Contents
Partially compliant

ISO 27448: self cleaning performance of photocatalytic materials by water contact angle

ISO 27448 rates photocatalytic self cleaning by tracking the water contact angle while UV light breaks down an oleic acid film. The Dropometer reads that angle from 10° to 175° with ±0.35° accuracy, on a drop shape method validated in two peer reviewed papers. You supply the UV lamp and radiometer, and final angles below 10° need a goniometer that reads down to 0°.

What brings you here?

Who this is for
Makers of self cleaning materials such as glass, tiles, facade panels and photocatalytic coatings, and the labs that test them.
Compliance tier
Partially compliant: the Dropometer reads the water contact angle from 10° up. It has no UV source or radiometer and does not read below 10°.
Measurement
Sessile drop water contact angle, 10° to 175° range, ±0.35° accuracy (Dropometer datasheet).
Setup
About 2 minutes. Battery powered, 1 kg, sits next to your UV bench.
Last updated
October 20, 2026
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Free one page checklist for ISO 27448: what to prepare, the settings to lock, which part the Dropometer covers and what to record. Made for coating and glass labs.

Talk to an expert

Book a 15 minute demo on your coated sample

Tell us your coating, substrate and UV setup. We will show the measurement live and tell you plainly which part of ISO 27448 the Dropometer covers and which part it does not.

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View the official standard
Gurdeep-Saini-Photo
Written by
Gurdeep Singh Saini
Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.
COO at Droplet Lab
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Droplet-Lab logo
Technical Review by
Droplet Lab Team
Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.
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Verified against ISO 27448
Gurdeep-Saini-Photo
Written By

Gurdeep Singh Saini

COO at Droplet Lab

Holds a BASc in Mechanical Engineering from Ryerson University (now Toronto Metropolitan University) and an MASc from York University. He develops the automatic edge and baseline detection behind the Dropometer's analysis.

Droplet-Lab logo
Reviewed By

Droplet Lab Team

Droplet Lab builds precision instruments and software for surface science measurement, specialising in contact angle analysis and surface tension characterisation. Used by researchers across materials science, pharmaceuticals, coatings, and advanced manufacturing, Droplet Lab's Dropometer has contributed to studies published in peer-reviewed journals including Advanced Functional Materials (Impact Factor 19). The team combines instrument engineering with deep domain knowledge in wettability science with a focus on practical accuracy.

Featured Studies & Publications

Research Paper Contact angle measurement with a smartphone
Research Paper Surface tension measurement with a smartphone using a pendant drop

Evidence box

Standard

ISO 27448:2009, Fine ceramics (advanced ceramics, advanced technical ceramics): test method for self-cleaning performance of semiconducting photocatalytic materials, measurement of water contact angle. It is one of the ISO testing methods for photocatalytic materials from ISO/TC 206, alongside ISO 10678 for the photocatalytic activity of surfaces in an aqueous medium by degradation of methylene blue. ISO lists it as confirmed in 2020, with a later systematic review closed in March 2026.

Compliance tier

Partially compliant. The Dropometer reads the water contact angle from 10° to 175°. The method also needs UVA lamps at a set irradiance, a radiometer, an oleic acid coating step and a contact angle meter that reads down to 0°. The Dropometer provides none of the UV parts and does not read below 10°.

Instrument performance

Contact angle range 10° to 175°, accuracy ±0.35°, display resolution 0.01°, camera 10 frames per second, from the Dropometer product specification.

Peer reviewed method

The drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers. See our validation publications.

Customer evidence

We have no published client paper or case study on photocatalytic coatings to this method yet. For a related workflow, see self cleaning and anti soiling validation.

What it does not tell you

ISO describes the water contact angle as one factor in self cleaning performance. The final angle does not measure how fast the coating breaks down other soils. A methylene blue test to ISO 10678 measures photocatalytic activity in water, and other international standards cover air purification and antibacterial activity.

