Conductive Polymer-based Composites Research Articles

Low percolation threshold polyvinylidene fluoride/multi‐walled carbon nanotube composites: A perspective of electrical conductivity, crystalline, rheological and mechanical properties

AbstractRecently, conductive polymer‐based composites (CPC) have gained considerable interest for their outstanding processing, mechanical, electrical properties, and resistance tunability. Multi‐walled carbon nanotube (MWCNT) was introduced into polyvinylidene fluoride (PVDF) as the conductive filler via means of melt blending in this work. Effects of MWCNT on crystalline structure, thermodynamic behavior, electrical conductivity, processing and mechanical properties of PVDF/MWCNT were under investigation. By measuring the volume resistivity of PVDF/MWCNT, it was observed to have declined from 1.54 × 1012 to 3.71 × 101 Ω∙m with the MWCNT content changed from 0.7 to 1 vol%, which plummeted by 11 orders of magnitude. Therefore, it can be inferred that the percolation threshold of MWCNT lies within the range of 0.7–1 vol%. Additionally, the percolation threshold is obtained as 0.81 vol% by fitting using the percolation theory equation. Around the percolation threshold, PVDF/MWCNT composites exhibit negligible alterations in their rheological properties when contrasted with pure PVDF, yet their mechanical properties are improved. Furthermore, MWCNT does not substantially impact the crystalline structure and thermodynamic behavior of PVDF/MWCNT.Highlights The percolation threshold of MWCNT in PVDF is 0.81 vol%. The volume resistivity of the 1 vol% MWCNT sample was only 3.71 Ω∙m. 1 vol% MWCNT exhibit favorable rheological and mechanical properties.

Research Progress on Intrinsically Conductive Polymers and Conductive Polymer-Based Composites for Electromagnetic Shielding.

Electromagnetic shielding materials are special materials that can effectively absorb and shield electromagnetic waves and protect electronic devices and electronic circuits from interference and damage by electromagnetic radiation. This paper presents the research progress of intrinsically conductive polymer materials and conductive polymer-based composites for electromagnetic shielding as well as an introduction to lightweight polymer composites with multicomponent systems. These materials have excellent electromagnetic interference shielding properties and have the advantages of electromagnetic wave absorption and higher electromagnetic shielding effectiveness compared with conventional electromagnetic shielding materials, but these materials still have their own shortcomings. Finally, the paper also discusses the future opportunities and challenges of intrinsically conductive polymers and composites containing a conductive polymer matrix for electromagnetic shielding applications.

A facile method to fabricate water-dispersible hetero-structured AuNPs@BNNS hybrid filler and its application for enhancing thermal conductivity

Chemical inertness of BNNS seriously restricts its application for fabricating thermally conductive polymer-based composites with uniform dispersion and low interfacial thermal resistance. In this work, by using self-initiated photografting and photopolymerization (SIPGP) method, over 40 wt% polyacrylic acid (PAA) macromolecular chains can be grafted onto BNNS in only 2 h for improving polarity and water dispersibility of BNNS, and the content of grafted PAA can be easily tuned by the reaction time. Furthermore, based on the coordination effect between carboxyl groups of PAA and Au3+/AuNPs, large amount of AuNPs can be immobilized onto BNNS to form hetero-structured AuNPs@BNNS hybrid filler, and such filler is beneficial for decreasing interfacial thermal resistance between fillers, constructing thermally conductive network in relatively lower filler content and improving comprehensive thermal conductivity. Finally, AuNPs@BNNS/NFC composite with only 30 wt% filler can reach in-plane and through-plane thermal conductivities of 19 and 1.22 W/(m·K) simultaneously. Therefore, this study provides a simple and effective method to fabricate water-dispersible and hetero-structured AuNPs@BNNS hybrid filler, which can be used for preparation of high-efficiency thermal management materials for electronic devices effectively.

