Dielectric Relaxation Dynamics Research Articles

Vogel–Fulcher analysis of relaxor dielectrics with the tetragonal tungsten bronze structure: Ba6MNb9O30 (M = Ga, Sc, In)

In-depth analysis of the relaxor behaviour of Ba6MNb9O30 (M = Ga, Sc, In) tetragonal tungsten bronze (TTB) ceramics was carried out. Powder X-ray diffraction and scanning electron microscopy were performed in order to confirm the formation of desired phases and to determine the microstructure. Low-temperature dielectric spectroscopy was used in order to characterise the dielectric properties of these materials; the degree of relaxor behaviour was investigated in relation with the increase of ionic radius of the M cation on the B-site of the TTB structure. The dynamics of dielectric relaxation of dipoles was studied by fitting the dielectric permittivity data to the Vogel–Fulcher (VF) model in order to monitor the reproducibility and validity of the physical results. Restrictions to the VF fit were attempted besides the regular “free-fit” by constraining some of the fundamental relaxation parameters to physically sensible values. We show that VF fits are very sensitive to the fitting range resulting in a large range of fundamental parameters for the dielectric relaxation processes, and that the restriction of the frequency domain due to experimental noise or instrumentation limits has a dramatic influence on the values obtained.

Ultrathin polymer films by single molecule deposition

While physical vapour deposition of glass forming materials below their glass transition temperature, Tg, is an exciting route towards glasses with an extremely high packing density, strong kinetic and thermodynamic stability, vapour deposition of polymer systems is less evident and has so far not been investigated systematically.Here we have successfully prepared ultrathin films of low molecular mass polystyrene (800g/mol) by thermal evaporation from the melt into a UHV chamber at a maximum deposition rate of 1nm/h. Samples were studied in situ and in real-time by dielectric spectroscopy, chip-based ac-calorimetry and a quartz crystal microbalance, both during deposition and after reaching the final sample thickness of 5nm.During film growth well below the bulk-Tg, an initially retarded deposition kinetics was observed along with an accelerated dielectric relaxation dynamics compared to the bulk glass transition. Subsequent temperature cycling above the bulk-Tg revealed continuous changes in the (dielectric) glass transition dynamics and finally lead to desorption of the material at elevated temperatures without restoring the “dielectric” bulk glass transition dynamics.In contrast, simultaneous specific heat spectroscopy revealed bulk dynamics, a striking discrepancy that was discussed in terms of a dominant and accelerated response of PS end-groups in the dielectric spectra in combination with terminal sub-chain dynamics and some degree of end-group segregation.

Dielectric relaxation in ionic liquids: Role of ion-ion and ion-dipole interactions, and effects of heterogeneity

A semi-molecular theory for studying the dielectric relaxation (DR) dynamics in ionic liquids (ILs) has been developed here. The theory predicts triphasic relaxation of the generalized orientational correlation function in the collective limit. Relaxation process involves contributions from dipole-dipole, ion-dipole, and ion-ion interactions. While the dipole-dipole and ion-ion interactions dictate the predicted three relaxation time constants, the relaxation amplitudes are determined by dipole-dipole, ion-dipole, and ion-ion interactions. The ion-ion interaction produces a time constant in the range of 5-1000μs which parallels with the conductivity dominated dielectric loss peak observed in broadband dielectric measurements of ILs. Analytical expressions for two time constants originating from dipolar interactions in ILs match exactly with those derived earlier for dipolar solvents. The theory explores relations among single particle rotational time, collective rotational time, and DR time for ILs. Use of molecular volume for the rotating dipolar ion of a given IL leads to a predicted DR time constant much larger than the slowest DR time constant measured in experiments. In contrast, similar consideration for dipolar liquids produces semi-quantitative agreement between theory and experiments. This difference between ILs and common dipolar solvents has been understood in terms of extremely low effective rotational volume of dipolar ion, argued to arise from medium heterogeneity. Effective rotational volumes predicted by the present theory for ILs are in general agreement with estimates from experimental DR data and simulation results. Calculations at higher temperatures predict faster relaxation time constants reducing the difference between theory and experiments.

