Term: persistence length https://doi.org/10.1351/goldbook.P04515 Definition: The average projection of the end-to-end vector on the tangent to the chain contour at a chain end in the limit of infinite chain length. The persistence length (symbol a) is the basic characteristic of the worm-like chain. Related Terms: 1) chain length (http://doi.org/10.1351/goldbook.C00956). 2) worm-like chain (<em>in polymers</em>) (http://doi.org/10.1351/goldbook.W06692). Source: Purple Book, 1st ed., p. 51 (http://old.iupac.org/publications/books/author/metanomski.html) Citation: 'persistence length' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04515 License: 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. Disclaimer: 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.