Contents
Printing Wetting, Ink Adhesion and Film Performance

Ink Beading, Bleed and Uneven Print: Troubleshooting Ink Surface Tension, Viscosity and Wetting on Paper and Film

Most ink problems on press come down to how the ink wets the substrate. Measure ink surface tension by pendant drop and the ink contact angle on your paper, board or film, log viscosity from your viscometer, and find the cause of beading, bleed and uneven print before the next run.

Who this is for: Ink formulators, inkjet and flexo print engineers, label and packaging printers, and labs printing functional inks.

Where it fits: Ink development and qualification, incoming ink checks, press troubleshooting and substrate changes.

What it does not do: It does not measure viscosity, millisecond dynamic surface tension or drop formation in the printhead.

Method
Pendant drop surface tension of the ink; sessile drop contact angle of the ink and water on the substrate
Standard
Follows the pendant drop approach of EN ISO 19403-3:2024; substrate surface energy per ISO 19403-2
Setup
About 2 minutes
Book a 15 minute demo Request a quote
Cyan, magenta, yellow and black ink swirling in water
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
Read More
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.
Read More
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
Why it matters

Why ink surface tension and wetting matter

70 to 30 mN/m

A sensor ink at 70 mN/m was not printable. After adding surfactant it measured about 30 mN/m on the Dropometer and printed on a Dimatix materials printer.

Scotti and Lesch, Electrochimica Acta 576:149649, 2026

28 to 35 mN/m

surface tension window, with 10 to 12 mPa·s viscosity, published for one industrial piezo inkjet printhead.

Ricoh MH5420/MH5440 printhead specifications

1 < Z < 10

range of the inverse Ohnesorge number for stable drop formation, which depends on surface tension, viscosity, density and nozzle size together.

Reis and Derby, MRS Proceedings 625, 2000, as reviewed by Derby, Engineering 1(1), 2015

Sources: Scotti S., Lesch A., Fully inkjet printed poly(N isopropylacrylamide)/graphene electrodes for electroanalytical sensing with pH switchable selectivity, Electrochimica Acta, 2026; Ricoh MH5420/MH5440 printhead specifications; Derby B., Additive manufacture of ceramics components by inkjet printing, Engineering, 2015. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this ink check does and what it does not

A quick reference for ink and print teams checking fit before reading further.

Evidence Box

Problem this solves

Ink that beads, crawls, bleeds, mottles or prints unevenly, or an ink that will not jet, with no number to say whether the ink or the substrate changed.

Standards

EN ISO 19403-3:2024 covers surface tension of liquid coating materials by pendant drop. ASTM D3825 for fast bubble dynamic surface tension was withdrawn in 2016.

Peer reviewed method

The Dropometer drop shape method was validated against a KRUSS DSA100E in two peer reviewed papers, in Review of Scientific Instruments and Colloids and Surfaces A.

Customer case study

A University of Bologna lab took a sensor ink from 70 mN/m, not printable, to about 30 mN/m with surfactant, measured on the Dropometer, and printed it.

Published research

Printhead makers publish surface tension and viscosity windows, and inkjet studies define printable ranges from both together.

Honest limit

Viscosity needs a viscometer, and millisecond dynamic surface tension needs a bubble pressure tensiometer.

Who this is for

What ink problem are you trying to fix?

Pick the card closest to your role. Each one points to the part of this page that answers it.

Ink formulator

You need an ink to wet a new paper, board or film, or to sit inside a printhead window. Surface tension before and after each additive change shows whether the formulation moved where you wanted.

Lock the test temperature; surface tension changes with it.

Print or press engineer

Prints bead, bleed or look uneven after a change of ink lot, substrate or room conditions. Checking ink surface tension and the ink contact angle on the substrate separates an ink problem from a substrate problem.

Measure the ink as used on press, not only the fresh lot.

Functional printing lab

You print sensors, electronics or other functional inks on a materials printer. Pendant drop surface tension, with viscosity from a viscometer, tells you whether an ink is in the printable range before you load a cartridge.

Volatile inks evaporate from the drop; read quickly and at a fixed time.
Fit check

Is this the right check for your ink problem?

