Conductive Polymer Composites Research Articles

Preparation and thermal conductivity of bimodal diamond particles reinforced phenolic resin composites

AbstractThermal conductive polymer composites have broad application prospects in the field of thermal management. However, due to intrinsically low thermal conductivity of polymers, even if fillers with high mass fraction are filled, the thermal conductivity of polymer composites cannot be significantly improved. In this paper, bimodal diamond particles (70 wt.% 150 μm and 22 wt.% 25 μm) were incorporated into phenolic resin to construct continuous heat transfer pathways by close packing, thereby enhancing its thermal conductivity. The results indicated that diamond particles with smaller particle size can effectively bridge the gaps between larger ones, forming a continuous for heat conduction. As a result, a maximum thermal conductivity value of 12.45 W/(m·K) can be achieved, which is 65.5 times, 9.8 times and 8.4 times higher than pure phenolic resin, 25 μm diamond particles reinforced phenolic resin composite and 150 μm diamond particles reinforced phenolic resin composite, respectively. Furthermore, heat dissipation and water cooling experiments also confirm the superior heat dissipation performance of phenolic resin composites reinforced with bimodal diamond particles. When the heating voltage is 10 V and the water cooling rate is 30 mL/min, the upper surface temperature of bimodal diamond composites is 129.2°C lower than that of pure phenolic resin. This investigation provides a new type of polymer composite with high thermal conductivity, which has promising prospects for application in thermal management. It also provides new insights for preparing polymer composites with high thermal conductivity by close packing of bimodal particles.Highlights Surface modification of the filler enhances its combination with resin. The interfacial bonding will be enhanced by D–OH bond on diamond surface. Bimodal diamond particles lead to the formation of a closely packed structure. This special structure can form a three‐dimensional heat conduction network. The highest TC of the DD/PR composite is 12.45 W/(m·K).

High temperature co-polyester thermoplastic elastomer nanocomposites for flexible self-regulating heating devices

Pyroresistive polymer composites are smart materials with great promise in numerous fields of electronic devices, including temperature and strain sensors, self-regulating heating, and over-current/over-temperature protective devices. However, the operational window of these materials is limited by the phase transition temperatures of the polymer matrix and the brittleness of the composites. Herein, a conductive polymer composite based on a co-polyester thermoplastic elastomer reinforced with graphene nanoplatelets (GNPs) was developed, which exhibits a positive temperature coefficient (PTC) switching temperature of 200 °C. This system shows a more gradual increase in resistivity with temperature and a less pronounced drop in resistivity past the critical transition temperature than other PTC composites. Moreover, Joule heating experiments revealed the ability to regulate at a predefined maximum temperature (within 150 – 200 °C), tuneable through parameters such as filler concentration, applied voltage and thermal boundary conditions, as also demonstrated by multiphysics simulations. Due to the more gradual PTC curve, this composite can produce steady state heating far below the PTC peak, unlike almost all other PTC materials: a unique advantage for self-regulating heating devices as the polymer is not in a melt state, reducing polymer degradation, filler mobility and increasing safety margin before onset of NTC behaviour.

Enhancement of thermal conductivity in PDMS/CFP composites using a dredging-plugging thermal network

In the preparation of thermally conductive polymer composites (TCPC), it is necessary to incorporate a filler network in the polymer matrix. Further enhancement of the thermal conductivity (TC) of TCPCs is challenging due to the exceptional heat absorption of the polymer matrix, which results in heat flow losses in the network. To address this issue, a novel procedure, termed thermal network dredging-plugging, has been proposed. In this study, polydimethylsiloxane (PDMS) composites with a carbon fiber powder (CFP) network and a CFP/glass ball (GB) network enhanced by dredging-plugging were prepared by a coating method. The TC of the PDMS/CFP system increased with an increase in CFP loading from 0 to 12 wt% and a decrease in sample thickness from 0.4 to 0.2 mm. At a 12 wt% CFP loading, the PDMS/CFP composites exhibited a maximum TC of 4.687 W/(mK). With the addition of GBs ranging from 0 to 2 wt%, the dredging-plugging CFP/GB network increased the maximum TC by a factor of 1.26 relative to the dredged CFP network. In conjunction with the thermal resistance method, a mathematical model that considers both the plugging and dilution effects of GBs was constructed. The calculated TCs were validated by using the prepared PDMS/CFP/GB composites, with average absolute relative errors ranging from 0.5 % to 4.19 %. In addition to TC enhancement, the mechanical properties and thermal management of the PDMS composites were evaluated.

