ISO 19403-5:2017

Overview

ISO 19403-5:2017 - part of the ISO 19403 series on wettability - specifies an optical test method to determine the polar and dispersive fractions of the surface tension of liquids from contact-angle measurements on a solid that has only a dispersive contribution to its surface energy. The standard is intended primarily for the characterization of liquid coating materials and assumes the liquid’s surface tension and the reference solid’s surface free energy are known. Applicability can be restricted for liquids with non-Newtonian rheology.

Key topics and requirements

• Principle (stepwise):
  • Measure the liquid’s total surface tension (e.g., per ISO 19403-3, EN 14370 or ISO 1409).
  • Determine the reference solid’s surface free energy (ISO 19403-2).
  • Measure the contact angle of the test liquid on the dispersive reference solid (ISO 19403-2).
  • Calculate the dispersive fraction using either Owens–Wendt–Rabel–Kaelble (OWRK) or Wu methods.
  • Calculate the polar fraction as total surface tension minus dispersive fraction.
• Reference solids: Use chemically and topologically homogeneous dispersive materials (examples: PTFE or paraffin). Preferred reference surface roughness R < 0.3 µm. PTFE and paraffin have recommended surface free energy target values (see standard).
• Test conditions: Conduct tests at (23 ± 2) °C and relative humidity (50 ± 5) %.
• Precision guidance: Typical tolerances specified - surface tension ±1%; reference solid surface free energy preferably 0.3 mJ/m² (not exceeding 0.5 mJ/m²); contact-angle repeatability for static method ~1° and dynamic ~3°.
• Reporting: Detailed test-report requirements (identification, methods used, number of drops, drop volumes/dosing speed, device type, results with mean and standard deviation, calculation method-OWRK or Wu, deviations).

Applications and users

ISO 19403-5 is used where knowledge of liquid wettability and surface-energy components is critical:

• Coatings and paints formulators assessing wetting behavior on low-energy substrates
• Surface scientists and R&D laboratories studying liquid–solid interactions
• Quality control and characterization labs verifying coating performance or surface treatments
• Manufacturers of adhesives, inks, lubricants and cleaning agents where polar/dispersive balance affects spreading and adhesion

Keywords: ISO 19403-5, wettability, surface tension, contact angle, polar fraction, dispersive fraction, OWRK method, Wu method, PTFE reference, coating materials.

Related standards

• ISO 19403-1 (terminology and general principles)
• ISO 19403-2 (determination of surface free energy of solids by contact angle)
• ISO 19403-3 (surface tension of liquids - pendant drop method)
• EN 14370, ISO 1409 (alternative surface-tension methods)

This standard provides a reproducible approach to partition liquid surface tension into polar and dispersive components, enabling more reliable assessment of wetting and adhesion performance in coatings and surface engineering.