Multilayered graphene/boron nitride/thermoplastic polyurethane composite films with high thermal conductivity, stretchability, and washability for adjustable-cooling smart clothes

Flexible and Thermally Insulating Porous Materials Utilizing Hollow Double-Shell Polymer Fibers

The global climate change is mainly caused by carbon dioxide (CO2) emissions. To help reduce CO2 emissions and conserve thermal energy, sustainable materials based on flexible thermal insulation are developed to minimize heat flux, drawing inspiration from natural systems such as polar bear hairs. The unique structure of hollow double-shell fibers makes it possible to achieve low thermal conductivity in the material while retaining exceptional elasticity, allowing it to adapt to insulation systems of any shape. The layered system of porous mats reaches a thermal conductivity coefficient of 0.031 W∙m⁻¹∙K⁻¹ and enables to reduce the heat transfer. The results achieved using scanning thermal microscopy (SThM) correlate with the simulated heat flow in the case of individual fibers. This research study brings new insights into the energy efficiency of domestic environments, thereby addressing the growing demand for sustainable and high-performance insulation materials for saving energy loss and reducing pollution footprint.

Bioinspired electrically stable, optically tunable thermal management electronic skin via interfacial self-assembly

The skin is the largest organ in the human body and serves vital functions such as sensation, thermal management, and protection. While electronic skin (E-skin) has made significant progress in sensory functions, achieving adaptive thermal management akin to human skin has remained a challenge. Drawing inspiration from squid skin, we have developed a hybrid electronic-photonic skin (hEP-skin) using an elastomer semi-embedded with aligned silver nanowires through interfacial self-assembly. With mechanically adjustable optical properties, the hEP-skin demonstrates adaptive thermal management abilities, warming in the range of +3.5°C for heat preservation and cooling in the range of -4.2°C for passive cooling. Furthermore, it exhibits an ultra-stable high electrical conductivity of ∼4.5×104 S/cm, even under stretching, bending or torsional deformations over 10,000 cycles. As a proof of demonstration, the hEP-skin successfully integrates stretchable light-emitting electronic skin with adaptive thermal management photonic skin.

Application of Nanohybrid Substrates with Layer-by-Layer Self-Assembling Properties to High-Sensitivity Surface-Enhanced Raman Scattering Detection

The present study was conducted to prepare and investigate large-area, high-sensitivity surface-enhanced Raman scattering (SERS) substrates. Organic/inorganic nanohybrid dispersants consisting of an amphiphilic triblock copolymer (hereafter referred to simply as "copolymer") and graphene oxide (GO) were used to stabilize the growth and size of gold nanoparticles (AuNPs). Ion-dipole forces were present between the AuNPs and copolymer dispersants, while the hydrogen bonds between GO and the copolymer prevented the aggregation of GO, thereby stabilizing the AuNP/GO nanohybrids. Transmission electron microscopy (TEM) revealed that the AuNPs had particle sizes of 25-35 nm and a relatively uniform size distribution. The AuNP/GO nanohybrids were deposited onto the glass substrate by using the solution drop-casting method and employed for SERS detection. The self-assembling properties of two-dimensional sheet-like GO led to a regular lamellar arrangement of AuNP/GO nanohybrids, which could be used for the preparation of large-area SERS substrates. Following removal of the copolymer by annealing at 300 °C for 2 h, measurements were obtained under scanning electron microscopy. The results confirmed that 2D GO nanosheets were capable of stabilizing AuNPs, with the final size reaching approximately 40 nm. These AuNPs were adsorbed on both sides of the GO nanosheets. Because the GO nanosheets were merely 5 nm-thick, a good three-dimensional hot-junction effect was generated along the z-axis of the AuNPs. Lastly, the prepared material was used for the SERS detection of rhodamine 6G (R6G), a commonly used highly fluorescent dye. An enhancement factor (EF) of up to 3.5 × 106 was achieved, and the limit of detection was approximately 10-10 M. Detection limits of 10-10 M and < 10-10 M were also observed with the detection of Direct Blue 200 and the biological molecule adenine. It is therefore evident that AuNP/copolymer/GO nanohybrids are large-area flexible SERS substrates that hold great potential in environmental monitoring and biological system detection applications.