Executive summary

What this standard measures, who uses it and how the Dropometer fits

ISO 27448 rates the self cleaning performance of photocatalytic surfaces, such as titanium dioxide coated glass and tiles, by tracking the water contact angle while UV light breaks down an oleic acid film. Makers of self cleaning glass, facade panels, tiles and other building materials use it to compare the performance of photocatalytic materials across products and batches. The Dropometer is partially compliant: it reads the water contact angle from 10° to 175° with ±0.35° accuracy, but it has no UV source or radiometer, and it cannot read the near 0° angles that very active, superhydrophilic coatings reach.

The method cleans each specimen under UV, then coats it with oleic acid so the surface turns water repellent. It then irradiates the specimen with ultraviolet light (UVA) from a black light lamp, the UV light source, at a fixed irradiance and reads the water contact angle at five points at set intervals. The results are the final contact angle and the irradiation time taken to reach it.

The Dropometer contact angle and surface energy kit acts as the contact angle meter between UV exposures. Your own black light lamp and radiometer set the irradiance, and a goniometer that reads down to 0° covers final angles below 10°. For self cleaning products in the field, see self cleaning and anti soiling validation, including solar panels. For background, read the consumer products guide, or use the measurement method selector to pick a method.

Some self cleaning coatings work the other way: they are hydrophobic or superhydrophobic, so drops roll off and carry dirt away. That calls for a sliding angle, not this standard. See sliding angle measurement, the roll off and sliding angle glossary entry, reproducible sliding angle measurement and the roll off angle experiment on hydrophobic surfaces.

Further reading: water contact angle reference values for common surfaces, choosing a contact angle goniometer for ISO and GLP regulated, high throughput QC, and contact angle work on ski wax by a university lab, in the ski wax case study and our analysis of the ski wax and friction thesis. Those are water repellent surfaces, not photocatalytic coatings.

How the Dropometer fits the measurement of water contact angle

The ISO 27448 measurement, step by step, in our own words

From coated specimen to a final contact angle

These steps outline the procedure and show where the Dropometer fits and where other equipment takes over. They do not replace the standard. Buy the current edition and follow its specimen, irradiance, interval and reporting rules.

±0.35°

Contact angle accuracy

From the Dropometer product specification. Display resolution is 0.01°.

10° to 175°

Contact angle range

Covers the angle before UV and the fall to 10°. Final angles below 10° need a goniometer that reads to 0°.

About 2 min

Setup

Base plate, phone holder, LED and syringe. No PC needed. The UV lamp is yours.

1

Prepare and clean the specimens

Cut five flat specimens to the size the standard specifies and handle them with clean gloves. Clean each one under UV for the time and irradiance the standard specifies, using your own black light lamp and radiometer. The Dropometer has no UV source.

2

Apply the oleic acid film

Coat each specimen with oleic acid by one of the two routes the standard gives: dip coating from a dilute solution in n-heptane, then oven drying, or wiping on a weighed amount by hand. Record which route you used, because it sets the UV irradiance for the test.

3

Read the angle before UV

Level the base plate, mount the phone and LED, and fill the syringe with distilled water. Set the automatic dropper to one fixed drop volume and keep it for the whole test. Read the angle at five points, at the time after placement the standard specifies. The mean must be 20° or more for a valid test.

4

Irradiate under your UV lamp

Place the specimen under your black light lamp at the irradiance the standard sets for your oleic acid route, checked at the specimen surface with your radiometer. Keep the room inside the temperature and humidity band the standard specifies, and record both.

5

Read the angle at each interval

At each interval, move the specimen to the Dropometer, read five points and return it to the lamp. Automatic edge and baseline detection gives the same reading from the same image. Once readings approach 10°, plan to confirm on a goniometer that reads down to 0°.

6

Find the final angle and report

Stop when three consecutive means vary by 10% or less, or when the angle reaches 5° or less. Report the final angle, UV time, lamp, irradiance, oleic acid route and room conditions. State any reading taken on a second instrument. For field checks after the lab test, see self cleaning and anti soiling validation.

7

Watch the full measurement

This video shows a complete Dropometer contact angle measurement, from setup to result. It covers the steps above in one run.

Dropometer contact angle measurement, start to finish.

Validated measurement approach

Independent benchmarking and publication-based validation references.

