Relaxation Processes in Liquids and Glass-Forming Systems: What Can We Learn by Comparing Neutron Scattering and Dielectric Spectroscopy Results?

AbstractNon-linear dielectric spectroscopy (NLDS) is employed as an effective tool to study relaxation processes and phase transitions of a poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) relaxor-ferroelectric (R-F) terpolymer in detail. Measurements of the non-linear dielectric permittivity $${\varepsilon _{2}^{'}}$$ ε 2 ′ reveal peaks at 30 and 80$$\,^\circ$$ ∘ C that cannot be identified in conventional dielectric spectroscopy. By combining the results from NLDS experiments with those from other techniques such as thermally stimulated depolarization and dielectric-hysteresis studies, it is possible to explain the processes behind the additional peaks. The former peak, which is associated with the mid-temperature transition, is found in all other vinylidene fluoride-based polymers and may help to understand the non-zero $$\varepsilon _\mathrm {2}^{'}$$ ε 2 ′ values that are detected on the paraelectric phase of the terpolymer. The latter peak can also be observed during cooling of P(VDF-TrFE) copolymer samples at 100$$\,^\circ$$ ∘ C and is due to conduction and space-charge polarization as a result of the accumulation of real charges at the electrode–sample interface.

Download Full-text

Quasielastic Neutron Scattering: An Advanced Technique for Studying the Relaxation Processes in Condensed Matter

X-ray and Neutron Techniques for Nanomaterials Characterization ◽

10.1007/978-3-662-48606-1_14 ◽

2015 ◽

pp. 761-813 ◽

Cited By ~ 1

Author(s):

Madhusudan Tyagi ◽

Suresh M. Chathoth

Keyword(s):

Neutron Scattering ◽

Condensed Matter ◽

Relaxation Processes ◽

Advanced Technique ◽

Quasielastic Neutron ◽

Quasielastic Neutron Scattering

Download Full-text

A microscopic look at the Johari-Goldstein relaxation in a hydrogen-bonded glass-former

Scientific Reports ◽

10.1038/s41598-019-50824-7 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 2

Author(s):

F. Caporaletti ◽

S. Capaccioli ◽

S. Valenti ◽

M. Mikolasek ◽

A. I. Chumakov ◽

...

Keyword(s):

Time Domain ◽

Glassy State ◽

Center Of Mass ◽

Relaxation Processes ◽

Undercooled Liquid ◽

Microscopic Scale ◽

Glass Forming ◽

Full Explanation ◽

Molecular Scale ◽

Hydrogen Bonded

Abstract Understanding the glass transition requires getting the picture of the dynamical processes that intervene in it. Glass-forming liquids show a characteristic decoupling of relaxation processes when they are cooled down towards the glassy state. The faster (βJG) process is still under scrutiny, and its full explanation necessitates information at the microscopic scale. To this aim, nuclear γ-resonance time-domain interferometry (TDI) has been utilized to investigate 5-methyl-2-hexanol, a hydrogen-bonded liquid with a pronounced βJG process as measured by dielectric spectroscopy. TDI probes in fact the center-of-mass, molecular dynamics at scattering-vectors corresponding to both inter- and intra-molecular distances. Our measurements demonstrate that, in the undercooled liquid phase, the βJG relaxation can be visualized as a spatially-restricted rearrangement of molecules within the cage of their closest neighbours accompanied by larger excursions which reach out at least the inter-molecular scale and are related to cage-breaking events. In-cage rattling and cage-breaking processes therefore coexist in the βJG relaxation.

Download Full-text