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Shape memory polymers are gaining significant interest as one of the major constituent materials for the emerging field of 4D printing. While 3D-printed metamaterials with shape memory polymers show unique thermomechanical behaviors, their thermal transport properties have received relatively little attention. Here, we show that thermal transport in 3D-printed shape memory polymers strongly depends on the shape, solid volume fraction, and temperature and that thermal radiation plays a critical role. Our infrared thermography measurements reveal thermal transport mechanisms of shape memory polymers in varying shapes from bulk to octet-truss and Kelvin-foam microlattices with volume fractions of 4%–7% and over a temperature range of 30–130 °C. The thermal conductivity of bulk shape memory polymers increases from 0.24 to 0.31 W m−1 K−1 around the glass transition temperature, in which the primary mechanism is the phase-dependent change in thermal conduction. On the contrary, thermal radiation dominates heat transfer in microlattices and its contribution to the Kelvin-foam structure ranges from 68% to 83% and to the octet-truss structure ranges from 59% to 76% over the same temperature range. We attribute this significant role of thermal radiation to the unique combination of a high infrared emissivity and a high surface-to-volume ratio in the shape memory polymer microlattices. Our work also presents an effective medium approach to explain the experimental results and model thermal transport properties with varying shapes, volume fractions, and temperatures. These findings provide new insights into understanding thermal transport mechanisms in 4D-printed shape memory polymers and exploring the design space of thermomechanical metamaterials.

We propose and demonstrate a two-dimensional 4-bit fully optical nonvolatile memory using Ge2Sb2Te5 (GST) phase change materials, with encoding via a 1550 nm laser. Using the telecom-band laser, we...

Heterogeneous and complex electronic packages may require unique thermomechanical structures to provide optimal heat guiding. In particular, when a heat source and a heat sink are not aligned and do not allow a direct path, conventional thermal management methods providing uniform heat dissipation may not be appropriate. Here we present a topology optimization method to find thermally conductive and mechanically stable structures for optimal heat guiding under various heat source-sink arrangements. To exploit the capabilities, we consider complex heat guiding scenarios and three-dimensional (3D) serpentine structures to carry the heat with corner angles ranging from 30 deg to 90 deg. While the thermal objective function is defined to minimize the temperature gradient, the mechanical objective function is defined to maximize the stiffness with a volume constraint. Our simulations show that the optimized structures can have a thermal resistance of less than 32% and stiffness greater than 43% compared to reference structures with no topology optimization at an identical volume fraction. The significant difference in thermal resistance is attributed to a thermally dead volume near the sharp corners. As a proof-of-concept experiment, we have created 3D heat guiding structures using a selective laser melting technique and characterized their thermal properties using an infrared thermography technique. The experiment shows the thermal resistance of the thermally optimized structure is 29% less than that of the reference structure. These results present the unique capabilities of topology optimization and 3D manufacturing in enabling optimal heat guiding for heterogeneous systems and advancing the state-of-the-art in electronics packaging.

Ultralight architected materials are favorable for thermal insulation purposes in gas turbines, hypersonic, electronic packaging, and aerospace applications. The effective mechanical properties and thermal conductivity of these structures can be engineered via their architectural configurations, making them an excellent candidate to meet requirements of these applications. Advanced manufacturing has paved the path for fabrication of these structures, reaching the properties that is beyond the material space capacity. Among all architected materials, ultralight hollow nickel lattices by exhibiting 99.9% porosity and complete recoverability after compression above 50% strain have appeared very promising. The challenge for reporting accurate data on the thermal conductivity of these structures is performing a non-contact measurement methodology. Here, we designed a new IR thermography-based setup for thermal conductivity measurement of mesoscale cellular materials. The effective thermal conductivity of two hollow doped nickel samples with volume fraction of 0.09% and two different surface finishes (rough and polished) is measured as a function of compressive force and temperature. Surface properties is proposed as a new control knob for changing the effective thermal properties in the architected materials.

Plasmonic structures have long proved their capabilities to concentrate and manipulate light in micro- and nano-scales that facilitate strong light-matter interactions. Besides electromagnetic properties, ultra-small plasmonic structures may lead to novel applications based on their mechanical properties. Here we report efficient coupling between optical absorption and mechanical deformation in nanoscales through plasmonically enhanced fishbone nanowires. Using tailorable absorbers, free-space radiation energy is converted into heat to thermally actuate the suspended nanowires whose deformation is sensed by the evanescent fields from a waveguide. The demonstration at 660 nm wavelength with above 30% absorption shows the potential of the device to detect nW/√Hz power in an uncooled environment.

Technological advances in fabrication method have paved the path to achieve periodic metamaterials in the scale of micrometer and nanometer which enable us to manipulate the thermal and mechanical properties of the selected materials independently. While mechanical properties of these artificial lattices have been very well studied, their thermal properties have remained unaddressed. These architectural features will follow the combined behavior of design and material instead of following them individually. In this paper, we report the impact of controlling length and pitch sizes of microlattices that leads to a design space for desired thermal conductivity. The results are supported by the implementation of conventional Fuchs & Sondheimer (FS) size effect simulation on Matthiessen’s rule following by several models on Effective Medium Theory (EMT) for capturing the volume fraction. By choosing carbon as our case study, we applied a material with a wide range of thermal conductivity in contemplation of elevating our design space.