Stiffness-tunable device encapsulating magnetorheological fluids in a thin flexible polymer structure

Abstract

We herein propose a liquid encapsulation method for a submillimeter-size polydimethylsiloxane (PDMS) membrane. We selected a magnetorheological (MR) fluid as the liquid to be encapsulated in the membrane, the stiffness of which is tuned by an external magnetic field. The proposed method consists of two steps. First, a PDMS bump was made to contact a MR fluid, and a MR fluid droplet was formed on top of the bump. Next, the droplet was dipped in a PDMS casting solution and fully covered with a PDMS casting solution layer. Finally, the droplet was encapsulated in the membrane after curing. We experimentally confirmed that the radius of the PDMS bump and the viscosity of the MR fluid were variable parameters that could determine the height of the structure. We also evaluated the stiffness characteristics of the structure. The calculated Young's modulus indicated that the stiffness varied from 70 kPa to 180 kPa in the presence of an external magnetic field. The results indicated that the structure could emulate relatively soft materials and could be applied to a tactile display used in palpation.