Dielectric spectroscopic studies of three important active pharmaceutical ingredients - clofoctol, droperidol and probucol

Sahra, M.; Thayyil, Mohamed Shahin; Bansal, Arvind K.; Ngai, K. L.; Sulaiman, M.K.; Shete, Ganesh; Hussan, K.P. Safna

doi:10.1016/j.jnoncrysol.2018.10.046

Cited by 21 publications

(20 citation statements)

References 41 publications

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“…As it stands, the general finding casts serious doubt on the verity of the narrow frequency dispersion and the large value of of polar glass-formers taken by dielectric spectroscopy. Potentially it also questions the worth of dielectric spectroscopy in the study of the dynamics of glass-formers, and validity of the results from DS accumulated over the past hundred years, as well as the recently found correlation of with  found by Paluch et al [15] and repeatedly verified by others [19,18]. The seriousness of the situation requires an in-depth consideration of the dynamics of polar glass-formers, not only the structural -relaxation but also the presence of the accompanying and universal JG -relaxation.…”

Section: Discussionmentioning

confidence: 94%

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Is there Universality in the Dielectric Response of Polar Glass Formers?

Ngai

Wojnarowska

Paluch

2021

Preprint

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The frequency dispersion of structural α-relaxation obtained from broadband dielectric spectroscopy measurements is relatively narrow in many polar glass-formers. On the other hand, it becomes much broader when probed by other techniques, including photon correlation spectroscopy (PCS), nuclear magnetic resonance (NMR), and mechanical shear modulus. Therefore, the dynamics of glass-formers observed by dielectric permittivity spectroscopy (DS) is called into question. Herein we propose a way to resolve this problem. First, we point out an unresolved Johari-Goldstein (JG) β-relaxation is present nearby the α-relaxation in these polar glass-formers. The dielectric relaxation strength of the JG β-relaxation is sufficiently weak compared to the α-relaxation so that the narrow dielectric frequency dispersion faithfully represents the dynamic heterogeneity and cooperativity of the α-relaxation. However, when the other techniques are used to probe the same glass-former, there is a reduction of relaxation strength of α-relaxation relative to that of the JG β-relaxation. Additionally, the separation between the α and the JG β relaxations in dielectric permittivity) decreases when probed by mechanical shear modulus. These changes in relation of α- to JG β-relaxation, when examined by the other techniques, engender the non-negligible contribution of the latter to the former. Hence the apparent α-relaxation is broader than observed by the dielectric permittivity. The broadening is artificial because it is due to a confluence of the α and JG β relaxations with a disparity in their relaxation strengths much less when the other techniques than by dielectric permittivity are used. This explanation is supported by showing the α-relaxation of polar glass-formers becomes broader when the dielectric data are represented in terms of the electric modulus instead of permittivity. The broadening, in this case, is again due to a reduction of the relaxation strength of the α-relaxation relative to that of the JG β-relaxation in the electric modulus representation. A corollary of the explanation applicable to weakly polar glass-formers having JG β-relaxation widely separated from the α-relaxation is the prediction that the frequency dispersion of dielectric α-relaxation is nearly the same as that of the electric modulus, and there is no significant additional broadening when probed by the other techniques. A host of experimental data from the literature and our new measurements are given to support the explanation for polar glass-formers and the ancillary prediction for weakly polar glass-formers. Thus the narrow frequency dispersion of the intense relaxation in polar glass-formers observed by dielectric permittivity is real and genuinely represents the dynamically heterogeneous and cooperative dynamics of α-relaxation. By contrast, the broad dispersion found by the other techniques is artificial and misleading.

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Section: Discussionmentioning

confidence: 94%

“…K from dielectric spectroscopy) and the narrowing of the -relaxation increasing rapidly with the dipole moment  and (Tg). Subsequent tests of the correlation have repeatedly confirmed it [ 16,17,18,19 ].…”

Section: Introductionmentioning

confidence: 89%

Is there Universality in the Dielectric Response of Polar Glass Formers?

Ngai

Wojnarowska

Paluch

2021

Preprint

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“…Potentially. the worth of dielectric spectroscopy in the study of the dynamics of glass-formers, and validity of the results from DS accumulated over the past hundred years, as well as the recently found correlation of with Δε found by Paluch et al, are questioned 15 and repeatedly verified by others 18 , 19 . The seriousness of the situation requires an in-depth consideration of the dynamics of polar glass-formers, not only the structural α-relaxation but also the presence of the accompanying and universal JG β-relaxation.…”