Preparation and optimization of conductive PDMS composite foams with absorption-dominated electromagnetic interference shielding performance via silvered aramid microfibers

Electromagnetic interference (EMI) shielding materials with absorption-dominated EMI shielding mechanism can effectively annihilate electromagnetic waves (EMW) and avoid their repeated EMW pollution. However, it is difficult to achieve this goal for conductive polymer-based composites (CPC), because the interface impedance mismatch between air and CPC leads to massive reflection of EMW at the interface. Pores are beneficial to EMW penetrating into the interior of CPC and causing their multiple reflection, scattering and absorption in pores, thus endowing CPC with absorption-dominated EMI shielding characteristic. Herein, highly conductive silvered aramid microfibers (CAMF) were first synthesized via dopamine-assisted electroless deposition of silver coating on aramid microfibers (AMF), and then the conductive porous PDMS composite foams (PDMSF) with absorption-dominated EMI shielding characteristic were prepared and optimized via salt template method. As a result, PDMSF with 1.7 vol% silver content, the conductivity of PDMSF can reach 10-1 S/m, the EMI shielding efficiency (EMI SE) can reach 36.7 dB in X-band, and the average absorption ratio in EMI SE is 87%, while the density of PDMSF is only 0.28 g/cm3. The combination of lightweight, high EMI SE and absorption-dominated EMI shielding characteristic makes the porous PDMSF the latent EMI shielding materials in special constructions (e.g. military, confidential and nuclear facilities, etc.), aerospace, military equipments and transportation, etc.

Highly thermally conductive polymer-based composites with 3D exfoliated BNNS/functionalized SiC networks prepared by rapid solidification and hot pressing

High thermal conductivity polymer-based packaging materials can achieve effective heat diffusion, which is of great significance for the performance and longevity of electronic devices. Exfoliated boron nitride nanosheets (s-BNNS) containing smaller particle sizes, fewer layers, and more hydroxyl groups were prepared by ball milling and strong ultrasonic treatment in this work. The functionalized SiC (m-SiC) was obtained by ternary blend organic silanol modification, which promoted the compatibility between fillers and fillers, as well as fillers and matrix. By a facile strategy of rapid solidification and hot pressing, s-BNNS were distributed between and on the surface of m-SiC fillers to form m-SiC/s-BNNS/polyamide 6/polyethylene terephthalate (PA6/PET) composite films with 3D thermally conductive networks. The thermal conductivity of m-SiC/s-BNNS/PA6/PET composite reached a superior 6.98 W/(m·K) at a filler loading 85 wt%, which was 124.67% higher than that of SiC/PA6/PET composite without 3D thermal network formation. More interestingly, reverse non-equilibrium molecular dynamics (RNEMD) simulations show that the hybrid SiC/BNNS filler greatly reduces the porosity within the composite compared to only one kind of filler, which in turn improves the composite's thermal conductivity.

Advances in Thermoelectric Composites Consisting of Conductive Polymers and Fillers with Different Architectures.

Stretchable wireless power is in increasingly high demand in fields such as smart devices, flexible robots, and electronic skins. Thermoelectric devices are able to convert heat into electricity due to the Seebeck effect, making them promising candidates for wearable electronics. Therefore, high-performance conductive polymer-based composites are urgently required for flexible wearable thermoelectric devices for the utilization of low-grade thermal energy. In this review, mechanisms and optimization strategies for polymer-based thermoelectric composites containing fillers of different architectures will be introduced, and recent advances in the development of such thermoelectric composites containing 0- to 3-dimensional filler components will be presented and outlooked.

Effect of functional filler morphology on the crystallization behavior and thermal conductivity of PET resin: A comparative study of three different shapes of BN as heterogeneous nucleating agents

Functional fillers play a vital role in thermally conductive polymer-based composites. However, little attention has been paid to how functional fillers with the same composition but different morphologies affect the crystallinity of the matrix and the final thermal conductivity of polymeric composites. In this work, two-dimensional boron nitride nanosheet (2-D BNNS), one-dimensional boron nitride whisker (1-D BNW) and one-dimensional boron nitride nanotube (1-D BNNT) acting as both nucleating agents and thermally conductive fillers were melt-mixed with Polyethylene terephthalate (PET) resin, respectively, and the effects of filler morphology on the crystallization behavior of PET and thermal conductivity of the PET/BN composites were investigated and compared. Results indicate that three kinds of BN all play a better heterogeneous nucleation role in crystallization of PET, which significantly accelerates the crystallization rate and improves the crystallinity of PET, but the modifying effect is not the same. The thermal conductivity of PET is improved by increasing the crystallinity of the polymer with a very low content of 0.5 wt% of BN in PET. The BNNT with regular shape and minimum size achieves the best effect in nucleation and improvement of thermal conductivity, followed by BNW and BNNS. Experimental fact illustrates that the functional fillers with the same composition but different shapes can produce different modification effects on both crystallinity of matrix and the final thermal conductivity of the polymeric composites.

