Nanowire-Polymer Nanocomposites as Thermal Interface Material (original) (raw)
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Electrically and Thermally Conducting Nanocomposites for Electronic Applications
2010
Nanocomposites made up of polymer matrices and carbon nanotubes are a class of advanced materials with great application potential in electronics packaging. Nanocomposites with carbon nanotubes as fillers have been designed with the aim of exploiting the high thermal, electrical and mechanical properties characteristic of carbon nanotubes. Heat dissipation in electronic devices requires interface materials with high thermal conductivity. Here, current developments and challenges in the application of nanotubes as fillers in polymer matrices are explored. The blending together of nanotubes and polymers result in what are known as nanocomposites. Among the most pressing current issues related to nanocomposite fabrication are (i) dispersion of carbon nanotubes in the polymer host, (ii) carbon nanotube-polymer interaction and the nature of the interface, and (iii) alignment of carbon nanotubes in a polymer matrix. These issues are believed to be directly related to the electrical and thermal performance of nanocomposites. The recent progress in the fabrication of nanocomposites with carbon nanotubes as fillers and their potential application in electronics packaging as thermal interface materials is also reported.
Silver nanowire array-polymer composite as thermal interface material
Journal of Applied Physics, 2009
Silver nanowire arrays embedded inside polycarbonate templates are investigated as a viable thermal interface material for electronic cooling applications. The composite shows an average thermal diffusivity value of 1.89ϫ 10 −5 m 2 s −1 , which resulted in an intrinsic thermal conductivity of 30.3 W m −1 K −1. The nanowires' protrusion from the film surface enables it to conform to the surface roughness to make a better thermal contact. This resulted in a 61% reduction in thermal impedance when compared with blank polymer. An ϳ30 nm Au film on the top of the composite was found to act as a heat spreader, reducing the thermal impedance further by 35%. A contact impedance model was employed to compare the contact impedance of aligned silver nanowire-polymer composites with that of aligned carbon nanotubes, which showed that the Young's modulus of the composite is the defining factor in the overall thermal impedance of these composites.
Non-Linear Thermal Conductivity Enhancement in Nanocomposites with Aligned-Cnt Implementation
Carbon nanotubes (CNTs) have been expected to enhance thermal conductivity in various materials including composites, for applications such as thermal interface materials. However, the thermal properties of bulk CNTs and CNT composites tend not to achieve the high values of individual nanotubes. Factors that cause such scaling effects include CNT morphology (length, alignment, entanglement, etc.), and inter-CNT/CNTmedium boundary properties. It is critical to evaluate and minimize these effects. However, structure-property relationships are not yet well understood, and thus effective use of CNTs has not been achieved for the majority of currently existing CNT polymer composites. In this work, consistent CNT samples with well-controlled morphology were fabricated by embedding aligned CNTs in polymer to create aligned CNT polymer nanocomposites (A-CNTPNCs), as shown in Figure 1. A-CNT-PNCs were thoroughly evaluated for their anisotropic thermal properties, and a non-linear increasing ...
Polymer Bulletin, 2020
A new version of the semi-empirical Halpin-Tsai (H-T) model is presented to evaluate the effective thermal conductivity of general carbon nanotubes (CNTs)reinforced polymer nanocomposites. The model captures the influences of the CNTs alignment, random orientation, aggregation, waviness, length, diameter and the CNT/polymer interfacial thermal resistance parameters. In order to verify the suitability of the new H-T model, the numerically calculated thermal conductivities are compared with existing experimentally measured ones. An excellent predictability is found of the modified H-T model over a wide range of the tests. The consideration of the CNT waviness and the interfacial thermal resistance parameters is seriously essential for a more realistic prediction in all conditions. For aligned CNTreinforced polymer nanocomposites, considering the alignment factor seems to be very important. Moreover, in the case of well-dispersed CNTs into the matrix, it is necessary to incorporate the CNT random orientation parameter. Additionally, when CNTs are not well dispersed, the CNT aggregation and random orientation parameters must be incorporated in the analysis. The effects of the CNT volume fraction, length, diameter and non-straight shape on the nanocomposite thermal conducting behavior are estimated in details. The results clearly expose that it is needed to eliminate the aggregation, use the straight CNTs and form a strong interface if the full potential of CNT reinforcement is to be realized. Finally, the thermal conductivities of CNT-shape-memory polymer nanocomposites at different temperatures are obtained.