It measures ink surface tension and how the ink wets the substrate. It does not measure viscosity.

Good fit if

Ink beads, crawls or pulls back from film or coated board.
Ink bleeds, feathers or mottles on paper.
You check new ink lots against a surface tension range.
You reformulate with surfactants or wetting additives.
You print functional inks on a materials printer.

Less relevant if

You need viscosity; use a viscometer or rheometer.
You need surface tension at millisecond surface ages.
Your problem is colour density or drying only.
Your ink is strongly non Newtonian and will not form a stable drop.
Summary

How surface tension and contact angle help fix ink problems

The answer in under a minute.

Measure ink surface tension by pendant drop and the ink contact angle on your paper, board or film, at a locked temperature. An ink with higher surface tension than the substrate can wet will bead; an ink that spreads and absorbs too fast will bleed. Log viscosity from your viscometer, then fix the ink or the substrate.

The Dropometer surface tension and contact angle kit runs both measurements. The EN ISO 19403-3 page covers the pendant drop method, and the University of Bologna case study shows an ink brought into the printable range. A labels manufacturer uses the same kit for inks and adhesives. Our surface tension measurement guide explains the method.

Expert Quote

Expert perspective on measuring, not looking up

“

The critical micelle concentration is not a number you look up; it is where the surface-tension curve flattens, and the only honest way to know it is to measure it.

Dr. Alidad Amirfazli

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

The problem

Why inks bead, bleed and print unevenly

An ink has to wet the substrate before it can spread, dry and hold, and how well it wets depends on its surface tension against the surface energy of the paper, board or film. When the ink surface tension is too high for the substrate, the ink beads or crawls and leaves gaps. Paper fibres absorb ink and moisture, so on porous paper the balance of spreading and absorption decides dot gain and bleed: sizing slows penetration and fillers speed it up. Uneven absorption causes mottle. In flexo, ink transfer to the substrate and ink flow into an even film depend on the same wetting balance. Low surface tension contaminants can cause craters, because a difference of 1 to 2 mN/m is enough for a contaminant to spread on a wet film. Inkjet adds another limit: an ink only jets cleanly inside a window of surface tension and viscosity, and ink drying at idle nozzles can lead to clogs and missing jets. Air bubbles and wetting of the nozzle plate also affect printhead performance. Viscosity changes with temperature, and solvent loss on press shifts both viscosity and surface tension. Without a measurement, teams fix ink problems by trial and error on press, which costs runs, substrate and time.

Ink beads, crawls or pulls back on film or coated board.
Ink bleeds or feathers into paper fibres.
Solid areas look mottled or uneven.
Craters or pinholes appear in the printed film.
Nozzles clog or jets go missing after idle time.
Troubleshooting

Common ink problems and what to check

Why:

  • A liquid must have surface tension lower than or equal to the substrate surface energy to wet it.

How to detect:

  • Ink surface tension is high for this substrate, and the ink contact angle on it is high; drops bead instead of spreading.

Corrective action:

Lower ink surface tension with a wetting additive, or raise substrate surface energy. Our page on corona treatment monitoring covers film treatment.

Why:

  • Unsized or highly filled paper absorbs ink quickly, and spreading faster than penetration causes dot gain and bleed.

How to detect:

  • The ink contact angle on the paper drops to near zero within moments.

Corrective action:

  • Check paper sizing and coating, and adjust ink surface tension or additive level.

Why:

  • Small surface tension differences let low surface tension droplets spread and form craters.

How to detect:

  • Surface tension shifts between lots, or replicate drops scatter.

Corrective action:

  • Check additive levels and cleanliness, and compare with a retained reference ink.

Why:

  • Printheads jet cleanly only inside a published surface tension and viscosity range.

How to detect:

  • Surface tension or viscosity sits outside the printhead specification at jetting temperature.

Corrective action:

  • Adjust the formulation and measure viscosity on a viscometer at the same temperature.

Why:

  • Evaporation at idle nozzles creates concentration gradients that change jetting and can leave dried ink.

How to detect:

  • Ink taken from the press reads differently from the fresh lot.

