Static permittivity, density, speed of sound, and refractive index of 2-propoxyethanol mixtures with water in a wide temperature range
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, εr, sound speed, u, and refractive index, nD, 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 εr. Based on the physicochemical data obtained, the coefficients of volumetric expansion, α, isentropic coefficients of compressibility, βS, and Kirkwood’s correlation factors, gK. 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 εr/∂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, nD, and permittivity, εr, 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, βS, Kirkwood factors, gK, 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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