Bonding and Adhesion Reliability

Plasma Treatment Verification for Adhesion: Check Each Plasma Surface Treatment Before Coating or Bonding

Atmospheric plasma and vacuum plasma treatment change the surface you cannot see, and the effect varies with settings, part geometry and time. Measure water contact angle on the treated substrate before coating, printing or bonding, so a weak or faded treatment is caught while the part can still be treated again.

Who this is for: Process, quality and R&D engineers running plasma treatment systems in electronics, medical device, automotive and plastics manufacturing.

Where it fits: Right after plasma treatment and before any bonding or coating step, including ink; also when you set up or change treatment settings.

What it does not do: It does not measure adhesion strength or replace your adhesion tests. It shows whether the treatment changed the surface as intended.

Method

Sessile drop water contact angle and surface free energy

Standards

Supplements ASTM F22 water break and ASTM F21 atomizer screens

Setup

About 2 minutes

Book a 15 minute demo Request a quote

Tweezers peeling a white coating off a plastic panel, showing poor adhesion

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

What plasma treatment does to the water contact angle and adhesion

83.1° to 24.1°

saline contact angle on machined titanium before and after vacuum plasma treatment, measured with the Dropometer by Harvard researchers (77.3° to 15.7° on rough discs).

Ho et al., Biomimetics 10:571 (2025)

97.1° to 14°

water contact angle on neutral polypropylene before and after 180 s of 50 W oxygen plasma.

Mandolfino et al., Polymers 11(2):202 (2019)

Up to +386.6%

lap shear strength of epoxy joints on plasma treated polypropylene compared with untreated, depending on treatment settings.

Mandolfino et al., Polymers 11(2):202 (2019)

Sources: K. Ho, T. Shiba, C.-Y. Chen, D. M. Kim, Biomimetics 10:571, 2025 (a customer publication that used the Dropometer); C. Mandolfino, E. Lertora, C. Gambaro, M. Pizzorni, Polymers 11(2):202, 2019. Figures come from these studies, not from Droplet Lab measurements.

Quick reference

What this plasma treatment check does and what it does not

A quick reference for engineers and quality managers checking fit before reading further.

Evidence Box

Problem this solves

Coatings, inks and adhesives that fail because a plasma treatment was weak, uneven or had faded before the next step.

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 publication

Harvard School of Dental Medicine researchers used the Dropometer to measure contact angle before and after vacuum plasma treatment of titanium (Ho et al., Biomimetics, 2025).

Customer case study

Harvard's Center for Nanoscale Systems added a Dropometer for its users; five labs used it in seven publications in under three years.

Related standards

ASTM F22 (water break) and ASTM F21 (atomizer) screen for hydrophobic films. Contact angle supplements these tests; it does not replace them.

Honest limit

Contact angle shows that the treatment changed the surface. Your adhesion tests still decide whether the coating or bond is good.

Who this is for

What plasma treatment problem are you trying to solve?

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

Process engineer

You run an in-line atmospheric plasma or a vacuum plasma chamber and need to know that every part was treated, not just that the machine ran. A water contact angle check after treatment shows the result on the part.

If treated parts match the baseline, check the coating, ink or adhesive process next.

Quality manager

Dyne inks give a pass or fail at set levels and depend on the operator's eye. A contact angle reading gives a number you can trend and file with the batch.

Gates must come from your own adhesion tests, not a value copied from another substrate or line.

R&D engineer

You are setting up a new plasma surface treatment and need to compare gases, power, speed and distance. Contact angle and surface free energy show which settings improve wettability most, and how each surface modification lasts.

The lowest contact angle is not always the best setting; confirm with adhesion and aging tests.

Fit check

Is a contact angle check right for your plasma treatment process?

It helps when you need to confirm what the plasma did to the surface. It helps less when the coating, ink or adhesive itself is the problem.

Good fit if

You treat polymers such as PP, polyethylene or PTFE, or metals, glass or composites, before coating, printing or bonding.

Treated parts wait before the next step, or storage conditions vary.

Parts have complex geometry, so some areas may see less treatment.

You want a number to trend instead of a dyne ink pass or fail.

You are changing gases, power, speed, distance or treatment systems.

Less relevant if

Failures are cohesive, inside the coating or adhesive.

You need adhesion strength values. Only adhesion tests such as peel, pull off or lap shear give those.

The treated area is too small or curved for a drop to sit on.

You need the surface chemistry itself; that needs XPS or similar surface analysis.

