Thermal and mechanical characterization of high performance polymer fabrics for applications in wearable devices

Abstract

With advances in flexible and wearable device technology, thermal regulation will become increasingly important. Fabrics and substrates used for such applications will be required to effectively spread any heat generated in the devices to ensure user comfort and safety, while also preventing overheating of the electronic components. Commercial fabrics consisting of ultra-high molecular weight polyethylene (UHMW-PE) fibers are currently used in personal body armor and sports gear owing to their high strength, durability, and abrasion resistance. In addition to superior mechanical properties, UHMW-PE fibers exhibit very high axial thermal conductivity due to a high degree of polymer chain orientation. However, these materials have not been widely explored for thermal management applications in flexible and wearable devices. Assessment of their suitability for such applications requires characterization of the thermal and mechanical properties of UHMW-PE in the fabric form that will ultimately be used to construct heat spreading materials. Here, we use advanced techniques to characterize the thermal and mechanical properties of UHMW-PE fabrics, as well as other conventional flexible materials and fabrics. An infrared microscopy-based approach measures the effective in-plane thermal conductivity, while an ASTM-based bend testing method quantifies the bending stiffness. We also characterize the effective thermal behavior of fabrics when subjected to creasing and thermal annealing to assess their reliability for relevant practical engineering applications. Fabrics consisting of UHMW-PE fibers have significantly higher thermal conductivities than the benchmark conventional materials while possessing good mechanical flexibility, thereby showcasing great potential as substrates for flexible and wearable heat spreading application.

Thermal management and control of wearable devices

“…The thermal conductivity of natural fibers typically ranges from 0.025 to 0.1 W/m K while that of synthetic polymers is highly dependent on the crystallinity and molecular chain orientation as well as chemical composition.

Figure 2 Thermally conductive flexible or stretchable materials and structures (A) Dyneema denim fabric wave structures ( Candadai et al., 2021 ). Reprinted under Creative Commons License https://creativecommons.org/licenses/4.0/ .

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“… (A) Dyneema denim fabric wave structures ( Candadai et al., 2021 ). Reprinted under Creative Commons License https://creativecommons.org/licenses/4.0/ .…”

“…Thermal conductivity values that are an order of magnitude higher than those of typical amorphous polymers were obtained at high draw ratios. In more recent studies, semi-crystalline polyethylene fibers and nanofibers whose polymer chains were aligned using mechanical and/or electrostatic stretching have been reported to have thermal conductivity values well in excess of 20 W/m K ( Shen et al., 2010 ; Candadai et al., 2021 ). Fabrics made of such high-conductivity polymer fibers can achieve both high thermal conductivity (>9 W/m K) and good mechanical flexibility, 3-4 orders of magnitude higher than typical metals and comparable to commercial specialty fabrics.…”

Novel Biphasically and Reversibly Transparent Phase Change Material to Solve the Thermal Issues in Transparent Electronics

“…The separation of thermal and functional sections is problematic for tiny structural devices that require effective thermal management. Furthermore, certain portable transparent gadgets that come into close touch with customers require even more consideration for human thermal discomfort or even skin burns produced by heating up during usage, as well as the flexibility needed for ease of wear. , As transparent electronics continue to evolve toward miniaturization and integration, a transparent, compact mechanism for effective heat management is clearly required.…”

State-of-the-art, opportunities, and challenges in bottom-up synthesis of polymers with high thermal conductivity

“…The atomic-level design and synthesis of thermally conductive polymers by bottom-up approaches will provide new opportunities for making polymers with metal-like thermal conductivity, probing relationships between thermal transport properties and structures, and developing theory for better understanding thermal transport mechanisms. 34,44,75 Thermal transport properties in polymers can be manipulated through tuning the monomer composition, 4,9,10,31,83–85 crystallinity, 9,10,37,86,87 molecular weight, 88–93 type of cross-link, 88,94–100 monomer sequence of the copolymer, 101,102 intrachain and interchain interactions, 13,33,48,97,103–112 chain orientation and assembly, 12,15,21,32,36,40,65,69,75,113–124 functional group, 12,34,82 density, 125 and/or chain morphology. 12,15,24,32,35,75,77,95,126–137 In contrast to bottom-up synthesis strategies, top-down methods, such as stretching, 29 solution shearing, 42 extrusion, 5 and thermal annealing 138 also provide new possibilities for engineering polymer chain structures and making polymers with high thermal conductivity.…”