Generic Structural Relaxation in Supercooled Liquids

Pabst, Florian; Gabriel, Jan Philipp; Böhmer, Till; Weigl, Peter; Helbling, Andreas; Richter, Timo; Zourchang, Parvaneh; Walther, Thomas; Blochowicz, Thomas

doi:10.1021/acs.jpclett.1c00753

Cited by 64 publications

(91 citation statements)

References 43 publications

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“…The spectral shape of the structural relaxation received a lot of attention recently 1 , 2 , 37 . One of the topics that have been widely discussed is the generic line shape of the structural relaxation (following ∝ ω −1/2 at high frequencies) and possible deviations from such universal behavior due to the contribution of cross-correlations among various dipole moments 38 , as indicated by the recent theory of Déjardin et al 39 . It was evidenced that slow Debye mode in the dielectric response of some materials (e.g.…”

Section: Resultsmentioning

confidence: 99%

The dielectric response of phenothiazine-based glass-formers with different molecular complexity

Rams-Baron

Jędrzejowska

Jurkiewicz

et al. 2021

Sci Rep

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We examined a series of structurally related glass-forming liquids in which a phenothiazine-based tricyclic core (PTZ) was modified by attaching n-alkyl chains of different lengths (n = 4, 8, 10). We systematically disentangled the impact of chemical structure modification on the intermolecular organization and molecular dynamics probed by broadband dielectric spectroscopy (BDS). X-ray diffraction (XRD) patterns evidenced that all PTZ-derivatives are not ‘ordinary’ liquids and form nanoscale clusters. The chain length has a decisive impact on properties, exerting a plasticizing effect on the dynamics. Its elongation decreases glass transition temperature with slight impact on fragility. The increase in the medium-range order was manifested as a broadening of the dielectric loss peak reflected in the lower value of stretching parameter βKWW. A disagreement with the behavior observed for non-associating liquids was found as a deviation from the anti-correlation between the value of βKWW and the relaxation strength of the α-process. Besides, to explain the broadening of loss peak in PTZ with the longest (decyl) chain a slow Debye process was postulated. In contrast, the sample with the shortest alkyl chain and a less complex structure with predominant supramolecular assembly through π–π stacking exhibits no clear Debye-mode fingerprints. The possible reasons are also discussed.

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Section: Resultsmentioning

confidence: 99%

The dielectric response of phenothiazine-based glass-formers with different molecular complexity

Rams-Baron

Jędrzejowska

Jurkiewicz

et al. 2021

Sci Rep

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show abstract

“…A serious challenge to a verity of the dynamics of polar glass-formers obtained by dielectric permittivity spectroscopy (DS) was issued by the recent publications by Körber et al 19 , Gabriel et al 62 , and Pabst et al 22 . The challenge is that the narrow frequency dispersion of the intense dielectric α-loss peak in ε ″( f ) becomes much broader when the same material is probed by other spectroscopies including PCS (depolarized light scattering) and NMR 19 , 36 and also shear mechanical modulus G ″( f ) 21 .…”

Section: Discussionmentioning

confidence: 99%

“…In the lower panel of Fig. 4 we compare M ″( f ) with the susceptibility χ″( f ) from PCS (or DLS) obtained by Pabst et al, which has = 0.49 21 , 22 . There is excellent agreement in frequency dependence between M ″( f ) and χ″( f ).…”

Section: Experimental Verificationsmentioning

confidence: 92%

“…Relying on the common spectral shape emerging from the combination of different susceptibility results, he explained the correlation between and Δ ε ( T g ) of the dielectric α process of van der Waals liquids. Also, Pabst et al 21 , 22 found that the light scattering spectra of the same systems almost perfectly superimpose and show a generic line shape of the structural relaxation, following the ω −1/2 -dependence at high frequencies. In dielectric spectra, the generic behavior found by other techniques holds only for nonpolar systems with a low dipole moment.…”

Section: Introductionmentioning

confidence: 90%

“…S1 for TEP and Fig. S2 for TPP) 21 , 22 , 44 , 45 . This property is like KDE, PDE, aroclor, and glycerol, as well as the other highly polar glass-formers 16 , 17 conforming to the correlation of with Δε found 15 .…”

Section: Experimental Verificationsmentioning

confidence: 99%

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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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Schnelle kollektive Wasserstoffbrückenbindungsdynamik in Hexafluorisopropanol im Kontext seiner chemischen Aktivität

Caporaletti,

Gunkel,

Fernández‐Ibáñezhttps

et al. 2024

Angewandte Chemie

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Using fluorinated mono‐alcohols, in particular hexafluoro‐isopropanol (HFIP), as a solvent can enhance chemical reaction rates in a spectacular manner. Previous work has shown evidence that this enhancement is related to the hydrogen‐bond structure of these liquids. Here, we investigate the hydrogen‐bond dynamics of HFIP and compare it to that of its non‐fluorinated analog, isopropanol. Ultrafast infrared spectroscopy show that the dynamics of individual hydrogen‐bonds is about twice as slow in HFIP as in isopropanol. Surprisingly, from dielectric spectroscopy we find the opposite behavior for the dynamics of hydrogen‐bonded clusters: collective rearrangements are 3 times faster in HFIP than in isopropanol. This difference indicates that the hydrogen‐bonded clusters in HFIP are smaller than in isopropanol. The differences in cluster size can be traced to changes in the hydrogen‐bond donor and acceptor strengths upon fluorination. The smaller cluster size can boost reaction rates in HFIP by increasing the concentration of reactive, terminal OH‐groups of the clusters, whereas the fast collective dynamics can increase the rate of formation of hydrogen bonds with the reactants. The longer lifetime of the individual hydrogen bonds in HFIP can enhance the stability of the hydrogen‐bonded clusters, and so increase the probability of reactant‐solvent hydrogen bonding.

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Generic Structural Relaxation in Supercooled Liquids

Cited by 64 publications

References 43 publications

The dielectric response of phenothiazine-based glass-formers with different molecular complexity

The dielectric response of phenothiazine-based glass-formers with different molecular complexity

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

Schnelle kollektive Wasserstoffbrückenbindungsdynamik in Hexafluorisopropanol im Kontext seiner chemischen Aktivität

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