Title: enthalpy relaxation
Long Title: IUPAC Gold Book - enthalpy relaxation
DOI: 10.1351/goldbook.12765
Status: current

Definition
Enthalpy change observed near the glass transition when a sample is heated at a rate different from that at which it was cooled down, or observed after annealing in the glassy state below the glass-transition temperature.

Notes
1) Enthalpy relaxation is caused by the transformation of a glassy material to a more stable glass.
2) Enthalpy relaxation can be described by the Kohlrausch–Williams–Watts equation.
3) Moduli, stress–strain behaviour, and molecular motions are affected by enthalpy relaxation.
4) Enthalpy relaxation reflects physical aging.

Related Terms
- Kohlrausch–Williams–Watts equation: https://goldbook.iupac.org//terms/view/12778
- glassy state: https://goldbook.iupac.org//terms/view/12774

Source
- PAC, 2013, 85, 1017. 'Glossary of terms relating to thermal and thermomechanical properties of polymers (IUPAC Recommendations 2013)' on page 1026 (https://doi.org/10.1351/PAC-REC-12-03-02)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/12765/html
- json: https://goldbook.iupac.org/terms/view/12765/json
- xml: https://goldbook.iupac.org/terms/view/12765/xml

Citation: Citation: 'enthalpy relaxation' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.12765
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Accessed: 2026-04-18T06:00:26+00:00