Graphene Nanoplatelet/Multiwalled Carbon Nanotube/Polypyrrole Hybrid Fillers in Polyurethane Nanohybrids with 3D Conductive Networks for EMI Shielding

This work reports the preparation of graphene nanoplatelet (GNP)/multiwalled carbon nanotube (MWCNT)/polypyrrole (PPy) hybrid fillers via in situ chemical oxidative polymerization with the addition of a cationic surfactant, hexadecyltrimethylammonium bromide. These hybrid fillers were incorporated into polyurethane (PU) to prepare GNP/MWCNT/PPy/PU nanohybrids. The electrical conductivity of the nanohybrids was synergistically enhanced by the high conductivity of the hybrid fillers. Furthermore, the electromagnetic interference (EMI) shielding effectiveness (SE) was greatly increased by interfacial polarization between the GNPs, MWCNTs, PPy, and PU. The optimal formulation for the preparation of GNP/MWCNT/PPy three-dimensional (3D) nanostructures was determined by optimization experiments. Using this formulation, we successfully prepared GNP/PPy nanolayers (two-dimensional) that are extensively covered by MWCNT/PPy nanowires (one-dimensional), which interconnect to form GNP/MWCNT/PPy 3D nanostructures. When incorporated into a PU matrix to form a nanohybrid, these 3D nanostructures form a continuous network of conductive GNP-PPy-CNT-PPy-GNP paths. The EMI SE of the nanohybrid is 35-40 dB at 30-1800 MHz, which is sufficient to shield over 99.9% of electromagnetic waves. Therefore, this EMI shielding material has excellent prospects for commercial use. In summary, a nanohybrid with excellent EMI SE performance was prepared using a facile and scalable method and was shown to have great commercial potential.

Highly Thermally Conductive Epoxy Composites with AlN/BN Hybrid Filler as Underfill Encapsulation Material for Electronic Packaging

In this study, the effects of a hybrid filler composed of zero-dimensional spherical AlN particles and two-dimensional BN flakes on the thermal conductivity of epoxy resin were studied. The thermal conductivity (TC) of the pristine epoxy matrix (EP) was 0.22 W/(m K), while the composite showed the TC of 10.18 W/(m K) at the 75 wt% AlN–BN hybrid filler loading, which is approximately a 46-fold increase. Moreover, various essential application properties were examined, such as the viscosity, cooling rate, coefficient of thermal expansion (CTE), morphology, and electrical properties. In particular, the AlN–BN/EP composite showed higher thermal stability and lower CTE (22.56 ppm/°C) than pure epoxy. Overall, the demonstrated outstanding thermal performance is appropriate for the production of electronic packaging materials, including next-generation flip-chip underfills.

Filler dimensionality effect on the performance of paraffin-based phase change materials

HYPOTHESIS

Phase change materials have the potential for use in high-density thermal energy storage. However, their low thermal conductivity and the need for shape stabilization restrict their performances and implementation in various fields. The inclusion of thermally conductive nanomaterial as a single or hybrid filling is expected to form 3D network that enhances the thermal performances of phase change materials. The encapsulation of the colloidal composites in a polymer matrix stabilizes the phase change material.

EXPERIMENTS

A paraffin matrix was loaded with carbon-based fillers of various dimensionalities, namely, 1D-carbon nanotubes, 2D-graphene nanoplatelets, and 3D-graphite flakes. The thermal conductivity of the colloidal composite was measured by transient plane source and the latent heat capacity by differential scanning calorimetry techniques. Modeling the thermal conductivity by the effective medium approach predicts the experimental results.

FINDINGS

The thermal conductivity of the phase change material loaded with fillers is enhanced from 0.2 to 11 W (m K)^-1 (×55) compared with a filler-free paraffin matrix. We attribute this enhancement to the synergetic effect of the hybrid fillers (8 vol% graphite flakes and 12 vol% graphene nanoplatelets) and consequent compression (25 bar) of the colloidal composite. Moreover, the obtained phase change material is completely stable during charging and discharging cycles.