Nanocarbon‐Based Hybrid Fillers in Thermally Conductive Polymer Composites: A Review

With the broad commercialization of microelectronics, 5G communication, and new energy vehicles, the demand for polymer composites with high thermal conductivity (TC) increases. Carbon‐based nanomaterials have high TC, are of lightweight and low cost, and have been widely studied as thermally conductive fillers for composites. In this article, carbon‐based thermal conductive fillers in polymer composites are focused on. It summarizes the treatments of functionalization, directional arrangement, and dispersion of carbon‐based nanofillers. Moreover, from the perspective of nanocarbon, hybrid nanofillers are divided into three categories: carbon/carbon, carbon/ceramics, and carbon/metal for the first time, and the thermal conductive effect of these hybrid fillers is discussed. Finally, potential areas for future research and development of thermal interface materials are discussed.

Enhancing Thermal Conductivity in Polymer Composites through Molding-Assisted Orientation of Boron Nitride.

Incrementing thermal conductivity in polymer composites through the incorporation of inorganic thermally conductive fillers is typically constrained by the requirement of high filler content. This necessity often complicates processing and adversely affects mechanical properties. This study presents the fabrication of a polystyrene (PS)/boron nitride (BN) composite exhibiting elevated thermal conductivity with a modest 10 wt% BN content, achieved through optimized compression molding. Adjustments to molding parameters, including molding-cycle numbers, temperature, and pressure, were explored. The molding process, conducted above the glass transition temperature of PS, facilitated orientational alignment of BN within the PS matrix predominantly in the in-plane direction. This orientation, achieved at low filler loading, resulted in a threefold enhancement of thermal conductivity following a single molding time. Furthermore, the in-plane alignment of BN within the PS matrix was found to intensify with increased molding time and pressure, markedly boosting the in-plane thermal conductivity of the PS/BN molded composites. Within the range of molding parameters examined, the highest thermal conductivity (1.6 W/m·K) was observed in PS/BN composites subjected to five molding cycles at 140 °C and 10 MPa, without compromising mechanical properties. This study suggests that compression molding, which allows low filler content and straightforward operation, offers a viable approach for the mass production of polymer composites with superior thermal conductivity.

Effects of conductive phase content on magnetic sensitivity of spiral conductive polymer composite

Flexible magnetic field sensors are essential for small dimensions, excellent precision, and flexibility in narrow gap or pipe environments. A spiral conductive polymer composite has been proposed for magnetic field detection. To investigate how conductive phase content impacts its magnetic sensitivity, the relationship between magnetic flux density and voltage difference/magnetic sensitivity was examined with different carbon nanotube contents (1 wt%∼20 wt%). From the perspectives of the equivalent network and magnetic susceptibility, the voltage difference /magnetic sensitivity of the composite was analysed by varying its carbon nanotube content. The addition of carbon nanotubes creates a contradiction in the magnetic sensitivity caused by internal equivalent impedance or induced current. The experiments demonstrate that the interpolar voltage difference /magnetic sensitivity first increases and then sharply decreases with increasing carbon nanotube content within composites. The optimum carbon nanotube content is about 8 wt%, which can be an optimal sensitive material choice for a flexible magnetic sensor.

Pyroresistive response of percolating conductive polymer composites

Pyroresistive response of percolating conductive polymer composites

Modelling effective thermal conductivity in polymer composites: A simple cubic structure approach

In this study, we propose the simple cubic model, a distinctive thermal-conductive mathematics for modelling the effective thermal conductivity in polymer composites, taking both filler size and interface thermal resistance into account. This model is constructed by delineating heat transport paths within simple cubic structural units, leveraging principles involving Fourier's law, minimum thermal resistance, specific equivalent thermal conductivity, and thermal resistance network. Demonstrating broad applicability, the simple cubic model accurately predicts effective thermal conductivity within a 0–40 % volume fraction range of filler in polymer composites, maintaining less than 15 % error. Its robustness is validated across over 100 experimental datasets, encompassing various polymer matrices and granular filler types. This extensive validation underscores the model's efficacy, both with our experimental data and existing literature. The simple cubic model's insightful predictions make it valuable in designing and preparing thermally conductive polymer composites.

Comprehensive Investigation of the Temperature-Dependent Electromechanical Behaviors of Carbon Nanotube/Polymer Composites.

