High speed magneto-optical valve: Rapid control of the optical transmittance of aqueous solutions by magnetically induced self-assembly of superparamagnetic particle chains

Magneto-optical effects of magnetorheological fluids are of interest for applications including magnetic field sensors and optical modulators. Here, we describe the rapid control of the optical transmittance of a magnetorheological fluids by rotating columnar arrays of self-assembled superparamagnetic bead (SPB) chains by applying an external field using a permanent magnet. The columnar arrays of chains of magnetic beads acted as optical valves exhibiting distinct “on” and “off” states. For a given magnetic field, the maxima/minima of transmittance occurred when the applied field was parallel/perpendicular to light path and the intensity of light at the maxima varied with the strength of the applied field. Importantly, the response time for rotating the columnar arrays of magnetic chains was very rapid, and in the millisecond range. Our procedure provides a simple means for producing fast, magneto-optical switches that does not require cumbersome and power consuming electromagnetic coils and related perip...