Improving thermal conductivities of textile materials by nanohybrid approaches

The thermal transfer between individual body and the surroundings occurs by several paths such as radiation, evaporation, conduction, and convection. Thermal management is related with the heat transfer between the human body and the surroundings, which aims to keep the body temperature in the comfort range either via preserving or via emitting the body heat. The essential duty of clothing is to contribute to the thermal balance of the human body by regulating the heat and moisture transfer. In the case of poorly controlled body heat, health problems such as hyperthermia and heatstroke along with environmental problems due to higher energy consumption can occur. Recently, research has been focused on advanced textiles with novel approaches on materials synthesis and structure design, which can provide thermal comfort together with energy saving. This review article focuses on the innovative strategies basically on the passive textile models for improved thermal conductivity. We will discuss both the fabrication techniques and the inclusion of carbon-based and boron-based fillers to form nano-hybrid textile solutions, which are used to improve the thermal conductivity of the materials.

Piezoelectric Property Enhancement of PZT/Poly(vinylidenefluoride-co-trifluoroethylene) Hybrid Films for Flexible Piezoelectric Energy Harvesters

In this study, lead zirconate titanate (PZT) ceramic particles were added for further improvement. PZT belongs to the perovskite family and exhibits good piezoelectricity. Thus, it was added in this experiment to enhance the piezoelectric response of the poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) copolymer, which produced a voltage output of 1.958 V under a cyclic pressure of 290 N. In addition, to further disperse the PZT particles in the PVDF-TrFE matrix, tetradecylphosphonic acid (TDPA) was synthesized and employed to modify the PZT surface, after which the surface-modified PZT (m-PZT) particles were added to the PVDF-TrFE matrix. The TDPA on the PZT surface made it difficult for the particles to aggregate, allowing them to disperse in the polymer solution more stably. In this way, the PZT particles with piezoelectric responses could be uniformly dispersed in the PVDF-TrFE film, thereby further enhancing its overall piezoelectric response. The test results showed that upon the addition of 10 wt % m-PZT, the piezoelectric coefficient of m-PZT/PVDF-TrFE 10 wt % was 27 pC/N; and under a cyclic pressure of 290 N, the output voltage reached 3.426 V, which demonstrated a better piezoelectric response than the polymer film with the original PZT particles. Furthermore, the piezoelectric coefficient of m-PZT/PVDF-TrFE 10 wt % was 27.1 pC/N. This was exhibited by maintaining a piezoelectric coefficient of 26.8 pC/N after 2000 cycles. Overall, a flexible piezoelectric film with a high piezoelectric coefficient was prepared by following a simple fabrication process, which showed that this film possesses great commercial potential.

Immobilization of Air-Stable Copper Nanoparticles on Graphene Oxide Flexible Hybrid Films for Smart Clothes

Through the use of organic/inorganic hybrid dispersants—which are composed of polymeric dispersant and two-dimension nanomaterial graphene oxide (GO)—copper nanoparticles (CuNPs) were found to exhibit nano stability, air-stable characteristics, as well as long-term conductive stability. The polymeric dispersant consists of branched poly(oxyethylene)-segmented esters of trimellitic anhydride adduct (polyethylene glycol−trimethylolpropane−trimellitic anhydride, designated as PTT). PTT acts as a stabilizer for CuNPs, which are synthesized via in situ polymerization and redox reaction of the precursor Cu(CH₃COO)₂ within an aqueous system, and use graphene oxide to avoid the reduction reaction of CuNPs. The results show that after 30 days of storage the CuNPs/PTT/GO composite film maintains a highly conductive network (9.06 × 10⁻¹ Ω/sq). These results indicate that organic/inorganic PTT/GO hybrid dispersants can effectively maintain the conductivity stability of CuNPs and address the problem of CuNP oxidation. Finally, the new CuNPs/PTT/GO composite film was applied to the electrocardiogram (ECG) smart clothes. This way, a stable and antioxidant-sensing electrode can be produced, which is expected to serve as a long-term ECG monitoring device.