Peer reviewed method

The Dropometer drop shape method is validated against a KRUSS DSA100E in two peer reviewed papers, one in Review of Scientific Instruments and one in Colloids and Surfaces A. The product specification gives a contact angle accuracy of ±0.35°.

Read the validation papers

Customer evidence

We have no published client paper or case study on photocatalytic coatings to ISO 27448 yet. The self cleaning use case shows how water contact angle checks fit coating validation for glass and solar panels.

Read the use case

Set limits for your photocatalytic materials

ISO 27448 · final contact angle · photocatalytic coating QC

ISO 27448 reports the final contact angle and the UV time to reach it for each specimen. The test is valid only if the mean angle before UV is 20° or more. You stop when three consecutive readings have a coefficient of variation of 10% or less, or when the angle reaches 5° or less (source: TCVN 8556:2010, the national adoption of ISO 27448:2009).

We found no pass or fail angle in the published summaries of the method. In a 2023 benchmark of industrial and experimental materials, the most active of the titanium dioxide photocatalytic films reached a final angle of 16 ± 4° after 20 min of UV, and other products took 360 and 3000 min (source: Peeters, Lenaerts and Verbruggen, Materials, 2023). That spread shows why limits must come from your own product.

Set your accept limit from a correlation study. Test coatings that stayed clean in field exposure and coatings that did not, then pick the final angle and UV time that separate them. Repeat the study when you change the coating, the substrate or the lamp.

Example output: water contact angle under UV

Example data for illustration only. These are not measured results. Your own coating, lamp and limits decide the numbers.

Example: three coated glass specimens, oleic acid by dip coating, UV at 1.0 mW/cm²

Specimen Angle before UV (°) Angle at 24 h UV (°) Final angle (°) CV of last 3 (%) Decision
Coating A, final at 72 h71.216.415.46.0Accept
Coating B69.8Below 10Below 10n/aBelow Dropometer range: confirm on a goniometer that reads to 0°
Coating C, final at 72 h73.558.454.07.4Above limit: hold the batch

How to read this table

Each value is the mean of five drop positions on one specimen. The decision column uses an example accept limit of a final angle of 20° or lower within 72 h of UV, set from a field correlation study. Readings below 10° are outside the Dropometer range, so no number is shown.

Example output chart

The same example data as the table, plotted over 72 h of UV. Coating B has no points after 8 h because its angle fell below the Dropometer's 10° lower limit.

Line chart of example water contact angles over 72 hours of UV on three coated glass specimens, with one coating levelling at about 15 degrees, one falling below the Dropometer's 10 degree limit and one levelling at 54 degrees

Example data, not measured results.

Business impact

What changes when the contact angle meter sits next to your UV bench

Metric Before Dropometer With Dropometer Results
Where the angle is read Shared lab goniometer, away from the UV bench Next to the UV bench, on battery for up to 8 h Dropometer product specification
Result format Water beading judged by eye An angle per drop from 10° to 175°, ±0.35° accuracy Dropometer product specification
Record Operator note Drop image and angle saved per reading No published benchmark
Final angles below 10° Goniometer that reads to 0° Still needs that goniometer Dropometer product specification

See the measurement on your own coating

Bring a coated specimen that cleaned well in the field and one that did not. We will read the water contact angle on both live.

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ROI estimate

Estimate the cost of the coating failures this test can catch

Enter your own numbers. The defaults are examples, not Droplet Lab results.

Quality cost snapshot

Estimate what wetting related failures cost you.

Example only. Use what you see in a trial on your own samples.
Your own figure.
Your own estimate.

Result

~0
Estimated annual cost today
~0
Estimated annual cost avoided
~0
Payback period

Annual exposure combines audit/CAPA cost, customer rejections, and recall probability; avoided exposure applies the risk reduction percentage.

