Flexible multifunctional polymer-based electromagnetic interference (EMI) shielding composite films have important application values in the fields of 5G communication technology, wearable electronic devices and artificial intelligence. In this work, Fe3O4/polyamic acid (PAA) nanofiber films are prepared by in-situ polymerization and electrospinning technology, and Ti3C2Tx nanosheets are deposited on the surface of the Fe3O4/PAA nanofiber films via vacuum-assisted filtration. Then, Janus Ti3C2Tx-(Fe3O4/polyimide (PI)) composite films are obtained by thermal imidization. The two sides of the Janus films exhibit completely different properties. The Fe3O4/PI side has excellent hydrophobicity and insulation property, and the Ti3C2Tx side has hydrophilicity and terrific conductivity. When the mass fraction of Ti3C2Tx is 80 wt.%, the Janus Ti3C2Tx-(Fe3O4/PI) composite film has excellent EMI shielding performances and mechanical properties, with EMI shielding effectiveness, tensile strength and Young’s modulus reaching 66 dB, 114.5 MPa and 5.8 GPa, respectively. At the same time, electromagnetic waves show different absorption shielding effectiveness (SEA) when incident from two sides of the Janus films. When the electromagnetic waves are incident from the Fe3O4/PI side, the SEA of the Janus film is 58 dB, much higher than that when the electromagnetic waves are incident from the Ti3C2Tx side (39 dB). In addition, the Ti3C2Tx side of the Janus Ti3C2Tx-(Fe3O4/PI) composite films also has excellent electrothermal and photothermal conversion performances. When the applied voltage is 4 V, the stable surface temperature reaches 108 °C; when it is irradiated by simulated sunlight with power density of 200 mW/cm2, the stable surface temperature reaches 95 °C. 

https://link.springer.com/content/pdf/10.1007/s12274-022-4358-7.pdf

Multifunctional Ti3C2Tx-(Fe3O4/polyimide) composite films with Janus structure for outstanding electromagnetic interference shielding and superior visual thermal management

Flexible polystyrene/graphene composites with epsilon-near-zero properties

Indium tin oxide (ITO) is widely used in transparent conductive films (TCFs); however, several disadvantages, such as high cost and toxicity of indium, limit its applications. Therefore, it is necessary to develop other materials that can replace ITO. Silver nanowires or single walled carbon nanotubes (SWCNTs) have attracted considerable interest owing to their unique electrical, optical, and thermal stabilities, and thus, they are ideal for transparent electrodes for flexible or stretchable devices. In this study, we develop a novel architecture of composite TCFs on a polyethylene naphthalate (PEN) flexible substrate. Herein, the silver nanowires-SWCNTs films with nested density structure were fabricated through ultrasonic spraying technology by varying the spraying width. For achieving enhanced transmittance, we combined the larger irregular grids and holes with fewer nanowires stacked in the longitudinal direction, more optical channels, and good carrier transport. Thereafter, aluminum-doped zinc oxide (AZO) was used as capping to the structure for enhancing the optical properties of the TCFs. The silver nanowires-SWCNTs/AZO (ASA) bilayer was obtained in the optimized architecture, which showed superior optoelectronic performance to that shown by commercial ITO with a high optical transmittance of 92% at the wavelength of 550 nm and low sheet resistance of 17 Ω/sq. In the specially structured conductive film, the significant improvement in the transmittance and uniformity of the sheet resistance was attributed to the effective nanowire junction contact compared to that in ordinary structure of silver nanowires, which reduced the mean density of small clusters of nanowires. Compared with the silver nanowires-SWCNTs films, the ASA bilayer film exhibited excellent resistance to boiling, mechanical bending (10,000 cycles), and CO2 plasma. Moreover, the sheet resistance of ASA changed slightly after the tape tests, thereby illustrating a strong adhesion to the PEN substrate after the enclosure of AZO. Meanwhile, the AZO capping layer can enhance the optical transmittance between 600 and 1500 nm. In addition, the amorphous silicon photovoltaic devices with flexible ASA TCFs exhibited a power conversion efficiency (PCE) of 8.67%. After bending for 3000 times, the PCE was decreased to 8.20%, thereby demonstrating the potential of developed films to replace traditional ITO. 

