ISO 19403-4:2017

Overview

ISO 19403-4:2017 - 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 a measured interfacial tension. The method uses pendant or ascending drops in a filled optical cell and drop contour analysis (Young–Laplace interpretation) to extract interfacial tension data. It is intended primarily for the characterization of liquid coating materials, especially when drying or evaporation effects occur during measurement, and assumes the surface tension of the test liquid and at least one suitable reference liquid are known. Applicability can be limited for non‑Newtonian liquids.

Key topics and technical requirements

• Principle: create a pendant/ascending drop of the test liquid inside a reference liquid and calculate interfacial tension from the drop shape using the Young–Laplace equation.
• Instrumentation: drop contour analysis system (digital image capture and analysis), dosing unit (needle 0.5–2.5 mm OD; straight or J-shaped), and an optically clear optical cell.
• Reference liquids: strictly dispersive, colorless hydrocarbons (e.g., n‑decane, n‑dodecane) or perfluoroalkanes (n‑perfluorohexane, n‑perfluorooctane) depending on solubility and contamination; cleaning and storage procedures are specified.
• Test conditions: perform measurements at (23 ± 2) °C, control vibrations/air flows and lighting, enter local gravity into software, allow equilibrium to avoid convection artifacts.
• Procedure essentials: sampling per ISO 15528, determine densities and density difference, produce sufficiently large drops, image capture and calibration, repeat measurements and calculate mean and standard deviation.
• Evaluation: calculation routes include Owens–Wendt–Rabel–Kaelble and Wu approaches to obtain dispersive and polar fractions from measured interfacial tensions.
• Documentation: precision, reporting requirements and traceability (saving original images) are addressed.

Applications and users

ISO 19403-4:2017 is useful for:

• Coatings and paints formulators assessing wettability and surface tension components of liquid coatings.
• Quality control and R&D laboratories measuring polar and dispersive surface tension fractions when evaporation or drying affects sessile-drop methods.
• Surface scientists, adhesives engineers, and material compatibility testing where interfacial behavior matters. Practical applications include optimizing primer/topcoat interactions, predicting spreading/adhesion, and screening solvents or additives for coating performance.

Related standards

• ISO 19403-1 (terminology and principles), ISO 19403-3 (pendant drop surface tension), ISO 19403-5 (dispersive reference surfaces)
• ISO 15528 (sampling), ISO 4618 (terms and definitions), ISO 1409, EN 14370

Keywords: ISO 19403-4:2017, wettability, surface tension, polar fraction, dispersive fraction, interfacial tension, drop contour analysis, pendant drop, coatings testing.