Influence of the Drop Volume and Applied Magnetic Field on the Wetting Features of Water-based Ferrofluids

Abstract

In this work, the influence of the drop volume and applied magnetic field on the wetting features of water-based ferrofluids, is experimentally investigated. Firstly, water drops with volume in the range of 0.1–100 micro-liters are placed, by using micro-pipettes, on bare and coated acrylic plates, to gain reference data concerning the contact angle. Then, drops of water-based ferrofluid, with the volume ranging from 1 to 10 micro-liters, are set on bare acrylic plates, which are placed into the uniform magnetic field created, in normal direction to the plate, by using permanent magnets. Since the ferrofluid drops are elongated along the magnetic field, the contact angle increases at augmentation of the magnetic flux. Besides, when a critical magnetic flux is exceeded, ferrofluid drop loose contact with the plate and jumps towards the magnet. A heuristic equation to predict the fluctuation of the liquid surface tension versus the drop volume, and also versus the ratio of the applied magnetic field energy to the kinetic energy of the magnetic particles dispersed into the water-based ferrofluid, is suggested.