Contents
Hard-to-Measure Parts, Liquids and Sites

Contact Angle and Surface Tension of Corrosive Liquids: Acids, Alkalis, Plating Solutions, Ionic Liquids and Electrolytes

Corrosive liquids attack steel needles, glass and printed parts, and they change as they absorb water or evaporate. Measure their surface tension by pendant drop and their contact angle on your substrate with a liquid path chosen for the chemistry, a fresh needle per liquid and the right density.

Who this is for: Battery, plating, etching, semiconductor wet process and chemical R&D labs that work with acids, strong alkalis, ionic liquids and electrolytes.

Where it fits: Formulation development, incoming and in use bath checks, separator and electrode wetting, and substrate compatibility studies.

What it does not do: It does not make a liquid safe to handle or replace your EHS controls, and a pendant drop result is not a regulatory test for plating tanks.

Method
Pendant drop surface tension and sessile drop contact angle, with disposable plastic needles or parts made for the chemistry
Standard
Pendant drop follows the approach of EN ISO 19403-3:2024; ASTM D1331 covers ring and plate methods only
Setup
About 2 minutes
Book a 15 minute demo Request a quote
Corrosive Substances Hazard Symbol. Vector illustration
Why it matters

Why corrosive liquids need their own measurement setup

73, 76, 74 mN/m

surface tension of water, 45 wt% and 72 wt% sulfuric acid at 294 K: it rises and then falls with concentration, so you cannot assume a value from strength alone.

Torn and Nathanson, J. Phys. Chem. B 106:8064, 2002, citing Myhre et al., 1998

46.2° vs 15.2°

contact angle of an EC/DMC LiPF6 electrolyte on an uncoated polyethylene separator versus a ceramic coated one, after 10 minutes.

Hofmann et al., Int. J. Mol. Sci. 16:20258, 2015

6 to 8% water

taken up from air within 48 hours by the ionic liquid [C4mim][BF4], which sharply lowers its viscosity; so called hydrophobic ionic liquids are hygroscopic.

Seddon, Stark and Torres, Pure Appl. Chem. 72(12):2275, 2000

Sources: Torn R. D., Nathanson G. M., J. Phys. Chem. B, 2002; Hofmann A. et al., Interaction of high flash point electrolytes and PE based separators for Li ion batteries, Int. J. Mol. Sci., 2015; Seddon K. R., Stark A., Torres M. J., Pure and Applied Chemistry, 2000. Figures come from these sources, not from Droplet Lab measurements.

Quick reference

What this corrosive liquid check does and what it does not

A quick reference for labs handling aggressive liquids, checking fit before reading further.

Evidence Box

Problem this solves

Surface tension and contact angle of liquids that corrode needles and parts, contaminate each other, or change with water uptake and evaporation.

Standards

EN ISO 19403-3:2024 covers pendant drop surface tension. ASTM D1331 has ring and plate methods only. No standard was found for electrolyte or acid surface tension.

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 studies

A battery R&D team uses disposable plastic needles because its electrolytes attack steel; a plating chemistry maker had PTFE slide mounts made for caustic solutions.

Published research

Separator, electrode and electrolysis studies use contact angle to compare how electrolytes wet coated and uncoated surfaces.

Honest limit

Compatible parts must be chosen for each chemistry. Your EHS team decides where and how a liquid may be handled.

Who this is for

What corrosive liquid question are you trying to answer?

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

Battery or electrochemistry R&D

You compare electrolytes, additives and separator coatings. Surface tension of each electrolyte and its contact angle on separators and electrodes show which combinations wet, without metal in the liquid path.

Use a fresh plastic needle for every electrolyte.

Plating or wet process engineer

You run plating, etching, stripping or cleaning baths. Surface tension of the bath and its contact angle on parts show additive depletion and wetting changes between batches.

Regulatory plating tank tests use stalagmometers or ring and plate tensiometers.

Ionic liquid or chemical R&D

You formulate ionic liquids, concentrated acids or alkalis. Pendant drop needs little liquid, and water uptake and temperature can be controlled and recorded.

Record water content and density with every surface tension value.
Fit check

Is this the right check for your liquid?

