Microscale model of ferrogel samples with different polymer matrix structure

Abstract

Ferrogels is a group of soft magnetically active composite materials with polymer gel (generally hydrogel) matrix filled by ferromagnetic colloid particles. Pronounced interrelation between magnetic and mechanical properties of ferrogels together with their biocompatibility make ferrogels attractive for various bio-medical applications. Evolution of ferrogel internal structure plays pivotal role in formation of unique magnetic mechanical behavior of ferrogel. Difficulty of direct observation on the structure scales enhances importance of theoretical (and numerical) study on ferrogels. The paper presents the results of modeling the behavior of a small ferrogel sample (up to 1000 magnetic particles) obtained using the method of coarse-grained molecular dynamics. The composite matrix is imitated by a quasi-regular mesh of ideal spring-beads chains, and single-domain magnetic particles with uniaxial anisotropy are placed in nodes of this mesh. The state of the sample is considered in the absence of external action, as well as in cycles of quasi-static magnetization for two variants of the topology of the polymer network (simple cubic and diamond-like), for different values of the magnetic moment of particles, their concentration, and anisotropy energy. Simulation has shown that samples with softer matrix (i.e. of diamond-like structure) demonstrate more noticeable magnetic deformation effects. The presence of magnetic anisotropy excites additional local stresses during particle moment reorientations, which complicates particles clustering and sample magnetization. Moreover, it has been found that anisotropy energy determines the character of the field induced change in the sample volume.