Underwater Adhesion Measurements using the JKR Technique

Abstract

The JKR (Johnson–Kendall–Roberts) method of contact mechanics has been widely utilized for measuring adhesion properties between a deformable elastomeric lens and various materials. Such measurements are normally performed in air. We attempted to verify whether the JKR technique could be practical for evaluating adhesion properties under water. After modifying the common JKR apparatus to be suitable for underwater studies, two types of hydrophobic coating systems, silicone/silicone and silicone/silanized silicon wafer, were used. The work of adhesion (W _A ) values obtained from loading measurements and under zero load were found to be slightly smaller than the values estimated using surface energies and contact angles of water formed on the surfaces of these coatings. One possible cause for the slightly smaller values could be contamination/alteration of the coating surface properties upon immersion in water. The results suggested that, with proper control of experimental conditions, the JKR technique could be extended to evaluate adhesion properties under water.

Keywords:

• Bioadhesion
• Silanized surfaces
• Silicone elastomer
• Underwater adhesion
• Underwater JKR
• Water contact angle

ACKNOWLEDGMENTS

Financial support from Ohio Sea Grant (Project R/MB-2) and Ohio Board of Regents (R5905-OBR) is greatly appreciated. We are grateful to Professor Manoj K. Chaudhury for many valuable discussions and Carlos A. Barrios for the initial experimental attempts. We also thank Professor Hugh R. Brown, who has also attempted to study underwater adhesion phenomena using the JKR technology and presented some of his early findings at both Adhesion Society and American Physical Society meetings in 2005, for his inspiration of this research work.

Notes

*The lens contacting this coating was also cured at room temperature.

Notes: Data were measured, using our JKR apparatus, under water between a silicone lens and a silicone coating or a silanized Si wafer. Each data point resulted from at least six measurements. The estimated W _A values, using Equation (8) and γ _sv of 22 and 18 mJ/m² for silicone and silanized Si wafer, respectively, are presented for comparison. The values inside [] were estimated from the receding water contact angles on the coatings, whereas those inside () were the possible equilibrium value (W _A ) extrapolated from the measured loading G value by assuming this value was ∼0.7 W_A. The average ratio (from four different sets) of the G value at a 30 s waiting time to the average of all G values in the range of 1200 s to 2400 s for the silicone lens (cured at 150°C) in contact with the silanized Si wafer (see Figure 2) was 0.7.