Thermal conductivity of polymers and polymer nanocomposites
Materials Science and Engineering: R: Reports
Polymers are widely used in industry and in our daily life because of their diverse functionality, light weight, low cost and excellent chemical stability. However, on some applications such as heat exchangers and electronic packaging, the low thermal conductivity of polymers is one of the major technological barriers. Enhancing the thermal conductivity of polymers is important for these applications and has become a very active research topic over the past two decades. In this review article, we aim to: 1). systematically summarize the molecular level understanding on the thermal transport mechanisms in polymers in terms of polymer morphology, chain structure and inter-chain coupling; 2). highlight the rationales in the recent efforts in enhancing the thermal conductivity of nanostructured polymers and polymer nanocomposites. Finally, we outline the main advances, challenges and outlooks for highly thermal-conductive polymer and polymer nanocomposites.
Inter-carbon nanotube contact in thermal transport of controlled-morphology polymer nanocomposites
Nanotechnology, 2009
Directional thermal conductivities of aligned carbon nanotube (CNT) polymer nano-composites were calculated using a random walk simulation with and without intercarbon nanotube contact effects. The CNT-contact effect has not been explored for its role in thermal transport, and it is shown here to significantly affect the effective transport properties including anisotropy ratios. The primary focus of the paper is on the non-isotropic heat conduction in aligned-CNT polymeric composites, because this geometry is an ideal thermal layer as well as it constitutes a representative volume element of CNT-reinforced polymer matrices in hybrid advanced composites under development. The effects of CNT orientation, type (single vs. multi-wall), inter-CNT contact, volume fraction and thermal boundary resistance on the effective conductivities of CNT-composites are quantified. It is found that when the CNT-CNT thermal contact is taken into account, the maximum effective thermal conductivity of the nanocomposite decreases ~4 times and ~2 times for the single-walled and the multi-walled CNTs, respectively, at 20% CNT volume fraction.
Journal of Physical Chemistry C, 2010
An off-lattice Monte-Carlo simulation was used to study non-isotropic heat conduction in aligned carbon nanotube (CNT)-polymer nanocomposites (PNCs) focusing on the effects of CNT-CNT contact and CNT distribution on heat transfer. CNT-CNT contact significantly affects the effective transport properties of PNCs, including anisotropy ratios, but has not been studied extensively either theoretically or experimentally. Previous studies have considered the effective thermal conductivities of CNT-PNCs using only a very large CNT-CNT thermal boundary resistance (TBR) value compared with that of the CNT-matrix. CNT-CNT TBR may be reduced by various techniques, potentially below the CNT-matrix TBR, to further enhance thermal transport. Therefore, in this work, heat transport with CNTs in contact is studied for a wide range of CNT-CNT TBR values, varying from 2 to 25×10 -8 m 2 K/W. Other important factors, such as CNT contact degree (or CNT isolation degree), CNT spatial distribution, and CNT-CNT TBR relative to CNT-matrix TBR are also investigated for 1-20% volume fraction of CNTs. The simulation results indicate that when CNT-CNT contact is significant or CNT-CNT TBR is low (relative to the CNT-matrix TBR), then heat transport is dominated by CNT-CNT contact effects, rather than CNT-matrix interfacial effects. As an example, effective thermal conductivity on the nanocomposite parallel to the CNT axis is shown to increase by up to ~4X due to CNT-CNT contact effects. These simulation results can be very useful for developing techniques to enhance the effective thermal conductivity of composites using conductive nanomaterials embedded in (polymer) matrices, and assist experimentalists in interpreting heat conduction results.