Corrective action:

  • Measure in use ink, review idle and capping settings, and check printhead maintenance.

Why:

Temperature, drop size and evaporation change the reading. Our guide to reproducible surface tension measurement covers fair comparisons.

How to detect:

  • A reference ink reads differently between sessions.

Corrective action:

Lock temperature, needle and drop age, and measure a reference ink every session. Our water and temperature experiment shows the temperature effect.

Not sure whether the ink or the substrate changed?

Send a good and a bad ink lot with your substrate, and we will compare them on a call.

Book a 15 minute demo
Lab records

What an ink troubleshooting record contains

Each check produces a record you can file with the ink lot and print job. It can feed into your existing quality records.

Material

Ink type and lot, substrate and lot, printer or press.

Method settings

Temperature, humidity, needle size, drop age at reading and ink density.

Ink readings

Surface tension from replicate pendant drops, with median and spread.

Substrate readings

Ink and water contact angle on the substrate at a fixed read time.

Viscosity

Value and temperature from your viscometer, recorded with the drop data.

Drop images

Automatic edge and baseline detection gives the same reading from the same image, so a reviewer can recheck any result.

Measurements

What to measure when ink beads, bleeds or prints unevenly

Ink

Equilibrium surface tension by pendant drop

Why it matters: It decides whether the ink can wet the substrate and whether it fits a printhead window.

How to interpret: Compare with your printhead or press specification and with a reference lot. One printhead maker publishes 28 to 35 mN/m; your own window comes from your printer and print results.

When it is not enough: It is an equilibrium value. Surfactant inks can have much higher surface tension at millisecond ages.

Substrate

Ink contact angle on the substrate

Why it matters: It shows directly whether this ink wets this paper, board or film.

How to interpret: A high angle that holds means beading; an angle that falls to near zero fast on paper warns of bleed.

When it is not enough: On porous paper the drop absorbs, so read at a fixed early time.

Substrate

Substrate surface energy

Why it matters: It shows how much a new paper, film or coating can accept.

How to interpret: Compare with the ink surface tension; the ink should be lower.

When it is not enough: Values depend on the model and probe liquids used.

Ink

Viscosity from a viscometer

Why it matters: Viscosity and surface tension together decide jetting and levelling.

How to interpret: Record it at the same temperature as the surface tension.

When it is not enough: The Dropometer does not measure viscosity.

Validation

Validated measurement approach for ink surface tension

How the Dropometer itself has been validated, and how the check fits the pendant drop standard.

Peer reviewed method

The Dropometer drop shape method is published in Review of Scientific Instruments and Colloids and Surfaces A. Contact angle was validated against a KRUSS DSA100E, with a published accuracy of 0.35°.

See the validation papers

How it fits EN ISO 19403-3

EN ISO 19403-3:2024 specifies an optical pendant drop method for the surface tension of liquid coating materials, and notes that restrictions can apply for non Newtonian liquids. The Dropometer uses pendant drop shape analysis. At the University of Bologna it measured a sensor ink before and after a surfactant change in a study published in Electrochimica Acta.

Read the University of Bologna case study
QC Protocol

How to troubleshoot an ink by surface tension and wetting

Six steps per ink and substrate. Repeat after any change of ink lot, substrate or conditions.

1

Lock the method

Fix test temperature, needle size, drop age at reading and the ink density at that temperature.

3

Measure the ink

Measure several pendant drops and reject any drop that is not symmetric or too small to deform under gravity.

4

Measure on the substrate

Place ink drops on the paper, board or film and record the contact angle at a fixed read time.

5

Add viscosity

Measure viscosity on your viscometer at the same temperature and record it with the drop data.

We completed our gage R&R study on the unit and it performed very well.

Brandon Barbee

Corporate Quality Engineer, Zeus Industries, Polymer Manufacturing

Download the ink surface tension and wetting SOP

A two page SOP you can adapt for your inks and substrates, with the method lock, how to set gates from your printhead window and print results, a troubleshooting table and a record sheet.

Surface tension measurement with the Dropometer

Example output

Example ink troubleshooting log

Example data only. Your values and gates will differ and must come from your own printer and print results.

