Title: characteristic length
Long Title: IUPAC Gold Book - characteristic length
DOI: 10.1351/goldbook.C00977
Status: current

Definition
The term characteristic length or scale refers, in general, to the parameter which characterizes the density profile (of a given physical quantity). The static (equilibrium) or dynamic character of a characteristic length must be specified. The terms out of plane and in plane refer to characteristic lengths normal or parallel to the interface, respectively. Since interfacial layer 'thickness' and characteristic length correspond to various concepts, the current usage where an out of plane characteristic length is referred to as the interfacial layer thickness, is confusing and should be abandoned.

Related Terms
- interface: https://goldbook.iupac.org//terms/view/I03082
- interfacial layer: https://goldbook.iupac.org//terms/view/I03085

Source
- PAC, 1994, 66, 1667. 'Thin films including layers: terminology in relation to their preparation and characterization (IUPAC Recommendations 1994)' on page 1674 (https://doi.org/10.1351/pac199466081667)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/C00977/html
- json: https://goldbook.iupac.org/terms/view/C00977/json
- xml: https://goldbook.iupac.org/terms/view/C00977/xml

Citation: Citation: 'characteristic length' 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.C00977
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Accessed: 2026-06-04T11:32:17+00:00