The performances of flexible piezoresistive sensors based on polymer nanocomposites are significantly affected by the environmental temperature; therefore, comprehensively investigating the temperature-dependent electromechanical response behaviors of conductive polymer nanocomposites is crucial for developing high-precision flexible piezoresistive sensors in a wide-temperature range. Herein, carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composites widely used for flexible piezoresistive sensors were prepared, and then the temperature-dependent electrical, mechanical, and electromechanical properties of the optimized CNT/PDMS composite in the temperature range from -150 to 150 °C were systematically investigated. At a low temperature of -150 °C, the CNT/PDMS composite becomes brittle with a compressive modulus of ∼1.2 MPa and loses its elasticity and reversible sensing capability. At a high temperature (above 90 °C), the CNT/PDMS composite softens, shows a fluid-like mechanical property, and loses its reversible sensing capability. In the temperature range from -60 to 90 °C, the CNT/PDMS composite exhibits good elasticity and reversible sensing behaviors and its modulus, resistivity, and sensing sensitivity decrease with an increasing temperature. At room temperature (30 °C), the CNT/PDMS composite exhibits better mechanical and piezoresistive stability than those at low and high temperatures. Given that environmental temperature changes have significant effects on the sensing performances of conductive polymer composites, the effect of ambient temperature changes must be considered when flexible piezoresistive sensors are designed and fabricated.

Aqueous Conductive Polymer Composites with Good Printability and Conductivity for Flexible Electronics

Aqueous Conductive Polymer Composites with Good Printability and Conductivity for Flexible Electronics

Unravelling the role of poly(methyl methacrylate) (PMMA) molecular weight in poly(vinylidene fluoride) (PVDF)/PMMA/expanded graphite (ExGr) blend nanocomposites: Insights into morphology, thermal behavior, electrical conductivity, and wetting property

Poly(vinylidene fluoride) (PVDF) based conducting polymer composites with carbon nanomaterials can be used for mechanical energy harvesting through piezoelectric or triboelectric effect. This study aims to investigate the influence of PMMA molecular weight on the electrical, thermal, and wetting properties of PVDF/40 wt.% PMMA blend nanocomposites reinforced with expanded graphite (ExGr). The blend nanocomposites with 40 wt.% PMMA have been prepared by solution blending method by using two different molecular weights of PMMA whose melt flow indices are 2 g/10 min and 2.3 g/10 min. The coexistence of the electroactive gamma and non-polar alpha phases of PVDF in the blend nanocomposites has been confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry analyses. While overall crystallinity (%) of low molecular weight PMMA employed blend nanocomposites is lower than that of high molecular weight PMMA blended nanocomposites, the electroactive gamma phase has been found to increase in the former blend nanocomposites. The dispersion of graphite nanosheets has been observed to be better in high molecular weight PMMA employed blend nanocomposites which results in higher electrical conductivity. Impedance analysis of PVDF-40 wt.% PMMA-2 wt.% ExGr blend nanocomposite with high molecular weight PMMA results in enhanced interjunction capacitance (74.5 pF) in comparison to low molecular weight PMMA mixed blend nanocomposites (68 pF). Water contact angle (WCA) increases with molecular weight of PMMA and ExGr loading level. Thermogravimetric analysis has shown that the char content (above 500°C) is slightly higher for the blend with low molecular weight PMMA than with high molecular weight PMMA.

Preparation of Highly Thermally Conductive Hexagonal Boron Nitride‐Polyvinyl Alcohol/Polydimethylsiloxane Composite Using Combined Freeze‐Drying and Spatial Confining Forced Network Assembly Method

With the rapid advancement of electronic products, an increasing number of electronic components are being integrated onto chips, leading to a higher power consumption per unit area. Consequently, effective heat dissipation has become increasingly important. To address this heat dissipation challenge, this article introduces and prepares a highly thermally conductive polymer composite based on freeze‐drying, coupled with the spatial confining forced network assembly (SCFNA) method. The freeze‐drying process is used to create a three‐dimensional thermal conductive network. This network provides a well‐defined heat path. The SCFNA method enhances the regularity of the thermal conductive network within the matrix. Ultimately, this results in the significant thermal conductivity enhancement of the polymer composite. After freeze‐drying, when the mass ratio of hexagonal boron nitride to polyvinyl alcohol is 4:1, the sample prepared by SCFNA presents 72.6% higher thermal conductivity than the one obtained through direct infiltration. This achievement holds significant value for the advancement of polymer composites with high‐thermal conductivity and excellent mechanical properties. It can improve the low‐dissipation performance of polymer thermal conductive composite systems, meet the needs of high‐performance and low‐dissipation use of thermal management materials, and reduce the working temperature of electronic chips.