It measures surface tension and wetting with a liquid path chosen for your chemistry. It does not make a liquid safe.

Good fit if

Your liquids attack steel needles or standard parts.
You test several liquids and must avoid cross contamination.
You compare electrolytes on separators or electrodes.
You have small volumes of costly or hazardous liquid.
You can work in a fume hood or glovebox your EHS team approves.

Less relevant if

You need a regulatory plating tank result; use the named method.
Your liquid needs a sealed or heated cell we have not agreed for it.
You need millisecond dynamic surface tension.
Your EHS team does not allow open drops of the liquid.
Summary

How to measure corrosive liquids reliably

The answer in under a minute.

Use a liquid path that the chemistry cannot attack, such as disposable plastic needles or PTFE parts, and change the needle for every liquid. Enter the liquid's own density at the test temperature, control water uptake and evaporation, and read surface tension by pendant drop and contact angle on your substrate. Your EHS team sets where you work.

The Dropometer surface tension and contact angle kit is modular, so parts in the drop's path can be made for your chemistry. A battery R&D case study uses plastic needles for electrolytes, and a plating chemistry case study uses PTFE slide mounts. The EN ISO 19403-3 page covers pendant drop, and our chemicals guide adds background.

Expert Quote

Expert perspective on liquid and solid

A contact angle is a thermodynamic property: fix the liquid and the solid and the same angle appears whether the drop sits on a plate or climbs a capillary.

Dr. Alidad Amirfazli

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

The problem

Why corrosive liquids are hard to measure

Many wetting measurements assume water and a stainless steel needle. Corrosive liquids break both assumptions. Stainless steel such as 316L is not usable in 10% hydrofluoric acid or in hydrochloric acid at 5% and above, according to corrosion tables, and corroding metal can contaminate the drop it delivers. Glass is attacked by hydrofluoric acid and by hot concentrated alkali, and some plastics fail in concentrated sulfuric or nitric acid, so every wetted part has to suit the liquid. The liquids change too. Surface tension of sulfuric acid rises and then falls with concentration, while potassium hydroxide solutions rise well above water. Ionic liquids take up several percent water from air within hours and become less viscous, and their surface tension can shift with it. Open drops evaporate, which concentrates the liquid. Pendant drop needs the liquid's own density at the test temperature, and a water density will give a wrong answer. On top of this, each liquid must stay separate to avoid cross contamination, and handling must meet your safety rules. Without a planned setup, results reflect the hardware and handling more than the liquid.

Needles discolour or corrode after a few tests.
Surface tension readings drift over minutes.
Results change when you switch liquids without changing the needle.
Ionic liquid values differ from day to day.
Printed or plastic stage parts swell, crack or stain.
Troubleshooting

Why corrosive liquid readings go wrong and what to check

Why:

  • Acids, some electrolytes and halides corrode steel needles and contaminate the drop.

How to detect:

  • Needles discolour, or readings change as the needle ages.

Corrective action:

Use disposable plastic needles, as the battery R&D team does, and change them between liquids.

Why:

  • Glass, some plastics and printed parts are attacked by specific acids and alkalis.

How to detect:

  • Stage parts stain, swell or crack after spills.

Corrective action:

Check each wetted material against a chemical resistance chart, and ask us about PTFE parts like those in the plating chemistry case study.

Why:

  • Pendant drop fits the drop shape with the density difference, so a wrong density gives a wrong surface tension.

How to detect:

  • Values look off for a concentrated liquid that is much denser than water.

Corrective action:

  • Enter the liquid's density at the test temperature, measured or from a reliable table.

Why:

  • Hygroscopic ionic liquids and concentrated acids absorb water from air and change.

How to detect:

  • Readings drift with time open to air, or differ between humid and dry days.

Corrective action:

  • Keep liquids sealed and dry, measure quickly and record water content.

Why:

  • Open drops lose volume and concentrate over minutes.

How to detect:

  • The drop shrinks and surface tension shifts during a long read.

Corrective action:

Use fresh drops, shorter reads or a covered cell. Our surface tension measurement guide covers drop handling.

Why:

Traces of one liquid change the next. Our guide to reproducible contact angle measurement covers fair comparisons.

