Overview
EN ISO 19403-4:2024 (Paints and varnishes - Wettability - Part 4) specifies an optical test method to determine the polar and dispersive fractions of the surface tension of liquids from an interfacial tension measurement. Published October 2024 and adopted by CEN, this standard updates the 2020 edition and is intended primarily for the characterization of liquid coating materials where alternative measurements may be affected by drying or evaporation.
Key topics and technical requirements
- Principle: Uses pendant or ascending drops imaged inside an optical cell filled with a reference liquid. The drop shape, analysed by the Young–Laplace equation, yields the interfacial tension from which surface energy components are calculated.
- Optical methods: Requires a state-of-the-art drop contour analysis system with digital image capture and analysis (lighting, dosing unit, optical cell, imaging/analysis unit).
- Apparatus specifics:
- Dosing unit and needles (straight or J-shaped) to produce drops that deviate from spherical shape; recommended needle outside diameters 0.5–2.5 mm.
- Optical cell wall thickness requirement reduced to 2 mm (updated in this edition).
- Reference liquids must be transparent (updated requirement).
- Data analysis: Calculation routes include Owens–Wendt–Rabel–Kaelble (OWRK) and Wu methods to derive dispersive and polar fractions from measured interfacial tensions and known reference liquid surface tensions.
- Procedure controls: Cleaning and conditioning of reference liquids, test conditions, sampling and repeatability requirements are specified.
- Limitations: Restrictions apply when testing non-Newtonian liquids (see ISO 3219-1:2021). The method assumes known surface tensions for both test and reference liquids.
Applications
- Quality control and R&D for paints, varnishes and liquid coatings to quantify surface energy components affecting wetting, adhesion and spreading.
- Situations where conventional surface tension tests fail due to drying/evaporation or where interfacial methods give more reliable results.
- Surface science and formulation development for improved substrate wetting, adhesion promotion, and coating performance optimization.
- Useful in laboratories performing surface energy and wettability testing, coating manufacturers, formulation chemists, and academic researchers.
Who should use this standard
- Coating formulators, QC laboratories, materials scientists, and surface analysis labs.
- Manufacturers and testers of paints, varnishes, adhesives and inks needing reproducible polar/dispersive surface energy data.
- Certification bodies and test houses applying ISO/CEN methods for comparative and regulatory testing.
Related standards (normative references)
Keywords: EN ISO 19403-4:2024, surface tension measurement, interfacial tension, polar dispersive fractions, drop contour analysis, pendant drop method, paints and varnishes, wettability standard.
