Magnetic property of oriented films of cellulose nanocrystal/carrageenan composites containing iron oxide nanoparticles: Effect of anisotropic aggregation of the nanoparticles

摘要

Magnetically anisotropic materials were fabricated in film form from cellulose nanocrystal (CNC)/i-carrageenan (i-Car) gelatinous composites (5-30 wt% CNC) via repeated "in situ synthesis" of iron oxide nanoparticles therein and subsequent drawing of the inorganic-polysaccharide hybrids in a wet process. Basic magnetic properties of the film samples were examined by superconducting quantum interference device (SQUID) magnetometry. After three cycles of the in situ synthesis process, the saturation magnetization of as-dried (undrawn) hybrid samples reached a practically high value of 15 emu (g sample)(-1) thereabout at 298 K, reflecting a remarkable capacity of i-Car as a gel matrix for the iron oxide synthesis. The drawn samples showed different amplitudes in the magnetization (M-parallel to > M-perpendicular to.) when measured in two setups where the applied field was parallel (parallel to) or perpendicular (perpendicular to) to the draw direction. The extent of the anisotropy was relatively higher at the composition of CNC/i-Car = 10/90 (w/w) than the other explored compositions, indicating that similar to 10 wt% is an optimal concentration of CNC as orientation promoter in the drawing of such inorganic-hybridized i-Car networks. Morphological observations were made for selected drawn hybrids by FE-SEM and atomic force/magnetic force microscopy. It was revealed that iron oxide nanoparticles (10-30 nm phi) were assembled in a long larger aggregate (<1 mm length and <100 nm diameter) and arrayed along the draw direction. A specific response of the drawn films to an external magnetic stimulus was also visualized, and it was reasonably attributed to an effect of the magneto-anisotropy coming from the preferred orientation of the particle aggregates. (C) 2016 Elsevier Ltd. All rights reserved.