(538g) Ferrofluid High Internal Phase Emulsion Polymer Foams for Soft, Deformable Magnetic Elastomer Composites

Magnetic materials are vital in traditional electronics for critical functionalities, but these magnetic components are rigid and not deformable. However, there is a rapidly increasing need for soft, deformable electronics, a dynamic, ever-growing field pushing the boundaries of the state-of-the-art in wearable health monitors/sensors, biomimetic robotics, and human−machine interface biocompatibility. Typical magnetic materials are difficult to integrate into these soft, deformable electronics due to high modulus and inelastic behavior. Therefore, to utilize the vast functionality of traditional, rigid electronics, magnetic materials must be engineered to be deformable, yet high performing. A previously unexplored avenue for such materials is encapsulating a high concentration of magnetic particles that are in fluid, particularly ferrofluids (FF), inside of polymer composite pores utilizing high internal phase emulsification. This is a distinct method of magnetic material incorporation of magnetic particles from magnetorheological elastomers, as the particles have complete freedom to orient and form chains in a fluid while the material in bulk is still solid. In this work, formulation factors, including the emulsifiers, curing kinetics, and interfacial interaction of emulsified nanoparticles, that are essential for fabricating effectual ferrofluid high internal phase emulsion polymer foams (polyHIPE) utilizing polydimethylsiloxane (PDMS) are manipulated to ensure a stable cured dispersion of ferrofluid and successful inclusion of the ferrofluid inside of PDMS pores. Porous structure, magnetic properties, and mechanical behavior were all characterized of the successfully fabricated final FF/PDMS polyHIPE. Visible particle aggregation with pores ranging from 10 and 50 μm were observed from digital microscopy. The FF/PDMS polyHIPE had an M_s of 18 A•m²/kg and susceptibility of 0.69. These properties are expectedly reduced as compared to neat ferrofluid, however they are an improvement on ferrofluid polymer dispersions in previous published work. Coercivity and magnetic remanence decreased, as well, in respect to the neat ferrofluid used. Rheological behavior demonstrated a significantly lower modulus of the FF/PDMS polyHIPE than both neat PDMS and any magnetic composite materials currently in literature. The FF/PDMS polyHIPE fabricated and characterized in this work demonstrated both the promising potential for deformable magnetic materials to be based on emulsification of high concentrations of magnetic fluid into elastomers and conceivable future possibility to fabricate much higher performing deformable materials utilizing higher concentrations of magnetic fluids that possess superior magnetic behavior.