Section: Discussionmentioning

confidence: 84%

Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids

Ngai

Wojnarowska

Paluch

2021

Sci Rep

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The studies of molecular dynamics in the vicinity of liquid–glass transition are an essential part of condensed matter physics. Various experimental techniques are usually applied to understand different aspects of molecular motions, i.e., nuclear magnetic resonance (NMR), photon correlation spectroscopy (PCS), mechanical shear relaxation (MR), and dielectric spectroscopy (DS). Universal behavior of molecular dynamics, reflected in the invariant distribution of relaxation times for different polar and weekly polar glass-formers, has been recently found when probed by NMR, PCS, and MR techniques. On the other hand, the narrow dielectric permittivity function ε*(f) of polar materials has been rationalized by postulating that it is a superposition of a Debye-like peak and a broader structural relaxation found in NMR, PCS, and MR. Herein, we show that dielectric permittivity representation ε*(f) reveals details of molecular motions being undetectable in the other experimental methods. Herein we propose a way to resolve this problem. First, we point out an unresolved Johari–Goldstein (JG) β-relaxation is present nearby the α-relaxation in these polar glass-formers. The dielectric relaxation strength of the JG β-relaxation is sufficiently weak compared to the α-relaxation so that the narrow dielectric frequency dispersion faithfully represents the dynamic heterogeneity and cooperativity of the α-relaxation. However, when the other techniques are used to probe the same polar glass-former, there is reduction of relaxation strength of α-relaxation relative to that of the JG β relaxation as well as their separation. Consequently the α relaxation appears broader in frequency dispersion when observed by PCS, NMR and MR instead of DS. The explanation is supported by showing that the quasi-universal broadened α relaxation in PCS, NMR and MR is captured by the electric modulus M*(f) = 1/ε*(f) representation of the dielectric measurements of polar and weakly polar glass-formers, and also M*(f) compares favorably with the mechanical shear modulus data G*(f).

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“…The spectra obtained at ambient pressure but different temperatures are normalized by the corresponding maximum peak values. To analyze the frequency dispersion of the conductivity relaxation, we applied the Kohlrausch stretched exponential function where β KWW is the fractional exponent. The narrower the width of the loss peak, the larger is the β KWW value.…”

Section: Resultsmentioning

confidence: 99%

Effect of Cation n-Alkyl Side-Chain Length, Temperature, and Pressure on the Glass-Transition Dynamics and Crystallization Tendency of the [C_nC₁Pyrr]⁺[Tf₂N]⁻ Ionic Liquid Family

Szklarz

Adrjanowicz

et al. 2019

J. Phys. Chem. C

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This work focuses on the influence of nonpolar side-chain length on the glass-transition dynamics and crystallization behavior of a family of nonaromatic pyrrolidinium-based ionic liquids bearing the bis(trifluoromethanesulfonyl)imide counterion, [C n MPyrr]+[Tf2N]−, where n varies from 4 to 8. A combination of different experimental techniques, including differential scanning calorimetry and shear-mechanical and dielectric spectroscopy, enabled us to investigate the fundamental relationship between charge transport and structural relaxation as well as its impact on the dynamic properties of the investigated samples on approaching the glass transition. In contrast to recent experimental findings reported for imidazolium-based analogues, we demonstrate no evidence of the slow supramolecular mode in the rheological and dielectric responses of the studied pyrrolidinium-cation-based ionic liquids. Finally, we studied the crystallization tendencies for each sample under both ambient and elevated pressures and further compared behaviors of the samples with good glass-forming ability under isochronal conditions, characterized by the same conductivity relaxation time, τ M . Pressure seems to not exert a pronounced impact on the overall crystallization rate for the tested samples. Obtained results so as to the proposed methodology may shed new light on the properties affecting the physical stability of ionic liquids at various thermodynamic conditions, which is a key prerequisite for their rational and efficient applications in different sectors of technology.

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Dielectric spectroscopic studies of three important active pharmaceutical ingredients - clofoctol, droperidol and probucol

Cited by 21 publications

References 41 publications

Is there Universality in the Dielectric Response of Polar Glass Formers?

Is there Universality in the Dielectric Response of Polar Glass Formers?

Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids

Effect of Cation n-Alkyl Side-Chain Length, Temperature, and Pressure on the Glass-Transition Dynamics and Crystallization Tendency of the [C_nC₁Pyrr]⁺[Tf₂N]⁻ Ionic Liquid Family

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Dielectric spectroscopic studies of three important active pharmaceutical ingredients - clofoctol, droperidol and probucol

Cited by 21 publications

References 41 publications

Is there Universality in the Dielectric Response of Polar Glass Formers?

Is there Universality in the Dielectric Response of Polar Glass Formers?

Comparative analysis of dielectric, shear mechanical and light scattering response functions in polar supercooled liquids

Effect of Cation n-Alkyl Side-Chain Length, Temperature, and Pressure on the Glass-Transition Dynamics and Crystallization Tendency of the [CnC1Pyrr]+[Tf2N]− Ionic Liquid Family

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Effect of Cation n-Alkyl Side-Chain Length, Temperature, and Pressure on the Glass-Transition Dynamics and Crystallization Tendency of the [C_nC₁Pyrr]⁺[Tf₂N]⁻ Ionic Liquid Family