Organic phase change materials are usually insulating in nature, and they are unlikely to directly trigger latent heat storage through an electrical way. Here we report a multifunctional phase change composite in which the energy storage can be driven by small voltages (e.g., 1.5 V) or light illumination with high electro-to-heat or photo-to-thermal storage efficiencies (40% to 60%). The composite is composed of paraffin wax infiltrated into a porous, deformable carbon nanotube sponge; the latter not only acts as a flexible encapsulation scaffold for wax but also maintains a highly conductive network during the phase change process (for both solid and liquid states). Uniform interpenetration between the nanotube network and paraffin wax with high affinity results in enhanced phase change enthalpy and thermal conductivity compared to pure paraffin wax. Our phase change composite can store energy in practical ways such as by sunlight absorption or under voltages applied by conventional lithium-ion batteries.
Single-Frequency Thermal Wave Radar Imaging (SF-TWRI) was introduced and used to obtain quantitative thickness images of coatings on an aluminum block and on polyetherketone, and to image blind subsurface holes in a steel block. In SF-TWR, the starting and ending frequencies of a linear frequency modulation sweep are chosen to coincide. Using the highest available camera frame rate, SF-TWRI leads to a higher number of sampled points along the modulation waveform than conventional lock-in thermography imaging because it is not limited by conventional undersampling at high frequencies due to camera frame-rate limitations. This property leads to large reduction in measurement time, better quality of images, and higher signal-noise-ratio across wide frequency ranges. For quantitative thin-coating imaging applications, a two-layer photothermal model with lumped parameters was used to reconstruct the layer thickness from multi-frequency SF-TWR images. SF-TWRI represents a next-generation thermography method with superior features for imaging important classes of thin layers, materials, and components that require high-frequency thermal-wave probing well above today's available infrared camera technology frame rates.
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