Overview
ISO 7392:2024 - Fine bubble technology - Evaluation method for determining surface tension of ultrafine bubble dispersions - specifies standardized procedures to measure the surface tension of ultrafine bubble (UFB) dispersions in water. The standard adopts three widely available, sensitive measurement methods - Wilhelmy, du Noüy and the pendant drop method - and addresses practical testing, sample handling and reporting to ensure reliable, comparable results for UFB systems, including liquids that contain UFBs in dilute surfactant solutions (see Annex D).
Key topics and technical requirements
- Measurement methods: Procedures and apparatus guidance for the Wilhelmy, du Noüy and pendant drop methods, chosen for sensitivity to the small surface-tension changes caused by UFBs and broad instrument availability.
- Apparatus and cleanliness: Recommendations on instrument selection (tensiometers and optical profilometry), choice of measuring units (plate, ring, needle) and strict cleaning routines (e.g., ethanol immersion and heating for plate/ring; detergent rinse for cups/syringes) to avoid contamination that can mask UFB effects.
- Sample handling: Use airtight containers without an air–liquid interface, gentle pouring/syringing to avoid altering UFB populations, and gentle rolling to maintain homogeneity.
- Environmental control: Measurements in a temperature-controlled room; sample temperature measured immediately before testing (accuracy 0.1 °C) and kept within ±2 °C during replicated tests.
- Blank correction: Mandatory measurement of blank water to quantify the explicit influence of UFBs (subtract blank water results from sample results).
- Calculations and software: Use manufacturer-supplied software for pendant drop optical profilometry; Wilhelmy/du Noüy calculations per ISO 304:1985 when needed.
- Test report content: Instrument model and software version, needle specification (pendant drop), water properties (pH, conductivity), temperature and droplet retention time, results, and any factors influencing the outcome.
Practical applications
- Evaluating UFB performance in cleaning, desalting, machining coolant and detergent formulations.
- Product development and QC for appliances integrating UFB generation (e.g., showerheads, washers).
- Research on UFB mechanisms (bubble–substrate interactions) and optimization of surfactant–UFB combinations.
- Environmental and civil engineering applications where UFBs assist contaminant removal.
Who should use this standard
- R&D laboratories and materials scientists studying fine/ultrafine bubbles
- Quality control teams in detergents, coolants and appliance manufacturing
- Instrument manufacturers and metrology labs validating tensiometers
- Regulatory or standards bodies establishing UFB performance criteria
Related standards
Keywords: ISO 7392:2024, ultrafine bubble (UFB), surface tension measurement, Wilhelmy method, du Noüy method, pendant drop method, fine bubble technology, tensiometer, UFB dispersion.
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