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1. Pushing the Limits of Heat Conduction in Covalent Organic Frameworks Through High‐Throughput Screening of Their Thermal Conductivity

   https://doi.org/10.1002/smll.202401702  

   Thakur, Sandip ; Giri, Ashutosh ( April 2024 , Small)

   Tailor‐made materials featuring large tunability in their thermal transport properties are highly sought‐after for diverse applications. However, achieving `user‐defined’ thermal transport in a single class of material system with tunability across a wide range of thermal conductivity values requires a thorough understanding of the structure‐property relationships, which has proven to be challenging. Herein, large‐scale computational screening of covalent organic frameworks (COFs) for thermal conductivity is performed, providing a comprehensive understanding of their structure‐property relationships by leveraging systematic atomistic simulations of 10,750 COFs with 651 distinct organic linkers. Through the data‐driven approach, it is shown that by strategic modulation of their chemical and structural features, the thermal conductivity can be tuned from ultralow (≈0.02 W m⁻¹K⁻¹) to exceptionally high (≈50 W m⁻¹K⁻¹) values. It is revealed that achieving high thermal conductivity in COFs requires their assembly through carbon–carbon linkages with densities greater than 500 kg m⁻³, nominal void fractions (in the range of ≈0.6–0.9) and highly aligned polymeric chains along the heat flow direction. Following these criteria, it is shown that these flexible polymeric materials can possess exceptionally high thermal conductivities, on par with several fully dense inorganic materials. As such, the work reveals that COFs mark a new regime of materials design that combines high thermal conductivities with low densities.

    

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2. Thermal Conductivity Determination of Ga-In Alloys for Thermal Interface Materials Design

   https://doi.org/10.3390/thermo2010001  

   Maivald, Parker ; Sridar, Soumya ; Xiong, Wei ( March 2022 , Thermo)

   Thermal interface material (TIM) that exists in a liquid state at the service temperature enables efficient heat transfer across two adjacent surfaces in electronic applications. In this work, the thermal conductivities of different phase regions in the Ga-In system at various compositions and temperatures are measured for the first time. A modified comparative cut bar technique is used for the measurement of the thermal conductivities of GaxIn1−x (x = 0, 0.1, 0.214, 0.3, and 0.9) alloys at 40, 60, 80, and 100 °C, the temperatures commonly encountered in consumer electronics. The thermal conductivity of liquid and semi-liquid (liquid + β) Ga-In alloys are higher than most of the TIM’s currently used in consumer electronics. These measured quantities, along with the available experimental data from literature, served as input for the thermal conductivity parameter optimization using the CALPHAD (calculation of phase diagrams) method for pure elements, solution phase, and two-phase region. A set of self-consistent parameters for the description of the thermal conductivity of the Ga-In system is obtained. There is good agreement between the measured and calculated thermal conductivities for all of the phases. Due to their ease of manufacturing and high thermal conductivity, liquid/semi-liquid Ga-In alloys have significant potential for TIM in consumer electronics. 

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3. Thermal transport in monocrystalline and polycrystalline lithium cobalt oxide

   https://doi.org/10.1039/C9CP01585J  

   He, Jinlong ; Zhang, Lin ; Liu, Ling ( June 2019 , Physical Chemistry Chemical Physics)

   Efficient heat dissipation in batteries is important for thermal management against thermal runaway and chemical instability at elevated temperatures. Nevertheless, thermal transport processes in battery materials have not been well understood especially considering their complicated microstructures. In this study, lattice thermal transport in lithium cobalt oxide (LiCoO 2 ), a popular cathode material for lithium ion batteries, is investigated via molecular dynamics-based approaches and thermal resistance models. A LiCoO 2 single-crystal is shown to have thermal conductivities in the order of 100 W m −1 K −1 with strong anisotropy, temperature dependence, and size effects. By comparison, polycrystalline LiCoO 2 is more isotropic with much lower thermal conductivities. This difference is caused by random grain orientations, the thermal resistance of grain boundaries, and size-dependent intra-grain thermal conductivities that are unique to polycrystals. The grain boundary thermal conductance is calculated to be in the range of 7.16–25.21 GW m −2 K −1 . The size effects of the intra-grain thermal conductivities are described by two empirical equations. Considering all of these effects, two thermal resistance models are developed to predict the thermal conductivity of polycrystalline LiCoO 2 . The two models predict a consistent thermal conductivity–grain size relationship that agrees well with molecular dynamics simulation results. The insights revealed by this study may facilitate future efforts on battery materials design for improved thermal management. 

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4. Thermoelectric properties of the aliovalent half-Heusler alloy Zn 0.5 Ti 0.5 NiSb with intrinsic low thermal conductivity

   https://doi.org/10.1039/D3TA04514E  

   Kennedy, Blair F. ; Kimber, Simon A. ; Checchia, Stefano ; Shawon, A. K. ; Zevalkink, Alexandra ; Suard, Emmanuelle ; Buckman, Jim ; Bos, Jan-Willem G. ( November 2023 , Journal of Materials Chemistry A)

   Aliovalent substitutions lead to bond disorder and low lattice thermal conductivities in half-Heusler thermoelectrics.

    

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5. Tunable analog thermal material

   https://doi.org/10.1038/s41467-020-19909-0  

   Xu, Guoqiang ; Dong, Kaichen ; Li, Ying ; Li, Huagen ; Liu, Kaipeng ; Li, Longqiu ; Wu, Junqiao ; Qiu, Cheng-Wei ( November 2020 , Nature Communications)

   Naturally-occurring thermal materials usually possess specific thermal conductivity (κ), forming a digital set ofκvalues. Emerging thermal metamaterials have been deployed to realize effective thermal conductivities unattainable in natural materials. However, the effective thermal conductivities of such mixing-based thermal metamaterials are still in digital fashion, i.e., the effective conductivity remains discrete and static. Here, we report an analog thermal material whose effective conductivity can be in-situ tuned from near-zero to near-infinityκ. The proof-of-concept scheme consists of a spinning core made of uncured polydimethylsiloxane (PDMS) and fixed bilayer rings made of silicone grease and steel. Thanks to the spinning PDMS and its induced convective effects, we can mold the heat flow robustly with continuously changing and anisotropicκ. Our work enables a single functional thermal material to meet the challenging demands of flexible thermal manipulation. It also provides platforms to investigate heat transfer in systems with moving components.

    

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