Materials scienceLesson 3 of 4 in the course Polymers

Glass Transition: Measurement, Molecular Dynamics, and Materials Applications

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson introduces the glass transition, the difference between glassy and rubbery behavior, and the meaning of glass-transition temperature.

The glass transition is a gradual, reversible change in an amorphous material from a hard, relatively brittle state to a softer, viscous or rubbery state as temperature increases. It can also occur in the amorphous regions of a semicrystalline material. An amorphous solid that exhibits this behavior is called a glass.

All flashcards

What is the glass transition?
A gradual change in an amorphous material between relatively hard, brittle behavior and softer, viscous or rubbery behavior.
What is vitrification?
Cooling a viscous liquid into a glassy state without requiring it to crystallize.
What is glass-forming ability?
A material’s tendency to form a glass when quenched rather than crystallizing.
What is dynamic heterogeneity near the glass-transition range?
The coexistence of relatively mobile regions and regions that are much less mobile.
What processing window do bulk metallic glasses have?
Between TgT_g and TxT_x, they are supercooled liquids that can be shaped before crystallizing.

Quiz questions

  1. How does the glass transition differ from crystallization?Answer: It is a broad, dynamic change in behavior rather than a first-order transition with discontinuities in properties.
  2. What change does differential scanning calorimetry commonly use to identify TgT_g?Answer: A change in heat capacity or its associated energy response during heating.
  3. What does dynamic heterogeneity mean in a material near its glass-transition range?Answer: Regions with different levels of molecular mobility coexist within the material.
  4. How does time–temperature superposition construct a master curve?Answer: It horizontally shifts measurements from different temperatures to a common reference temperature.
  5. What transition behavior is commonly observed in miscible and immiscible polymer blends?Answer: Miscible blends commonly show one glass transition, while immiscible blends can show multiple transitions.

Based on the Wikipedia article Glass transition, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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