2.3. Characterization

X-ray diffraction (XRD, X Pert PRO MPD, Almelo, the Netherlands) was used to test the crystal structure of Fe₃O₄. The scanning range was from 5° to 70° and the scanning speed was 3.6°/min.

Particle sizes were characterized by Laser Particle Size Analyzer (Master sizer 2000, Malvern Instruments Ltd., Malvern, UK), ethanol was used as a dispersant, and the shade was 3.5%.

The specific surface areas were tested by a specific surface area and pore size tester (ST-MP-9, Quantachrome Instruments, Beijing, China). The test results were analyzed by the multipoint Brunauer-Emmet-Teller (BET) method. Before the test, samples were kept at 423 K in a vacuum environment for about 2 h.

VSM (BKT-4500Z, Quantum Design Ltd., San Diego, CA, USA) was carried out to measure the saturated magnetic strengths of particles, in open circuit mode at normal temperature.

The morphology of the poly(butyl-methacrylate)-based composite material was studied by scanning electron microscopy (SEM; ZEISS EV0 MA15, Carl Zeiss microscopy Co., Ltd., Jena, Germany). To prepare samples for SEM analysis, the composites were quenched in liquid nitrogen and cryogenically fractured.

Elemental analysis was carried out at Energy Dispersive Spectrometer (EDS; Elementar, Langenselbold, Germany) for determination of the Fe, O and C content.

Dynamic mechanical analysis (DMA) was carried out on Q800 (TA Instruments, New Castle, DE, USA) by using a dual cantilever clamp and a testing method of temperature ramp-frequency sweep with a frequency of 1 Hz. The samples were trimmed to dimensions of 20 mm long, 12 mm wide and 3 mm thick. The oscillation strain amplitude was set to be 15 mm.