How to detect:

  • Readings jump when you change liquids.

Corrective action:

  • Keep each liquid in its own needle and syringe and clean the stage between liquids.

Not sure which parts suit your chemistry?

Tell us what your liquids contain, and we will discuss the liquid path on a call.

Book a 15 minute demo
Lab records

What a corrosive liquid measurement record contains

Each check produces a record you can file with the liquid lot, beside your safety and quality records. It can feed into your existing quality records.

Liquid

Composition, concentration, lot, age and water content if relevant.

Liquid path

Needle type and diameter, syringe, wetted parts and location, such as a hood or glovebox.

Method settings

Temperature, density used, drop size, drops per liquid and read time.

Readings

Surface tension and contact angle on each substrate, with median and spread.

Handling

Cleaning, disposal and any deviation from the SOP.

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 on corrosive liquids

Liquid

Surface tension by pendant drop

Why it matters: It shows whether a bath or formulation changed, and how readily it will wet.

How to interpret: Compare with your own in specification lots measured the same way. Published values differ by liquid: about 29 mN/m for one EC/DMC LiPF6 electrolyte and 73 to 76 mN/m for sulfuric acid solutions.

When it is not enough: It is an equilibrium value, not a millisecond dynamic value.

Wetting

Contact angle on your substrate

Why it matters: It shows whether the liquid wets separators, electrodes, parts or masks.

How to interpret: Compare coated and uncoated or treated and untreated surfaces under the same read time.

When it is not enough: On porous separators the drop soaks in, so report the time with the value.

Stability

Surface tension over time and water content

Why it matters: Water uptake and evaporation change aggressive liquids during use.

How to interpret: Repeat on aged or exposed samples and log water content.

When it is not enough: It does not identify which component changed.

Inputs

Density at test temperature

Why it matters: Pendant drop needs it; concentrated liquids are far from water's density.

How to interpret: Use a measured value or a reliable table at the same temperature.

When it is not enough: Errors in density pass straight into the result.

Validation

Validated measurement approach for aggressive liquids

How the Dropometer itself has been validated, and how customers set it up for corrosive liquids.

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

Customer setups for corrosive liquids

A North American battery R&D team runs the Dropometer with long disposable plastic needles on the automatic dropper, because some of its electrolytes attack steel. A global plating chemistry maker had PTFE slide mounts made for the tilting stages at two sites, for caustic plating, stripping and etching solutions.

Read the battery case study
QC Protocol

How to measure corrosive liquids by pendant drop and contact angle

Six steps per liquid. Agree location and protective equipment with your EHS team first.

1

Agree the setup

Confirm the location, protective equipment and disposal route with your EHS team.

2

Fit the liquid path

Fit disposable plastic needles or parts chosen for the chemistry, with a fresh needle for this liquid.

3

Calibrate

Measure the needle outside diameter, enter it as the image scale and level the stage.

4

Surface tension

Form drops close to detachment size with the liquid's density entered, and record the median. Our wettability glossary entry explains the link to wetting.

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 corrosive liquids SOP

A two page SOP you can adapt for your liquids, with the liquid path and method lock, acceptance ranges, a troubleshooting table and a record sheet.

Surface tension measurement with the Dropometer

Surface tension measurement with the Dropometer

Example output

Example corrosive liquid log

Example data only. Your values and ranges will differ and must come from your own lots.

How to read this log

Each liquid used its own fresh needle and its own density. The ionic liquid left open to air read lower and was flagged for water uptake. The electrolyte wet the coated separator far better than the uncoated one. Our electrical and electronics guide covers related materials.

Example corrosive liquid log

Liquid Condition Density used (g/mL) Surface tension (mN/m) Substrate Contact angle (°)
Electrolyte A Fresh, dry 1.27 29.6 PE separator, uncoated 47
Electrolyte A Fresh, dry 1.27 29.6 PE separator, ceramic coated 16
Ionic liquid B Sealed 1.20 43.8 Glass slide 52
Ionic liquid B Open to air 24 h 1.19 42.1 Glass slide 48
Plating bath C In use, week 3 1.12 38.5 Copper coupon 31

Example data, not customer data. Pendant drop at 23 °C; disposable plastic needles; median of 5 drops; contact angle read at 10 s.

