Title: Flory–Fox assumption
Long Title: IUPAC Gold Book - Flory–Fox assumption
DOI: 10.1351/goldbook.12264
Status: current

Definition
Assumption that the Kirkwood–Riseman theory can be applied to linear isolated macromolecules in solution, independent of whether they are in the theta state.

Note
The Kirkwood–Riseman relationships between \(r_{D}\) and \(r_{\eta}\) and the root-mean-square radius of gyration, \(\lt\!s^{2}\!\gt\), are then \[r_{D} = 0.675 \lt\!s^{2}\!\gt^{1/2} = 0.675 \lt\!s_{\circ}^{2}\!\gt^{1/2} \alpha_{D}\] and \[r_{\eta} = 0.256 \lt\!s^{2}\!\gt^{1/2} = 0.256 \lt\!s_{\circ}^{2}\!\gt^{1/2} \alpha_{\eta}\] where \(r_{D}\) and \(r_{\eta}\) are the equivalent hydrodynamic radii in translational diffusive flow and viscous flow, and \(\alpha_{D}\) and \(\alpha_{\eta}\) are the corresponding expansion factors.

Related Terms
- Kirkwood–Riseman theory: https://goldbook.iupac.org//terms/view/12263
- equivalent hydrodynamic radii: https://goldbook.iupac.org//terms/view/12258
- root-mean-square radius of gyration: https://goldbook.iupac.org//terms/view/12191

Source
- PAC, 2015, 87, 71. 'Definitions of terms relating to individual macromolecules, macromolecular assemblies, polymer solutions, and amorphous bulk polymers (IUPAC Recommendations 2014)' on page 104 (https://doi.org/10.1515/pac-2013-0201)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/12264/html
- json: https://goldbook.iupac.org/terms/view/12264/json
- xml: https://goldbook.iupac.org/terms/view/12264/xml

Citation: Citation: 'Flory–Fox assumption' 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.12264
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Accessed: 2026-04-18T06:46:24+00:00