Summary

How to verify plasma treatment before coating or bonding

The answer in under a minute.

When a coating or bond fails after plasma, the root cause often lies at the surface. The treatment increases the surface energy so coatings, inks and adhesives can wet it for better adhesion, but the effect depends on settings, geometry and time. Measure water contact angle on each treated substrate right after treatment and compare it with a baseline from parts that passed your adhesion tests. If the angle drifts, treat again before the next step.

Your adhesion tests still decide what good looks like. This check tells you, on every part or batch, whether the plasma treatment achieved that surface. The Dropometer contact angle and surface energy kit runs it next to the line. Harvard researchers used it to measure vacuum plasma treated titanium; read our analysis of that paper and the Harvard shared facility case study. For the wider picture, read why contact angle matters for coatings and adhesives QC.

Expert Quote

Expert perspective on reading a treated surface

“

Droplet adhesion is three-dimensional. Two side-view angles give an estimate; the whole story is how the angle and the contact line vary all the way around the drop.

The problem

Adhesion challenges plasma treatment solves, and the ones it creates

Many materials like polypropylene, polyethylene and PTFE have a low surface energy, so coatings, inks and adhesives bead up instead of wetting them. Metals, glass and composites carry thin organic films that do the same. Plasma treatment uses gas that has been made to ionize into ions and electrons and other charged particles. It removes organic contaminants and adds polar functional groups to the top few molecular layers, which modifies the surface properties and raises the surface energy without changing the bulk material. That is why plasma treatment is mainly used to improve adhesion before bonding, coating and printing. The catch is that the treatment is microscopic and invisible. Gas, power, speed, distance and part geometry change how much each area receives, over treatment can create weak boundary layers, and the effect fades with time and storage conditions. The machine log shows that the plasma ran; it does not show what the surface of the material looks like when the coating goes on.

Coatings, ink or adhesive peel cleanly from treated parts.

Adhesion is good at the centre of a part and poor at edges, corners or recesses.

Parts treated one day and coated days later fail more often.

Results change after a new gas, nozzle, line speed or treatment system.

Dyne ink results are borderline or differ between operators.

Troubleshooting

Root causes of poor adhesion after plasma treatment

Why:

Too little power, too short a time, the wrong gas or too great a distance leaves too few polar groups on the surface, so wettability and adhesion stay low.

How to detect:

Water contact angle stays close to the untreated value. The treated vs untreated surfaces experiment shows the size of change to expect.

Corrective action:

Raise power or time, or reduce speed or distance, then confirm on the part with a contact angle check.

Why:

Atmospheric plasma nozzles treat what they pass over at the set distance. Edges, recesses and curved areas often see less. Moroni et al. (2020) found PP surface free energy and joint strength changed with plasma distance and speed.

How to detect:

Spot to spot spread rises, with high angles at edges, corners or recesses.

Corrective action:

Map the part, then adjust the path, distance, speed or passes until every bond or coating area meets the gate.

Why:

The effect of plasma treatment on the surface fades as the surface reorganises and picks up airborne contaminants. Heat, humidity and long storage speed this up.

How to detect:

Contact angle rises with time after treatment. Measure at fixed times to find how long parts stay ready.

Corrective action:

Set a maximum time from treatment to coating or bonding, control storage conditions, and treat parts again if they go past it.

Why:

Heavy oils, silicone or mold release can be more than the plasma removes, and handling after treatment puts contamination back on.

How to detect:

A high angle with a wide spread, or values that drift from lot to lot. Our guide to sample prep and contamination control covers how to keep samples clean.

Corrective action:

As part of surface preparation, clean heavy contamination with a solvent first, handle treated parts with gloves, and keep them covered until the next step.

Why:

Too much energy can break polymer chains into a weak boundary layer that wets well but tears off under load.

How to detect:

Contact angle is very low, but adhesion tests fail with a thin layer of substrate on the coating. Compare with reference surface free energy values for common polymers as a sense check.

Corrective action:

Reduce power or time to the lowest setting that meets the gate, and confirm with adhesion and aging tests.

Why:

Cure, mix, film thickness and flash off all affect adhesion performance after a good treatment.

How to detect:

Treated surfaces match their baseline, but the coating or adhesive fails cohesively.

Corrective action:

Check the coating or adhesive process against its specification. A surface check will not find this cause.

Not sure whether the plasma reached the surface?

Bring an untreated part, a treated part that passed and one that failed to a call, and we will compare them on screen.

