Dielectric Dispersion Study of Glycol Ethers and Their Binary Mixtures with Water

Indian Journal of Pure & Applied Physics Vol. 56, April 2018, pp. 301-306 Dielectric dispersion study of glycol ethers and their binary mixtures with water J B Shinde, D N Rander, S B Jadhav, S M Sabnis, Y S Joshi & K S Kanse* Department of Physics & Electronics, Lal Bahadur Shastri Mahavidyalaya, Dharmabad 431 809, India Received 13 March 2018 The complex dielectric properties of glycol ethers with water at various concentrations have been measured using Agilent make Precision LCR meter E4980A in the frequency range of 20 Hz to 2 MHz at 25 °C with dielectric liquid test fixture 16452A. The electrical and dielectric properties of the binary mixtures have been represented in terms of complex dielectric function ε*(ω), electrical modulus M*(ω), electrical conductivity σ*(ω). All these parameters have been used to explain the various processes associated with the electric and dielectric properties of the binary mixtures of glycol ethers in aqueous solutions. The values of static dielectric constant of various concentrations have been reported at 2 MHz frequency. Further the excess dielectric properties for the binary mixtures have been evaluated to investigate the heterogeneous interactions in glycol ether-water molecules. Keywords: Glycol ether, LCR meter, Static dielectric constant, Heterogeneous interactions 1 Introduction 2 Experimental Glycol ethers are a group of solvents based on the 2.1 Materials alkyl ethers of ethylene glycol. In this study, the Ethylene glycol dimethyl ether (EGDME) and dielectric measurement of two glycol ethers namely diethylene glycol dimethyl ether (DEGDME) were ethylene glycol dimethyl ether and diethylene glycol obtained commercially from Alfa Aesar with purity dimethyl ether pure as well as in binary mixtures of 99%. The de-ionized water with HPLC grade was water have been carried out in the frequency range of obtained from Fisher Scientific India Pvt Ltd. They 20 Hz to 2 MHz at 25 °C. Ethylene glycol dimethyl were used without further purification. The solutions were prepared at different mole fractions of water in ether (1,2 dimethoxyethane) is also known as EGDME and DEGDME. monoglyme or dimethyl cellosolve with chemical composition C4H10O2. It is an aprotic ether used 2.2 Measurements and data analysis as solvent, especially in batteries. Diethylene glycol The dielectric properties of glycol ether – water dimethyl ether known as diglyme is a solvent with a binary mixtures at frequency range from 20 Hz to 2 MHz using Agilent precision LCR meter E4980A and high boiling point with chemical formula C6H14O3. It is a clear, colorless liquid with a slight ether-like odor. Agilent 16452A liquid dielectric test fixture have In literature, there is plenty of work on dielectric been measured. The static dielectric constants for pure liquid samples and whole concentrations of binary studies of monoalkyl ethers of ethylene glycols1-13. mixtures were determined by using ‘capacitive But the dielectric study of dimethyl ether of ethylene 14 measurement method’ with a short compensation at 2 glycol and diethylene glycol is limited . In present MHz. The detailed measurement techniques have work, the dielectric dispersion of these glycol ethers been described elsewhere15. in pure form as well as in water over complete composition range is studied. The electric modulus, 3 Results and Discussion complex conductivity and excess permittivity for the 3.1 Representation of dielectric spectra binary mixtures of glycol ether- water are evaluated. In present study, the dielectric constant values are Further the study is extended to express the hetero recorded at 2 MHz frequency. At lower frequencies, molecular interactions among the binary mixture. contribution of ionic conduction process and electrode polarization dominates the real part of dielectric —————— spectra (ε'). Due to these processes, at lower *Corresponding author (E-mail: [email protected]) frequencies, ε' has higher values as compared to their 302 INDIAN J PURE & APPL PHYS, VOL. 56, APRIL 2018 static dielectric constant. In the real part of dielectric space charge effects which often mask the dielectric permittivity spectra (Fig. 1(a,b)), the dielectric features of the spectra. The charge carriers move over permittivity for EGDME and DEGDME becomes long distances in the frequency range below the constant around 1 kHz while that for the binary frequency corresponding to the electric modulus (M") mixtures with water, it become steady in the loss peak. For the higher frequencies, the charge frequency range of few kHz to 0.2 MHz. carriers can perform localized motion within the The dielectric data can be highlighted by the potential well. Thus the electric modulus loss spectra processes such as tan (δ)= ε"(ω) / ε'(ω), ac show the transition of charge carriers from long range * 16 conductivity, σac(ω)= iωε (ω) and the modulus , to short range mobility. The Fig. 3(a,b) exhibits M" * * M (ω)=1/ε (ω). The formulations