Surface thermodynamics of binary mixtures of aliphatic alcohols in heavy water

https://doi.org/10.1016/j.jct.2012.02.017Get rights and content

Abstract

The surface tension, σ, of binary mixtures of heavy water and homologous series of aliphatic alcohols (methanol, ethanol, and 1-propanol) were measured over the entire concentration range at various temperatures. The surface tension of these aqueous binary mixtures shows more concentration dependence on the heavy water-rich side. Addition of a small amount of alcohol reduces the surface tension of heavy water drastically. The surface thermodynamic functions such as surface entropy and surface enthalpy have been derived from the temperature dependence of the surface tension values. The magnitude of these thermodynamically quantities is discussed in terms of the nature and type of intermolecular interactions in binary mixtures. The presence of a maximum point in the surface entropy diagram in all systems is explained by the formation of clathrate-like solvates at the surface of these systems. The surface tension of the above mentioned binary systems were correlated with empirical and thermodynamic based models. The Myers–Scott (MS) model with three adjustable parameters gives good results when values of Δσ are large.

Highlights

► Surface tension of novel binary mixtures of (alcohol + heavy water) determined. ► Surface entropy, surface enthalpy and intermolecular interaction functions were calculated. ► Hydrogen bonding plays pivotal role in these systems. ► The surface tension data of binary mixtures were correlated with MS and FLW models.

Introduction

Among experimental methods of investigating intermolecular interactions and forces in liquids, the surface tension is distinguished because of its simplicity and precision. The surface tension reveals information about the structure and energetics of the surface region between two phases. Variation in surface energy depends on variation in molecular forces and that of the density of patching or molecular size [1], [2]. The surface tension of a liquid mixture is an important property in process design, because it plays an important role in affecting the mass and heat transfer at the interface. Surface tension of mixtures is often very sensitive to small changes in composition of the mixtures, and a detailed knowledge of this dependency is important for many fields including separation processes, emulsion, and atomization of fuels, environmental engineering, reaction catalysis, and biomembranes [3], [4], [5].

In the present work, we report surface tension of binary mixtures of heavy water (D2O) in alcohols (methanol, ethanol, and 1-propanol) over the entire concentration range at T = (288.15, 298.15, 308.15, and 318.15) K. As far as we know, there are no references in the literature about the surface tension for the systems. The experimental data have been used to find surface tension deviation, Δσ, and the surface thermodynamic functions (surface entropy and surface enthalpy). Alcohols, either alone or in solution (water), are very widely used in the chemical, pharmaceutical and cosmetic industries [6], [7], [8], [9]. The replacement of hydrogen (1H) by deuterium (2H) at H2O results in deuterium oxide (D2O, heavy water). Although heavy water (D2O) is the primary coolant and moderator in nuclear reactors, it has been used for the measurement of some physiologic statuses in humans. The D2O has some toxic biological effects on both benign and malignant cells and tissues [10], [11]. In addition to weight, other important properties of heavy water differ from those of regular water, in principle among them are pH, freezing point, boiling point, surface tension and viscosity. These properties, among others, influence the manner and speed with which heavy water undergoes or supports chemical interactions.

A few empirical and thermodynamic-based equations are available to correlate the surface tension; some of them have recently proposed and are well founded on a thermodynamic basis. Fu et al. was proposed a two-parameter equation to correlate the surface tension data with the composition in the binary systems which are based on the local composition concept due to Wilson equation [12]. Other empirical equations such as Redlich–Kister [13] and Myers–Scott [14] have been applied for the correlation of binary surface tension data. In the present paper, the surface tension results for binary mixtures were correlated with the models of Myers–Scott (MS) and Fu et al. (FLW).

Section snippets

Materials

Methanol (mass fraction purity > 0.99), ethanol (mass fraction purity > 0.99) and 1-propanol (mass fraction purity > 0.99) were purchased from Merck and used without further purifications. The heavy water (Merck, mass fraction purity > 0.99) was used without any pre-treatment. The summary of requirements for sample description is reported in table 1. The purity of reagents was checked by comparing the measured surface tension with those reported in the literature [15], [16], [17], [18], [19]. The

Thermodynamic investigation of the surface tension of binary mixtures

Table 3 contains the experimental results for surface tension of aqueous (D2O) solutions of methanol, ethanol and 1-propanol as a function of mole fraction at temperatures of (288.15, 298.15, 308.15, and 318.15) K.

Figure 1 shows the behaviour of surface tension of alcohol in heavy water at the selected temperatures. In all the systems, the surface tension, σ, decreased with increasing alcohol concentration. This trend is non-linear, with the change in surface tension caused by a given change in

Conclusions

This paper reports the new experimental values for surface tension for the binary mixtures of alcohol (methanol, ethanol, and 1-propanol) in heavy water over ranges of composition at various temperatures. The experimental results show that by adding alcohol the surface tension decreases (non-linear) but by increasing the temperature (at constant mole fraction) the surface tension decreases linearly. The results obtained reveal that only the methanol/heavy water mixture failed to display the

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