Book a 15 minute demo

Quality records

What a plasma treatment record contains

Each check produces a record you can file with the batch. These records can feed into your existing quality records under ISO 9001, ISO 13485, IATF 16949 or your sector's quality system.

Part identity

Part number, material, supplier lot and the area measured.

Treatment settings

Atmospheric or vacuum plasma, gas, power, speed or time, distance and operator.

Method settings

Probe liquid, drop volume and the reading time after each drop lands.

Readings

Contact angle at each spot, the median and the spread, plus surface free energy where measured.

Decision

Release, treat again or hold, with the time from treatment to the next step.

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 after plasma surface treatment

Primary check

Water contact angle on the treated substrate

Why it matters: It shows whether the treatment raised surface energy enough for wetting and adhesion.

How to interpret: Compare with an untreated reference and a treated baseline from parts that passed adhesion tests. There is no universal pass value; set gates per material and process from your own correlation study.

When it is not enough: It cannot tell you the coating or adhesive is right or fully cured.

Uniformity

Spot to spot spread across the treated area

Why it matters: Uneven treatment from geometry or path shows up as spread before the median moves.

How to interpret: A median inside the gate with a wide spread still means part of the area was missed.

When it is not enough: It cannot replace mapping complex parts at the areas that matter.

Surface energy

Surface free energy from water and diiodomethane

Why it matters: Plasma mainly raises the polar part, which relates to how adhesives and coatings wet the surface.

How to interpret: Use it to compare gases and settings, and to see what changed when the water angle drifts.

When it is not enough: Values depend on the model and liquids used; compare within one method.

Time window

Contact angle versus time after treatment

Why it matters: It shows how long treated parts stay ready in your storage conditions.

How to interpret: Set the maximum time from treatment to the next step where the angle starts to drift.

When it is not enough: Heat, humidity and packaging change the window, so check it again when they change.

Validation

Validated measurement approach for plasma treated surfaces

How the Dropometer itself has been validated, and where customers have published with it.

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 publication on plasma treatment

Harvard School of Dental Medicine researchers used the Dropometer to measure saline contact angle on titanium before and after vacuum plasma treatment. Angles fell from 83.1° to 24.1° on machined discs and from 77.3° to 15.7° on rough discs (Ho et al., Biomimetics, 2025).

Read our analysis of the paper

QC Protocol

How to implement plasma treatment verification in the manufacturing process

The steps below assume one material, one treatment system and one coating or adhesive. Repeat steps 1 to 3 for each new combination.

1

Lock the method

Fix the probe liquid, drop volume, reading time after the drop lands, lighting and spots. Our contact angle measurement guide covers the basics.

2

Baseline untreated and treated

Measure an untreated part and a treated part that passed your adhesion tests, at five or more spots each.

3

Set the gates

Treat parts at lower and higher settings, coat or bond them, and run adhesion tests. Set release, treat again and hold bands where adhesion changes. Keep your ASTM F22 water break or ASTM F21 atomizer screen if your process uses one.

4

Check after treatment

Check each part or batch after treatment and before coating, printing or bonding, within the time window you set for the production process.

5

Release, treat again or hold

Release parts inside the gates. Treat again outside them, and hold parts that fail twice.

6

Record and watch the trend

Store readings with the part, lot and treatment settings, and check the baseline again after any change to gas, nozzle or treatment system.

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 plasma treatment verification SOP

A two page SOP you can adapt for your material, plasma system and coating or adhesive, with the method lock, gate setting steps and a record sheet.

Contact angle and surface energy measurement with the Dropometer

Example output

What a plasma treatment verification record looks like

Example data only. Your gates and values will differ and must come from your own adhesion tests.

How to read this record

Example gate: within 8° of the treated baseline with spread up to 4°. The grey row is an untreated reference. Green rows are released, amber rows are treated again, red rows are held.

Sessile drop contact angle measurement: DI Water on Teflon surface, left contact angle 108.4°, right 107°

Example plasma treatment log

Part	Treatment	Area	Time since treatment	Median (°)	Spread SD (°)	Versus baseline	Result
Untreated reference	None	Face	n/a	94.2	1.6	Untreated	Reference only
Batch 41 coupons	Atmospheric air plasma	Face	5 min	48.7	2.0	Baseline	Release
Housing 5120	Atmospheric air plasma	Face	20 min	50.9	2.4	+2.2	Release
Housing 5121	Atmospheric air plasma	Inner corner	20 min	63.5	5.1	+14.8	Treat again
Housing 5122	Atmospheric air plasma	Face	4 days	76.0	3.3	+27.3	Hold: treat again and retest

Example data, not customer data. Water contact angles on a molded polymer housing, read at a fixed time after deposition.

