12765 IUPAC Gold Book - enthalpy relaxation 10.1351/goldbook.12765 12765 current 1 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. Enthalpy relaxation is caused by the transformation of a glassy material to a more stable glass. Enthalpy relaxation can be described by the Kohlrausch–Williams–Watts equation. Moduli, stress–strain behaviour, and molecular motions are affected by enthalpy relaxation. Enthalpy relaxation reflects physical aging. Kohlrausch–Williams–Watts equation https://goldbook.iupac.org//terms/view/12778 glassy state https://goldbook.iupac.org//terms/view/12774 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) https://goldbook.iupac.org/terms/view/12765/html https://goldbook.iupac.org/terms/view/12765/json https://goldbook.iupac.org/terms/view/12765/plain 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 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-04-18T06:01:11+00:00