Yimin Yao

Ice‐Templated Assembly Strategy to Construct 3D Boron Nitride Nanosheet Networks in Polymer Composites for Thermal Conductivity Improvement

Owing to the growing heat removal issue of modern electronic devices, polymer composites with high thermal conductivity have drawn much attention in the past few years. However, a traditional method to enhance the thermal conductivity of the polymers by addition of inorganic fillers usually creates composite with not only limited thermal conductivity but also other detrimental effects due to large amount of fillers required. Here, novel polymer composites are reported by first constructing 3D boron nitride nanosheets (3D-BNNS) network using ice-templated approach and then infiltrating them with epoxy matrix. The obtained polymer composites exhibit a high thermal conductivity (2.85 W m(-1) K(-1)), a low thermal expansion coefficient (24-32 ppm K(-1)), and an increased glass transition temperature (T(g)) at relatively low BNNSs loading (9.29 vol%). These results demonstrate that this approach opens a new avenue for design and preparation of polymer composites with high thermal conductivity. The polymer composites are potentially useful in advanced electronic packaging techniques, namely, thermal interface materials, underfill materials, molding compounds, and organic substrates.

Silver Nanoparticle-Deposited Boron Nitride Nanosheets as Fillers for Polymeric Composites with High Thermal Conductivity

Polymer composites with high thermal conductivity have recently attracted much attention, along with the rapid development of the electronic devices toward higher speed and performance. However, a common method to enhance polymer thermal conductivity through an addition of high thermally conductive fillers usually cannot provide an expected value, especially for composites requiring electrical insulation. Here, we show that polymeric composites with silver nanoparticle-deposited boron nitride nanosheets as fillers could effectively enhance the thermal conductivity of polymer, thanks to the bridging connections of silver nanoparticles among boron nitride nanosheets. The thermal conductivity of the composite is significantly increased from 1.63 W/m-K for the composite filled with the silver nanoparticle-deposited boron nitride nanosheets to 3.06 W/m-K at the boron nitride nanosheets loading of 25.1 vol %. In addition, the electrically insulating properties of the composite are well preserved. Fitting the measured thermal conductivity of epoxy composite with one physical model indicates that the composite with silver nanoparticle-deposited boron nitride nanosheets outperforms the one with boron nitride nanosheets, owning to the lower thermal contact resistance among boron nitride nanosheets’ interfaces. The finding sheds new light on enhancement of thermal conductivity of the polymeric composites which concurrently require the electrical insulation.

Highly Thermally Conductive Composite Papers Prepared Based on the Thought of Bioinspired Engineering

The rapid development of modern electronics and three-dimensional integration sets stringent requirements for efficient heat removal of thermal-management materials to ensure the long lifetime of the electronics. However, conventional polymer composites that have been used widely as thermal-management materials suffer from undesired thermal conductivity lower than 10 W m(-1) K(-1). In this work, we report a novel thermally conductive composite paper based on the thought of bioinspired engineering. The advantage of the bioinspired papers over conventional composites lies in that they possess a very high in-plane thermal conductivity up to 21.7 W m(-1) K(-1) along with good mechanical properties and high electrical insulation. We attribute the high thermal conductivity to the improved interfacial interaction between assembled components through the introduction of silver nanoparticles and the oriented structure based on boron nitride nanosheets and silicon carbide nanowires. This thought based on bioinspired engineering provides a creative opportunity for design and fabrication of novel thermally conductive materials, and this kind of composite paper has potential applications in powerful integrated microelectronics.

