Thermally conductive yet electrically insulating polymer composites are urgently required for thermal management applications of modern electrical systems and electronic devices because of their multifunctionality and ease of processing. However, the thermal conductivity enhancement of polymer composites is usually at the price of the loss of lightweight, the deterioration of flexibility, and electrical insulation. Here we report advanced polymer nanocomposites containing orientated boron nitride nanosheets (BNNSs), which simultaneously exhibit high thermal conductivity enhancement, excellent electrical insulation, and outstanding flexibility. These nanocomposite films can be easily constructed by electrospinning polymer/BNNSs nanocomposite fibers, vertically folding the electrospun nanocomposite fibers and the subsequent pressing. The nanocomposite films exhibit thickness-dependent in-plane thermal conductivity, which can reach 16.3 W/(m·K) in the 18 μm thick nanocomposite film with 33 wt % BNNSs. In add...

Highly Thermally Conductive Yet Electrically Insulating Polymer/Boron Nitride Nanosheets Nanocomposite Films for Improved Thermal Management Capability.

Two-Dimensional Materials for Thermal Management Applications

Graphene-based composites for electrochemical energy storage

Phase change materials (PCMs) have triggered considerable attention as candidates for solar‐thermal energy conversion. However, their intrinsic low thermal conductivity prevents the rapid spreading of heat into the interior of the PCM, causing low efficiencies in energy storage/release. Herein, anisotropic and lightweight high‐quality graphene aerogels are developed by directionally freezing aqueous suspensions of polyamic acid salt and graphene oxide to form vertically aligned monoliths, followed by freeze‐drying, imidization at 300 °C and graphitization at 2800 °C. After impregnating with paraffin wax, the resultant phase change composite (PCC) exhibits a high transversal thermal conductivity of 2.68 W m−1 K−1 and an even higher longitudinal thermal conductivity of 8.87 W m−1 K−1 with an exceptional latent heat retention of 98.7%. When subjected to solar radiation, solar energy is converted to heat at the exposed surface of the PCC. As a result of the PCC's high thermal conductivity in the thickness direction, heat can spread readily into the interior of the PCC enabling a small temperature gradient of <3.0 K cm−1 and a fast charging feature. These results demonstrate the potential for real‐time and fast‐charging solar‐thermal energy conversion using phase change materials with tailored anisotropy in their thermal properties.

Thermally Conductive Phase Change Composites Featuring Anisotropic Graphene Aerogels for Real-Time and Fast-Charging Solar-Thermal Energy Conversion

As a material possessing extremely high thermal conductivity, graphene has been considered as the ultimate filler for fabrication of highly thermally conductive polymer composites. In the past decade, graphene and its derivatives were demonstrated in many studies to be very effective in enhancing the thermal conductivity of various polymers. This paper reviews current progress in the development of graphene/polymer composites with high thermal conductivity. We began with the effects of isotopes, defects/doping, edges and substrate, polycrystallinity, functionalization, size and layer number, and folding/twisting on the thermal conductivity of graphene. We then modelled the thermal conductivity of graphene/polymer composites and, through molecular dynamics (MD) simulations, demonstrated its dependence on interfacial thermal conductance as well as size, dispersion and volume fraction of graphene. After a critique of recent studies on thermally conductive graphene/polymer composites and their potential applications, we identified several outstanding issues, new challenges and opportunities for future endeavours.

Thermal conductivity of graphene-based polymer nanocomposites

Due to low density, extremely high electrical and thermal conductivities, graphene has great potential to construct lightweight thermal conductive paper for high-power electric devices. However, the remarkable properties of graphene are on a molecular level and difficult to achieve when processed into macroscopic paper. Here, an effective route to construct ultrahigh conductive graphene paper is developed. First, large-volume, high-concentration, plane-defect-free, few-layer graphene dispersion is fast produced from graphite at high yield through ball milling. The exfoliated graphene dispersion is further processed into graphene paper through fast filtration, thermal treatment, and mechanical compression. The electrical and thermal conductivities of the resultant graphene paper are as high as 2231 S cm−1 and 1529 W m−1 K−1, superior to previously reported graphene papers. Structural analyses confirm that the ultrahigh conductivities are attributed to high quality of graphene sheets, their compact ordered stacking, and large graphitic crystalline domain size, which improve electron and phonon transport within basal plane of graphene sheet and between graphene sheets.

Ultrahigh Conductive Graphene Paper Based on Ball-Milling Exfoliated Graphene

Due to a three-dimensional network structure filled with abundant water, a hydrogel is an ideal candidate for an underwater superoleophobic material, which has many promising applications in the fields of anti-bioadhesion, antifouling coating, oil/water separation, metal cleaning, and small oil-droplet manipulation. However, its practical applications are greatly limited by its poor mechanical properties. In this study, we prepared a strong underwater superoleophobic poly(N-isopropylacrylamide)–clay nanocomposite hydrogel through a simple filtration method. The nanocomposite hydrogel has a large number of mountain-like protrusions on its filtered surface and a layered structure in the interior. It is demonstrated that the rough surface structure improves its oil-repellent capability, leading to superoleophobicity with self-cleaning properties, while the interior layered structure endows the hydrogel with excellent tensile modulus and strength, superior to those of reported underwater superoleophobic hydrogels. It is demonstrated that the strong, underwater superoleophobic hydrogel is further developed as an oil/water separation film. We believe that this strong nanocomposite hydrogel will promote the development of underwater superoleophobic hydrogels toward practical applications.

A strong, underwater superoleophobic PNIPAM–clay nanocomposite hydrogel

The invention provides a deformation controllable hydrogel actuator and a preparation method thereof. The deformation controllable hydrogel actuator is prepared from an inorganic nano-material, poly(isopropyl acrylamide) and water, wherein the concentration distribution of the inorganic nano-material in a thickness direction is non-uniform, so as to form an asymmetrical heterojunction structure; in a plane direction, the non-uniform asymmetrical structure can be randomly patterned according to requirements, so that various reversible deformation triggered by temperature is realized. The preparation method comprises the following steps: mixing isopropyl acrylamide monomer, an initiator and the inorganic nano-material to form uniform pre-gel; pouring the pre-gel into a rectangular mold; covering one layer of mask plate on the pre-gel; evaporating partial water to induce the concentration of the inorganic nano-material to be not uniformly distributed in the thickness direction of an exposed region; then carrying out in-situ polymerization to fix a patterned non-uniform structure, so as to form the deformation controllable hydrogel actuator. The method is simple and feasible and easy to realize; the deformation controllable hydrogel actuator can be used for soft robots, drug delivery, microfluidic valves and artificial muscle.

Preparation method of deformation controllable hydrogel actuator

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Ultrahigh Conductive Graphene Paper Based on Ball-Milling Exfoliated Graphene

A strong, underwater superoleophobic PNIPAM–clay nanocomposite hydrogel

Preparation method of deformation controllable hydrogel actuator