Inductive activation of magnetite filled shape memory polymers
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Thermally activated shape memory polymers are a desirable material for use in dynamic structures due to their large strain recovery, light weight, and tunable activation. The addition of ferromagnetic susceptor particles to a polymer matrix provides the ability to heat volumetrically and remotely via induction. Here, remote induction heating of magnetite filler particles dispersed in a thermoset matrix is used to activate shape memory polymer as both solid and foam composites. Bulk material properties and performance are characterized and compared over a range of filler parameters, induction parameters, and packaging configurations. Magnetite filler particles are investigated over a range of power input, in order to understand the effects of particle size and shape on heat generation and flux into the matrix. This investigation successfully activates shape memory polymers in 10 to 20 seconds, with no significant impact of filler particles up to 10wt% on mechanical properties of shape memory foam. Performance of different particle materials is dependent upon the amplitude of the driving magnetic field. There is a general improvement in heating performance for increased content of filler particles. Characterization indicates that heat transfer between the filler nanoparticles and the foam is the primary constraint in improved heating performance. The use of smaller, acicular particles as one way to improve heat transfer, by increasing interfacial area between filler and matrix, is further examined.