What probe liquids are used in ASTM D7490 surface energy measurement?

The most common probe liquid combination for OWRK analysis is deionised water (high polar component, γL = 72.8 mN/m) paired with diiodomethane (high dispersive component, γL = 50.8 mN/m). This pair provides the best separation of dispersive and polar surface energy components for most solid surfaces.

What contact angle indicates a hydrophilic vs. hydrophobic surface?

Contact angle θ 90° indicates hydrophobic surfaces where water beads. Complete wetting (θ ≈ 0°) occurs when surface energy is very high. Superhydrophobic surfaces (θ > 150°) have very low surface energy — such as PTFE and lotus-effect structured surfaces.

Why is surface energy important for adhesive bonding?

For an adhesive to wet and bond a surface, the adhesive's surface tension must be lower than the substrate's critical surface tension (related to its surface energy). If the substrate surface energy is too low (e.g., untreated polyethylene at ~31 mJ/m²), many adhesives cannot wet it adequately. Surface treatment raises surface energy to 40–60+ mJ/m² — enabling reliable adhesive bonding.

How does plasma treatment change the surface energy of a polymer?

Plasma treatment (oxygen, air, or nitrogen plasma) introduces polar functional groups (hydroxyl, carbonyl, amino) onto the polymer surface through reactive ion bombardment — increasing the polar component of surface energy from near zero to 10–30 mJ/m², significantly improving wettability and adhesion. The effect is temporary — surfaces recover hydrophobicity over hours to days as the activated groups migrate inward (hydrophobic recovery).

Can ASTM D7490 be used to evaluate the effectiveness of anti-fouling coatings?

Yes. Anti-fouling and easy-clean coatings are designed to have very low surface energy — minimising adhesion of fouling organisms, dirt, and contaminants. ASTM D7490 contact angle measurement directly quantifies surface energy before and after coating application, verifying that the anti-fouling treatment achieves the intended low surface energy. Advancing and receding contact angle hysteresis additionally characterises surface heterogeneity relevant to fouling resistance.

Dr. Bhargav Raval, Author at Infinita Lab

Author Bio

Dr. Bhargav Raval is a Materials Scientist and Client Engagement Engineer with expertise in nanomaterials, polymers, and advanced material characterization. He holds a Ph.D. in Nanosciences from the Central University of Gujarat, where his research focused on graphene-based materials for flexible electronics.

Professionally, he has led R&D in sensor technologies and coatings, including polymer-functionalized piezoelectric sensors for breath-based cancer diagnostics. In his current role, Dr. Raval works closely with clients to understand technical requirements, design testing strategies, and deliver tailored solutions in materials selection, failure analysis, and performance evaluation.

He effectively bridges scientific depth with practical outcomes, ensuring client-focused project execution. With peer-reviewed publications in high-impact journals and a proven record of applying materials science to real-world challenges, Dr. Raval continues to drive innovation at the intersection of research, engineering, and client engagement.