Signal order

The order to check signals on corrosive liquids

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

1

Liquid path

Rules out corroded needles and attacked parts.

2

Density and temperature

Rules out wrong inputs to the pendant drop fit.

3

Water uptake and evaporation

Rules out a liquid that changed during the test.

4

Surface tension

Shows whether the lot or bath changed.

FAQ

Common questions about measuring corrosive liquids

Questions chemistry, battery and plating labs ask about pendant drop and contact angle.

Yes. A battery R&D team uses long disposable plastic needles on the Dropometer's automatic dropper, changed between liquids, because some of its electrolytes attack steel. The case study describes the setup. Confirm with us which needles suit your liquids before ordering.

Chemical resistance charts rate PTFE, PFA and FEP highly for most strong acids and bases. Polypropylene fails in concentrated sulfuric and nitric acid, PEEK interacts severely with concentrated sulfuric, nitric and hydrofluoric acid, glass is attacked by hydrofluoric acid and hot alkali, and 316L steel fails in hydrochloric and hydrofluoric acid. Check each part for your exact liquid.

It depends on the liquid. Sulfuric acid read 73, 76 and 74 mN/m for water, 45 wt% and 72 wt% at 294 K. Studies report that hydrochloric and nitric acid lower or only slightly raise water's surface tension, while potassium hydroxide solutions rise well above water. Measure your own liquid.

Many ionic liquids are hygroscopic, even the so called hydrophobic ones. One took up 6 to 8% water from air within 48 hours, which sharply lowered its viscosity, and a pendant drop study attributed lower in air surface tension mainly to water uptake. Keep samples dry and sealed, and record water content.

Not usually, but viscous drops take longer to settle. One study found pendant drops of a 1000 mPa·s fluid reached equilibrium within about 1 second, with early readings much higher than the final value. Record a short time series and use the settled value.

No. US EPA Method 306B and 40 CFR 63.342 set limits of 40 dynes/cm by stalagmometer or 33 dynes/cm by tensiometer following ASTM D1331, and pendant drop is not named. Use pendant drop for process development and monitoring, and the named method for compliance.

Poor wetting leaves active material unused and slows cell filling. In one study an EC/DMC LiPF6 electrolyte read 46.2° on an uncoated polyethylene separator and 15.2° on a ceramic coated one, and the authors noted contact angle alone is not a full characterization of separator wetting.

Your EHS team decides. OSHA requires quick drench or eye wash facilities where people may be exposed to corrosive materials, and university hydrofluoric acid procedures call for a fume hood above 5%, never working alone, suitable gloves and calcium gluconate gel on hand. Plan the measurement inside those controls.

Business impact

What changes when you set up for corrosive liquids

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

Before and with a corrosive liquid setup

Metric Before Dropometer With Dropometer Indicative Benchmark
Liquid path Steel needle and standard parts Plastic needles or PTFE parts for the chemistry Plastic needles for electrolytes that attack steel (Droplet Lab case study)
Cross contamination Shared needle between liquids Fresh needle per liquid No published benchmark; track on your own tests
Separator screening Cell builds to find wetting problems Contact angle on each separator first 46.2° uncoated vs 15.2° coated PE separator (Hofmann et al., 2015)
Ionic liquid stability Measured once Measured with water content logged 6 to 8% water uptake from air in 48 h (Seddon et al., 2000)

Talk through your liquids

Tell us what you need to measure. We will discuss the liquid path on a call.

Book a 15 minute demo

Estimate the value of measuring corrosive liquids in house

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

Corrosive liquid testing estimate

Estimate the value of measuring corrosive liquids in house.

Each Dropometer unit is US$5,000; the default models one unit.
Your own cost per test, including shipping hazardous samples where relevant.
Preparation, measurement, cleaning and analysis per liquid.
No published benchmark. Use your own estimate and start low if unsure.

Result

~0
Candidates saved per month
~0
Monthly savings
~0
Payback period
~0
First year net benefit

Monthly savings = materials saved + technician time saved from reduced iterations.

