Magnetite nanoparticles/chiral nematic liquid crystal composites with magnetically addressable and magnetically erasable characteristics

Abstract

A magnetite (Fe₃O₄) nanoparticle/chiral nematic liquid crystal (N*-LC) composite was prepared and filled into a planar treated cell. The Fe₃O₄ nanoparticles had been modified by oleic acid so that they could be better dispersed in the composite. When a magnetic field was scanned on the outer surface of the cell locally, Fe₃O₄ nanoparticles moved towards the inner surface of the cell correspondingly, and the black expected information was displayed. When the magnet was applied to the opposite outer surface, the information was erased. After polymer network walls were prepared in the composite, the resolution of the information displayed increased. Then, through the formation of hydrogen bonds between the nanoparticles and chiral pyridine compound (CPC) doped in the composite, the pitch length of the N*-LC could be adjusted by altering the intensity of the applied magnetic field. The composite doped with CPC could potentially be used as a material for a type of reflective colour paper with magnetically controllable characteristics.

Keywords:

• chiral nematic liquid crystals
• selective reflection
• hydrogen bond
• pitch

Acknowledgements

This study was financially supported by the National Natural Science Foundation of China (Grant No. 20674005 and No. 50725208), Key Program for Panel Display of 863 Program of China (Grant No. 2008AA03A318), State Key Project of Fundamental Research for Nanoscience and Nanotechnology (Grant No. 2006CB932301) and Doctoral Fund of the Ministry of Education of China (Grant No. 20050425850).