Wettability of Magnetically Susceptible Surfaces

Abstract

We study the wetting properties by water of composite surfaces constructed from solid micrometer-size magnetic particles anchored at the interface of polymer films, in relation to the structure of the surface determined by atomic force microscopy and confocal microscopy. We measure the advancing and receding contact angles as functions of the anchoring position of the particles, and we show that the wetting hysteresis is caused mainly by the hydrophilicity of the magnetic particles. We show that the structure and the wettability of these surfaces can be strongly modified by the action of external magnetic field gradients. The effects of tangential gradients are dominant over normal ones and can be distinguished in two regimes according to their magnitude: the wetting hysteresis is controlled either by the hydrophilicity of the particles or by the induced roughness of the surface.