Thermally conductive polymer-based composites: fundamentals, progress and flame retardancy/anti-electromagnetic interference design

Heat conduction, electromagnetic compatibility, flame retardancy mechanism, ways to enhance thermal conductivity and multifunctional design including heat conduction, flame retardancy and electromagnetic compatibility for polymer-based composites.

Recent advances and perspectives in conductive-polymer-based composites as cathode materials for high-performance lithium–sulfur batteries

The advantages and recent advances of conductive polymer-based composites as cathode materials for high-performance lithium–sulfur batteries are summarized.

Simple large-scale method of recycled graphene films vertical arrangement for superhigh through-plane thermal conductivity of epoxy composites

Highly thermal conductive polymer-based materials are essential for modern microelectronic devices. However, conventional thermal conductive polymer-based composites exhibit constrained thermal conductivity even at a high content of highly thermal conductive fillers due to the lack of significant thermal conductive paths. In this work, effective thermal conductive paths were constructed with macro recycled graphene film fragments that were vertically arranged by a method of area restricting in the vertical direction under mechanical force. The resulting composites with vertically arranged structure displayed highly through-plane thermal conductivity of 20.97 W m−1 K−1 at 32.63 wt% graphene film fragments loading. Another three contrast experiments in different adding ways of fillers were as well accomplished to confirm the excellent vertically arranged structure. This study not only provides a simple way to obtain highly thermal conductive composites but also offers a strategy of making full use of wastes from industrial applications. The facile method for obtaining the superhigh though-plane thermal conductivity enlightens us to practical application. The recycled graphene films as millimeter-particles in this study can be expanded to other millimeter-particles arrangements. The mechanical force used for vertically arranged structure can be broadened to other forces such as vacuum or hydraulic pressure.

A high-performance thermal conductive and outstanding electrical insulating composite based on robust neuron-like microstructure

Owing to the rapid development of highly integrated electronic devices, research on reliable and efficient Thermal interface materials (TIMs) has promising prospects. Boron nitride (BN) is regarded as an excellent functional filler due to its high in-plane thermal conductivity and low cost. However, the fabrication of highly thermally conductive polymer-based composites with multifunctional properties remains challenging. Presented here is an efficient and scalable technique to realize the robust neuron-like microstructure network with oriented BN platelets formed in Polyethersulfone (PES) and Polyvinylidene fluoride (PVDF) based composites. The neuron-like microstructure, with well-developed synapses, guarantee effective thermal pathways and robust interface interaction under complex conditions. The oriented BN layer in the composite ensures a high thermal conductivity of 12.13 W m−1 K−1, indicating a thermal enhancement efficiency of 156.6% per 1 vol% filler compared to the polymer-based matrix. Combined with outstanding electrical resistivity over 1015 Ω·cm and superior usage stability over 120 °C, the composite also exhibits superior performance in application tests in the mobile communication system and laptop chip cooling module making it promising in the intelligent robot industry and advanced electronic packaging field.

Lightweight, few-layer graphene composites with improved electro-thermal properties as efficient heating devices for de-icing applications

Conductive polymer-based composites with electro-thermal properties are gaining great interest in several challenging technological applications. They are more and more employed as integrated heating devices within smart buildings or de-icing materials for application spanning from the aerospace sector to that of civil engineering. Their lightweight character along with high thermal efficiency and moderate production costs, make them highly attractive alternative to the use of classical electrothermal systems based on costly and heavier metals. Here we describe a convenient approach to the preparation of few-layer graphene-based (FLG) polymer composites obtained from the surface coating of selected polymer matrices with an electrically conductive and thin FLG “skin”. We demonstrated that low FLG concentrations at the outmost polymer surface, together with an excellent and homogeneous surface adhesion, allowed to get fast-responsive and lightweight heatable devices while keeping unchanged the properties of the underlying polymers. A controlled low-temperature post-treatment of the composites ensured an extremely high adhesion of FLG sheets to the hosting polymer substrate. The as-prepared composites have shown fast on/off heating response and exceptional performance once employed as lightweight and low-power heating devices with de-icing properties.

