Comparative study of optical properties by clay minerals with magnetic coating in colloidal dispersion under an external magnetic field

Abstract In this paper, representative nanoscale clay minerals@Fe3O4 nanocomposites (palygorskite@Fe3O4 nanorods, sepiolite@Fe3O4 nanowires and montmorillonite@Fe3O4 nanosheets) have been used as building blocks to prepare stable colloid solutions-. All of them produce a similar magnetically controlled liquid crystal with Bragg diffraction under an external magnetic field. Their optical properties are affected by magnetic field intensity, magnetic field direction and solid content. Since the building blocks of these three magnetically controlled liquid crystals are rod-shaped, fibrous, and sheet-like respectively, there are a lot of differences in orientation structures and optical properties between them. Under the external magnetic field, palygorskite@Fe3O4 and sepiolite@Fe3O4 can form a one-dimensional ordered structure on a solid substrate, while montmorillonite@Fe3O4 can form two-dimensional order structure. A bright Bragg diffraction light can be obtained by aligning palygorskite@Fe3O4 and montmorillonite@Fe3O4 sols on a solid substrate at a concentration of 0.0125 mg/mL, while sepiolite@Fe3O4 cannot. The light transmittance of the three liquid crystals is also different. Palygorskite@Fe3O4 is better than montmorillonite@Fe3O4, and montmorillonite@Fe3O4 is better than sepiolite@Fe3O4. The comparative study of these three different magnetic-clay-mineral-composite-based dispersions is meaningful and interesting from both fundamental and applied perspectives.