ASIAA/CCMS/IAMS/LeCosPA/NTNU-Physics/NTU-Physics Joint Colloquium
Time: March 21 (Tue) 14:20
Place: Room 104(Chin-Pao Yang Lecture Hall), CCMS-New Phys. building
Speaker: Hong-Yu Chu (National Cheng Chi University)
Topic: Ferrofluid drop in DC/AC magnetic field
Abstract:
We report that the responses of the ferrofluid drop in the time-constant and time-varying magnetic field. Ferrofluid material not only exhibits the fluid property like surface tension and element transport but also can be manipulated by the magnetic field. A model is proposed that regards the bulk magnetization of the ferrofluid drop in the magnetic field as a magnetic dipole. The magnetic length coefficient denoting the ratio of the magnetic length of the dipole and the length of the major axis of the deformed drop is found scaling relation and is consistent with experimental results. The prolate-shaped traveling ferrofluid drops are demonstrated to measure the gradient of the magnetic field in space. We also report the stretch–shrink–rotation motion of a ferrofluid drop in a time-varying magnetic field along the x direction. The drop performs stretch and shrink motion at low magnetic field due to the balance of magnetic force and surface tension as observed in many investigations, but it exhibits rotating motion at high magnetic field. We find that the size of elongated drop shows transitions at Rayleigh frequency of drop and at the frequency with maximum growth rate. The phase diagram of growth rate to the frequency and the strength of applied magnetic field reveals the threshold for drop to rotate. It is suspected that the induced transverse magnetization for the magnetic torque is associated with the phase lag between the time-varying magnetic field and the deformation of drop which leads to the rotation of drop.