Method settings: ultraviolet light, drop and timing

Lock these before you compare coatings, batches or labs

Parameter Recommended Setting Technical Rationale
Test liquid Distilled water This is a water contact angle method.
Drop volume One fixed volume, reported A 2023 benchmark notes the standard does not set a drop volume; its authors used 4 µL. The automatic dropper doses down to 0.05 µL.
Reading time As the standard specifies, a few seconds after placement At 10 frames per second the Dropometer suits a fixed reading time of this length.
Positions and specimens Five points per specimen, five specimens The final angle is set per specimen from the mean of five points.
UV irradiance 1.0 or 2.0 mW/cm², from your own lamp and radiometer The UV irradiation level depends on the oleic acid route (TCVN 8556:2010). The Dropometer has no UV source.
Stop rule CV of three consecutive means 10% or less, or angle 5° or less The Dropometer cannot confirm the 5° point. Readings below 10° need a goniometer that reads to 0°.
Fit model Young-Laplace or polynomial, the same for every reading Both models are in the Dropometer software. Low angles give flat drops, so keep one model per study.
Environment 23 ± 5 °C and 40 to 70% RH; record both Conditions from TCVN 8556:2010. The Dropometer runs at 10 to 45 °C and has no temperature or humidity control.

Is ISO 27448 the right test, or methylene blue to ISO 10678?

Pick the method by the question you need answered

Start: How does your coating keep itself clean?

Water spreads as UV cleans the surface

Signals:

Your coating is a UV active photocatalyst, such as titanium dioxide, and its final angle stays at 10° or above.

Rule-out:

Use ISO 27448, this page. The Dropometer is partially compliant: it reads the angles and your own UV lamp and radiometer run the exposure.

Final angle near 0°

Signals:

Your coating turns superhydrophilic, or you must confirm the 5° stop point.

Rule-out:

Use ISO 27448 with a goniometer that reads down to 0° for the final readings. The Dropometer covers the earlier readings from 10° up.

Drops roll off and carry dirt away

Signals:

Your coating is water repellent and cleans by roll off, not by UV.

Rule-out:

Use a sliding angle test such as ISO 19403-7. See sliding angle measurement.

Photocatalytic activity, not wetting

Signals:

You need to know how fast the coating breaks down a dye in water.

Rule-out:

Use the methylene blue test to ISO 10678. The Dropometer does not run that test.

Decision tree at a glance

Start from how your coating cleans itself. Blue boxes are measurements the Dropometer runs; for ISO 27448 that is the angle reading from 10° up, with your own UV lamp.

Decision tree for choosing between ISO 27448 angle readings on the Dropometer, ISO 27448 with a goniometer that reads to 0 degrees, a sliding angle test and the ISO 10678 methylene blue test

Is ISO 27448 the right test?

Interpreting the falling water contact angle

What the falling angle tells you, and what it does not

A falling angle means the film is breaking down: Oleic acid makes the surface hydrophobic. As UV and the photocatalyst break the film down by photodegradation, the surface turns hydrophilic, each water droplet spreads and the angle falls.
The plateau is the result: The final angle and the UV time to reach it rate the coating. A faster fall to a lower plateau points to stronger self cleaning activity.
Below 10° needs a second instrument: A reading that leaves the Dropometer range is a sign of strong activity, but the final value must come from a goniometer that reads to 0°.
Wetting is one factor: ISO treats the water contact angle as one factor in self cleaning. Pair it with field exposure or a methylene blue test.
Expert perspective

Why one contact angle is not the whole self cleaning story

Wettability is set by the top five to ten ångström of a surface: what the liquid actually sees. It doesn't matter what lies beneath; that outermost layer is what you are really measuring.

Dr. Alidad Amirfazli

Department of Mechanical Engineering, York University, Co-founder and Scientific Advisor, Droplet Lab

Common pitfalls and limits for semiconducting photocatalytic coatings

Honest limits of the method and of the Dropometer

The Dropometer reads from 10°. It cannot confirm the 5° stop point or report a final angle below 10°.
The Dropometer has no UV source or radiometer. A drifting lamp changes the illumination and the UV time to the final angle, so check irradiance at the specimen surface.
The Dropometer has no temperature or humidity control. Condition specimens and test in a room inside the band the standard specifies, and record it.
Each move between lamp and stage risks contamination. Wear clean gloves and keep fingers off the test area.
The method excludes porous, rough, highly water repellent and visible light active materials. Indoor light photocatalysts have their own standard, ISO 19810.
FAQ

Frequently asked questions

What does ISO 27448 measure?

