Correlation between the adhesion force of hydrophobic surfaces and contact angle

Understanding how macroscopic wetting relates to nanoscopic adhesion is essential for characterizing solid-liquid interfacial interactions. In this study, we examine the correlation between adhesion force and contact angle for a hydrophobic fluorocarbon self-assembled monolayer (1H,1H,2H,2H-perfluorooctanethiol, FOTT) interacting across water-dimethyl sulfoxide (DMSO) mixtures of varying molar composition. Adhesion forces were quantified through atomic force microscopy (AFM) pull-off measurements using symmetric FOTT-functionalized probes and substrates prepared by chemical vapor deposition (CVD), while wettability was assessed via sessile drop contact angle measurements on the same surfaces. Increasing the water molar fraction in the solvent mixture resulted in concurrent increases in both adhesion force and contact angle, revealing a direct empirical relationship between nanoscopic adhesion and macroscopic wetting behavior. Solid-liquid interfacial tensions estimated from AFM data using the Derjaguin-Muller-Toporov (DMT) model showed good agreement with values obtained from contact angle measurements and Zisman plot analysis. Together, these results highlight the complementarity of AFM and contact angle techniques and provide experimental evidence linking adhesion forces to wettability for hydrophobic fluorocarbon surfaces in aqueous solvent mixtures.