Influence of intramolecular dynamics on the relaxation spectra of simple liquids

Zeißler, Rolf; Pabst, Florian; Böhmer, Till; Blochowicz, Thomas

doi:10.1039/d3cp01172k

Cited by 3 publications

(1 citation statement)

References 40 publications

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“…The closer to T g , the more difficult is to distinguish the different aspects of meta-CF 3 motion. A similar effect related to the vanishing bimodal character of the loss spectra due to the cooperativity onset was observed recently by Blochowicz et al for lower molecular-weight liquids 23 . To describe the temperature dependence of relaxation times for the ortho-CF 3 with physically reliable parameters, we used two VFT functions.…”

Section: Resultssupporting

confidence: 84%

The influence of molecular shape on reorientation dynamics of sizable glass-forming isomers at ambient and elevated pressure

Błażytko,

Rams-Baron,

Paluch

2024

Sci Rep

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We used dielectric spectroscopy to access the molecular dynamics of three isomers with a structure based on a sizable, partially rigid, and non-polar core connected to a polar phenylene unit differing in the position of the polar group, and, consequently, the direction and magnitude of the dipole moment to address the question how unique molecular properties, in particular large size and elongated shape, affect the dynamics. The position of the polar group differentiates the molecular shape and isomer’s anisotropy and leads to different thermal and dynamic properties of the isomers. The shape of permittivity loss spectra was governed by magnitudes of the longitudinal and transverse components of dipole moment to a large extent. For para isomer with negligible traverse component of dipole moment, the narrowest loss peak was found while for meta isomer, the bimodal loss peak was observed at high temperatures. Its shape evolved on cooling limiting the possibility of individual mode separation near glass transition where the dynamics were more cooperative. High-pressure dielectric studies showed that sizable isomers were characterized by the pronounced sensitivity of glass transition temperature, Tg, to compression. Observed high activation volumes, such as 735 cm3/mol at Tg for para isomer, were found to correlate with the length scale of dynamic cooperativity. The number of dynamically correlated molecules depended on molecular shape and varied among isomers while the determined values were much smaller than that reported for other glass-forming liquids. We discussed here the obtained results in the context of the specific properties of the systems studied showing the overriding role of anisotropy.

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Section: Resultssupporting

confidence: 84%

The influence of molecular shape on reorientation dynamics of sizable glass-forming isomers at ambient and elevated pressure

Błażytko,

Rams-Baron,

Paluch

2024

Sci Rep

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Revealing complex relaxation behavior of monohydroxy alcohols in a series of octanol isomers

Böhmer

Richter

Gabriel

et al. 2023

The Journal of Chemical Physics

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We investigate the reorientation dynamics of four octanol isomers with very different characteristics regarding the formation of hydrogen-bonded structures by means of photon-correlation spectroscopy (PCS) and broadband dielectric spectroscopy. PCS is largely insensitive to orientational cross-correlations and straightforwardly probes the α-process dynamics, thus allowing us to disentangle the complex dielectric relaxation spectra. The analysis reveals an additional dielectric relaxation contribution on time scales between the structural α-process and the Debye process. In line with nuclear magnetic resonance results from the literature and recent findings from rheology experiments, we attribute this intermediate contribution to the dielectric signature of the O–H bond reorientation. Due to being incorporated into hydrogen-bonded suprastructures, the O–H bond dynamically decouples from the rest of the molecule. The relative relaxation strength of the resulting intermediate contribution depends on the respective position of the hydroxy group within the molecule and seems to vanish at sufficiently high temperatures, i.e., exactly when the overall tendency to form hydrogen bonded structures decreases. Furthermore, the fact that different octanol isomers share the same dipole density allows us to perform an in-depth analysis of how dipolar cross-correlations appear in dielectric loss spectra. We find that dipolar cross-correlations are not solely manifested by the presence of the slow Debye process but also scale the relaxation strength of the self-correlation contribution depending on the Kirkwood factor.

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Glass spectrum, excess wing phenomenon, and master curves in molecular glass formers: A multi-method approach

Rössler,

Becher

2024

The Journal of Chemical Physics

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The relaxation spectra of glass formers solely displaying an α-peak and excess wing contribution collected by various methods are reanalyzed to pin down their different spectral evolution. We show that master curve construction encompassing both α-peak and emerging excess wing works for depolarized light scattering (DLS) and nuclear magnetic resonance (NMR) relaxometry. It reveals the self-part of the slow dynamics’ spectrum. Master curves are to be understood as a result of a more extensive scaling covering all temperatures instead of strict frequency–temperature superposition. DLS and NMR display identical relaxation spectra; yet, comparing different systems, we do not find a generic structural relaxation at variance with recent claims. Dielectric spectroscopy (DS) spectra show particularities, which render master curve construction obsolete. The DS α-peak is enhanced or suppressed with respect to that of DLS or NMR, yet, not correlated to the polarity of the liquid. Attempting to single out the excess wing from the overall spectrum discloses a stronger exponential temperature dependence of its amplitude compared to that below Tg and a link between its exponent and that of the fast dynamics’ spectrum. Yet, such a decomposition of α-peak and excess wing appears to be unphysical. Among many different glasses, the amplitude of the excess wing power-law spectrum is found to be identical at Tg, interpreted as a relaxation analog to the Lindemann criterion.

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Influence of intramolecular dynamics on the relaxation spectra of simple liquids

Abstract: The shape of the structural relaxation peak in the susceptibility spectra of supercooled liquids is of great interest, as it promises to provide information about the distribution of molecular mobilities...

Cited by 3 publications

References 40 publications

The influence of molecular shape on reorientation dynamics of sizable glass-forming isomers at ambient and elevated pressure

The influence of molecular shape on reorientation dynamics of sizable glass-forming isomers at ambient and elevated pressure

Revealing complex relaxation behavior of monohydroxy alcohols in a series of octanol isomers

Glass spectrum, excess wing phenomenon, and master curves in molecular glass formers: A multi-method approach

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