Producing a magnetically anisotropic soft material: synthesis of iron oxide nanoparticles in a carrageenan/PVA matrix and stretching of the hybrid gelatinous bulk

Abstract

We propose a method for preparing magnetically anisotropic soft materials that includes chemical loading (in situ synthesis) of iron oxide nanoparticles in a matrix composed of κ-carrageenan (Car) and poly(vinyl alcohol) (PVA) followed by mechanical stretching of the hybrid in a wet process. Anionic Car was used to accommodate the iron oxide nanoparticles and was blended in advance with PVA, which has the ability of high orientation. Scanning electron microscopy revealed that the loaded granular iron oxide nanoparticles (50–100 nm) formed elliptical clusters upon stretching of the hybrid composite. Wide-angle X-ray diffraction measurements indicated that the PVA constituent was oriented in the draw direction. With the orientation of the composite matrix, the incorporated iron oxide nanoparticles gathered to form elliptical clusters. The drawn samples showed different amplitudes in the magnetization (M|| > M⊥) when measured in two setups in which the applied field was parallel (||) or perpendicular (⊥) to the draw direction. The specific responses of the drawn sheets to an external magnetic stimulus were visualized and were reasonably attributed to an effect of the magnetic anisotropy created by the preferred orientation of the nanoparticle aggregates. We prepared magnetically anisotropic soft materials by in situ synthesis of iron oxide nanoparticles in a matrix composed of κ-carrageenan and PVA followed by mechanical stretching of the hybrid in a wet process. With the orientation of the composite matrix, the incorporated iron oxide nanoparticles gathered to form elliptical clusters. The drawn samples showed different magnetizations depending on the direction of magnetic field application. The specific responses were macroscopically visualized and were attributed to the magnetic anisotropy created by the preferred orientation of the nanoparticle aggregates.