Surface thermodynamics of aqueous solutions of alkylethanolamines

https://doi.org/10.1016/S0378-3812(01)00391-0Get rights and content

Abstract

The surface tension of aqueous solutions of methyldiethanolamine and dimethylethanolamine has been measured at temperatures from 298.15 to 328.15 K over the whole range of concentrations. The surface tensions of these aqueous binary mixtures show more concentration dependence on the water-rich side. Addition of a small amount of alkylethanolamine reduces the surface tension of water drastically. This effect is related to the presence of hydrophobic groups such as (CH3) which tend to remain more on the water surface. The thermodynamics of the water surface, the surface entropy and surface enthalpy have been calculated for six (alkylethanolamine+water) mixtures. The surface thermodynamic properties of these mixtures are classified in two categories: those aqueous solutions of ethanolamines with an end hydrophobic group and those without. The surface entropy of the category without an end hydrophobic group is similar to the water surface while the surface properties of the category with an end hydrophobic group are much different from the water surface.

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.

    List of symbols

    a

    constant value in Eq. (5)

    b

    constant value

References (24)

  • H. Touhara et al.

    J. Chem. Thermodyn.

    (1982)
  • Y. Maham et al.

    J. Chem. Thermodyn.

    (2000)
  • Y. Maham et al.

    J. Chem. Soc. Faraday Trans.

    (1997)
  • R.M. DiGuilio et al.

    J. Chem. Eng. Data

    (1992)
  • R.M. Diguilio et al.

    J. Chem. Eng. Data

    (1992)
  • Y. Maham et al.

    J. Solution Chem.

    (1994)
  • Y. Maham et al.

    Can. J. Chem.

    (1995)
  • Y.-Q. Zhang et al.

    Thermochim. Acta

    (1995)
  • M. Pagé et al.

    Can. J. Chem.

    (1993)
  • T.T. Teng et al.

    J. Chem. Eng. Data

    (1994)
  • Y. Maham et al.

    J. Chem. Eng. Data

    (1997)
  • C. Mathonat et al.

    J. Chem. Eng. Data

    (1997)
  • Cited by (53)

    • Surface tension of binary mixtures of (ionic liquid + tributyl phosphate)

      2019, Journal of Chemical Thermodynamics
      Citation Excerpt :

      For all the three systems, variations with temperature are linear. These linear phenomena of surface tension with temperature has been observed in previous studies for aqueous mixtures of alkylalkanolamines [36,37]. From Fig. 3, it can be obviously seen that the δγ values over the entire range of composition are all negative.

    • Investigation of surface thermodynamics for DEAE-[N<inf>1111</inf>][Gly], DEAE-[Bmim][Gly] and DEAE-[Bmim][Lys] aqueous solutions

      2018, Journal of Molecular Liquids
      Citation Excerpt :

      Such similar behavior has been reported in the work of Maham et al. and Gliński et al. [54–55,57]. In general, the end alkyl group has a dominant effect on the surface thermodynamic properties and the size of this alkyl group is a dominant factor in reducing these properties [53], e.g., the cations ([N1111]+ and [Bmim]+) affect the surface entropy very differently. As the butyl group in [Bmim]+ is larger than the methyl group in [N1111]+, the surface entropies and surface enthalpies of DEAE-[N1111][Gly] aqueous solutions are higher than those of DEAE-[Bmim][Gly] and DEAE-[Bmim][Lys] aqueous solutions.

    View all citing articles on Scopus
    View full text