Dielectric Relaxation and Solvation Dynamics in a Prototypical Ionic Liquid + Dipolar Protic Liquid Mixture: 1-Butyl-3-Methylimidazolium Tetrafluoroborate + Water

Dielectric and solvation data on mixtures of 1-butyl-3-methylimidazilium tetrafluoroborate ([Im41][BF4]) + water are reported and used to examine the utility of dielectric solvation models. Dielectric permittivity and loss spectra (25 °C) were recorded over the frequency range 200 MHz to 89 GHz at 17 compositions and fit to a 4-Debye form. Dynamic Stokes shift measurements on the solute coumarin 153 (C153), made by combining fluorescence upconversion (80 fs resolution) and time-correlated single photon counting data (20 ns range), were used to determine the solvation response at 7 compositions (20.5 °C). All properties measured here were found to depend upon mixture composition in a simple continuous manner, especially when viewed in terms of volume fraction. Solvation response functions predicted by a simple dielectric continuum model are similar to but ∼7-fold faster than the spectral response functions measured with C153. The solvation data are in better agreement with the recently published predictions of a semimolecular model of Biswas and co-workers [J. Phys. Chem. B 2011, 115, 4011], but these latter predictions are systematically slow by a factor of ∼3.

Dielectric Relaxation in Dimethyl Sulfoxide/Water Mixtures

Dielectric spectra of dimethyl sulfoxide (DMSO)/water mixtures, over the entire concentration range, were measured using the transmission line method at frequencies from 45 MHz to 26 GHz and at temperatures of 298-318 K. The relaxation times of the mixtures showed a maximum at an intermediate molar fraction of DMSO. A water structure "breaking effect", manifested by a reduced average number of hydrogen bonds per water molecule, was observed in dilute aqueous solutions based on the dielectric relaxation dynamics analysis. The increase in the dielectric relaxation time in DMSO/water mixtures was attributed to the spatial (steric) constraints of DMSO molecules on the hydrogen bond network, rather than being due to hydrophobic hydration of the methyl groups. The interactions between water and DMSO molecules in DMSO-rich mixtures are also discussed.

Dielectric relaxation dynamics in a dual-frequency nematic liquid crystal doped with C.I. Acid Red 2

The dielectric relaxation dynamics of a dual-frequency liquid crystal-dye composite were studied and the effect of the photoinduced isomerization of the azo dye on the dielectric spectrum of the cell under illumination by an argon-ion laser operating at wavelength of 514.5 nm and irradiance of 550 mW cm −2. It was found that the illumination process has a profound influence on the dielectric spectrum of the dye-doped dual-frequency liquid crystal in the low-frequency range.

An investigation into the thermal behaviour of an amorphous drug using low frequency dielectric spectroscopy and modulated temperature differential scanning calorimetry.

The objective of the study was to investigate the use of low frequency dielectric spectroscopy as a means of characterizing the thermal transitions of an amorphous drug substance, indometacin, with particular emphasis on modelling the response using the Dissado-Hill function. The low frequency dielectric behaviour of indometacin was measured over a temperature range of 10-160 degrees C and a frequency range of 10(-3)-10(6) Hz. Modulated temperature differential scanning calorimetry (MTDSC) studies were also performed on equivalent samples, showing a glass transition, recrystallization and melting. Isothermal low frequency dielectric spectra of the sample at temperatures below recrystallization showed the dynamic dielectric relaxation associated with the amorphous phase, while changes in the real and imaginary permittivities were observed that were associated with recrystallization and subsequent melting. A small discontinuity was observed immediately above the recrystallization process in the MTDSC and dielectric data, suggested to correspond to a solid state transformation. The use of the Dissado-Hill function as a means of modelling the dielectric behaviour has also been described. The study suggests that low frequency dielectric spectroscopy, used in conjunction with MTDSC and Dissado-Hill modelling, may be a useful tool for the characterization of amorphous and crystalline drugs.

