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1. Electrically insulating flexible films with quasi-1D van der Waals fillers as efficient electromagnetic shields in the GHz and sub-THz frequency bands

   Barani, Z. ; Kargar, F. ; Ghafouri, Y. ; Ghosh, S. ; Godziszewski, K ; Baraghani, S ; Yashchyshyn, Y. Cywiński ; Rumyantsev, S. ; T. T. Salguero, and A. ( February 2021 , Advanced materials)

   null (Ed.)

   Polymer composite films containing fillers comprising quasi-1D van der Waals materials, specifically transition metal trichalcogenides with 1D structural motifs that enable their exfoliation into bundles of atomic threads, are reported. These nanostructures are characterized by extremely large aspect ratios of up to ≈106. The polymer composites with low loadings of quasi-1D TaSe3 fillers (<3 vol%) reveal excellent electromagnetic interference shielding in the X-band GHz and extremely high frequency sub-THz frequency ranges, while remaining DC electrically insulating. The unique electromagnetic shielding characteristics of these films are attributed to effective coupling of the electromagnetic waves to the high-aspect-ratio electrically conductive TaSe3 atomic-thread bundles even when the filler concentration is below the electrical percolation threshold. These novel films are promising for high-frequency communication technologies, which require electromagnetic shielding films that are flexible, lightweight, corrosion resistant, inexpensive, and electrically insulating. 

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2. Electrically Insulating Flexible Films with Quasi‐1D van der Waals Fillers as Efficient Electromagnetic Shields in the GHz and Sub‐THz Frequency Bands

   https://doi.org/10.1002/adma.202007286  

   Barani, Zahra ; Kargar, Fariborz ; Ghafouri, Yassamin ; Ghosh, Subhajit ; Godziszewski, Konrad ; Baraghani, Saba ; Yashchyshyn, Yevhen ; Cywiński, Grzegorz ; Rumyantsev, Sergey ; Salguero, Tina T. ; et al ( February 2021 , Advanced Materials)

   Polymer composite films containing fillers comprising quasi‐1D van der Waals materials, specifically transition metal trichalcogenides with 1D structural motifs that enable their exfoliation into bundles of atomic threads, are reported. These nanostructures are characterized by extremely large aspect ratios of up to≈10⁶. The polymer composites with low loadings of quasi‐1D TaSe₃fillers (<3 vol%) reveal excellent electromagnetic interference shielding in the X‐band GHz and extremely high frequency sub‐THz frequency ranges, while remaining DC electrically insulating. The unique electromagnetic shielding characteristics of these films are attributed to effective coupling of the electromagnetic waves to the high‐aspect‐ratio electrically conductive TaSe₃atomic‐thread bundles even when the filler concentration is below the electrical percolation threshold. These novel films are promising for high‐frequency communication technologies, which require electromagnetic shielding films that are flexible, lightweight, corrosion resistant, inexpensive, and electrically insulating.

    

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3. On‐Demand Programming of Liquid Metal‐Composite Microstructures through Direct Ink Write 3D Printing

   https://doi.org/10.1002/adma.202200182  

   Haake, Aaron ; Tutika, Ravi ; Schloer, Gwyneth M. ; Bartlett, Michael D. ; Markvicka, Eric J. ( April 2022 , Advanced Materials)

   Soft, elastically deformable composites with liquid metal (LM) droplets can enable new generations of soft electronics, robotics, and reconfigurable structures. However, techniques to control local composite microstructure, which ultimately governs material properties and performance, is lacking. Here a direct ink writing technique is developed to program the LM microstructure (i.e., shape, orientation, and connectivity) on demand throughout elastomer composites. In contrast to inks with rigid particles that have fixed shape and size, it is shown that emulsion inks with LM fillers enable in situ control of microstructure. This enables filaments, films, and 3D structures with unique LM microstructures that are generated on demand and locked in during printing. This includes smooth and discrete transitions from spherical to needle‐like droplets, curvilinear microstructures, geometrically complex embedded inclusion patterns, and connected LM networks. The printed materials are soft (modulus < 200 kPa), highly deformable (>600 % strain), and can be made locally insulating or electrically conductive using a single ink by controlling the process conditions. These capabilities are demonstrated by embedding elongated LM droplets in a soft heat sink, which rapidly dissipates heat from high‐power LEDs. These programmable microstructures can enable new composite paradigms for emerging technologies that demand mechanical compliance with multifunctional response.

    

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4. Thermal Properties of the Binary‐Filler Hybrid Composites with Graphene and Copper Nanoparticles

   https://doi.org/10.1002/adfm.201904008  

   Barani, Zahra ; Mohammadzadeh, Amirmahdi ; Geremew, Adane ; Huang, Chun‐Yu ; Coleman, Devin ; Mangolini, Lorenzo ; Kargar, Fariborz ; Balandin, Alexander A. ( September 2019 , Advanced Functional Materials)

   The thermal properties of epoxy‐based binary composites comprised of graphene and copper nanoparticles are reported. It is found that the “synergistic” filler effect, revealed as a strong enhancement of the thermal conductivity of composites with the size‐dissimilar fillers, has a well‐defined filler loading threshold. The thermal conductivity of composites with a moderate graphene concentration off_g= 15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approachesf_Cu≈ 40 wt%, followed by saturation. The effect is attributed to intercalation of spherical copper nanoparticles between the large graphene flakes, resulting in formation of the highly thermally conductive percolation network. In contrast, in composites with a high graphene concentration,f_g= 40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. A thermal conductivity of 13.5 ± 1.6 Wm⁻¹K⁻¹is achieved in composites with binary fillers off_g= 40 wt% andf_Cu= 35 wt%. It has also been demonstrated that the thermal percolation can occur prior to electrical percolation even in composites with electrically conductive fillers. The obtained results shed light on the interaction between graphene fillers and copper nanoparticles in the composites and demonstrate potential of such hybrid epoxy composites for practical applications in thermal interface materials and adhesives.

    

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5. Robust Three‐Component Elastomer–Particle–Fiber Composites with Tunable Properties for Soft Robotics

   https://doi.org/10.1002/aisy.202000166  

   Mohammadi Nasab, Amir ; Sharifi, Siavash ; Chen, Shuai ; Jiao, Yang ; Shan, Wanliang ( November 2020 , Advanced Intelligent Systems)

   Materials with tunable properties, especially dynamically tunable stiffness, have been of great interest for the field of soft robotics. Herein, a novel design concept of robust three‐component elastomer–particle–fiber composite system with tunable mechanical stiffness and electrical conductivity is introduced. These smart materials are capable of changing their mechanical stiffness rapidly and reversibly when powered with electrical current. One implementation of the composite system demonstrated here is composed of a polydimethylsiloxane (PDMS) matrix, Field's metal (FM) particles, and nickel‐coated carbon fibers (NCCF). It is demonstrated that the mechanical stiffness and the electrical conductivity of the composite are highly tunable and dependent on the volume fraction of the three components and the temperature, and can be reasonably estimated using effective medium theory. Due to its superior electrical conductivity, Joule heating can be used as the activation mechanism to realize ≈20× mechanical stiffness changes in seconds. The performance of the composites is thermally and mechanically robust. The shape memory effect of these composites is also demonstrated. The combination of tunable mechanical and electrical properties makes these composites promising candidates for sensing and actuation applications for soft robotics.

    

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