Effect of temperature and composition on the surface tension and surface properties of binary mixtures containing DMSO and short chain alcohols

https://doi.org/10.1016/j.jct.2016.06.004Get rights and content

Highlights

  • Surface tension of DMSO + alcohol (methanol, ethanol and isopropanol) at various temperatures was measured.

  • The surface tension data of binary mixtures were correlated with four equations.

  • Intermolecular interaction of DMSO with alcohol was discussed.

  • The surface mole fraction of alcohol increase with increasing the length of alcohol chain.

Abstract

Surface tension of binary mixtures of methanol, ethanol and isopropanol with DMSO (dimethyl sulfoxide) was measured over the whole range of composition at atmospheric pressure of 82.5 kPa within the temperatures between (298.15 and 328.15) K. The experimental measurements were used to calculate in surface tension deviations (Δσ). The sign of Δσ for all temperatures is negative (except of methanol/DMSO system) because of the factors of hydrogen bonding and dipole–dipole interactions in the DMSO-alcohol systems. Surface tension values of the binary systems were correlated with FLW, MS, RK and LWW models. The mean standard deviation obtained from the comparison of experimental and calculated surface tension values for binary systems with three models (FLW, MS and RK) at various temperatures is less than 0.83. Also, the results of the LWW model were used to account for the interaction energy between alcohols and DMSO in binary mixtures. The temperature dependence of σ (surface tension) at fixed composition of solutions was used to estimate surface enthalpy, Hs, and surface entropy, Ss. The results obtained show that the values of the thermodynamic parameters for alcohol/DMSO mixtures decrease with increasing alkyl chain length of alcohol. Finally, the results are discussed in terms of surface mole fraction and lyophobicity using the extended Langmuir (EL) isotherm.

Introduction

Among the various experimental methods, surface tension is one of the most powerful techniques that provide information about surfaces and intermolecular interaction. The study of the surface properties in liquid mixtures is of great interest from both scientific and industrial points of view [1], [2], [3].

Dimethyl sulfoxide (DMSO) is a non-aqueous dipolar aprotic solvent used in pharmaceuticals, surface cleaners, extraction, electrochemistry and as a solvent for polymers. As pure solvent, DMSO has a large dipole moment and high dielectric constant (the relative dielectric constant ε = 46.50 and dipole moment μ = 4.06 D at 298.15 K) [4], [5], [6].

Also, alcohols are considered to be a water-like solvent in terms of hydrogen-bonding ability and are an important solvent due to their use in the chemical, pharmaceutical, fuel cell, cosmetic industries and others [7], [8], [9], [10].

This study is a continuation of our systematic experimental research on surface properties of binary liquid mixtures that contain polar or polar aprotic solvents [1], [2], [3], [11], [12]. The experimental values of surface tension of the binary systems consisting of DMSO with methanol, ethanol and isopropanol were determined over the whole range of composition at (298.15, 308.15, 318.15 and 328.15) K.

After surveying the literature, a number of research studies have been located on the surface tensions of DMSO with alkanols binary mixtures at various temperatures. However, no surface tension values were previously reported for DMSO with isopropanol at different temperatures and DMSO with methanol and ethanol at (308.15, 318.15 and 328.15) K [1], [2], [13], [14], [15].

After experimental measurements, the data obtained were analysed using various methods. In the first section, the concentration dependence of the surface tension of binary DMSO-alcohol mixtures at various temperatures are correlated using Fu et al. (FLW) [16], the Myers-Scott (MS) [17] and Redlich-Kister (RK) [18] and Li et al. (LWW) equations, and then in a new approach, the effect of alcohol structure on the interaction energy values (between alcohols and DMSO) is discussed in the binary systems [19], [20].

In the second section of this work, by employing the measured surface tensions at various temperatures, the thermodynamic properties of the surface (Hs and Ss) have been obtained. Finally, a Langmuir type isotherm model (or the extended Langmuir (EL)) is employed to determine the surface concentrations from the knowledge of the bulk mole fractions. The results provide information on the molecular interactions between the unlike molecules that exist at the surface and the bulk at various temperatures [20], [21].

Section snippets

Materials

All compounds were purchased from Merck and used without any further purification. Purity of each compound was ascertained by gas chromatography (GC type Agilent 7820A Agilent Technologies). The water mass fraction of the all components was determined by Karl Fisher (K.F.) titration, and it was found to be less than 0.0008 for DMSO and less than 0.004 for alcohols. Chemicals were kept in dark bottles. The detailed information of the materials used in the experiment is listed in Table 1.

The

Correlation of surface tension and concentration in binary mixtures

The concentration dependence of the surface tension of mixtures can be represented in terms of the surface tension deviation, Δσ, defined as:Δσ=σ-i=1nxiσiwhere σ is the surface tension of the mixture, and σi is the surface tension of the pure component I at the same temperature and pressure of the mixture, xi is the mole fraction of the component I and n is the number of components.

A few empirical and thermodynamic-based equations are available to correlate the surface tension; some of them

Conclusion

In this paper, surface tension values for binary mixtures of alcohol (methanol, ethanol and isopropanol) with DMSO, are reported over ranges of composition at various temperatures. In all systems, the surface tension of mixtures decreases with increasing temperature. The results of the present study show that by adding alcohol to DMSO the surface tension decreases non-linearly and most surface tension changes occur at a low concentration of alcohol. The surface tension deviation, Δσ, is

Acknowledgments

The authors are grateful to Dr. S. Maryam Sajjadi who kindly read the manuscript and made many helpful suggestions. Also, we gratefully acknowledge the financial support received for this research work from the Research Council of Semnan University.

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