Stretching-Induced Thermal Conductivity Change in Shape-Memory Polymer Composites

Abstract

Abstract Active thermal materials like thermal diodes, regulators, and switches have the potential to revolutionize thermal management, creating an opportunity for significant energy savings. We present results on a proposed thermal switching composite that changes its thermal conductivity based on applied strain. The composite is constructed of highly crystalline, high aspect ratio cellulose nanocrystal (CNC) nanorods embedded in a shape-memory polymer matrix. The properties of the matrix allow for changes to the mechanical state to be indefinitely retained and also for the state to be reversed; this work is the first step in demonstrating that the thermal state exhibits similar reversibility. Measurements of the neat matrix polymer show a factor of three increase in thermal conductivity with applied strain up 100% and abrupt decrease beyond this strain level. A twofold increase in the thermal conductivity is achieved for the proof-of-concept composite at 100% strain. By comparing the measured results to a Maxwell mixing model, the primary drivers of the thermal conductivity change are traced to changes in crystallinity of the matrix and CNC alignment.