Wettability of Ionic Liquids in High Magnetic Fields

Here, we demonstrate that high magnetic fields alter the wettability of water and ionic solutions on the single-crystal α-Al₂O₃. We investigated the relationship between the substrate crystal orientation, material magnetism, liquid conductivity, and the surface contact angle. Applying high magnetic fields decreased the water contact angles on all of the surface orientations studied, and the reduction was larger for more magnetic substrates. For ionic solutions, high magnetic fields increased the contact angle on the (0001) α-Al₂O₃ surface but decreased the contact angles on the (112 ̅0), (101̅0), and (011̅2) surfaces. We attribute these orientation-dependent ionic solution responses to competition between the field-induced sample magnetization energy and the Lorentz force acting on the ionic solution. Overall, this work provides new magnetic-field-based strategies for changing the wettability and provides guidelines for fabricating novel microfluidic systems or biointerfaces with in situ magnetic control.