Significantly enhanced phonon mean free path and thermal conductivity by percolation of silver nanoflowers

Fillers and methods to improve the effective (out-plane) thermal conductivity of polymeric thermal interface materials - A review

The internet of things and growing demand for smaller and more advanced devices has created the problem of high heat production in electronic equipment, which greatly reduces the work performance and life of the electronic instruments. Thermal interface material (TIM) is placed in between heat generating micro-chip and the heat dissipater to conduct all the produced heat to the heat sink. The development of suitable TIM with excellent thermal conductivity (TC) in both in-plane and through-plane directions is a very important need at present. For efficient thermal management, polymer composites are potential candidates. But in general, their thermal conductivity is low compared to that of metals. The filler integration into the polymer matrix is one of the two approaches used to increase the thermal conductivity of polymer composites and is also easy to scale up for industrial production. Another way to achieve this is to change the structure of polymer chains, which fall out of the scope of this work. In this review, considering the first approach, the authors have summarized recent developments in many types of fillers with different scenarios by providing multiple cases with successful strategies to improve through-plane thermal conductivity (TPTC) (k⊥). For a better understanding of TC, a comprehensive background is presented. Several methods to improve the effective (out-plane) thermal conductivity of polymer composites and different theoretical models for the calculation of TC are also discussed. In the end, it is given a detailed conclusion that provides drawbacks of some fillers, multiple significant routes recommended by other researchers to build thermally conductive polymer composites, future aspects along with direction so that the researchers can get a guideline to design an effective polymer-based thermal interface material.

Eco-friendly chitosan@silver/plant fiber membranes for masks with thermal comfortability and self-sterilization

The surgical masks have been essential consumables for public in the COVID-19 pandemic. However, long-time wearing masks will make wearers feel uncomfortable and massive discarded non-biodegradable masks lead to a heavy burden on our environment. In this paper, we adopt degradable chitosan@silver (CS@Ag) core-shell fibers and plant fibers to prepare an eco-friendly mask with excellent thermal comfort, self-sterilization, and antiviral effects. The thermal network of CS@Ag core-shell fibers highly improves the in-plane thermal conductivity of masks, which is 4.45 times higher than that of commercial masks. Because of the electrical conductivity of Ag, the fabricated mask can be electrically heated to warm the wearer in a cold environment and disinfect COVID-19 facilely at room temperature. Meanwhile, the in-situ reduced silver nanoparticles (AgNPs) endow the mask with superior antibacterial properties. Therefore, this mask shows a great potential to address the urgent need for a thermally comfortable, antibacterial, antiviral, and eco-friendly mask.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-022-04582-x.

High-Temperature Skin Softening Materials Overcoming the Trade-Off between Thermal Conductivity and Thermal Contact Resistance

The trade-off between thermal conductivity (κ) and thermal contact resistance (R_c ) is regarded as a hurdle to develop superior interface materials for thermal management. Here a high-temperature skin softening material to overcome the trade-off relationship, realizing a record-high total thermal conductance (254.92 mW mm^-2 K^-1 ) for isotropic pad-type interface materials is introduced. A highly conductive hard core is constructed by incorporating Ag flakes and silver nanoparticle-decorated multiwalled carbon nanotubes in thermosetting epoxy (EP). The thin soft skin is composed of filler-embedded thermoplastic poly(ethylene-co-vinyl acetate) (PEVA). The κ (82.8 W m^-1 K^-1 ) of the PEVA-EP-PEVA interface material is only slightly compromised, compared with that (106.5 W m^-1 K^-1 ) of the EP core (386 µm). However, the elastic modulus (E = 2.10 GPa) at the skin is significantly smaller than the EP (26.28 GPa), enhancing conformality and decreasing R_c from 108.41 to 78.73 mm² K W^-1 . The thermoplastic skin is further softened at an elevated temperature (100 °C), dramatically decreasing E (0.19 GPa) and R_c (0.17 mm² K W^-1 ) with little change in κ, overcoming the trade-off relationship and enhancing the total thermal conductance by 2030%. The successful heat dissipation and applicability to the continuous manufacturing process demonstrate excellent feasibility as future thermal management materials.