How to read this log

Example window: 28 to 35 mN/m and ink contact angle on the film at or below 30°. Lot A printed well. Lot B was high in surface tension and beaded on the film. Lot C was in range when fresh, but the ink taken from the press after a long run had shifted, pointing to solvent loss. Our article on dynamic surface tension explains why fast processes can still differ.

Sessile droplet contact angle measurement showing left angle of 50.1° and right angle of 54.9° on a test surface

Example ink troubleshooting log

Ink lot Sample Surface tension (mN/m) Viscosity (mPa·s, viscometer) Contact angle on film (°) Print result
A Fresh 31.2 11 22 Even print
B Fresh 38.5 11 48 Beads on film
C Fresh 32.0 10 24 Even print
C From press after 6 h 34.9 14 31 Uneven, missing jets

Example data, not customer data. Water based inkjet ink on treated PE film; pendant drops at 25 °C; median of 5 drops; viscosity from a separate viscometer.

Signal order

The order to check signals when ink misbehaves

Check these in order. Each one rules out a cause before you look at the next.

1

Method and reference ink

Rules out temperature, drop and evaporation effects.

2

Ink surface tension

Shows whether the ink lot changed or sits outside the window.

3

Contact angle on the substrate

Shows whether this ink wets this substrate. Our ink adhesion on film page covers the film side.

4

Viscosity at temperature

Shows jetting and levelling effects from a viscometer.

5

Press conditions

Confirms drying, idle time and printhead state last. Our packaging guide covers printed packaging.

FAQ

Common questions about ink problems and troubleshooting

Questions ink and print teams ask about beading, bleed and surface tension.

Why does ink bead on film or coated board?

Beading means the ink cannot wet the surface. A liquid needs surface tension lower than or equal to the substrate surface energy to spread, so either the ink surface tension is too high or the substrate surface energy is too low. Measure both, then add a wetting additive or treat the substrate. Our page on corona treatment monitoring covers film treatment.

How do I fix ink bleed on paper?

Bleed and feathering come from ink spreading and absorbing into paper fibres faster than it sets. Sizing slows penetration and fillers speed it up. Measure the ink contact angle on the paper at a fixed early time, compare papers and ink lots, and adjust sizing, coating or ink surface tension.

What surface tension should an inkjet ink have?

It depends on the printhead. One industrial printhead maker publishes 28 to 35 mN/m with 10 to 12 mPa·s viscosity. Inkjet studies also use the inverse Ohnesorge number, with stable drops reported between about 1 and 10, which needs surface tension, viscosity, density and nozzle size together. Use your printhead specification first.

Can the Dropometer measure ink viscosity?

No. It measures surface tension by pendant drop and contact angle on the substrate. Viscosity needs a viscometer or rheometer, ideally at the same temperature. In the University of Bologna study, viscosity came from a separate viscometer while surface tension came from the Dropometer.

Static or dynamic surface tension?

Pendant drop gives equilibrium surface tension and changes over seconds to minutes. Surfactant inks can have much higher surface tension at the millisecond ages of jetting and drop impact. For those, use a bubble pressure tensiometer; ASTM D3825 for that method was withdrawn in 2016. Our dynamic surface tension glossary entry explains the difference.

Why do nozzles clog?

Ink evaporates from the nozzle exit during idle periods, which changes its composition and can leave dried ink that blocks jets. Air bubbles and wetting of the nozzle plate also affect printhead performance. Check idle, capping and maintenance settings, and measure ink taken from the press against the fresh lot.

Why do surface tension readings drift?

Temperature, evaporation from the drop and contamination all move the reading. Lock the test temperature, read at a fixed drop age, use clean glass syringes and a reference ink. Drops that are too small barely deform and give large errors, so use a drop close to the size where it would detach. Our reproducible surface tension guide covers this.

Does better wetting give more vibrant colors?

Even wetting and controlled absorption give a smoother ink distribution on the surface, which helps solid areas look uniform instead of mottled. Colour density also depends on pigment, ink film and substrate, so treat wetting as one factor and confirm with your own print measurements.

