What Contact Angle Mapping Reveals About Composites and Aluminum
Adhesion depends on surface chemistry you can’t see, and a surface can look properly prepared and still be uneven. In this on-demand webinar, Sonia Stanciu, Ph.D., Senior Materials Scientist at Brighton Science, presents research first shared at CAMX 2026. Using robotic water contact angle mapping, the team measured carbon fiber reinforced epoxy composites and aluminum point by point after solvent wiping, hand sanding, grit blasting, and atmospheric plasma treatment. They then tracked how each surface aged over 24 hours.
Key Takeaways
- Appearance isn’t evidence. A visibly over-abraded area on a sanded composite measured the same water contact angle as the lightly sanded edges. Only mapping showed how far the damage spread.
- Abrasion can lower surface energy on composites. Hand sanding and grit blasting are low-control methods that can damage resin and fibers. Abrasives that shed stearates leave a low-energy residue that reduces adhesion.
- Uniformity matters as much as the average. Effective prep lowers both the mean contact angle and the standard deviation. Mapping caught a spot the plasma pass missed and weak areas in a grit blast process.
- One method can help one material and hurt another. Aluminum needed grit blasting before plasma treatment, because otherwise the plasma activated the weak oxide layer instead of the metal. On composites, the same blasting would likely lower surface energy.
- Peel ply protects but doesn’t activate. A composite measured 51° after peel ply removal. Atmospheric plasma treatment brought it to 19°.
- Metals age faster than composites. Plasma-treated composite stayed under 20° after 24 hours. Plasma-treated aluminum rose from 14° to 37° overnight without grit blasting, and only to 28° with it. Metals often need shorter out times.
Questions from the Live Q&A
What causes a prepared surface to lose surface energy before bonding?
Every prepared surface ages. Airborne hydrocarbons, oxygen, humidity, silicones, mold release agents, and abrasive residues lower surface energy over time, so contaminated environments shorten out time.
Why measure contact angle with water?
Water is highly polar, so it measures the polar component of surface energy, which is the part that surface preparation changes. It is also nondestructive to the part.
Can water contact angle be measured on curved parts?
Yes. The robotic system can be programmed with a different height at each measurement point, so it stays at the correct distance on contoured surfaces.
How many measurements confirm a part is ready?
It depends on part size, likely contaminants, the pass/fail threshold, and acceptable risk. Brighton Science’s applications team can help define a sampling plan.