Signal order

The order to check signals after plasma treatment

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

1

Contact angle versus treated baseline

Shows whether the treatment achieved the surface you qualified.

2

Distance from untreated

An angle close to the untreated reference means the treatment was missed or has faded.

3

Spot to spot spread

Shows whether geometry or path left areas under treated.

4

Time since treatment

Links a drift to storage time and conditions.

5

Surface free energy

A two liquid reading shows what changed. The surface free energy calculator turns contact angles into a value.

FAQ

Common questions about plasma treatment verification

Questions teams ask about plasma treatment, dyne testing and contact angle.

How do you verify plasma treatment?

Measure water contact angle on the treated part soon after treatment and compare it with an untreated reference and a baseline from parts that passed adhesion tests. A drop that spreads more means higher surface energy. Check several spots to see uniformity, and repeat after storage to see how long the treatment lasts. Dyne inks and water break tests give quick screens alongside it.

Is contact angle better than dyne ink testing?

They answer different needs. A dyne test evaluates wetting tension with inks at set levels and gives a fast pass or fail, and the result depends on the operator's reading of the ink. Contact angle measurement gives a number for each spot that you can trend, compare between lines and file with the batch. Many teams keep dyne inks for quick checks and use contact angle to set and review the gates.

What is the difference between atmospheric plasma and vacuum plasma?

Atmospheric plasma runs in open air, often in-line, with a nozzle that treats what it passes over. Vacuum plasma treats whole parts inside a chamber at low pressure, which suits complex geometry and batches. Both raise surface energy; the settings, gas and part shape decide how evenly. Corona treatment is a related treatment technology used mostly on films. The verification check is the same for both types of plasma.

How long does plasma treatment last?

It varies depending on the type of material, gas, settings and storage conditions. Some surfaces stay ready for hours, others for days, and heat and humidity shorten the window. Moroni et al. (2020) saw only small changes in PP joint failure load when bonding was delayed up to 24 hours at their settings. Measure contact angle at fixed times on your own parts to set the window.

Can plasma treatment be too strong?

Yes. Too much power or time can break polymer chains into a weak boundary layer that wets very well but tears away under load. A very low contact angle with failed adhesion tests is the sign. Set gates from adhesion results, not from the lowest angle you can reach.

Which materials benefit from plasma treatment?

Low surface energy polymers such as polypropylene, polyethylene and PTFE benefit most, along with silicones, textiles and composites. Metals and glass also benefit when plasma cleaning technology removes thin organic films. Wettability determines how easily a liquid spreads on a surface; our glossary entry on wettability explains it, and the medical device guide covers plasma before coating and bonding of device parts.

What should we look for in an instrument for this check?

It should measure contact angle and surface free energy on parts next to the line, use a published method and give repeatable results across operators. Check how it handles small and curved areas. Our guide to the best contact angle goniometer for industrial QA compares options.

Business impact

What changes when you verify plasma treatment on the part

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

Before and with plasma treatment verification

Metric	Before Dropometer	With Dropometer	Indicative Benchmark
Proof the treatment worked	Machine log shows the plasma ran	Contact angle on the part	Vacuum plasma cut titanium contact angle from 83.1° to 24.1° (Ho et al., 2025)
Effect of treatment on adhesion	Assumed from settings	Gates set from adhesion tests	Plasma raised epoxy lap shear on PP by up to 386.6% (Mandolfino et al., 2019)
Uniformity on complex parts	Unknown until a coating fails	Mapped spot by spot	No published benchmark; track on your own parts
Time from treatment to next step	Set by habit	Set from measured drift	No published benchmark; track on your own parts
Failure investigation	Plasma, coating and cure all suspected	Record shows whether the surface matched baseline	No published benchmark; track on your own parts

See the check on your own treated parts

Bring an untreated part, a treated part that passed and one that failed. We will show the difference on a call.

Book a 15 minute demo

Estimate the cost of failures from weak or faded plasma treatment

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

Instrument cost ($) Each Dropometer unit is $5,000; the default models 1 unit.

Rework events / month

Avg rework cost per event ($) Count only rework traced to weak or faded plasma treatment, not all assembly rework.

Failures preventable (%) Use your own failure analysis; start low if unsure.

