Dénes Szabó

Direct observation of abrupt shape transition in ferrogels induced by nonuniform magnetic field

Unidirectional elongation of magnetic field sensitive polymer gels, called ferrogels, have been studied. In ferrogels, finely distributed colloidal particles having superparamagnetic behavior are incorporated into a swollen network. These particles couple the shape of the gel to the nonuniform magnetic field. Shape distortion occurs instantaneously and disappears when the external field is removed. A discontinuous elongation and contraction in response to infinite-small change in the external magnetic field has been observed and a theoretical interpretation based on coupled magnetic and rubber elastic properties is provided.

MAGNETISM AND COMPRESSIVE MODULUS OF MAGNETIC FLUID CONTAINING GELS

We have investigated the magnetism and have measured the compressive modulus of magnetic fluid containing gels, called ferrogels, in the presence of magnetic field. No hysteresis was shown in the magnetization curve of the ferrogel suggesting a super paramagnetic response. The equilibrium compressive modulus of the ferrogel was measured up to 4 kOe and the modulus with field was much higher than that without field. The mean change in modulus increased with increasing magnetic field, and it saturates above 2 kOe. The mean and maximum change in modulus at 4 kOe was 31 and 71 Pa which corresponds to 19% and 46% increases of that without field, respectively. The change in modulus has been analyzed theoretically and is well explained in terms of the magnetism of ferrogels.

Kinetics of the shape change of magnetic field sensitive polymer gels

Abstract This study focuses on the dynamical behaviour of magnetic-field-sensitive polymer gels. These gels have been prepared by introducing nanosized magnetic particles into polymer gels homogeneously. We have studied the kinetics of the motion of magnetic gels. The highest working frequency of magnetic gels has been established, and a simple, completed Kelvin model was suggested to describe the dynamical behaviour.

Magnetic Field Sensitive Polymeric Actuators

The recent advances in application of soft materials like polymer gels represent the beginnings of a new branch of engineering. Since the pioneering work done by Katchalsky’s group, it has been recognised that the contractile activity of polymer gels can be used to function as muscle-like soft linear actuators in advanced robotics, micromachines, biomimetic energy-transducing devices and controlled delivery systems [1–4].

MUSCULAR CONTRACTION MIMICED BY MAGNETIC GELS

The ability of magnetic-field-sensitive gels to undergo a quick controllable change of shape can be used to create an artificially designed system possessing sensor- and actuator functions internally in the gel itself. The peculiar magneto-elastic properties may be used to create a wide range of motion and to control the shape change and movement, that are smooth and gentle similar to that observed in muscle. Magnetic field sensitive gels provide attractive means of actuation as artificial muscle for biomechanics and biomimetic applications.

Nonhomogeneous, non-linear deformation of polymer gels swollen with magneto-rheological suspensions

Polymer gels swollen with a magneto-rheological suspension are highly elastic materials with considerable magnetic susceptibility. In this work the magnetic field induced deformation and motion of these magnetic polymer systems is discussed. We present a continuum material model by introducing magnetic equations into non-linear elasticity theory. The material properties of these magnetic rubber-like substances are characterized with a Langevin type magnetization and a neo-Hookean strain energy function. The non-linear character of the equations that describe the material properties and the nonhomogeneity of the deformation lead to a unique deformation mechanism. In order to demonstrate the characteristics of the magnetic field induced deformations we present numerical and finite element calculations and compare them with experimental results.

Comparative studies of electric- and magnetic-field-sensitive polymer gels

In this paper we give a summary of the effects of electric field on the shape and motility of polymer gels. We look over the advantages and disadvantages of the different stimuli from the applicability point of view. We also present the characteristic features of shape distortion of magnetic field sensitive gels which have been developed in our laboratory. A comparative study has been performed on the efficiency of biological muscles and magnetic gels. A simplified model for ferrogels functioning as artificial muscles is also presented.