Dielectric hysteresis, relaxation dynamics, and nonvolatile memory effect in carbon nanotube dispersed liquid crystal

Self-organizing nematic liquid crystals (LCs) impart their orientational order onto dispersed carbon nanotubes (CNTs) and obtain CNT-self-assembly on a macroscopic dimension. The nanotube-long axis, being coupled to the nematic director, enables orientational manipulation via the LC nematic reorientation. Electric-field-induced director rotation of a nematic LC+CNT system is of potential interest due to its possible application as a nanoelectromechanical system. Electric field and temperature dependence of dielectric properties of a LC+CNT composite system have been investigated to understand the principles governing CNT assembly mediated by the LC. In the LC+CNT nematic phase, the dielectric relaxation on removing the applied field follows a single-exponential decay, exhibiting a faster decay response than the pure LC above a threshold field. The observed dielectric behaviors on field cycling in the nematic phase for the composite indicates an electromechanical hysteresis effect of the director field due to the LC-CNT anchoring mechanism. Observations in the isotropic phase coherently combine to confirm the presence of anisotropic pseudonematic domains stabilized by the LC-CNT anchoring energy. These polarized domains maintain local directors and respond to external fields, but do not relax back to the original state on switching the field off, showing nonvolatile memory effect.

Dielectric Relaxation Dynamics of Water in Model Membranes Probed by Terahertz Spectroscopy

We study hydrated model membranes, consisting of stacked bilayers of 1,2-dioleoyl- sn-glycero-3-phosphocholine lipids, using terahertz time-domain spectroscopy and infrared spectroscopy. Terahertz spectroscopy enables the investigation of water dynamics, owing to its sensitivity to dielectric relaxation processes associated with water reorientation. By controlling the number of water molecules per lipid molecule in the system, we elucidate how the interplay between the model membrane and water molecules results in different water dynamics. For decreasing hydration levels, we observe the appearance of new types of water dynamics: the collective bulklike dynamics become less pronounced, whereas an increased amount of both very slowly reorienting (i.e., irrotational) and very rapidly reorienting (i.e., fast) water molecules appear. Temperature-dependent measurements reveal the interconversion between the three distinct types of water present in the system.

Dielectric Relaxation in Dimethyl Sulfoxide/Water Mixtures Studied by Microwave Dielectric Relaxation Spectroscopy

Dielectric spectra of dimethyl sulfoxide (DMSO)/water mixtures, over the entire concentration range, have been measured using the transmission line method at frequencies from 45 MHz to 26 GHz and at temperatures of 298-318 K. The relaxation times of the mixtures show a maximum at an intermediate molar fraction of DMSO. The specific structure of mixtures in different concentration regions was determined by the dielectric relaxation dynamics, obtained from the effect of temperature on the relaxation time. A water structure "breaking effect" is observed in dilute aqueous solutions. The average number of hydrogen bonds per water molecule in these mixtures is found to be reduced compared to pure water. The increase in the dielectric relaxation time in DMSO/water mixtures is attributed to the spatial (steric) constraints of DMSO molecules on the hydrogen-bond network, rather than being due to hydrophobic hydration of the methyl groups. The interaction between water and DMSO by hydrogen bonding reaches a maximum at a DMSO molar fraction of 0.33, reflected by the maximum activation enthalpy for dielectric relaxation in this concentration, suggesting the formation of a stoichiometric compound, H2O-DMSO-H2O. In highly concentrated solutions, negative activation entropies are observed, indicating the presence of aggregates of DMSO molecules. A distinct antiparallel arrangement of dipoles is obtained for neat DMSO in the liquid state according to the Kirkwood correlation factor (g(K) = 0.5), calculated from the static permittivity. The similarity of the dielectric behavior of pure DMSO and DMSO-rich mixtures suggests that dipole-dipole interactions contribute significantly to the rotational relaxation process in these solutions.

Bias dependent dielectric relaxation dynamics of electrically tuned large-scale aligned zinc oxide nanorods in nematic liquid crystal host

It was observed that mixed ZnO nanorods and twisted nematic liquid crystals (LCs) show highly ordered molecular system. The observed molecular relaxation arose due to a reorientation of long molecular axis of the order of 400 kHz for pure ZLI-1636, while such relaxation was shifted to a lower frequency for mixture. By using the proposed equations, f=fDB−α exp[−EV/(B−BC)] and σ=σDB−sα exp[−sEV/(B−BC)], the obtained equivalent activation energy was increased remarkably by the introduction of ZnO nanorods in pure LC. A strong long-range interaction is established in 0.01% ZnO nanorods mixed LC system.