Scrap cost per event ($) Count only scrap traced to this failure mode.

Other monthly savings ($)

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 a plasma treatment check cannot tell you

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

A low angle shows good wetting, not good adhesion; over treatment can wet well and still fail.

Rough, textured or curved areas pin drops; compare like with like at a fixed time.

Gates do not transfer between materials, gases or treatment systems.

It does not identify which functional groups formed; that needs surface analysis.

It does not find process problems in the adhesives or coatings applied to the surface afterwards.

Measure the part or a witness coupon treated with it, not a coupon from another batch.

The check confirms that the treatment changed the surface as intended. Adhesion strength, cure, durability and surface chemistry still need adhesion tests, aging tests or surface analysis.

Book a 15 minute demo Request a quote

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.

Ho, K., Shiba, T., Chen, C.-Y., Kim, D. M. Plasma treatment to remove titanium surface contaminants and improve implant biocompatibility: an in vitro study. Biomimetics 10:571, 2025. Customer publication that used the Dropometer; the link goes to our analysis of the paper. https://dropletlab.com/validation/citations/analysis/plasma-treatment-to-remove-titanium-surface-contaminants-and-improve-implant-biocompatibility-an-in-vitro-study/

2.

Mandolfino, C., Lertora, E., Gambaro, C., Pizzorni, M. Functionalization of neutral polypropylene by using low pressure plasma treatment: effects on surface characteristics and adhesion properties. Polymers 11(2):202, 2019. https://doi.org/10.3390/polym11020202

3.

Moroni, F., Musiari, F., Sciancalepore, C., Messori, M. Influence of atmospheric pressure plasma process parameters on the mechanical behavior of thermoplastic joints. International Journal of Adhesion and Adhesives 102:102650, 2020. https://doi.org/10.1016/j.ijadhadh.2020.102650

4.

ASTM F22. Standard test method for hydrophobic surface films by the water break test. https://dropletlab.com/industry-standards/astm-f22/

5.

ASTM F21. Standard test method for hydrophobic surface films by the atomizer test. https://dropletlab.com/industry-standards/astm-f21/

6.

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

7.

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

8.

Droplet Lab validation papers

9.

Customer publications that cite the Dropometer

10.

Harvard shared facility case study

11.

Our analysis of Ho et al. (2025)

Plasma Treatment Verification for Adhesion: Check Each Plasma Surface Treatment Before Coating or Bonding

Featured Studies & Publications

What plasma treatment does to the water contact angle and adhesion

83.1° to 24.1°

97.1° to 14°

Up to +386.6%

What this plasma treatment check does and what it does not

Evidence Box

What plasma treatment problem are you trying to solve?

Process engineer

Quality manager

R&D engineer

Is a contact angle check right for your plasma treatment process?

Good fit if

Less relevant if

How to verify plasma treatment before coating or bonding

Expert perspective on reading a treated surface

Adhesion challenges plasma treatment solves, and the ones it creates

Root causes of poor adhesion after plasma treatment

Not sure whether the plasma reached the surface?

What a plasma treatment record contains

Part identity

Treatment settings

Method settings

Readings

Decision

Drop images

What to measure after plasma surface treatment

Water contact angle on the treated substrate

Spot to spot spread across the treated area

Surface free energy from water and diiodomethane

Contact angle versus time after treatment

Validated measurement approach for plasma treated surfaces

How to implement plasma treatment verification in the manufacturing process

Lock the method

Baseline untreated and treated

Set the gates

Check after treatment

Release, treat again or hold

Record and watch the trend

Download the plasma treatment verification SOP

What a plasma treatment verification record looks like

Example plasma treatment log

The order to check signals after plasma treatment

Contact angle versus treated baseline

Distance from untreated

Spot to spot spread

Time since treatment

Surface free energy

Common questions about plasma treatment verification

What changes when you verify plasma treatment on the part

Before and with plasma treatment verification

See the check on your own treated parts

Estimate the cost of failures from weak or faded plasma treatment

Estimate avoided rework from weak, uneven or faded plasma treatment.

What a plasma treatment check cannot tell you

Standards, evidence and related surface treatment workflows

ASTM F22

ASTM F21

Harvard shared facility

Ho et al. (2025): our analysis

Dropometer

Bonding and adhesion reliability

Silicone and invisible residue detection

PCB surface prep

Medical device guide

How this page was created

Drafting assistance

Technical review

Verification steps

Updates

Report a correction

References