It measures how the water contact angle on a photocatalytic surface falls under UV light, after the surface is coated with oleic acid. The final contact angle and the UV time to reach it rate self cleaning performance. It is aimed at semiconducting photocatalytic materials such as titanium dioxide, the semiconductor behind most self cleaning glass.

Can the Dropometer run ISO 27448?

In part. The Dropometer reads the water contact angle from 10° to 175° with ±0.35° accuracy, so it covers the angle before UV and the fall to 10°. It has no UV source or radiometer, so you supply the black light lamp. Final angles below 10°, and the 5° stop point, need a goniometer that reads down to 0°.

What happens when the angle falls below 10° in an ISO 27448 test?

The reading leaves the Dropometer range. Move the specimen to a goniometer that reads down to 0° for the remaining readings, and report which instrument gave the final angle. Not every coating gets there: a 2023 benchmark reported a final angle of 16 ± 4° for its most active titanium dioxide film.

What UV light does ISO 27448 call for?

A fluorescent black light lamp giving UVA between 300 and 400 nm, with a peak near 351 nm. The irradiance at the specimen is 1.0 or 2.0 mW/cm², depending on how the oleic acid was applied (source: TCVN 8556:2010, the national adoption of ISO 27448:2009). Check it with a calibrated radiometer. Other light sources, including visible light lamps, fall outside this method.

Which materials does ISO 27448 not cover?

Water permeable substrates, rough surfaces that hide the drop, highly hydrophobic materials, granular materials and visible light sensitive photocatalysts. For indoor light photocatalysts, see ISO 19810. For water repellent coatings that clean by roll off, see ISO 19403-7.

Is a low water contact angle the same as a self cleaning surface?

No. A low angle shows the oleic acid film has broken down and water spreads. It does not show the full self cleaning properties of the coating: how it handles real soil, rain or abrasion. Use the angle to compare coatings and batches, and set limits from field exposure on your own product.

Which ISO standard covers photocatalysis besides ISO 27448?

ISO 27448 is the ISO test for self cleaning by water contact angle measurements. Other ISO standards from the same committee rate photocatalysis in other ways: ISO 10678 by degradation of methylene blue in water, and separate standards cover air purification and antibacterial activity. Each rates a different property, so a coating can do well on one and poorly on another. The Dropometer runs only the contact angle part.

Legal note

This page summarises ISO 27448 in our own words and does not reproduce the standard. Buy the current edition from ISO before you write a procedure. The Dropometer is partially compliant with this method. Droplet Lab does not certify compliance. Your own method validation does.

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How this page was created

Sources, review and tools

Transparency 4 checklist items
01

Sources

ISO 27448:2009 listing (ISO); ISO 27448:2009 sample pages (iTeh); TCVN 8556:2010, national adoption of ISO 27448:2009; Peeters, Lenaerts and Verbruggen, Benchmarking the photocatalytic self cleaning activity of industrial and experimental materials with ISO 27448:2009, Materials 16 (2023) 1119, the Dropometer product specification and Droplet Lab validation papers.

02

Drafting assistance

Drafted with Claude (Anthropic) from the sources listed, then reviewed by Droplet Lab.

03

What we did not do

We did not copy text from the standard. Buy the current edition for the full procedure.

04

Last checked

October 2026

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References

1. ISO 27448:2009. iso.org/standard/53953.html
2. ISO 27448:2009 sample pages (iTeh). iteh.es/catalog/standards/iso/4cb913a4-54cd-44fe-ab7d-99be0778d233/iso
3. TCVN 8556:2010, national adoption of ISO 27448:2009. thuvienphapluat.vn/TCVN/Cong-nghiep/TCVN-8556-2010-Gom-min-thu-tinh-na
4. Peeters, Lenaerts and Verbruggen, Benchmarking the photocatalytic self cleaning activity of industrial and experimental materials with ISO 27448:2009, Materials 16 (2023) 1119. mdpi.com/1996-1944/16/3/1119
5. Droplet Lab. Peer reviewed validation papers in Review of Scientific Instruments and Colloids and Surfaces A. dropletlab.com/validation/publications/
6. Droplet Lab. Dropometer product specification, 2026. dropletlab.com/products/dropometer/