Magnetite (Fe3O4) nanoplates (F) have anisotropic shapes and high aspect ratios, which are expected to show new alignments under magnetic field. To control the dispersion of F, one available method is to introduce polymer chains on the surface of F to develop the advantages of two materials. F were first synthesized and then were modified by poly(methyl methacrylate) (PMMA) chains via surface-initiated atom transfer radical polymerization (SI-ATRP). Before grafting PMMA chains, a transmission electron microscope (TEM) image in Figure 1a indicated that the unmodified F show a stacked alignment under magnetic field. However, the PMMA-modified F (FP) indeed showed good dispersion stability, lyotropic liquid-crystalline properties, and a fast response to the external magnetic field in organic solution. More importantly, Figure 1b indicated that FP could show a nematic columnar structure under magnetic field. The nematic columnar structure along the magnetic field direction is a new example for the magnetic responsiveness of FP in compare with the stacked alignment of unmodified F in Figure 1c. In fact, the existence of PMMA chains affected the interparticle interaction between two nanoplates as shown in Figure 1d. The ultrasmall-angle synchrotron X-ray scattering (USAXS) measurements also verified that the lyotropic liquid crystals could form a uniaxially aligned nematic columnar structure under magnetic field. Hence, the long PMMA chains provided us more possibilities to change and control the alignments of F utilizing the magnetic field.

Stimuli responsiveness of lyotropic liquid-crystalline PMMA-Grafted Fe3O4 nanoparticles with anisotropic shapes under magnetic field

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