Dielectric Relaxation, Ion Conductivity, Solvent Rotation, and Solvation Dynamics in a Room-Temperature Ionic Liquid

Dielectric susceptibility and related conductivity of the neat ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI+PF6-) are studied via molecular dynamics computer simulations. Both ion translations and reorientations contribute to dielectric relaxation, while their cross-correlation does not play any significant role. Interestingly, ion translational dynamics are found to enhance the static dielectric constant epsilon 0. The increment in epsilon 0 is attributed to rapid development of large anticorrelation in the autocorrelation function of the ionic current, i.e., hindered ion translations of strong librational character. One consequence of hindered translational dynamics is that the real part of conductivity has a maximum in the terahertz region and decreases with diminishing frequency. This in turn yields significant dielectric absorption in the far-IR region, consonant with recent terahertz time-domain spectroscopy measurements. Reorientational dynamics of cations show a marked deviation from diffusion. The well-known relation in the diffusion regime for reorientational correlation times tau R(l) proportional, variant [ l( l + 1)] (-1) fails completely for EMI+PF6-, where l is the order of Legendre polynomials used in the expansion of reorientational time correlation functions. It is found that dielectric continuum theory generally does not provide a reliable framework to describe solvation dynamics in EMI+PF6- even though the inclusion of ion conductivity in dielectric relaxation tends to improve the continuum description. This is ascribed mainly to electrostrictive effects absent in many continuum formulations.

Dielectric secondary relaxation and phenylene ring dynamics in bisphenol-A polycarbonate

A detailed dielectric investigation of the secondary relaxation on a series of bisphenol-A polycarbonate samples with different treatments that influence the local polymer structure is presented. Dielectric spectroscopy measurements were performed in the frequency range 10−2–106Hz. The structural changes induced by different thermo-mechanical treatments, as well as by polymer crystallization, lead to a reduction of the dielectric losses that is not uniform over the whole frequency range but more pronounced in the high frequency side of the γ-relaxation peak. These effects have been rationalized in terms of the great coupling between the motions of the phenylene rings and those of the dipolar entity of the repeating unit (namely the carbonate group). Furthermore, it is shown that the same approach allows rationalizing the marked differences between the dielectric and mechanical secondary relaxations.

Dynamic dielectric response of PLZT-P(VDF/TFE) nanocomposites

Dynamic dielectric relaxation of polymer P(VDF/TFE)(0.98/0.02) loaded with lead lanthanum zirconate titanate (Pb0.92La0.08)(Zr0.65Ti0.35)O3(PLZT 8/65/35) ceramic nanopowders was studied in the frequency range from 100 Hz to 1 MHz and at temperatures from 100 K to 450 K. The PLZT nanopowders were prepared by the sol-gel method using: lead(II)acetate trihydrate, lanthanum acetate hydrate, zirconium(IV)propoxide and titanium(IV)propoxide. The crystallization process of PLZT powders was monitored by means of XRD analysis (Philips PW 3710) using Cu-Kα radiation in the range 20° ≤ 2Θ ≤ 60°. The powders were analyzed before and after burning of the organic remains. The morphology observations of the powders were made using Hitachi S-4700 scanning electron microscope (SEM), and the grain size distributions were measured on a Zetasizer Nano ZS by the DLS method. The PLZT-P(VDF/TFE) composite samples of 0-3 connectivity were prepared from ceramic and polymer powders by the hot-pressing method. The volume fraction of the ceramics Θ amounted 0.1, 0.15 and 0.2. The dielectric response of the ceramics-polymer composite was found as a combination of the responses of pure polymer and the ceramics: (i) the addition of the PLZT ceramics increases the value of the dielectric permittivity ϵ, (ii) the composite shows the maximum of the permittivity coming from the PLZT ceramics, (iii) the dielectric absorption spectrum of the composites is dominated by the α-relaxation in pure polymer.

Investigation of structural relaxation and surface modification of ultrathin films of poly(ethylene terephthalate)

We studied dynamic properties of ultrathin films of poly(ethylene terephthalate) spincoated on different substrates, by means of dielectric spectroscopy and surface patterning experiments. We did not observe any variations of structural dielectric relaxation dynamics for films spincoated on aluminium substrate having thicknesses down to 40 nm. On the same substrate, 13 nm thick films are instead characterized by a reduction of the chains mobility. Surprisingly the chains dynamics as probed by a surface nanopatterning experiment evidenced a strong dependence on the substrate interaction even for 50 nm thick films, where dielectric relaxation dynamics is unaffected. It can be deduced that different length scales characterise dielectric relaxation dynamics and the processes related to the surface patterning, even if both are related to the chain mobility. Further experiments are wished to better understand this intriguing scenario.

