Recent advancements in supercapacitor technology

How to rationally design the microstructure of polymer nanocomposites to significantly improve their electromagnetic interference shielding effectiveness (EMI SE) is still a great challenge. Herein, we developed a template method for fabricating 3D porous graphene nanoplatelets/reduced graphene oxide foam/epoxy (GNPs/rGO/EP) nanocomposites, in which 3D rGO foam embedded with GNPs constructs a 3D electrical and thermal conductive network in the EP matrix. The 3D rGO framework resolves the agglomeration problem of GNPs, acts as an efficient bunch of channels for electrical transport and attenuates the entered electromagnetic wave. Benefiting from this 3D nanohybrid framework, the GNPs/rGO/EP nanocomposites containing 0.1 wt% rGO and 20.4 wt% GNPs exhibit an EMI SE value of 51 dB in the X-band range, an almost 292% improvement relative to the rGO/EP nanocomposites (∼13 dB) and 240% enhancement compared with the GNPs/EP nanocomposites without 3D microstructures (∼15 dB) and an excellent thermal conductivity of 1.56 W mK−1 and electrical conductivity up to 179.2 S m−1. This work provides a new strategy for the design of muti-functional epoxy nanocomposites for EMI shielding and efficient heat dissipation.

Superior electromagnetic interference shielding 3D graphene nanoplatelets/reduced graphene oxide foam/epoxy nanocomposites with high thermal conductivity

Fluorine-containing polyimide (PI) with low dielectric constant (e) value was firstly synthesized by a polycondensation reaction of 4, 4-(hexafluoroisopropyl) diphthalic anhydride (6FDA), 1, 3, 4-triphenyldiether diamine (APB) and 1, 3-bis(3-aminopropyl) tetramethyldisiloxane (GAPD). γ-glycidoxypropyltrimethoxysilane (KH-560) and aminopropylisobutyl polyhedral oligomeric silsesquioxane (NH2-POSS) were synchronously performed to functionalize the surface of boron nitride (f-BN) fillers, which were then utilized as thermally conductive fillers to fabricate the corresponding f-BN/PI composites. NH2-POSS was successfully grafted on the surface of BN fillers. All the f-BN/PI composites presented better thermal conductivities, dielectric and thermal properties than those of BN/PI composites at the same addition of BN fillers. The obtained thermal conductivity coefficient (λ) of the f-BN/PI composites with 30 wt% f-BN was 0.71 W/mK, higher than that of BN/PI composites with 30 wt% BN (λ of 0.69 W/mK). Modified Hashin-Shtrikman model demonstrated that f-BN possessed relatively lower thermal resistance with PI matrix. Meantime, the corresponding e and dielectric loss tangent (tanδ) value of the f-BN/PI composites was decreased to 3.32 and 0.004, respectively, lower than that of BN/PI composites with 30 wt% BN (e of 3.77 and tanδ of 0.007). Moreover, the corresponding heat resistance index (THRI) and glass transition temperature (Tg) of the f-BN/PI composites was further enhanced to 280.2 °C and 251.7 °C, respectively.

Enhanced thermal conductivities and decreased thermal resistances of functionalized boron nitride/polyimide composites

Biocompatible, self-healing, highly stretchable polyacrylic acid/reduced graphene oxide nanocomposite hydrogel sensors via mussel-inspired chemistry

An anisotropic thermally conductive film with tailorable microstructures and macroproperties is fabricated using a layer-by-layer (LbL) assembly of graphene oxide (GO) and nanofibrillated cellulose (NFC) on a flexible NFC substrate driven by hydrogen bonding interactions, followed by chemical reduction process. The resulting NFC/reduced graphene oxide (RGO) hybrid film reveals an orderly hierarchical structure in which the RGO nanosheets exhibit a high degree of orientation along the in-plane direction. The assembly cycles dramatically increase the in-plane thermal conductivity (λX) of the hybrid film to 12.6 W·m–1·K–1, while the cross-plane thermal conductivity (λZ) shows a lower value of 0.042 W·m–1·K–1 in the hybrid film with 40 assembly cycles. The thermal conductivity anisotropy reaches up to λX/λZ = 279, which is substantially larger than that of similar polymeric nanocomposites, indicating that the LbL assembly on a flexible NFC substrate is an efficient technique for the preparation of polymeric n...

