Tunable magnetochromic elastomer with instantaneous color changes

A controllable magnetochromic elastomer is developed by dissolving magnetic nanoparticles (MNPs) in poly(ethylene glycol)-200 (PEG-200) and emulsifying the solution in polydimethylsiloxane (PDMS) using a high-shear Speedmixer. The MNPs are aligned in order along the direction of the externally applied magnetic field, causing the material to become transparent and realizing a switch on/off function. Both particle size and size distribution were observed to affect magnetochromic response, and use of an ultrasonication bath was shown to prohibit MNP agglomerations. In addition, the surfactant surface-modified MNPs synthesized via co-precipitation were shown to possess both a smaller primary size and a narrower size distribution compared to non- treated commercial MNPs, leading to improved MNP dispersion stability in PEG-200. The optimized silicone elastomer-with 40 parts per hundred rubber (phr) PEG-200 and 3 wt% MNPs modified by citric acid surfactant-exhibits instantaneous and reversible color change when exposed to an external magnetic field. The color changing efficiency and fast response time of the magnetochromic elastomer developed here are suited to a variety of color tuning applications: e. g., bio-sensors and anticounterfeiting labels.