Piezoelectric Layered Structure with Conductive Polymer Composites as a Waveguide Layer: Swelling Monitoring Based on the Propagation of Love-Type Wave

Piezoelectric Layered Structure with Conductive Polymer Composites as a Waveguide Layer: Swelling Monitoring Based on the Propagation of Love-Type Wave

Unleashing the Potential of Boron Nitride Spheres for High‐Performance Thermal Management

AbstractHighly integrated and miniaturized electronic devices require advanced thermal management techniques to improve reliability and performance. Thanks to their high thermal conductivity and electrical insulation, boron nitride nanosheets (BNNSs) are commomly used as fillers to construct thermally conductive polymer composites for heat dissipation. However, the BNNS reinforced composites exhibit anisotropic thermal conductivity due to the anisotropic structure of BNNSs. Micro‐sized boron nitride spheres (BNSs) with isotropic thermal conductivity are considered one of the best solutions. Nevertheless, precisely measuring the thermal conductivity of BNSs remains a challenge, limiting the understanding of the thermal transport mechanism. Herein, we have successfully estimated the thermal conductivity of BNSs using the laser flash method. Factors influencing BNSs’ thermal conductivity, including precursor, polymer binder and sintering temperature, are also investigated. Under optimized conditions, BNSs exhibit high, isotropic thermal conductivity of 37.2±2.5 W/(m ⋅ K), and the BNS pellet outperforms its h‐BN counterpart in heat dissipation for an LED light. This superiority is attributed to outstanding heat transfer performance in the cross‐plane direction, in addition to high in‐plane thermal conductivity. This study provides a feasible method to estimate the thermal conductivity of spherical materials and highlights promising boron nitride materials with isotropic thermal conductivity for heat dissipation in advanced electronics.

Epoxy resin reinforced high-performance conductive composite foam with ultra-wide pressure sensing range

Flexible piezoresistive sensors based on conductive polymer composites (CPCs) have shown great potential and application in smart wearable devices, sports and health monitoring. Nevertheless, the practical use of many CPCs pressure sensors is often limited by their narrow monitoring range and low sensitivity. Here, a thermoplastic urethane/ epoxy resin/ carbon nanotubes/ polydopamine/ Ti3C2TX MXene (TPU/EP/CNT/PDA/MXene) composite foam was prepared using the commonly used freeze-drying and impregnation methods. Due to the high strength of the EP/TPU foam matrix and CNT@MXene's internal and external synergistic conductive network, the TECPMF has outstanding mechanical and conductive properties. As a result, the foam pressure sensor has an extremely wide monitoring range (0∼300 kPa) and a sensitivity of 2.42 kPa−1 (0∼5 kPa). Furthermore, the superior performance of the foam provides fast response (100 ms) and outstanding durability of more than 8000 cycles. The piezoresistive TECPMF sensor can be used for real-time monitoring of human movement, as well as the magnitude and position of various pressures and air pressures. These promise to enable a wide range of smart wearable and engineering applications. This work opens up a new avenue for the design of more advanced piezoresistive sensors.

MXene bridging graphite nanoplatelets for electrically and thermally conductive nanofiber composites with high breathability

Electrically and thermally conductive polymer composites (CPCs) have promising applications in flexible and wearable electronics, and it remains difficult for the trade-off between the electrical and thermal properties and the breathability. We propose a “MXene bridging graphite nanoplatelets (GNPs)” strategy to prepare conductive membranes with high conductivity and excellent breathability. Rigid GNPs are randomly distributed inside polyurethane nanofibers and expand the network. MXene nanosheets are decorated onto the nanofibers and bridge GNPs to reduce the thermal and electrical contact resistance. The synergy of MXene and GNPs improves electrical and thermal conductivity without sacrificing their breathability. The electrical and thermal conductivity of the composites can reach 64.4 S/m and 4.9 W (m K)−1, respectively. In addition, the nanofiber composites with strong interfacial interactions and thus superior durability show outstanding photothermal conversion and heat dissipation capability. This study can provide inspiration for designing multi-functional, breathable CPCs with potential applications in wearable electronics.

