Intermolecular Interactions and the Adhesion of Oleic Acid

Abstract

The method presented by Good, van Oss, and Chaudhury was applied to characterize intermolecular interactions and the adhesion of oleic acid to selected model surfaces. Interfacial tensions of oleic acid were on the order 11–12 mJ/m² in aqueous solutions and 31–32 mJ/m² at air. The dispersive contribution to the surface tension of oleic acid against different neutral interfaces was determined to be 24–31 mJ/m² in air. Contact angles of oleic acid on selected hydrophilic and hydrophobic model surfaces were measured both in air and in aqueous solution. Van der Waals (dispersive) interactions determined the wetting properties of oleic acid in air both on nonpolar and basic surfaces. As expected, the adhesion of oleic acid to hydrophilic surfaces was much lower and to hydrophobic surfaces higher in aqueous environment than in air. The adhesion in aqueous environment is mainly governed by the cohesive and adhesive properties of water. It was concluded that the GvOC method in this case was only capable to give qualitative information about Lewis acid-base and van der Waals properties of surfaces and liquids, an important limiting factor being the asymmetry of oleic acid and the common probe liquids (diiodomethane and water).

KEYWORDS:

• Acid-base properties
• contact angles
• GvOC method
• oleic acid
• van der Waals contribution

The work was funded by National Technology Agency of Finland (TEKES) as a part of the “Shine Pro”—project in the “Clean Surfaces”—technology program. M.Sc. Mika Harju is thanked from providing samples. Ms. Anna-Leena Anttila, Marja Kärkkäinen, and Ritva Kivelä for contact angle and surface tension and AFM measurements.

Notes

^a Receding angle 80°

^b Receding angle 90°

^a Calculated from Equation (3) assuming that the acid-base interactions between water and fluoropolymer are negligible and using 22.0 mJ m⁻² for the dispersion contribution for water.

^b Calculated values negative.

^c Assuming 22.0 mJ m⁻²for the dispersion contribution for water.

^a Using equation 6.

^b Calculated from its contact angle using Equation [3] and assuming 15.1 mJ/m² dispersion contribution for fluoropolymer and 35.4 mJ/m² for polyethylene.

^c Using a PDMS cap on oleic acid spin-coated on TiO₂, assuming a 24 mJ/m² dispersion contribution for PDMS.

^d Using Equations [7] and [8].

^a Using 29 mJ/m² for oleic acid; for explanation, see text.

^b Using 15.1 mJ/m² for fluoropolymer.

^a 180° equilibrium contact angle of water.