Measuring the deformation of a ferrogel sphere in a homogeneous magnetic field

Abstract

A sphere of a ferrogel is exposed to a homogeneous magnetic field. In accordance to theoretical predictions, it gets elongated along the field lines. The time-dependence of the elastic shear modulus causes the elongation to increase with time analogously to mechanic creep experiments, and the rapid excitation causes the sphere to vibrate. Both phenomena can be well described by a damped harmonic oscillator model. By comparing the elongation along the field with the contraction perpendicular to it, we can calculate Poisson's ratio of the gel. The magnitude of the elongation is compared with the theoretical predictions for elastic spheres in homogeneous fields.

Synthesis and characterization of uniaxial ferrogels with Ni nanorods as magnetic phase

“…Provided that a firm coupling of the particles to the polymer network -either by chemical linkage or steric confinement -exists, a mechanical response of the composite can be stimulated by an external magnetic field [2][3][4][5]. As an example, when a ferrogel is exposed to a magnetic field gradient, the magnetophoretic force acting on the particles is transferred to the polymer network leading to a large and rapid deformation of the ferrogel body.…”

Characterization of the actuator behavior of blended-system ferrogels

“…The surface effect has been studied extensively both theoretically [1], [9], [10], [11] and experimentally [12]. It was found that spheres of ferrogel can strain up to 2% when placed in a homogeneous magnetic field and form axisymmetrial non-spheroidal shapes with their axis aligned with the field direction.…”

Surface instabilities and magnetic soft matter

“…[16]. The magnetisation of the spherical sample was then measured by means of a fluxmetric magnetometer (Lake shore, model 480) at θ = 20 C. Figure 2 shows this data.…”

“…This is handy for many upcoming applications, such as soft actuators, magnetic valves, magnetoelastic mobile robots [8], artificial muscles [9] or magnetic controlled drug delivery [10][11][12][13]. Most of the applications are based on the continuous deformation of ferrogel bodies in gradient fields [14] or in homogeneous fields [15,16]. Another promising effect, which so far has not been exploited, is the drastic shape transition of ferrogels in the succession of the Rosensweig instability.…”