A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area.

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Interface design for high energy density polymer nanocomposites

Intrinsically conducting polymers (ICP) and conductive fillers incorporated conductive polymer-based composites (CPC) greatly facilitate the research in electromagnetic interference (EMI) s...

Electromagnetic Interference Shielding Polymers and Nanocomposites - A Review

Flame-retardant poly(vinyl alcohol)/MXene multilayered films with outstanding electromagnetic interference shielding and thermal conductive performances

Lightweight, flexible, and electrically conductive thin films with high electromagnetic interference (EMI) shielding effectiveness are highly desirable for next-generation portable and wearable electronic devices. Here, spin spray layer-by-layer (SSLbL) to rapidly assemble Ti3C2Tx MXene-carbon nanotube (CNT) composite films is shown and their potential for EMI shielding is demonstrated. The SSLbL technique allows strategic combinations of nanostructured materials and polymers providing a rich platform for developing hierarchical architectures with desirable cross-functionalities including controllable transparency, thickness, and conductivity, as well as high stability and flexibility. These semi-transparent LbL MXene-CNT composite films show high conductivities up to 130 S cm−1 and high specific shielding effectiveness up to 58 187 dB cm2 g−1, which is attributed to both the excellent electrical conductivity of the conductive fillers (i.e., MXene and CNT) and the enhanced absorption with the LbL architecture of the films. Remarkably, these values are among the highest reported values for flexible and semi-transparent composite thin films. This work could offer new solutions for next-generation EMI shielding challenges.

Layer-by-Layer Assembly of Cross-Functional Semi-transparent MXene-Carbon Nanotubes Composite Films for Next-Generation Electromagnetic Interference Shielding

In this study, we fabricated conductive poly(vinylidene fluoride) (PVDF)/carbon composites simply by dispersing multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets into a PVDF solution The electrical conductivity and the electromagnetic interference (EMI) shielding of the PVDF/carbon composites were increased by increasing the conductive carbon filler amounts Moreover, we also found that the EMI shielding properties of the PVDF/CNT/graphene composites were higher than those of PVDF/CNT and PVDF/graphene composites The mean EMI shielding values of PVDF/5 wt %-CNT, PVDF/10 wt %-graphene, and PVDF/CNT/graphene composite films with a thickness of 01 mm were 2241, 1870, and 2758 dB, respectively An analysis of the shielding mechanism showed that the main contribution to the EMI shielding came from the absorption mechanism, and that the EMI shielding could be tuned by controlling the films’ thickness The total shielding of the PVDF/CNT/graphene films increased from 2190 to 3646 dB as the

Flexible, Ultrathin, and High-Efficiency Electromagnetic Shielding Properties of Poly(Vinylidene Fluoride)/Carbon Composite Films.

Synergism between carbon materials and Ni chains in flexible poly(vinylidene fluoride) composite films with high heat dissipation to improve electromagnetic shielding properties

In this study, we found a simple and effective method to fabricate lightweight poly(vinylidene fluoride) (PVDF)/10 wt% graphene nanoplatelet (GnP) nanocomposite foams with excellent electromagnetic interference (EMI) shielding effectiveness To this end, solvent blending, film casting, and hot compression procedures were used The PVDF/10 wt%-GnP nanocomposite foams, which had different microcellular structures, were obtained by adjusting the foaming parameter Notably, the electrical conductivity and the EMI shielding properties decreased linearly with elevated foaming degree (ie, the void fraction) Furthermore, they quickly decreased, having a large slope with an increasing void fraction, when the void fraction was below the critical foaming degree of 55% void fraction When the void fraction was above this critical foaming degree, the electrical conductivity and EMI shielding values decreased slowly with a smaller slope The EMI shielding properties were critically determined by the foam thickness The EMI shielding properties of the PVDF/10 wt%-GnP foam with a void fraction of 487% increased from 124 to 322 dB at 265 GHz and from 152 to 374 dB at 40 GHz when the sample thickness increased from 15 to 30 mm We concluded that the PVDF/GnP composite foams with tunable electrical conductivity and light weight offered much promise for use as excellent EMI shielding materials Moreover, this study adopted a novel approach toward the design of conductive lightweight polymer/carbon composite foams for use in a wide range of electronic applications

Incorporating a microcellular structure into PVDF/graphene–nanoplatelet composites to tune their electrical conductivity and electromagnetic interference shielding properties

There is an urgent need for dielectric-based capacitors to manage the increase in storage systems related to renewable energy production. Such capacitors must have superior qualities that include light weight, a high dielectric constant, and ultra-low dielectric loss. Poly(vinylidene fluoride) (PVDF)/carbon (carbon nanotube (CNT) or graphene nanoplatelet (GnP)) nanocomposite foams are considered promising alternatives to solid PVDF/carbon nanocomposites. This is because they have excellent dielectric properties, which are due to the preferred orientation of their carbon materials occurring in the foaming process. In the PVDF/carbon foams, their microcellular structure significantly influenced their electrical conductivity and dielectric properties. In the PVDF/CNT composite foams, the electrical conductivity was increased by an increased degree of foaming that was below a critical foaming degree. The CNTs even formed conductive networks and this caused current leakage. Thus, in the PVDF/CNT foam sample with an expansion ratio of 4.0 where a high dielectric constant of 80.6 was obtained, a relatively high dielectric loss of 3.51 was observed at the same time. In the PVDF/GnP composite foams, the presence of a microcellular structure forcefully increased the distance between GnPs. This induced and produced the insulating quality of the PVDF/GnP foams. In addition, the parallel graphene nanoplatelets that accompanied this process were close together, and they isolated the polymer layer, or air, as a medium between themselves. An unprecedentedly high dielectric constant of 112.1 and an ultra-low dielectric loss of 0.032 at 100 Hz were obtained from the PVDF/GnP composite foam with a high expansion ratio of 4.4 due to charge accumulation at the aligned conductive filler/insulating polymer (or air bubble) interface.

A versatile foaming platform to fabricate polymer/carbon composites with high dielectric permittivity and ultra-low dielectric loss

In this study, we used a batch-foaming method to prepare closed-cell poly(vinylidene fluoride) (PVDF) foams with tailored microcellular structures. This is a simple, cost-effective, and environmentally-friendly method, and it offers a wide range of tunable microcellular structures. The cell size and porosity volume of PVDF foams can be effectively monitored at their saturation temperatures. The PVDF foam prepared at 169.5 °C possesses an ultra-low dielectric constant of k ∼ 1.1 and a thermal conductivity of 0.027 W m−1 K−1. We used numerous theoretical models to predict the effective dielectric permittivity of the microcellular PVDF foams, and found that the Bruggeman model was very close to the measured results. The ultra-low thermal conductivities of the PVDF foams were the result of a large number of air pockets in the microcellular structure. Based on these results, we concluded that this PVDF foam would be a promising low-k dielectric and heat insulating material.

Chongxiang Zhao

Papers

Flexible, Ultrathin, and High-Efficiency Electromagnetic Shielding Properties of Poly(Vinylidene Fluoride)/Carbon Composite Films.

Synergism between carbon materials and Ni chains in flexible poly(vinylidene fluoride) composite films with high heat dissipation to improve electromagnetic shielding properties

Incorporating a microcellular structure into PVDF/graphene–nanoplatelet composites to tune their electrical conductivity and electromagnetic interference shielding properties

A versatile foaming platform to fabricate polymer/carbon composites with high dielectric permittivity and ultra-low dielectric loss

Poly(vinylidene fluoride) foams: a promising low-k dielectric and heat-insulating material