ISO 19403-4:2024

Overview

ISO 19403-4:2024 specifies an optical test method to determine the polar and dispersive fractions of a liquid’s surface tension by measuring an interfacial tension with a reference liquid. Using pendant or ascending drops analyzed by drop contour imaging, the method derives polar/dispersive components (e.g., via Owens–Wendt–Rabel–Kaelble or Wu approaches) to characterize liquid coatings and other fluids where conventional measurements may be affected by drying or surface activity.

Keywords: ISO 19403-4, wettability, surface tension, polar and dispersive fractions, interfacial tension, drop contour analysis, pendant drop.

Key topics and technical requirements

• Principle: Create a pendant/ascending drop of the test liquid inside an optical cell filled with a reference liquid and compute interfacial tension from the drop shape using the Young–Laplace equation (see ISO 19403-1).
• Apparatus: State-of-the-art drop contour analysis system with digital imaging, dosing unit (needle OD 0.5–2.5 mm), and an optical cell with plane parallel walls (wall thickness < 2 mm).
• Reference liquids: Chemically homogeneous, strictly dispersive, transparent liquids (recommended n-alkanes such as n-decane, n-dodecane or perfluoroalkanes like n-perfluorohexane). Cleaned n-alkanes should show interfacial tension vs water ≥ 52 mN/m; recommended perfluoroalkanes ≥ 54 mN/m.
• Test conditions & sampling: Tests at (23 ± 2) °C; representative sampling per ISO 15528. Equilibration time may be needed to avoid convection or dissolution effects.
• Calculations: Determination of dispersive/polar fractions using established models (Owens–Wendt–Rabel–Kaelble, Wu) and reporting of densities, needle dimensions, and measured interfacial tension.
• Limitations: Restrictions apply for liquids with non‑Newtonian behavior (see ISO 3219‑1:2021).

Practical applications and users

• Who uses it:
  • Paint, varnish and coating R&D and QC laboratories
  • Surface science and interfacial characterization labs
  • Formulation scientists evaluating wetting, spreading and adhesion
  • Instrument manufacturers and suppliers of drop contour analysis systems
• Why it’s useful:
  • Characterizes liquid coating materials where drying or volatiles affect other methods
  • Provides component-level insight (polar vs dispersive) for adhesion promotion, substrate selection, and surface treatment optimization
  • Useful for troubleshooting wetting issues in coatings, inks and adhesives

Related standards

• ISO 19403-1 - Vocabulary and general principles (wettability)
• ISO 19403-3 - Surface tension by pendant drop method
• ISO 19403-5 - Measurements on reference surfaces
• ISO 3219-1 - Definitions on non-Newtonian behaviour
• ISO 15528 - Sampling of liquid coatings
• ISO 4618, ISO 1409, EN 14370 - referenced normative documents

This standard is essential when accurate decomposition of surface tension into polar and dispersive contributions is required for coatings and liquid-surface interactions, especially when optical pendant/ascending drop measurement avoids artifacts from drying or volatile loss.