Characterization of DNA degradation using direct current conductivity and dynamic dielectric relaxation techniques

The purpose of this study was to evaluate DNA degradation upon thermal heating using dielectric relaxation and direct current (DC) conductivity methods. Herring sperm DNA, human growth hormone (HgH) plasmid DNA, and secreted alkaline phosphatase (SEAP) plasmid DNA were used as the examples. DNA was heated at 80 degrees C for 1 hour. The dielectric relaxation spectra as a function of the applied field frequency were measured for HgH DNA at 0.5 hours and at 1 hour. The frequency range covered was from 10 kHz to 100 kHz. The DC conductivity measurements were made for all 3 kinds of DNA at 4 time points: 0 hours, 0.5 hours, 0.75 hours, and 1 hour. At each time point the DC conductivity was measured for each sample as a function of concentration via water dilution. The results show that the dielectric relaxation method is less sensitive in characterizing heat-driven DNA degradation. Conversely, DC conductivity is very sensitive. The semiquantitative dependence of the conductivity upon heating suggests that DNA degradation involves more than plasmid DNA nicking. Double strand and single strand breaks may also occur. In addition, herring sperm DNA, HgH DNA, and SEAP DNA, though similar in their DC conductivity functional forms upon dilution, exhibit significant differences in their responses to sustained heating.

Identification of dielectric and structural relaxations in glass-forming secondary amides

Dielectric relaxation dynamics of secondary amides is explored in their supercooled state near the glass transition temperature Tg by investigating N-ethylacetamide and its mixtures with N-methylformamide. All the samples are found to exhibit giant dielectric permittivities, reaching over 500 in N-methylformamide-rich mixtures around Tg. For both the neat and binary systems, the predominant relaxation peak is of the Debye-type throughout the viscous regime, which is an unexpected feature for a glass former with intermediate fragility. The present results combined with the earlier reported high-temperature data reveal that the dielectric strength delta epsilon(D) of the Debye relaxation extrapolates to zero at frequencies of 10(10)-10(11) Hz, which is about two orders of magnitude lower than the phonon frequency limit typical of the structural relaxation. This Debye process is remarkably similar to the dielectric behavior of many monohydroxy alcohols, which implies a common nature of purely exponential relaxation dynamics in these liquids. Based on the dielectric properties, we conclude that the Debye relaxation in the secondary amides is not a direct signature of the primary or alpha-relaxation, the latter being obscured at low temperatures due to the relatively low permittivity and close spectral proximity to the Debye peak. As in the case of monohydroxy alcohols, dielectric polarization and structure fluctuate on different time scales in secondary amides. The Kirkwood-Fröhlich correlation factors for Debye-type liquids are also discussed.

Interplay of surface and confinement effects on the molecular relaxation dynamics of nanoconfined poly(methyl methacrylate) chains.

The thermally stimulated current (TSC) signatures of the primary (alpha) transition and its precursor, the Johary-Goldstein (beta) relaxation, are used to probe effects of nanoconfinement on the dielectric relaxation dynamics of poly(methyl methacrylate) (PMMA) radically polymerised in situ 50 angstroms mean pore size silica-gel. Nanoconfinement leads to a broadened and low-temperature-shifted beta band (peaking at Tbeta, with deltaTbeta = T(conf.)beta - T(bulk)beta = -15 degrees C for a heating rate of 5 deg/min), signifying the occurrence of faster relaxing moieties compared to the bulk-like PMMA film. Furthermore, both TSCs and differential scanning calorimetry (DSC) estimate a rise of the glass transition temperature for the confined phase ([Formula: see text]= +13 degrees C) and an increased width for the corresponding transition signals, relative to the signals in the bulk. Simple free-volume and entropy models seem inadequate to provide a collective description of the above perturbations. The observation of a spatial heterogeneity regarding the relaxation dynamics is discussed in terms of the presence of a motional gradient, with less mobile segments near the interface and more mobile segments in the core, and the interplay of adsorption ( e.g., strong physical interactions that slow down molecular mobilities) and confinement effects ( e.g., lower entanglements concentration and local density fluctuations that provide regions of increased free space). The results suggest that in the case of high-molecular-weight polymers confined in small-pore systems, adsorption effects have considerable bearing on the glass transition phenomenon whereas confinement primarily influences side-chains' rotational mobilities. The confinement effect is expected to dominate over adsorption for PMMA phases occluded in higher pore sizes and silanised walls.

