these compounds with nano-pure distilled water were made by mass, with care being taken to minimize exposure to air (carbon dioxide).
Apparatus
The capillary-rise technique was used to measure the surface tension [16]. This consists of a
Conclusion
Surface tension measurements are a good way to obtain surface thermodynamic properties. The comparison of the values of the surface entropy and surface enthalpy for the aqueous solutions of these alkylethanolamines, helps us to conclude that the end alkyl group is a dominant factor on the surface property of the aqueous solutions. We need more data to add more light on the competition between the hydrophobic and hydrophilic groups on the water surface.
- a
constant value in Eq. (5)
- b
constant value
List of symbols
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