Static permittivity, density, speed of sound, and refractive index of 2-propoxyethanol mixtures with water in a wide temperature range

doi:10.1016/j.jct.2016.07.002

The Journal of Chemical Thermodynamics

Volume 102, November 2016, Pages 164-177

https://doi.org/10.1016/j.jct.2016.07.002 Get rights and content

Highlights

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The speed of sound, density, static permittivity and refractive index of propoxyethanol + water mixtures were measured.
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The temperature dependencies of molar volume, compressibility coefficients and static permittivity were analyzed.
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The values of derivatives of enthalpy, entropy and heat capacity with respect to pressure were calculated.
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Kirkwood’s correlation factor was determined.

Abstract

The static permittivity, ε_r, density, ρ, speed of sound, u, and refractive index, n_D, of water + 2-propoxyethanol mixtures were measured over the entire range of mixture composition in a wide temperature range. The experimental values of density and speed of sound were used to determine the molar volume, V_m, adiabatic compressibility, β_S, and their excess values. Also the values of partial molar volumes ${\overline{V}}_{1}$ and ${\overline{V}}_{2}$ as well as the thermodynamic parameters namely the entropy derivative after pressure, ∂S/∂p, enthalpy derivative after pressure, ∂H/∂p and molar heat derivative after pressure, ∂C/∂p of the mixtures were determined.

The experimental data of static permittivity were used to determine deviations from the additivity of permittivity, Δε_r, excess of this value, ε_r^E, temperature coefficient of permittivity, ∂ln ε_r/∂T, and their excesses, (∂ln ε_r/∂T)^E.

Using the results of refractometric analysis and static permittivity, the values of Kirkwood’s correlation factor, g_K, and their excess values, g_K^E, were also determined.

The concentration and temperature dependent results of the mixtures were used in the analysis of hydrogen bond interactions occurring between the molecules of water and 2-propoxyethanol.

Introduction

Physicochemical and thermodynamic properties of liquid mixed solvents are a valuable information source concerning the system internal structure and intermolecular interactions occurring in them [1], [2], [3], [4], [5]. So, the investigations of density, sound speed, permittivity and refractive index, especially within a wide temperature range, are a valuable tool to recognize and understand the microscopic properties of liquids, or finally to design theoretical models describing experimental data [6]. Excess thermodynamic functions and excess and deviation from additivity of other properties of mixed solvents are of paramount importance for understanding the interactions between the mixture components.

Mixed solvents have a variety of uses, ranging from chemical, biological and pharmaceutical to industrial applications [7], [8]. 2-Alkoxyethanols, including 2-prop- oxyethanol, constitute a very interesting group of compounds with a wide range of uses [6], [7], [9], [10], [11]. The properties of these compounds, being of interest to researchers, are connected with the structure of their molecules. The presence of ether oxygen and hydroxyl group determines their donor-acceptor properties and a possible formation of intra- and intermolecular associated molecules [9], [11], [12].

Literature data concerning the physicochemical properties of the mixtures of water and 2-propoxyethanol are exceptionally skimpy. The study of Douhéret et al. [13] concerns volumetric and acoustic investigations of this system but it has been exclusively limited to a temperature of 298.15 K. A paper by Shindo and Kusano [14] presents the values of density and refractive indices of the mixtures at a temperature of 298.15 K, only within the composition range of 0–0.55 mole fraction of 2-propoxyethanol.

In the present study, we determined the values of density, ρ, static permittivity, ε_r, sound speed, u, and refractive index, n_D, within the whole composition range of the water-2-propoxyethanol mixture and in a wide temperature range (288.15–318.15) K for ρ, n, u and (283.15–333.15) K for ε_r. Based on the physicochemical data obtained, the coefficients of volumetric expansion, α, isentropic coefficients of compressibility, β_S, and Kirkwood’s correlation factors, g_K. were determined. The examinations within a wide temperature range made it possible to determine a number of thermodynamic functions, such as the derivative of molar heat after pressure, ∂C/∂p, derivative of enthalpy after pressure, ∂H/∂p, and derivative of entropy after pressure, ∂S/∂p. It was also possible to determine the temperature coefficient of permittivity, ∂ln ε_r/∂T. A systematic study of so many physicochemical properties may be helpful in explaining the nature of interactions between the components of water–2-propoxyethanol mixtures. It is worth noting that such a detailed and comprehensive study of the mixtures of water and 2-propoxyethanol was carried out for the first time.

Section snippets

Chemicals

2-Propoxyethanol from Aldrich (mass fraction 0.994) was stored in a dark bottle and used without further purification. Water content determined by Karl-Fisher’s method amounted to 200 ppm. The water used for mixed solutions was distilled twice and then deionized on ionic exchangers. Electrolytic conductivity was equal to 1.2 · 10⁻⁷ S·cm⁻¹. Information concerning the solvents used are contained in Table 1aS.

The mixtures of water and 2-propoxyethanol were prepared by the gravimetric method with the

Results and discussion

The experimental values of density, ρ, sound speed, u, refractive index, n_D, and permittivity, ε_r, of the water–2-propoxyethanol mixtures are listed in Tables 2aS, 2bS, 2cS and 2dS, respectively (Supplementary Materials).

As is seen in Fig. 1, the values of density of the mixture of water and 2-propoxyethnol decrease with increasing the organic solvent content. At the beginning of adding 2-propoxyethanol, changes in density, especially at the lowest temperature investigated 288.15 K, are small.

Conclusions

The paper presents the precisely measured values of static permittivity, density, speed of sound and refractive index for the mixtures of water and 2-propoxyethanol in a complete range of the component composition and over a wide temperature range. Based on these parameters, the values of molar volumes, partial molar volumes, volume expansion coefficients, α, coefficient of compressibility, β_S, Kirkwood factors, g_K, and the values of excesses of these quantities were determined. The wide range

Acknowledgment

The present work was financed by the University of Lodz – Poland (Grant: B1511100000050.01).

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