Highly Anisotropic Thermal Conductivity of Layer-by-Layer Assembled Nanofibrillated Cellulose/Graphene Nanosheets Hybrid Films for Thermal Management

Inspired by mussels, dopamine (DOPA) was used as a green reducing agent for graphene oxide (GO) to prepare a superior flame retardant and high thermal conductive flexible film. The self-polymerization of dopamine occurred on the surface of GO nanosheets, accompanied by the reduction of GO. As the solvent was gradually removed, the reduced graphene sheets covered by polydopamine formed a layer-by-layer stacked film, where polydopamine acted as a linkage filled in the interlayer space. Herein, the experimental results indicated that the tensile strength of the constructed graphene/polydopamine composites film (GPF) was as high as 25 MPa. The in-plane thermal conductivity of this prepared film was 13.42 W m−1 K−1, whereas that in the cross-plane direction was 0.69 W m−1 K−1. The high anisotropy of the thermal conductivity was verified to be due to the high alignment of reduced graphene. Fire experiments showed that the GPF could effectively prevent flame spreading and propagation without ignition, and the heat release rate (HRR) curve showed that the GPF had no heat release below 500 °C. The peak HRR is only 40 W g−1 at 528 °C, whereas that of GO is 360 W g−1 at 165 °C. This phenomenon demonstrates that the GPF has excellent flame retardancy.

Green reduction of graphene oxide by polydopamine to a construct flexible film: superior flame retardancy and high thermal conductivity

Inspired by mussels, dopamine was used to modify graphene nanoplatelets (GnPs). The GnPs@polydopamine (GnPs@PDA) fillers were prepared as fillers and polyvinyl alcohol (PVA) composites were fabricated via casting method. Composites exhibited excellent flexibility and tensile strength increased by 12% at 2.5 wt.% GnPs@PDA loading. The thermal conductivity(λ) of the composites reached 13.4 W m−1 K−1 with loading 10 wt.% GnPs@PDA, which was increased by 4300% compared that of PVA. FTIR results of PVA/PDA films showed that PVA OH and C O stretching vibration have shifted, which proved that hydrogen bonds were formed between GnPs@PDA and PVA. The crystallinity of PVA decreased in the composites indicated that hydrogen bonds were formed between the PVA matrix and the PDA. In addition, the interface compatibility between the GnPs@PDA and PVA matrix was enhanced. Thus, an effective thermal conductive network was formed through hydrogen bonds in composites. These results lead a high λ for films.

Significantly enhanced thermal conductivity in polyvinyl alcohol composites enabled by dopamine modified graphene nanoplatelets

Microencapsulated ammonium polyphosphate MFAPP or VMFAPP with shell of melamine–formaldehyde or poly (vinyl alcohol)–melamine–formaldehyde resin was prepared by in situ polymerization, respectively. The flame-retardant performance of rigid polyurethane foam (PU) containing MFAPP or VMFAPP was analyzed by limiting oxygen index and UL-94 test. Thermal degradation behaviors of PUAPP, PUMFAPP and PUVMFAPP were studied using TG and TG–FTIR. Above results indicated that VMFAPP and MFAPP have better water resistance and flame retardancy compared with ammonium polyphosphate (APP) in PU composites. Flame-retardant properties of PUMFAPP and PUVMFAPP composites were rarely changed after hot water treatment. Due to better compatibility and the presence of active groups on the surface of APP, microencapsulation demonstrated a positive effect on the mechanical property of PU composites.

Thermal degradation and flame retardancy of microencapsulated ammonium polyphosphate in rigid polyurethane foam

Anisotropic thermal conductivity and flame retardancy of nanocomposite based on mesogenic epoxy and reduced graphene oxide bulk

In order to develop a highly efficient flame-retardant system, a phosphonate-based ionic liquid named 1-vinyl-3-(diethoxyphosphoryl)-propylimidazolium bromide (IL) was synthesized and introduced into epoxy resin (EP). With only 4 wt% loading, EP/IL composite passed UL-94 V-0 rating, and its limiting oxygen index value increased to 34.9% from 25.9% for neat epoxy resin. The char yield of EP/IL-2 (2 wt%) was improved by 58.3%, and its peak of heat release rate was reduced by 65% compared with that of neat EP. The reason is that the presence of IL promoted the forming of a compact and stable phosphorus-rich residual chars. Unlike traditional additive-type flame retardant, it is very interesting that the introduction of IL changed the color and transparency of EP few and enhanced mechanical property of neat EP remarkably. Owing to the excellent compatibility and steric effect between IL and EP matrix, tensile strength was increased to 108.6 MPa for EP/IL sample from 84.9 MPa for neat EP, indicating the outstanding reinforcement effect of IL on EP composites.

Fubin Luo

Papers

Green reduction of graphene oxide by polydopamine to a construct flexible film: superior flame retardancy and high thermal conductivity

Significantly enhanced thermal conductivity in polyvinyl alcohol composites enabled by dopamine modified graphene nanoplatelets

Thermal degradation and flame retardancy of microencapsulated ammonium polyphosphate in rigid polyurethane foam

Anisotropic thermal conductivity and flame retardancy of nanocomposite based on mesogenic epoxy and reduced graphene oxide bulk

An efficient phosphonate-based ionic liquid on flame retardancy and mechanical property of epoxy resin