Controlled self-assembly and alignment of organic-magnetic hybrid microrods

Growth control and alignment of rod-like self-assemblies have been studied widely since rod-like particulates have enormous potential as components of modern devices. In this study, size-controlled magnetic microrods were prepared by evaporation-induced self-assembly (EISA) from the self-assembling organic molecule and a magnetic γ-Fe₂O₃ nanoparticle mixture. Sizes of the magnetic microrods were controlled by adjusting solvent evaporation temperature to produce magnetic microrods in hundreds of micrometers with high aspect ratio. Thin microrods with an aspect ratio of 129.6 were obtained by lowering the temperature to at -20°C. The prepared magnetic microrods showed superparamagnetic properties similar to that of γ-Fe₂O₃ nanoparticles, while the pristine microrods showed diamagnetism. Unidirectional alignment of the magnetic microrods was achieved by applying an external magnetic field. Further, the prepared magnetic microrods had different refractive indices in the axial and radial directions, which is due to the alignment of chemical bonds of the building block molecules during self-assembly. The practical outcome of this study is that fabricating self-assembled structures into ordered structures with controlled sizes is readily achievable.