Enhanced the Thermal Conductivity of Polydimethylsiloxane via a Three-Dimensional Hybrid Boron Nitride@Silver Nanowires Thermal Network Filler

In this work, polydimethylsiloxane (PDMS)-based composites with high thermal conductivity were fabricated via a three-dimensional hybrid boron nitride@silver nanowires (BN@AgNWs) filler thermal network, and their thermal conductivity was investigated. A new thermal conductive BN@AgNWs hybrid filler was prepared by an in situ growth method. Silver ions with the different concentrations were reduced, and AgNWs crystallized and grew on the surface of BN sheets. PDMS-based composites were fabricated by the BN@AgNWs hybrid filler added. SEM, XPS, and XRD were used to characterize the structure and morphology of BN@AgNWs hybrid fillers. The thermal conductivity performances of PDMS-based composites with different silver concentrates were investigated. The results showed that the thermal conductivity of PDMS-based composite filled with 20 vol% BN@15AgNWs hybrid filler is 0.914 W/(m·K), which is 5.05 times that of pure PDMS and 23% higher than the thermal conductivity of 20 vol% PDMS-based composite with BN filled. The enhanced thermal conductivity mechanism was provided based on the hybrid filler structure. This work offers a new way to design and fabricate the high thermal conductive hybrid filler for thermal management materials.

Electron tunneling of hierarchically structured silver nanosatellite particles for highly conductive healable nanocomposites

Healable conductive materials have received considerable attention. However, their practical applications are impeded by low electrical conductivity and irreversible degradation after breaking/healing cycles. Here we report a highly conductive completely reversible electron tunneling-assisted percolation network of silver nanosatellite particles for putty-like moldable and healable nanocomposites. The densely and uniformly distributed silver nanosatellite particles with a bimodal size distribution are generated by the radical and reactive oxygen species-mediated vigorous etching and reduction reaction of silver flakes using tetrahydrofuran peroxide in a silicone rubber matrix. The close work function match between silicone and silver enables electron tunneling between nanosatellite particles, increasing electrical conductivity by ~5 orders of magnitude (1.02×10³ Scm⁻¹) without coalescence of fillers. This results in ~100% electrical healing efficiency after 1000 breaking/healing cycles and stability under water immersion and 6-month exposure to ambient air. The highly conductive moldable nanocomposite may find applications in improvising and healing electrical parts.

Self-healable conductive materials are of importance for emerging electronic technologies. Here, Suh et al. report a nanocomposite exhibiting high conductivity facilitated by electron tunneling between silver nanoparticles and its 100% recovery of conductivity after 1000 breaking and healing cycles.

Ultrasensitive detection of uric acid in serum of patients with gout by a new assay based on Pt@Ag nanoflowers

A ultrasensitive assay for the determination of uric acid (UA) based on Pt@Ag nanoflowers (Pt@Ag NFs) was constructed. H₂O₂ was formed by the reaction of uricase and UA and produced the hydroxyl radical (˙OH). The system was catalyzed by Pt@Ag NFs to change the color of 3,3′,5,5′-tetramethylbenzidine (TMB) from colorless to blue, and the morphology and chemical properties of Pt@Ag NFs were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. Under the optimized conditions, a linear relationship between the absorbance and UA concentration was in the range of 0.5–150 μM (R² = 0.995) with a limit of detection of 0.3 μM (S/N = 3). The method can be applied to detection of UA in actual samples with satisfactory results. The proposed assay was successfully applied to the detection of UA in human serum with recoveries over 96.8%. Thus, these results imply that the UA assay provides an effective tool in fast clinical analysis of gout.

A ultrasensitive assay for the determination of uric acid (UA) based on Pt@Ag nanoflowers (Pt@Ag NFs) was constructed.