Production and properties of electrically conductive polymer composites reinforced with cotton threads

AbstractThe problem of strength loss in electrically conductive composites made with dispersed fillers in the polymer binder is solved by spraying an aerosol of graphite on a textile material with a 3D weave of threads, or on knitwear of fibers with various structure and chemical composition. The loose microstructure of cotton fibers and the developed surface of elastic filaments made of synthetic polymers retain colloidal graphite particles in a layered composite during cyclic deformation. The electrical conductivity of knitwear with graphite changes during stretching due to the reversible displacement of graphite particles, first during straightening and then during stretching of elastic threads. The 130 ± 5 strain sensitivity GF and 12,000 ± 95 кPa−1 stress sensitivity QF of the composites presented in this paper exceed the corresponding parameters of known electrically conductive composites. The combination of a significant change in electrical conductivity with the elasticity of the developed knitwear‐based composite is important for the use in load cells, smart clothes, medical devices, and robotics.

Mechanically and Thermally Guided, Honeycomb-like Nanocomposites with Strain-Insensitive High Thermal Conductivity for Stretchable Electronics.

Thermal management materials have become increasingly crucial for stretchable electronic devices and systems. Drastically different from conventional thermally conductive materials, which are applied at static conditions, thermal management materials for stretchable electronics additionally require strain-insensitive thermal conductivity, as they generally undergo cyclic deformation. However, realizing such a property remains challenging mainly because conventional thermally conductive polymer composites generally lack a mechanically guided design. Here, we report a honeycomb-like nanocomposite with a three-dimensional (3D) thermally conductive network fabricated by an arrayed ice-templating technique followed by elastomer infiltration. The hexagonal honeycomb-like structure with thin, compact walls (≈ 40 μm) endows our composite with a high through-plane thermal conductivity (≈ 1.54 W m-1 K-1) at an ultralow boron nitride nanosheet (BNNS) loading (≈ 0.85 vol %), with an enhancement factor of thermal conductivity up to 820% and thermal-insensitive strain up to 200%, which are 2.7 and 2 times higher than those reported in the literature. We report an intelligent strategy for the development of advanced thermal management materials for high-performance stretchable electronics.

Self-healing thermally conductive polymer composites based on polyvinyl alcohol with dynamic borate ester and hydrogen bonds

Traditional thermally conductive polymer materials exhibit a propensity for damage when applied in dynamic environments, which leads to shortened service life and suboptimal utilization of resources. Herein, polyvinyl alcohol (PVA)-based thermally conductive composites with a self-healing capability are prepared based on dynamic borate ester bonds and hydrogen bonds. Poly(dopamine) functionalized graphene oxide (denoted as PGO) is used as a thermally conductive filler to achieve a high thermal conductivity (TC) of 0.79 W/(m·K) for the PGO/PVA composites, which is 527% of pure PVA (0.15 W/(m·K)). The improved TC of PGO/PVA composites is mainly attributed to the reduction in interface thermal resistance and the construction of heat conduction channels. Additionally, the PGO/PVA composites display a self-healing efficiency higher than 60% at room temperature without external simulation. Furthermore, the as-prepared PGO/PVA composites exhibit excellent mechanical properties, with a tensile strength of 409 kPa and an elongation at break of 479%, respectively. This work provides a promising strategy for fabricating thermally conductive polymer composites, which can be deployed as thermal interface materials for long-term applications.

Thermally Conductive Polymer Composites with Hexagonal Boron Nitride for Medical Device Thermal Management

Polymer composites with hexagonal boron nitride (hBN) have the potential to meet the heat dissipation and electrical insulation requirements of electronic and medical devices. In this study, hBN/polymer composites were fabricated with thermoplastic polyurethane (TPU) and epoxy as matrix materials. Three hBN powder types (BN1, BN2, BN3) with different platelet sizes and degrees of agglomeration were used. BN1 (with average size of 1 μm) and BN2 (with average size of 12 μm) mainly contained hBN platelets, while BN3 (with average size of 20 μm) contained both platelets and agglomerates of platelets. BN2 gave the highest thermal conductivity, while BN1 gave the lowest thermal conductivity. Thermal simulations were performed for a medical device with a limit for the maximum surface temperature. For the encapsulation of this device, several material combinations were simulated, using anisotropic thermal conductivity data. This included encapsulations with inner layers of commercial thermally and electrically conductive materials and an outer layer of the best thermally conductive (and electrically insulating) hBN/TPU composite fabricated by the authors.