A Combination of Boron Nitride Nanotubes and Cellulose Nanofibers for the Preparation of a Nanocomposite with High Thermal Conductivity

With the current development of modern electronics toward miniaturization, high-degree integration and multifunctionalization, considerable heat is accumulated, which results in the thermal failure or even explosion of modern electronics. The thermal conductivity of materials has thus attracted much attention in modern electronics. Although polymer composites with enhanced thermal conductivity are expected to address this issue, achieving higher thermal conductivity (above 10 W m-1 K-1) at filler loadings below 50.0 wt % remains challenging. Here, we report a nanocomposite consisting of boron nitride nanotubes and cellulose nanofibers that exhibits high thermal conductivity (21.39 W m-1 K-1) at 25.0 wt % boron nitride nanotubes. Such high thermal conductivity is attributed to the high intrinsic thermal conductivity of boron nitride nanotubes and cellulose nanofibers, the one-dimensional structure of boron nitride nanotubes, and the reduced interfacial thermal resistance due to the strong interaction between the boron nitride nanotubes and cellulose nanofibers. Using the as-prepared nanocomposite as a flexible printed circuit board, we demonstrate its potential usefulness in electronic device-cooling applications. This thermally conductive nanocomposite has promising applications in thermal interface materials, printed circuit boards or organic substrates in electronics and could supplement conventional polymer-based materials.

Polymer Composite with Improved Thermal Conductivity by Constructing a Hierarchically Ordered Three-Dimensional Interconnected Network of BN

In this work, we report a fabrication of epoxy resin/ordered three-dimensional boron nitride (3D-BN) network composites through combination of ice-templating self-assembly and infiltration methods. The polymer composites possess much higher thermal conductivity up to 4.42 W m-1 K-1 at relatively low loading 34 vol % than that of random distribution composites (1.81 W m-1 K-1 for epoxy/random 3D-BN composites, 1.16 W m-1 K-1 for epoxy/random BN composites) and exhibit a high glass transition temperature (178.9-229.2 °C) and dimensional stability (22.7 ppm/K). We attribute the increased thermal conductivity to the unique oriented 3D-BN thermally conducive network, in which the much higher thermal conductivity along the in-plane direction of BN microplatelets is most useful. This study paves the way for thermally conductive polymer composites used as thermal interface materials for next-generation electronic packaging and 3D integration circuits.

Boron nitride@graphene oxide hybrids for epoxy composites with enhanced thermal conductivity

Polymer-based materials have widely been used for electronics packaging owing to their excellent physical and chemical properties. However, polymer materials usually have low thermal conductivity, which thus may impair the performance and reliability of modern electronics. In this paper, we report an epoxy-based composite with increased thermal conductivity by using graphene oxide-encapsulated boron nitride (h-BN@GO) hybrids as fillers. The thermal conductivity of the obtained composites increased with the loading of h-BN@GO hybrids to a maximum of 2.23 W m−1 K−1 when the loading of h-BN@GO hybrids was 40 wt%, which is double that of composites filled with h-BN. This increase is attributed to the presence of GO, which improved the compatibility of h-BN with epoxy resin, along with the reduced interfacial thermal resistance between h-BN and epoxy resin. In addition, the effects of h-BN@GO hybrids on the thermal and dielectric properties of epoxy composites were also investigated. The prepared h-BN@GO/epoxy composites exhibit outstanding performance in dimensional stability, slightly reduced thermal stability, and enhanced dielectric properties, which make them suitable as excellent electronics packaging materials.

Highly thermally conductive polymer nanocomposites based on boron nitride nanosheets decorated with silver nanoparticles

The development of thermally conductive polymer composites is of critical importance to address the issue of heat aggregation in modern electronics with rapid-increasing power density. However, the thermal conductivity (K) of the polymer composites has long been limited to within 10 W m−1 K−1 due to the high interfacial thermal resistance. Herein, we have demonstrated a remarkable improvement in K upon the incorporation of boron nitride nanosheets doped with silver nanoparticles hybrids (BNNSs/AgNPs). The incorporation of BNNSs/AgNPs into liquid crystalline epoxy resin (LCER) yields an in-plane K of 12.55 W m−1 K−1 with 25.1 vol% boron nitride nanosheets (BNNSs). The interfacial thermal resistance among BNNSs has demonstrated to reduce by sintering silver nanoparticles (AgNPs) deposited on the surface of BNNSs, forming more thermally conductive networks with higher K. As a proof of concept application, the obtained composite was used as the substrate for light-emitting-diode chips and was demonstrated to be more effective in heat removal than the bulk LCER. This study establishes an efficient approach to prepare thermally conductive composites, which can be applied in the next generation of integrated circuits and three-dimensional electronics.

