Shear elasticity of isotropic magnetic gels.

The paper deals with a theoretical study of the effective shear modulus of a magnetic gel, consisting of magnetizable particles randomly and isotropically distributed in an elastic matrix. The effect of an external magnetic field on the composite modulus is the focus of our consideration. We take into account that magnetic interaction between the particles can induce their spatial rearrangement and lead to internal anisotropy of the system. Our results show that, if this magnetically induced anisotropy is insignificant, the applied field reduces the total shear modulus of the composite. Strong anisotropy can qualitatively change the magnetomechanic effect and induce an increase of this modulus with the field.

Hysteresis of the magnetic properties of soft magnetic gels.

We present results of an experimental and theoretical study of the magnetic properties of soft magnetic gels consisting of micron-sized magnetizable particles embedded in a polymer matrix. Experiments demonstrate hysteretic dependences of composite magnetization on an applied magnetic field and non-monotonic, with maximum, dependence of the sample susceptibilities on the field. We propose a theoretical approach which describes the main physical features of these experimental results.

Anisotropy of the magnetoviscous effect in ferrofluids containing nanoparticles exhibiting magnetic dipole interaction.

The aim of this work has been the investigation of the anisotropy of the viscosity of a ferrofluid with magnetically interacting particles which are able to form structures in an applied magnetic field. The results of the experiments show a significant deviation from the case of a fluid without strong dipolar interactions. Furthermore, we have determined the dependence of the ratio of the viscosity coefficients on shear rate providing an insight into the microstructural reasons for the observed effects.

Magnetic measurements on frozen ferrofluids as a method for estimating the magnetoviscous effect.

Magnetic measurements on frozen ferrofluids with and without significant structure formation in an applied magnetic field have been performed. The results of these investigations were compared with the magnetic field dependent rheological properties for two different kinds of ferrofluids. Magnetic experiments performed similarly to conventional field cooled-field warming magnetic tests show the contribution of magnetic domain blocking and structure reorganization to the rheology of ferrofluids. Our efforts have shown the possibility of giving an estimate of the magnetoviscous effect by considering the temperature dependence of the magnetization of a frozen sample.

Motion of ferroparticles inside the polymeric matrix in magnetoactive elastomers.

Ferroelastic composites are smart materials with unique properties including large magnetodeformational effects, strong field enhancement of the elastic modulus and magnetic shape memory. On the basis of mechanical tests, direct microscopy observations and magnetic measurements we conclude that all these effects are caused by reversible motion of the magnetic particles inside the polymeric matrix in response to an applied field. The basic points of a model accounting for particle structuring in a magnetoactive elastomer under an external field are presented.