Microwave dielectric relaxation and molecular dynamics in binary mixtures of poly(vinyl pyrrolidone)–poly(ethylene glycol)s in non‐polar solvent

AbstractDielectric relaxation study of binary mixtures of poly(vinyl pyrrolidone) (PVP) (Mw = 40 000 g mol−1) and poly(ethylene glycol)s (PEGs) (Mn = 200, 400 and 600 g mol−1) with concentration variation was carried out in dilute solutions of benzene at 10.1 GHz and 35 °C. The average relaxation time τo, corresponding to segmental motion τ1 and group rotations τ2 was determined for PVP–PEGs mixtures. A comparison of these mixtures relaxation times was made with the relaxation times of PEGs in benzene solvent. The evaluated τo values of PVP–PEGs mixtures in benzene solution are assigned to the reorientation of PEG molecules. It has been observed that the τo value of PVP–PEG200 mixtures increases with increasing concentration of PVP but their values are small in comparison with the τo value of PEG200 molecules. In the case of PVP–PEG400 and PVP–PEG600 mixtures, the evaluated values of τo are greater than the corresponding τo values of PEG400 and PEG600 molecules in benzene solvent. The variation in τo values in these systems has been discussed by considering the stretching effect in the PEGs molecular chains in PVP–PEGs mixtures in benzene solutions. The high value of distribution parameter α (≈0.4 to 0.7) suggests that in these mixtures there is a large contribution of segmental motion and group rotations to the relaxation processes. The nature of the formation of hydrogen‐bonded PVP–PEG complex heterogeneous network due to hydrogen bonding between carbonyl groups of PVP monomer units and terminal hydroxyl groups of PEGs is discussed. Furthermore, the elongation behaviour of PVP–PEG complex networks in benzene solvent and the molecular dynamics in the mixture due to breaking and reforming of hydrogen bonds has been explored by comparing the evaluated relaxation times and the Kirkwood correlation factor of pure PEG molecules for their possible use in drug control release systems. The relaxation times of these mixtures are independent of their viscosity, but the elongation of the mixture network is influenced by the PEG chain length and the number of hydroxyl groups in comparison with the number of carbonyl groups in the mixtures. Copyright © 2003 Society of Chemical Industry

Dielectric relaxation and molecular dynamics in poly(vinyl pyrrolidone)–ethyl alcohol mixtures in pure liquid state and in non-polar solvent

Dielectric relaxation and molecular dynamics in poly(vinyl pyrrolidone)–ethyl alcohol (PVP–E) mixtures with varying concentration in pure state and also in very dilute solutions of benzene were studied for their molecular conformation at 35 °C. Dielectric permittivity ε′ and dielectric loss ε″ of PVP–E mixtures were measured by a time domain reflectometry technique in the frequency range 10 MHz to 10 GHz. The value of static dielectric constant ε 0, dielectric relaxation time τ, and dielectric free energy of activation Δ F τ has been evaluated by fitting the complex dielectric data into Debye equation. The variation in ε 0 was discussed by considering the volume effect and the structuring effects of the PVP on ethyl alcohol molecules. The formation of cooperative domains between PVP and ethyl alcohol molecules, CD PVP–E and between the ethyl alcohol–ethyl alcohol molecules CD E and their dynamics in the PVP–E mixtures were explored by using the evaluated values of τ and Δ F τ . The PVP–E mixtures of low PVP concentration were also studied in very dilute solutions of benzene at 10.1 GHz. The value of average relaxation time τ 0, distribution parameter α, and relaxation time corresponding to the motion of small multimer species of alcohol molecules τ 1 and group rotation τ 2 has been determined. It has been observed that in dilute solution of benzene the value of τ 0 and τ 1 increases with the increase in concentration of PVP in PVP–E mixture but the τ 2 value is found independent of the mixture constituent concentration. The entanglement of the CD PVP–E and the increase in the length of CD E in dilute solution of benzene due to dissociation of the complexes between carbonyl and hydroxyl groups has been explored. The value of τ 2 is assigned to the rotation of –OH group about C–O bond in the ethyl alcohol species in dynamic equilibrium with larger steric hindrance due to hydrogen bonding.