Rational design of nanohybrids for highly thermally conductive polymer composites

With the miniaturization, integration and functionalization of electronic devices and the emergence of some new applications including lighting components, wearable electronics, and energy storage systems, extensive efforts have been dedicated to developing highly thermally conductive polymer-based composites. Especially, the nanohybrids constructed with various geometrically dissimilar thermally conductive nanofillers, as a fascinating building block for manufacturing advanced thermally conductive composites, have sparked intensive interest of researchers during the past few years. In this short review, we summarize the recent progresses on the nanohybrids for preparing highly thermally conductive polymer composites. The construction strategies of nanohybrids, thermal conduction mechanisms, structure-properties relationships as well as their potential applications are highlighted. Finally, the future potentials and challenges in this active research field are prospected.

Enhanced thermal conductivity of poly(lactic acid)/alumina composite by synergistic effect of tuning crystallization of poly(lactic acid) crystallization and filler content

Thermally conductive polymer-based composites have drawn significant interest in the field of heat management. Herein, taking polylactic acid/alumina (PLA/Al2O3) composite as the research system, we investigated the influences of the content of Al2O3 and the crystallinity of PLA on the thermal conductivity of PLA/Al2O3 composite, and discussed the synergistic effect between the matrix crystallinity and the filler content and the corresponding thermal conduction mechanism. Results show that Al2O3 plays a heterogeneous nucleation role in crystallization of PLA, which significantly accelerates the crystallization rate and improves the crystallinity of PLA. Both crystallinity of PLA matrix and Al2O3 content contribute to the final thermal conductivity of the composite. When the filler content is lower than 50 wt%, the improvement of thermal conductivity for composite is mainly determined by Al2O3 content, and contribution from the crystallinity of PLA is very limited. When the Al2O3 content is higher than 60 wt%, which is sufficient to format a heat conduction network in the matrix, the high crystallinity of PLA combined with high filler content brings a synergistic effect and significantly enhances the final thermal conductivity of the composite. For composite of PLA containing 70 wt% Al2O3, when the crystallinity of PLA matrix increases from 4.63 to 59.8%, the corresponding thermal conductivity of the PLA/Al2O3 composite enhanced by 26.8% from 0.82 to 1.04 W m−1 K−1, which is more than 5 times higher than that of neat PLA. Such a remarkable improvement in thermal conductivity only by changing matrix structure without further adding fillers is of great significance for polymer-based thermally conductive composites.

Highly thermally conductive polystyrene/polypropylene/boron nitride composites with 3D segregated structure prepared by solution-mixing and hot-pressing method

Continuous heat conduction networks are very significant for filler-filled polymer composites to enhance their thermal conductivity (TC). 3D segregated structure has been considered as an effective approach to construct continuous heat conduction networks. Herein, we prepared the polystyrene/polypropylene/boron nitride (PS/PP/BN) ternary composites with 3D segregated filler networks by solution-mixing and hot-pressing method. The ternary PS/PP/BN composite containing 50 wt% BN achieves TC of 5.57 W/m·K, which is 29 times than that of PS resin (0.19 W/m·K) and 2.76 folds of the PS/BN binary counterpart (2.02 W/m·K). More importantly, the ternary PS/PP/BN composite exhibits favorable thermal stability after 50 hot-cold cycles or thermal ageing test for 50 h, whose TC drops slightly by 3.2% and 3.4%, respectively. The typical 3D segregated structure has been constructed in our PS/PP/BN ternary composites, which can provide effective heat conduction pathways. Moreover, BN platelets align along the PP microspheres in the PS matrix during the hot-pressing process. These two factors make the TC of the PS/PP/BN ternary composites increase sharply. Our strategy can potentially pave the way for the easy, low-cost and large-scale preparation of highly thermally conductive polymer-based composites as thermal management materials.