are already peak values, the frequency fσ corresponding to these discussed in literature17. The electrode polarization peaks is related to the most probable ionic -1 (EP) relaxation can be explained by tan(δ) plot conductivity relaxation time τσ = (2πfσ) . From the (Fig. 2(a,b)). The loss peak of tan (δ) is corresponding graph of M"(ω), ionic conductivity relaxation time to the EP relaxation frequency fEP, which is used to (τσ) corresponding to the peak values of M"(ω) are -1 evaluate the EP relaxation time, τEP= (2πfEP) which is determined. associated with the overall dynamics of the absorbed ions on the electrode surfaces in the alternating 3.3 Complex conductivity electric field. On addition of water in glycol ethers The frequency dependent real part σ' and the (EGDME and DEGDME), the loss peak shifts imaginary part σ" of the alternating current (ac) towards the higher frequencies. complex conductivity σ*(ω) of the liquid samples were evaluated from the dielectric permittivity data. 3.2 Electric modulus M*(ω) In the σ'(ω) spectra for EGDME-water and The electric modulus obtained from the complex DEGDME-water binary mixtures (Fig. 4(a,b)), for relative permittivity spectra is useful to mask the pure water and water rich region (90% of water in Fig. 1 — Frequency dependent spectra of the real part of the relative dielectric function ε' for (a) EGDME-water and (b) DEGDME – water binary mixtures, respectively. SHINDE et al.: DIELECTRIC DISPERSION OF GLYCOL ETHERS AND THEIR BINARY MIXTURES WITH WATER 303 Fig. 2 — Frequency dependent spectra of dielectric loss, tanδ for (a) EGDME-water and (b) DEGDME –water binary mixtures, respectively. Fig. 3 ‒ Plots for imaginary part (M") of the complex electric modulus [M*(ω)] for (a) EGDME-water and (b) DEGDME –water binary mixtures, respectively. 304 INDIAN J PURE & APPL PHYS, VOL. 56, APRIL 2018 10-12 EGDME and DEGDME), the values of σac are very bond acceptor site. In the previous study it is low at 20 Hz and then increases rapidly up to few found that the ε0 value decreases with increase in hundred Hz. Thereafter, it becomes independent of chain length, the value of ε0 for frequency methoxyethanol>ethoxyethanol>butoxyethanol, where only addition of hydrophobic site (-CH2) get 3.4 Molecular interaction increased. Generally, only addition of hydrophobic The plot of the static dielectric constant (ε0) versus site reduces the ε0 value but for EGDME and mole fraction of water (Fig. 5) reveals a non linear DEGDME the ε0 values are almost same. As compared nature. The nonlinearity in the plot is greater for to EGDME, there is addition of hydrophobic as well as DEGDME-water than the EGDME-water mixtures. one extra hydrogen bond acceptor site in DEGDME. The dashed lines in the graph represent ideal nature of Therefore both these sites are offset to each other and dielectric constant according to the mixture makes the ε0 value almost same. compositions of EGDME-water and DEGDME-water. Further, the heterogeneous interactions among In practical, the plots are largely deviating from these molecules (EGDME-water and DEGDME- ideality. This deviation from ideality may be due to water) have been discussed using the excess dielectric E certain hetero molecular interaction among the glycol constant (ε0 ). The formulation to evaluate the excess E ether and water molecules. The chemical composition dielectric constant (ε0 ) is discussed in plenty of 10-12,18-19 E of EGDME and 2-ethoxyethanol (Monoethylether of papers . Using the same method the ε0 for ethylene glycol (EE)) is same but it is observed that these binary mixtures evaluated and plotted in Fig. 6. E the dielectric constant value of EGDME (ε0=7.25) is The values of ε0 are negative for all concentrations of 11 nearly half the value of EE (ε0=14.45). It suggests EGDME-water and DEGDME-water binary mixtures. the change in molecular dipole arrangement of these It shows an experimental confirmation of a certain two glycol ethers. It may be due to EE molecule has interaction among the unlike molecules through both the hydrogen bond donor and acceptor sites in hydrogen bonding which results such that the total same molecule whereas EGDME has only hydrogen number of effective dipoles get reduced. It also Fig. 5 — Static dielectric constant (ε0) versus mole fraction of water for binary mixtures of EGDME- and DEGDME with water. SHINDE et al.: DIELECTRIC DISPERSION OF GLYCOL ETHERS AND THEIR BINARY MIXTURES WITH WATER 305 E Fig. 6 — Excess dielectric constant (ε0 ) versus mole fraction of water for binary mixtures of EGDME- and DEGDME with water. suggests the formation of complex structure in glycol Acknowledgement ether–water through hydrogen bonding. The mole The financial support from the Science and fraction of water (XW) corresponding to the minimum Engineering Research Board (SERB), DST, New excess dielectric constant value provides the Delhi (Project No. SR/FTP/PS-203/2012) is gratefully stoichiometric ratio of stable complex structure.

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