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Aligning nickel particles for joule heating in epoxy shape memory polymer using a magnetic field and linear vibration

One of the major remaining barriers to the widespread adoption of thermally activated shape memory polymer is the method used to heat them. Presented is an investigation into using 5 μm nickel particles aligned into chains as embedded joule heaters for epoxy shape memory polymer. The high density of particle chain heaters reduces the time and energy required to reach transition by minimizing excess heat required due to the low thermal conductivity of the polymer by heating the material more uniformly. The chains are formed by curing the polymer in a uniform magnetic field generated by two sets of N42SH neodymium magnets above and below the sample approximately 57 mm apart. Modeling of the induced magnetic field within and between particles during curing and an analytical model predicting particle mobility in a fluid with respect to vibration frequency and amplitude are presented and discussed in context to this work. Since epoxy resin has a high viscosity, particle mobility is encouraged by sonicating the sample at 300 Hz at an amplitude of approximately 50 μm prior to polymerization using an industrial shaker and Teflon guides. Copper mesh electrodes are attached to the resulting samples using 10% by volume nickel particle shape memory polymer epoxy. Significant particle alignment is confirmed via optical microscope images. Electrical resistivity is measured as low as 57 Ω mm at nickel volume concentrations of 1.0%. Infrared images of the samples during heating are presented, and electrical energy required with respect to sample thermal capacity is estimated.