Achieving high thermal conductivity and mechanical reinforcement in ultrahigh molecular weight polyethylene bulk material

Exploring pure polymers with high thermal conductivity (TC) is promising to overcome the side effect of conventional thermally conductive polymer-based composites. However, the geometrical shape of high TC polymers was limited to the fibers and/or thin films. Here, we employed a home-made solid-state extrusion (SPE) apparatus to prepare a bulk material of ultrahigh molecular weight polyethylene (UHMWPE) with high TC. The in-plane TC reached 3.30 W/mK, which was 588% higher than that of the high-pressure (HP) molded counterpart (0.48 W/mK). Moreover, the TC of SPE UHMWPE showed an anisotropic ratio as high as 750%, which favored the heat dissipation along the in-plane direction as revealed by infrared thermal imaging. The increased and highly anisotropic TC was attributed to the formation of cylindrical crystals, highly oriented lamellae, as well as the monoclinic form of UHMWPE generated during SPE processing. Benefiting from this unique architecture, the mechanical performance was also greatly intensified, where the ultimate tensile strength increased from 41.6 MPa for HP UHMWPE to 107.7 MPa for SPE UHMWPE. The current study opens up a new pathway to fabricate bulk polymers with simultaneous enhancement of thermal conductivity and mechanical performance, which has great potential for the applications in thermal management fields.

Manipulating thermal conductivity of polyimide composites by hybridizing micro- and nano-sized aluminum nitride for potential aerospace usage

Electrically insulating yet thermally conductive polymer-based composites are highly sought after in aerospace field. In this work, for the first time, electrically insulating but thermally conductive polyimide (PI) composites are fabricated by simultaneously incorporating micro- and nano-sized aluminum nitride (AlN) particles via a simple, economic, and scalable method of ball milling and subsequent hot-pressing process. The thermal conductivity, dielectric, and mechanical properties of the PI composites depend on the ratio of micro-sized AlN (m-AlN) to nano-sized AlN (n-AlN) and the total content of AlN in the PI composites. The thermal conductivity of the PI composites with 40 wt% m-AlN and 20 wt% n-AlN is 1.5 ± 0.05 W·m−1·K−1, which is 10 times higher than that of bare PI. The PI composites hold a great potential in aerospace industries.

Practical PBT/PC/GNP composites with anisotropic thermal conductivity.

Most of the highly thermally conductive polymer-based composites currently face problems that must be solved before they can be directly used in industrial production. Herein, a practical polybutylene terephthalate (PBT)/polycarbonate (PC)/graphite nanoplatelet (GNP) thermally conductive composite with relative low filler content was prepared by a conventional melt-blending technique. GNPs selectively distributed and oriented in the PBT phase afford the composite a low percolation threshold and anisotropic thermal conductivity. Investigation of the influence of filler content on the final comprehensive performance showed that a prepared PBT/PC/GNP composite with 20 vol% GNPs exhibited superior performance in thermal conductivity, heat resistance, and mechanical properties. The in-plane and through-plane thermal conductivities of the composite were 5.82 W m−1 K−1 and 1.06 W m−1 K−1, respectively, which were increased by 2430% and 361% as compared to that of a neat PBT/PC blend. The Vicat softening temperature increased by 17.7 °C and reached 213.7 °C, while the mechanical properties also maintained a good application level.

Significant Ultra-low Percolation Threshold, Enhanced Positive Temperature Coefficient Effect and Dielectric Permittivity in Polymer-based Composites with Immiscible Polymers

AbstractSignificant conductive polymer-based composites consisting of immiscible semi-crystalline polymers PP and PVDF, at different volume ratios loaded with a certain concentration of CB were prepared by blending and sequent hot-pressing technology. The distributing status of CB in the polymers was evaluated through the micrographs of the composite. The percolation threshold of this kind of composite is much lower than those of the individual polymers. Even more, the composite at 1/1 volume ratio of PP and PVDF displays the best conductivity among different ratios at a certain concentration of CB, and it displays an outstanding PTC effect more than five orders of magnitude, and synchronously an enhanced dielectric permittivity about 24.9 at 100 Hz. These inimitable properties may owe to the formation of PP/PVDF co-continuous phases and a double-percolation effect in the composite. The novel polymer-based composite with ultra-low percolation threshold, enhanced PTC effect, as well as the significant dielectric permittivity is promising a potential application.