Polymer-Assisted Dispersion of Boron Nitride/Graphene in a Thermoplastic Polyurethane Hybrid for Cooled Smart Clothes

The avoidance and mitigation of energy wastage have attracted increasing attention in the context of global warming and climate change. With advances in materials science, diverse multifunctional materials with high thermal conductivity have shown excellent energy-saving potential. In this study, a hybrid film exhibiting high thermal conductivity with excellent stretchability and washability was prepared. First, a simple surface modification of boron nitride (BN) was performed to realize a modified boron nitride (BNOH) filler. Next, an organic dispersant was synthesized to enhance the dispersion of BNOH and graphene nanoplatelets (GNPs) in the proposed composite. Subsequently, a simple procedure was used to combine the dispersed GNPs and BNOH fillers with thermoplastic polyurethane (TPU) to fabricate a hybrid structure. The hybrid films composed of BNOH-GNP/TPU with a dispersant exhibited a high thermal conductivity of 12.62 W m^-1 K^-1 at a low filler loading of 20 wt.%. This hybrid film afforded excellent stretchability and washability, as indicated by the very small thermal-conductivity reduction to only 12.23 W m^-1 K^-1 after 100 cycles of fatigue testing and to 12.01 W m^-1 K^-1 after 10 washing cycles. Furthermore, the cooling and hydrophobicity properties of the hybrid film were enhanced when compared with neat TPU. Overall, our approach demonstrates a simple and novel strategy to break the passive effect of traditional commercial cooling clothing by combining a high-thermal-conductivity film with an active cooling source to amplify the cooling effect and develop wearable cooled smart clothes with great commercial potential.

Quasi-isotropically thermoconductive, antiwear and insulating hierarchically assembled hexagonal boron nitride nanosheet/epoxy composites for efficient microelectronic cooling

Herein, Pebax functionalized h-BNNSs (P-BNNSs) fabricated by a mechanical exfoliation and in-situ modification process are employed to improve the thermal conductivity and antiwear performance of epoxy resin (EP). Pebax can effectively improve the dispersibility of P-BNNSs, achieving hierarchical assembly of P-BNNSs in EP matrix during EP curing process to form a multinetwork structure only at a low P-BNNS filling contents (≤6 wt%). This multinetwork structure can act as excellent heat conductive pathways to realize simultaneously vertical and horizontal heat diffusion, obtaining quasi-isotropical thermal conductive P-BNNS/EP composites. Fascinatingly, a through-plane thermal conductivity of 3.9 W/(m·K) and an in-plane thermal conductivity of 2.9 W/(m·K) are obtained. More importantly, this special structure can simultaneously improve the antiwear, mechanical and electrically insulating performances of pure EP. The friction coefficients and wear rates of P-BNNS/EP composites (P-BNNS contents ≤ 6 wt%) are dramatically decreased to less than 0.2 and 1 × 10^-5 mm³/(N·m), comparing with those of pure EP which are over 0.6 and 2 × 10^-5 mm³/(N·m), respectively. The enhanced tensile stress of over 110 MPa and electric volume resistivity of over 1.50 × 10¹³ Ω·cm are also observed for P-BNNS/EP composite films. These improved properties make the P-BNNS/EP composites very promising as packaging or heat dissipation materials in the high density integration systems and high frequency printed circuit boards.

Enhanced Efficiency of Dye-Sensitized Solar Cells Based on Polymer-Assisted Dispersion of Platinum Nanoparticles/Carbon Nanotubes Nanohybrid Films as FTO-Free Counter Electrodes

In this study, polymer-assisted dispersants are used to stabilize the nanohybrids of platinum nanoparticles (PtNPs)/carbon nanotubes (CNTs) through non-covalent bond forces. These dispersants aim to replace the florine-doped tin oxide (FTO) glass in traditional dye-sensitized solar cells (DSSCs) as counter electrodes. The large specific surface area, high conductivity, and redox potential of PtNPs/CNT nanohybrids are used as the basis to utilize them as the counter electrode material to fabricate a dye-sensitized solar cell. The conductivity results indicate that the resistance of the PtNP/CNT nanohybrid film can be reduced to 7.25 Ω/sq. When carbon nanotubes are mixed with platinum nanoparticles at a weight ratio of 5/1, the photoelectric conversion efficiency of DSSCs can reach 6.28%. When using the FTO-containing substrate as the counter electrode, its conversion efficiency indicates that the micro-/nano-hybrid material formed by PtNPs/CNTs also exhibits an excellent photoelectric conversion efficiency (8.45%) on the traditional FTO substrate. Further, a large-area dye-sensitive cell is fabricated, showing that an 8 cm × 8 cm cell has a conversion efficiency of 7.95%. Therefore, the traditional Pt counter electrode can be replaced with a PtNP/CNT nanohybrid film, which both provides dye-sensitive cells with a high photoelectric conversion efficiency and reduces costs.