Highly transmitted silver nanowires-SWCNTs conductive flexible film by nested density structure and aluminum-doped zinc oxide capping layer for flexible amorphous silicon solar cells

Precise control of value and dispersion characteristics of negative permittivity is still an unsolved problem in the practical application of random metamaterials. In this work, the ternary percolation nanocomposites (CNTs-GR-CCTO) were prepared via a low-temperature sintering process by using graphene (GR), carbon nanotubes (CNTs), and copper calcium titanate (CCTO). As the total carbon contents increased, the three-dimensional carbon network was formed, and negative permittivity is realized, which exhibits the Lorentz-type and Drude-type dispersion behaviors. The synergistic effect between GR and CNTs was studied in detail. While the GR sheets separate the CNTs, the CNTs also act as wires to connect the GR sheets. Controlled conductive paths were created by changing the ratio of CNTs to GR, achieving precise regulation of the negative permittivity, which is further certified by the equivalent circuit analysis. We provide a novel strategy for the precise regulation of negative permittivity of carbon-matrix metamaterials, which will greatly facilitate applications of metamaterials with negative permittivity. Precise regulation of weakly negative permittivity is achieved in CaCu3Ti4O12 metacomposites by synergistic effects of carbon nanotubes and graphene.

Precise regulation of weakly negative permittivity in CaCu3Ti4O12 metacomposites by synergistic effects of carbon nanotubes and grapheme

Overview of MXene and conducting polymer matrix composites for electromagnetic wave absorption

Magnetic NiFe2O4/Polypyrrole nanocomposites with enhanced electromagnetic wave absorption

NiFe2O4/polypyrrole (NiFe2O4/PPy) nanocomposites are prepared by a simple surface-initiated polymerization method and demonstrate negative permittivity in the low frequency regions. These nanocomposites also exhibit significantly enhanced electromagnetic wave (EMW) absorption property in the high frequency regions. Compared with pure PPy, the enhanced negative permittivity is observed in the NiFe2O4/PPy nanocomposites with a NiFe2O4 loading of 5.0, 10.0, 20.0 and 40.0 wt%, indicating the formation of metal-like electrical conducting network in NiFe2O4/PPy nanocomposites. Moreover, the negative permittivity could be tuned by changing the NiFe2O4 loading. The minimum reflection loss (RL) of -40.8 dB is observed in the 40.0 wt% NiFe2O4/PPy composites with a thickness of only 1.9 mm. The effective absorption bandwidth below -10.0 and -20.0 dB reaches 6.08 and 2.08 GHz, respectively. The enhanced EMW absorption performance benefits from the improved independence matching, EMW attenuation capacity, and synergistic effects of conduction loss, dielectric loss (interfacial and dipole polarizations) and magnetic loss (exchange and natural resonances). This research work provides a guidance for the fabrication of nanocomposites with an excellent EMW absorption. 

Designing thermal radiation metamaterials is challenging especially for problems with high degrees of freedom and complex objectives. In this Letter, we develop a hybrid materials informatics approach which combines the adversarial autoencoder and Bayesian optimization to design narrowband thermal emitters at different target wavelengths. With only several hundreds of training data sets, new structures with optimal properties can be quickly determined in a compressed two-dimensional latent space. This enables the optimal design by calculating far less than 0.001% of the total candidate structures, which greatly decreases the design period and cost. The proposed design framework can be easily extended to other thermal radiation metamaterials design with higher dimensional features. 

/pdf/designing-thermal-radiation-metamaterials-via-a-hybrid-1iamauph.pdf

Pál Bárkányi

Papers

Magnetic NiFe2O4/Polypyrrole nanocomposites with enhanced electromagnetic wave absorption

Magnetic NiFe2O4/Polypyrrole nanocomposites with enhanced electromagnetic wave absorption

Designing thermal radiation metamaterials via a hybrid adversarial autoencoder and Bayesian optimization