Tunable thermal transport in 4D printed mechanical metamaterials

[Display omitted] •The thermal transport of 4D printed shape memory polymers strongly depends on their programmed deformation due to the interplay of conduction and radiation effects.•Stretching-dominated architecture enables sharp thermal conductance tuning due to buckling.•Bending-dominated architecture enables fine thermal conductance tuning in the absence of buckling.•4D printed shape memory polymer mechanical metamaterials with unique deformation and shape recoverability mechanisms can lead to a novel thermal switch. Here the authors present an active thermal control system using 4Dprinted shape memory polymers and demonstrate how distinct deformation mechanisms lead to unique, tunable thermal properties using stretching- and bending-dominated architectures. Infrared thermography measurements with varying temperature and compression settings show that at low strains, radiation drives the effective conductance increase as the view factors among the struts increase with increasing strain, and at higher strains, conduction drives the effective conductance increase as the strut-to-strut contact areas increase. The effective thermal conductance increases from 4.41mW/K to 14.52mW/K and from 3.23mW/K to 10.48mW/K for the Kelvin foam and octet-truss microlattices, respectively, as strain increases from 0% to approximately 70%. As the strain is adjusted, the stretching-dominated octet-truss architecture exhibits abrupt changes in shape and conductance due to buckling. The bending-dominated Kelvin foam architecture allows for gradual geometric changes and precise tuning of thermal conductance. These findings provide a new understanding of thermal transport phenomena in 4D-printed metamaterials, which may be a breakthrough in tunable thermal systems.