science

Johari–Goldstein relaxation

Johari–Goldstein relaxation is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Johari–Goldstein relaxation rather than just read about it. In short: Johari–Goldstein relaxation, also known as the JG β-relaxation, is a universal property of glasses and certain other disordered materials. Proposed in 1969 by Martin Goldstein, JG β-relaxation were described as a secondary relaxation mechanism required to explain the viscosity behavior of liquids approaching the glass transition in the potential energy landscape picture presented in Goldstein's seminal 1969 paper.

Key takeaways

Johari–Goldstein relaxation belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Johari–Goldstein relaxation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Johari–Goldstein relaxation from memory before moving on to harder problems.

Reference excerpt

Johari–Goldstein relaxation, also known as the JG β-relaxation, is a universal property of glasses and certain other disordered materials. Proposed in 1969 by Martin Goldstein, JG β-relaxation were described as a secondary relaxation mechanism required to explain the viscosity behavior of liquids approaching the glass transition in the potential energy landscape picture presented in Goldstein's seminal 1969 paper. Previous experiments on glass forming liquids showed multiple relaxation times present in liquids measured by time dependent compliance measurements. Gyan Johari and Martin Goldstein measured the dielectric loss spectrum of a set of rigid glass forming molecules to further test the hypothesis of Goldstein in 1969. The relaxation, a peak in mechanical or dielectric loss at a particular frequency, had previously been attributed to a type of molecular flexibility. The fact that such a loss peak shows up in glasses of rigid molecules lacking this flexibility demonstrated its universal character. The JG β-relaxation process is speculated to be a precursor of the structural α-relaxation, i.e., its occurrence facilitates viscous flow, however the microscopic mechanism of the β-relaxation has not been definitively identified.

Evidence for the universality and importance of the J. G. β-relaxation Johari determined the temperature dependence of the α-relaxation and β-relaxation as a function of frequency by measuring the dielectric loss ε″ as a function of frequency at multiple temperatures. They observed two peaks in the system with the lower frequency peak attributed to the structural α-relaxation and the higher frequency peak related to the fast (high frequency short time) β-relaxation. The peak in the high frequency ε″ response of the β-relaxation has also been shown to broaden and shift to lower frequencies. Furthermore, the α-relaxation peak changes more rapidly on cooling than the rate of JG β-relaxation, where the α-relaxation times diverge following the VFT law as glass transition temperature (Tg) is approached which is much faster than the Arrhenius temperature dependence observed for the peak in the β-relaxation curve over the same temperature ranges.

Relation to other relaxation mechanism The J.G. β-relaxation was developed based on the theoretical predictions of Martin Goldstein in his seminal 1969 paper discussing the potential energy landscape picture and activated energy barrier hopping for viscous liquids. These developments have often focused on understanding secondary relaxations below Tg that are present in small molecule and metallic glasses. Polymer glasses also show multiple relaxation mechanisms at temperatures below Tg, with β, γ, and δ relaxations having been measured well below Tg into the glassy state. However, the exact molecular mechanism for these relaxations is often subject to debate and how they may relate to J. G β-relaxations is not established by the literature.

References

Worked examples

Example 1 — a first encounter with Johari–Goldstein relaxation

Start with the simplest possible case. Write down what Johari–Goldstein relaxation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Johari–Goldstein relaxation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Johari–Goldstein relaxation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Johari–Goldstein relaxation

In research: Johari–Goldstein relaxation appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Johari–Goldstein relaxation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Johari–Goldstein relaxation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Critical phenomena, Glass, Phase transitions, so understanding it makes those chapters shorter.
In everyday life: Look for Johari–Goldstein relaxation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Johari–Goldstein relaxation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Johari–Goldstein relaxation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Johari–Goldstein relaxation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Johari–Goldstein relaxation in simple terms?

Why does Johari–Goldstein relaxation matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Johari–Goldstein relaxation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Johari–Goldstein relaxation.