Limits

What this setup cannot do for corrosive liquids

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

Every wetted part must be checked for the exact liquid.
Glass is unsuitable for hydrofluoric acid and hot alkali.
Pendant drop needs the liquid's own density.
Water uptake and evaporation change the liquid during the test.
It is not the named method for plating tank compliance.
Your EHS rules come first.

The Dropometer measures surface tension and contact angle with a liquid path chosen for your chemistry. Safe handling, regulatory tank tests, dynamic surface tension and full chemical analysis need their own controls and methods.

Book a 15 minute demo Request a quote
Related

Standards, evidence and related liquid workflows

These pages cover the pendant drop standard, customer setups for aggressive liquids and related wetting checks.

Standard

EN ISO 19403-3

Surface tension of liquids by pendant drop.

View use case

Case study

Plating chemistry maker

PTFE slide mounts for caustic solutions at two sites.

View use case

Case study

Battery R&D team

Plastic needles for electrolytes that attack steel.

View use case

Instrument

Dropometer

Surface tension, contact angle and surface energy.

View use case

Related use case

Hard to measure parts, liquids and sites

All hard to measure use cases in one place.

View use case

Related use case

Electrolyte wetting optimization

Electrolyte and separator wetting with additives.

View use case

Related use case

LIG electrode QC

Contact angle checks on graphene electrodes.

View use case

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.
Torn, R. D., Nathanson, G. M. Journal of Physical Chemistry B 106:8064 to 8069, 2002 (citing Myhre, Nielsen and Saastad, J. Chem. Eng. Data 43:617, 1998). https://www.atmos.albany.edu/facstaff/torn/pubs/torn_nathanson_2002.pdf
2.
Hofmann, A., Kaufmann, C., Muller, M., Hanemann, T. Interaction of high flash point electrolytes and PE based separators for Li ion batteries. International Journal of Molecular Sciences 16:20258 to 20276, 2015. https://doi.org/10.3390/ijms160920258
3.
Seddon, K. R., Stark, A., Torres, M. J. Pure and Applied Chemistry 72(12):2275, 2000. https://list.iupac.org/publications/pac/2000/7212/7212pdfs/7212seddon_2275.pdf
4.
Paap et al. International Journal of Molecular Sciences 23(21):13158, 2022. https://pmc.ncbi.nlm.nih.gov/articles/PMC9658333
5.
Tariq, M. et al. Surface tension of ionic liquids and ionic liquid solutions. Chemical Society Reviews 41:829 to 868, 2012. https://doi.org/10.1039/C1CS15146K
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.
Xu et al. Polymers 12(1):117, 2020. https://doi.org/10.3390/polym12010117
8.
Sheng, Y. et al. Frontiers in Energy Research 2:56, 2014. https://www.frontiersin.org/journals/energy-research/articles/10.3389/fenrg.2014.00056/full
9.
University of Florida grant report to NASA, 1973, with potassium hydroxide surface tension data (technical report, not peer reviewed). https://ntrs.nasa.gov/api/citations/19740011583/downloads/19740011583.pdf
10.
Markovich, T., Andelman, D., Podgornik, R. arXiv 1608.07797. https://arxiv.org/pdf/1608.07797
11.
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
12.
ASTM D1331-20(2024). Standard test methods for surface and interfacial tension of solutions of paints, solvents, solutions of surface active agents, and related materials. https://store.astm.org/d1331-20r24.html
13.
US EPA Method 306B, surface tension for chromium electroplating and anodizing tanks. https://19january2021snapshot.epa.gov/sites/static/files/2017-08/documents/method_306b.pdf
14.
40 CFR 63.342, standards for chromium electroplating and anodizing tanks. https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-63/subpart-N/section-63.342
15.
OSHA 29 CFR 1910.151, medical services and first aid. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.151
16.
Carnegie Mellon University EHS, standard operating procedure for hydrofluoric acid. https://www.cmu.edu/ehs/Laboratory-Safety/chemical-safety/documents/sop-for-the-use-of-hydrofluoric-acid.pdf
17.
Corning, facts about PYREX lab glass. https://www.corning.com/worldwide/en/products/life-sciences/resources/stories/the-cutting-edge/7-fast-facts-about-pyrex-lab-glass.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.
Contact angle measurement guide