Eastern-European Journal of Enterprise Technologies
This paper reports the experimental study carried out to establish the dependence of the thermal conductivity of polypropylene-based nanocomposites filled with carbon nanotubes on the main parameter of the temperature regime of their manufacturing ‒ the level of overheating a polymer melt relative to its melting point. The study has been conducted for nanocomposites that were manufactured by applying a method based on the mixing of components in the polymer melt applying a special disk extruder. During the composite manufacturing process, the level of melt overheating varied from 10 to 75 K, with the mass share of filler ranging from 0.3 to 10.0 %. It is shown that increasing the overheating of a polymer melt causes an increase in the thermal conductivity of the composites. However, when the overheating has reached a certain value, its further growth does not increase the thermal conductivity of nanocomposites. Based on the established pattern, the rational level of this overheating...
Advanced Materials, 2010
Among a broad range of carbonaceous materials, such as exfoliated graphite, graphene or diamond, carbon nanotubes (CNTs) are widely used as a thermal filler because of their exceptional intrinsic thermal conductivity (TC) and aspect ratios, which are larger than 1000. The TC of single-walled CNTs (SWNTs) has been reported as high as 6000 W m À1 K À1 , and that of multi-walled CNTs (MWNTs) was experimentally measured at 3075 W m À1 K À1 at room temperature, which remains above the performances of diamond (TC ¼ 2200 W m À1 K À1 ). Therefore the improvement of the TC of composites based on CNTs was extensively investigated over the past years. A recent work revealed that a TC of 0.28 W m À1 K À1 or a 40% increase had been reached in composites with a 10% weight fraction (wt%) of CNTs dispersed in polyvinylacetate matrix by using the classical sonication method. Another optimized configuration was proposed by Haddon and co-workers, who brought into play a hybrid filler based on the combination of SWNTs and graphite nanoplatelets. An improved TC of 1.7 W m À1 K À1 -about a fivefold increase-was obtained for epoxy composites. The hybrid loading mass fraction was as high as 10%, including 7 wt% graphite nanoplatelets and 3 wt% SWNTs.
Advanced Materials, 2009
In the past twenty years, substances with low or negative thermal expansivities have attracted much interest because of their significance in electronic packaging, precision equipment, and intelligent materials. [1-3] In electronic packaging systems, mismatch in the coefficient of thermal expansion (CTE) between various materials has become a key issue for developing the next generation of electronic packaging with higher system reliability. CTE values of polymer portions are much higher than those of silicon, ceramic, and copper metallization. These large CTE mismatches lead to thermal-stress accumulation at contact interfaces during both packaging and device performance, which triggers component failure by, for example, warpage and rupture. [4] So far, the effective approach to reduce the CTE of the polymer portion has been to add fillers of low or negative CTEs into polymer matrices. [2,4] The low or negative CTEs of carbon nanotube (CNTs), together with their low mass density and outstanding mechanical and thermal properties, renders them the right filler for advanced polymer nanocomposites in microelectronic applications. [5] One of the most important applications for these materials is CNT-polymer nanocomposites for thermal interface materials (TIMs) with enhanced thermal conductivity and, equally importantly, reduced CTEs. Thermal properties of polymer composites filled with randomly dispersed CNTs have been extensively studied in the past decade. [6] Unfortunately, real-life applications of these materials were inhibited by their low thermal conductivity and relatively high CTEs, caused mainly by the weak CNT-polymer interface. [3,6] Alternatively, researchers turned to a simple infiltration process to prepare polymer composites filled with aligned carbon nanotubes (ACNT), because the CNT alignment ensures much higher thermal conductivities than a random dispersion. [7] However, a CTE study of ACNT-polymer composites has never been reported. The ACNT/polymer interface is still an issue, as such COMMUNICATION www.advmat.de