Relaxation of glasses: The Kohlrausch exponent

Rault, J.

doi:10.1016/j.jnoncrysol.2010.08.031

Cited by 15 publications

(23 citation statements)

References 29 publications

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“…The reaction of sample polarization to a change in the electric field is delayed, which can be observed as a relaxation process with characteristic relaxation time. In polymers, two or three relaxation processes are most often observed, which are denoted with greek letters α, β, γ [24][25][26][27][28][29][30]. The (structural) α-process usually corresponds to the glass transition.…”

Section: Introductionmentioning

confidence: 99%

“…The α-process is among the slowest ones in polymers, the processes appearing at higher frequencies are customarily described as β-, γ-processes. At present, it is believed that β-process reflects rotational motions of polar group fragments containing single bonds, inside the molecule [26][27][28]. These motions can be treated as more or less free rotations of dipolar groups.…”

Section: Introductionmentioning

confidence: 99%

“…The α-and β-processes exhibit different temperature dependencies. The relaxation time of the process (β, γ) can usually be described with the Arrhenius formula [26][27][28][29][30]:…”

Section: Introductionmentioning

confidence: 99%

“…To describe dynamic properties of glass -e.g. the structural (α) relaxation time -an empirical formula proposed by Vogel, Tammann and Fulcher (VTF) is used [26][27][28][29][30]:…”

Section: Introductionmentioning

confidence: 99%

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Liquid crystal epoxy resins based on biphenyl group cured with aromatic amines - studied by dielectric spectroscopy

et al. 2013

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In this paper we investigate the dielectric response of cured epoxy resins based on biphenyl group. We chose two monomers, which were earlier synthesised, containing the same mesogen but with long and short symmetric tails. They were cured with standard amines (DDM, DMAP). Firstly we optimised conditions of the curing process by dielectric and optical observation in situ. Small differences in the dynamics of the curing process were observed in different mixtures. For the four selected products we made dielectric measurements in a wide range of frequency and temperature. Although, generally, dielectric response is similar in all the cured materials, differences can be seen in the details. At lower temperatures, quite strong relaxation process is seen in all products, its low activation energy points towards a β-process, which appears in many polymers. The Havriliak-Negami formula was fitted to the data and characteristic parameters of the observed relaxation processes were compared in detail. In some cases the α-process also appears. We conclude how the longer spacer and the type of curing process influence the electrical properties of the resin.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…The α-and β-processes exhibit different temperature dependencies. The relaxation time of the process (β, γ) can usually be described with the Arrhenius formula [26][27][28][29][30]:…”

Section: Introductionmentioning

confidence: 99%

“…To describe dynamic properties of glass -e.g. the structural (α) relaxation time -an empirical formula proposed by Vogel, Tammann and Fulcher (VTF) is used [26][27][28][29][30]:…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Liquid crystal epoxy resins based on biphenyl group cured with aromatic amines - studied by dielectric spectroscopy

et al. 2013

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“…These parameters, describing the electrical behavior of the sample, can also be linked with some mechanical properties. For example, in polymers, at least two relaxation processes (denoted with Greek letters α and β) are most frequently observed [15][16][17][18][19][20][21]. The structural α-process usually corresponds to the glass transition.…”

Section: Introductionmentioning

confidence: 99%

Curing Reaction and Dielectric Properties of Rigid and Elastic Liquid Crystal Epoxy Networks Modified with Nanofillers

Włodarska

2018

International Journal of Polymer Science

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The aim of the paper is to compare the progress of the curing reaction and the dielectric properties of liquid crystalline epoxy networks of different elasticity and to investigate how modification with nanofillers influences their properties. The study focuses on a liquid crystalline epoxy monomer with four aromatic rings in the mesogen, cross-linked with 4,4′-diaminodiphenylmethane (DDM) and pimelic acid (PA) to produce rigid and elastic polymer networks. The obtained results are compared to networks modified with nanofillers (diphenyl aluminum phosphate nanorods). The curing process is monitored in situ with broadband dielectric spectroscopy, which is a good tool to view the progress of the reaction. Two stages with different reaction dynamics are observed in the studied cases. Dielectric properties of the products cured with two chosen agents show significant differences in the obtained parameters (activation energy, glass transition, and fragility index) as well as in the dynamics of the α and β relaxations. Although the curing agent is the main factor determining the properties of the product, the nanofiller additive also modifies the values of specific parameters that characterize both the process of the reaction and the properties of the final composites. Particularly, adding the nanofiller raises the glass transition temperature in both the cases. The obtained results are in good agreement with the earlier calorimetric study.

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Changes in molecular relaxations and network properties of a triaromatic liquid crystal epoxy resin with nonterminal functional groups

Włodarska,

Mossety‐Leszczak,

Kisiel

et al. 2023

Journal of Polymer Science

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Two types of liquid crystal epoxy precursors and corresponding epoxy‐amine networks are investigated in this paper. The epoxy groups are non‐terminal in one of the monomers (NTEM) and terminal in the other one (MU22). Both monomers contain the same mesogen and exhibit liquid crystal properties. Structural differences between the carbon chains affect physical properties of the monomers and the products of curing, which involves a typical diamine—DDM (4,4′‐diaminodiphenylmethane). Phase transition temperatures, conditions of the curing reaction and glass transition temperatures in the cured products are determined through differential scanning calorimetry (DSC), optical observations (POM) and broadband dielectric spectroscopy (BDS). The modification of the carbon chains affects the phase transition temperatures, dielectric response, and the glass transition in the cured products. The dielectric response of NTEM monomer reveals two relaxation processes (β and γ) associated with molecular motions of polar groups in the mesogen (β‐process) and in the carbon chains (γ‐process). In contrast, MU22 only displays a similar β‐process. A segmental α‐process related to structural reorientation (connected with glass transition) appears in both cured products, but in NTEM the glass transition temperature is significantly lower. Local relaxations in the epoxy networks match the corresponding processes in their respective precursors.

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Relaxation of glasses: The Kohlrausch exponent

Cited by 15 publications

References 29 publications

Liquid crystal epoxy resins based on biphenyl group cured with aromatic amines - studied by dielectric spectroscopy

Liquid crystal epoxy resins based on biphenyl group cured with aromatic amines - studied by dielectric spectroscopy

Curing Reaction and Dielectric Properties of Rigid and Elastic Liquid Crystal Epoxy Networks Modified with Nanofillers

Changes in molecular relaxations and network properties of a triaromatic liquid crystal epoxy resin with nonterminal functional groups

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