Business impact

What changes when you measure ink and substrate

Typical changes in how teams work. Benchmarks are given only where a published source exists.

Before and with ink and substrate checks

Metric Before Dropometer With Dropometer Indicative Benchmark
Ink qualification Print trial on every lot Surface tension checked against the window first 28 to 35 mN/m published for one printhead (Ricoh MH5420)
Formulation changes Judged by print result Surface tension measured before and after each change 70 to about 30 mN/m with surfactant, then printable (Scotti and Lesch, 2026)
Substrate changes Found on press Ink contact angle measured on the new substrate No published benchmark; track on your own jobs
Press troubleshooting Trial and error Ink from the press compared with the fresh lot No published benchmark; track on your own jobs

See the measurement on your own inks

Send a good and a bad ink lot with your substrate. We will show the comparison on a call.

Book a 15 minute demo

Estimate avoided reprints from ink problems

Enter your own numbers. The result is an estimate, not a Droplet Lab claim.

Ink troubleshooting estimate

Estimate the value of catching ink and substrate wetting problems before the run.

Each unit is $5,000; default models 1 unit.
From your own records. No published benchmark.
Your own cost to reprint or rework one job with an ink problem.
No published benchmark. Use your own records; start low if unsure.
Substrate, ink and press time lost per problem, from your own records.
Any other monthly saving you can document from your own records.

Result

~0
Monthly savings
~0
Payback period
~0
First year net benefit

Monthly savings = preventable rework cost + preventable scrap cost + other monthly savings.

Limits

What surface tension and contact angle cannot tell you about an ink

Honest limits, so you know when to reach for another test.

It does not measure viscosity.
Pendant drop gives equilibrium, not millisecond, surface tension.
Non Newtonian inks can limit the method.
Volatile inks evaporate from the drop; read quickly.
Porous paper absorbs the drop; read early and at a fixed time.
Printhead windows differ; use your own specification.

Pendant drop surface tension and contact angle show whether an ink can wet a substrate and whether it sits in a window. Viscosity, millisecond dynamic surface tension, drop formation and colour need their own tests.

Book a 15 minute demo Request a quote
Related

Standards, evidence and related print workflows

These pages cover the pendant drop standard, customer examples and the print checks that sit beside this one.

Standard

EN ISO 19403-3

Surface tension of liquid coating materials by pendant drop.

View standard

Case study

University of Bologna

An inkjet sensor ink brought into the printable range.

Read case study

Case study

Labels manufacturer

Two R&D labs, one method for ink and adhesive wetting.

Read case study

Instrument

Dropometer

Surface tension, contact angle and surface energy.

View product

Related use case

Printing wetting and ink adhesion

All print and film use cases in one place.

View Page

Related use case

Ink adhesion on plastic film

Film surface checks before tape and rub tests.

View Page

Related use case

Corona treatment monitoring

Treatment level and decay before printing.

View Page

Guide

Surface tension measurement

How pendant drop surface tension works.

Read guide

How this page was created

Editorial and technical transparency notes for this page.

Transparency Details 4 checklist items
01

Drafting assistance

Drafted with Claude Opus 5.5 (Anthropic) using web search for sources, then edited by the Droplet Lab team.

02

Technical review

Reviewed and edited for technical accuracy by the Droplet Lab Team.

03

Verification steps

Standard identifiers, units, thresholds and key procedural claims are checked against cited sources before publication.

04

Updates

Reviewed every 12 months or when the underlying method changes.

Report a correction

Spotted an issue in this summary? Send a correction request and our team will review it.

Correction Request

We work hard to keep this page accurate and up to date. If you spot an error (wrong revision/year, missing requirement, incorrect interpretation, or broken link), tell us and we'll review it.

