Wetting dynamics of ferrofluids on substrates with different hydrophilicity behaviors
Abstract The present study is devoted to the analysis of the wetting dynamics of ferrofluid droplets on glass substrates presenting different hydrophilicities. By using the sessile drop technique, we investigate how the relaxation dynamics of the contact angle is affected by an external magnetic field. Our results show that the field effects on the shape and contact angle of ferrofluid drops are strongly sensitive to the effective interaction between the carrier liquid and the solid substrate. Considering a spherical cap approximation to the magnetic fluid droplet, we use the molecular-kinetic theory to analyze the time evolution of the contact angle. In particular, we estimate how the magnetic field affects the wetting free-energy and the surface density of adsorption sites. The present results show that the external magnetic field might play a significant role in the wetting dynamics of hydrocarbon-based magnetic droplets by affecting its activation free energy, the surface density of adhesion sites and the equilibrium contact angle.