Ultrafast Self-Healing Nanocomposites via Infrared Laser and Their Application in Flexible Electronics

The continuous evolution toward flexible electronics with mechanical robust property and restoring structure simultaneously places high demand on a set of polymeric material substrate. Herein, we describe a composite material composed of a polyurethane based on Diels-Alder chemistry (PU-DA) covalently linked with functionalized graphene nanosheets (FGNS), which shows mechanical robust and infrared (IR) laser self-healing properties at ambient conditions and is therefore suitable for flexible substrate applications. The mechanical strength can be tuned by varying the amount of FGNS and breaking strength can reach as high as 36 MPa with only 0.5 wt % FGNS loading. On rupture, the initial mechanical properties are restored with more than 96% healing efficiency after 1 min irradiation time by 980 nm IR laser. Especially, this is the highest value of healing efficiency reported in the self-healable materials based on DA chemistry systems until now, and the composite exhibits a high volume resistivity up to 5.6 × 1011 Ω·cm even the loading of FGNS increased to 1.0 wt %. Moreover, the conductivity of the broken electric circuit which was fabricated by silver paste drop-cast on the healable composite substrate was completely recovered via IR laser irradiating bottom substrate mimicking human skin. These results demonstrate that the FGNS-PU-DA nanocomposite can be used as self-healing flexible substrate for the next generation of intelligent flexible electronics.

Flexible dielectric papers based on biodegradable cellulose nanofibers and carbon nanotubes for dielectric energy storage

Flexible polymer-based dielectric materials that are used to store dielectric energy have widely been used in modern electronics and electric power systems, due to their relatively high energy density, light weight, low cost, etc. However, owing to the growing global environmental issues and a rapid consumption of nonrenewable polymer resources, there exists a strong desire to fabricate flexible dielectric materials using biodegradable materials. Here, we report on flexible dielectric papers based on biodegradable cellulose nanofibers (CNFs) and carbon nanotubes (CNTs) for dielectric energy storage. Highly ordered, homogeneous CNF/CNT papers have been fabricated using a facile vacuum-assisted self-assembly technique. The obtained paper possesses a high dielectric constant of 3198 at 1.0 kHz, thus leading to enhanced dielectric energy storage capability (0.81 ± 0.1 J cm−3), which is attributed to the presence of a low loading of CNTs (4.5 wt%). Moreover, the CNF/CNT papers are mechanically flexible and show improved mechanical strength. These findings enable feasible fabrication of high-performance flexible dielectric materials using ecofriendly materials.

Learning from Natural Nacre: Constructing Layered Polymer Composites with High Thermal Conductivity

Inspired by the microstructures of naturally layered and highly oriented materials, such as natural nacre, we report a thermally conductive polymer composite that consists of epoxy resin and Al2O3 platelets deposited with silver nanoparticles (AgNPs). Owing to their unique two-dimensional structure, Al2O3 platelets are stacked together via a hot-pressing technique, resulting in a brick-and-mortar structure, which is similar to the one of natural nacre. Moreover, the AgNPs deposited on the surfaces of the Al2O3 platelets act as bridges that link the adjacent Al2O3 platelets due to the reduced melting point of the AgNPs. As a result, the polymer composite with 50 wt % filler achieves a maximum thermal conductivity of 6.71 W m-1 K-1. In addition, the small addition of AgNPs (0.6 wt %) minimally affects the electrical insulation of the composites. Our bioinspired approach will find uses in the design and fabrication of thermally conductive materials for thermal management in modern electronics.