Contact us to report a correction
Sources

References

1.
Scotti, S., Lesch, A. Fully inkjet printed poly(N isopropylacrylamide)/graphene electrodes for electroanalytical sensing with pH switchable selectivity. Electrochimica Acta 576:149649, 2026. See our University of Bologna case study. https://dropletlab.com/validation/case-studies/university-of-bologna-inkjet-ink-surface-tension/
2.
Derby, B. Additive manufacture of ceramics components by inkjet printing. Engineering 1(1):113 to 123, 2015. https://doi.org/10.15302/J-ENG-2015014
3.
Reis, N., Derby, B. Ink jet deposition of ceramic suspensions: modeling and experiments of droplet formation. MRS Proceedings 625:117, 2000. https://doi.org/10.1557/proc-625-117
4.
Jang, D., Kim, D., Moon, J. Influence of fluid physical properties on ink jet printability. Langmuir 25(5):2629 to 2635, 2009. https://doi.org/10.1021/la900059m
5.
Ricoh MH5420/MH5440 industrial inkjet printhead specifications. https://www.ricoh.com/products/industrial-inkjet-printheads/ricoh-mh5420-mh5440
6.
Berry, J. D., Neeson, M. J., Dagastine, R. R., Chan, D. Y. C., Tabor, R. F. Measurement of surface and interfacial tension using pendant drop tensiometry. Journal of Colloid and Interface Science 454:226 to 237, 2015. https://doi.org/10.1016/j.jcis.2015.05.012
7.
Bubat, A., Scholz, W. Silicone additives for paints and coatings. Chimia 56(5):203 to 209, 2002. https://chimia.ch/chimia/article/download/2002_203/2872/13557
8.
Deegan, R. D. et al. Capillary flow as the cause of ring stains from dried liquid drops. Nature 389:827 to 829, 1997. https://doi.org/10.1038/39827
9.
Rentzhog, M., Fogden, A. Rheology and surface tension of water based flexographic inks and implications for wetting of PE coated board. Nordic Pulp and Paper Research Journal 20(4):399 to 409, 2005. https://doi.org/10.3183/npprj-2005-20-04-p399-409
10.
Li, R. et al. Ink penetration of uncoated inkjet paper and impact on printing quality. BioResources 10(4):8135 to 8147, 2015. https://doi.org/10.15376/biores.10.4.8135-8147
11.
Thorman, S., Yang, L., Hagberg, A., Strom, G. The impact of non uniform ink absorption on flexographic print mottle. Journal of Print and Media Technology Research 7(1):7 to 18. https://jpmtr.org/index.php/journal/article/view/77
12.
Rump, M. et al. Selective evaporation at the nozzle exit in piezoacoustic inkjet printing. Physical Review Applied 19(5):054056, 2023. https://doi.org/10.1103/PhysRevApplied.19.054056
13.
Wijshoff, H. The dynamics of the piezo inkjet printhead operation. Physics Reports 491(4 to 5):77 to 177, 2010. https://doi.org/10.1016/j.physrep.2010.03.003
14.
Mitsuyoshi, K., Tsuru, I., Hamada, D. Relationship between jetting performance and surface tension in micro second order on water based inkjet ink. NIP30, IS&T, 2014. https://doi.org/10.2352/ISSN.2169-4451.2014.30.1.art00011_1
15.
ISO 19403-3:2024. Paints and varnishes: wettability, part 3, determination of the surface tension of liquids using the pendant drop method. See our EN ISO 19403-3 page. https://www.iso.org/standard/87263.html
16.
ISO 19403-2:2024. Paints and varnishes: wettability, part 2, determination of the surface free energy of solid surfaces by measuring the contact angle. https://www.iso.org/standard/87262.html
17.
ASTM D3825-09. Standard test method for dynamic surface tension by the fast bubble technique (withdrawn 2016). https://store.astm.org/d3825-09.html
18.
Chen, X. et al. Contact angle measurement with a smartphone. Review of Scientific Instruments 89(3):035117, 2018. https://pubs.aip.org/aip/rsi/article-abstract/89/3/035117/368179/Contact-angle-measurement-with-a-smartphone
19.
Surface tension measurement with a smartphone using a pendant drop. Colloids and Surfaces A: Physicochemical and Engineering Aspects. https://www.sciencedirect.com/science/article/abs/pii/S0927775717307744
20.
Droplet Lab validation papers
21.
Customer publications that cite the Dropometer
22.
Surface tension measurement guide
23.
Why you need dynamic surface tension