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How to Distinguish Nonexponentiality and Nonlinearity in Isothermal Structural Relaxation of Glass-Forming Materials
1Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, Pardubice 532 10, Czech Republic.
The Journal of Physical Chemistry. B
|August 8, 2024
Summary
Structural relaxation in glass-forming materials exhibits nonexponentiality and nonlinearity, which can be separated using temperature jump experiments. A new method estimates parameters for nonexponentiality (ß) and nonlinearity (σ) in materials.
Area of Science:
- Materials Science
- Physical Chemistry
- Condensed Matter Physics
Background:
- Structural relaxation in glass-forming materials is characterized by nonexponentiality and nonlinearity.
- These properties are often intertwined and difficult to decouple.
- Understanding these features is crucial for predicting material behavior over time.
Purpose of the Study:
- To separate and quantify nonexponentiality and nonlinearity in structural relaxation.
- To propose a simple method for estimating material parameters related to these phenomena.
- To analyze the asymmetry of approach to equilibrium after temperature jumps.
Main Methods:
- Utilizing temperature down-jump and up-jump experiments of equal magnitude.
- Quantifying isothermal structural relaxation using the stabilization period (log(t_m/t_0)).
- Formulating the material parameter σ for phenomenological models.
Main Results:
- A method is proposed to describe relaxation as a sum or difference of nonexponentiality (1.181/ß) and nonlinearity ((σ/2.303)ΔT) terms.
- The material parameter σ quantifies relaxation time variation with structural changes.
- The method was tested on experimental and calculated data for polymers and other glass-formers.
Conclusions:
- Temperature jump experiments offer a way to distinguish between nonexponentiality and nonlinearity in structural relaxation.
- A straightforward method for estimating key material parameters (ß and σ) is presented.
- This approach aids in understanding structural relaxation kinetics for material design and aging evaluation.
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