Thermal Conductivity Of Polymers Research Articles

Research and Application Analysis of Thermal Conductive Polymer Materials

Research and Application Analysis of Thermal Conductive Polymer Materials

Healable, highly thermal conductive, flexible polymer composite with excellent mechanical properties and multiple functionalities

• Composite exhibits a high thermal conductivity of 12.6 W m −1 K −1 . • Composite has mechanical flexibility fitting flexible electronics application. • Composite shows an efficient healable of multiple functionalities. • Composite maintains elasticity at high temperature with healable ability. Flexible and electrically insulating polymers are ideal heat dissipation packaging materials for flexible electronic devices, but their inherent low thermal conductivity has gradually become a bottleneck for their application in high-performance flexible electronics. Here, we report a high thermal conductive polymer composite, which was synthesized by an effective and feasible method of implanting hydroxylated boron nitride nanosheets (hy-BNNSs) into self-healable elastomer material (SM). The introduction of hy-BNNSs endowed the composite with an ultrahigh in-plane thermal conductivity of 12.6 ± 0.71 W m −1 K −1 and excellent mechanical properties including superior flexibility, remarkable recovery ability and humidity stability. Moreover, the composite demonstrated the deformation recovery ability and dimensional stability at 70 °C, which are indispensable in flexible electronic applications, and are fairly rare in healable composites. Benefiting from dynamic characteristics of non-covalent hydrogen bonds and disulfide bonds within polymeric materials, the composite can restore the mechanical properties, heat dissipation properties, and dielectric properties. All the results demonstrate it an ideal candidate for thermal management in flexible electronic devices.

Determination of thermal conductivity of polymers by the method of differential scanning calorimetry with temperature modulation

Determination of thermal conductivity of polymers by the method of differential scanning calorimetry with temperature modulation

Tuning the polymer thermal conductivity through structural modification induced by MoS2 bilayers.

The present work refers to a physical and structural study of nanoconfined polymers in polymer-MoS2 nanocomposites as a function of MoS2-MoS2 interlayer distance. We applied reverse nonequilibrium molecular dynamics (RNEMD) simulations to investigate the thermal conductivity (λ) of polyamide oligomers confined by MoS2 bilayers. The results of this study indicate that thermal conductivity of polymer can be considerably enhanced when polymer chains are confined by MoS2 sheets, this behavior is more pronounced by charged surfaces. The presence of MoS2 surfaces leads to elongation as well as preferential alignment of polymer chains parallel to the MoS2 surfaces, which in turn results in higher order and denser packing of polymer content and hence larger thermal conductivity in comparison to the bulk polymer. Additionally, the analysis of the number of hydrogen bonds (HBs) in confined polymer chains suggests that a combined effect of the mentioned structural modification and enlarged values of HBs may cooperatively contribute to high polymer thermal conductivity, facilitating phonon transport. The results reported here suggest a significant way to design confined polymer-MoS2 composites for significantly improving thermal conductivity for a wide variety of applications.

Quasi-Isotropically Thermal Conductive, Highly Transparent, Insulating and Super-Flexible Polymer Films Achieved by Cross Linked 2D Hexagonal Boron Nitride Nanosheets.

Polymer-based thermal management materials (TIMs) show great potentials as TIMs due to their excellent properties, such as high insulation, easy processing, and good flexibility. However, the limited thermal conductivity seriously hinders their practical applications in high heat generation devices. Herein, highly transparent, insulating, and super-flexible cellulose reinforced polyvinyl alcohol/nylon12 modified hexagonal boron nitride nanosheet (PVA/(CNC/PA-BNNS)) films with quasi-isotropic thermal conductivity are successfully fabricated through a vacuum filtration and subsequent self-assembly process. A special structure composed of horizontal stacked hexagonal boron nitride nanosheets (h-BNNSs) connected by their warping edges in longitudinal direction, which is strengthened by cellulose nanocrystals, is formed in PVA matrix during self-assembly process. This special structure makes the PVA/(CNC/PA-BNNS) films show excellent thermal conductivity with an in-plane thermal conductivity of 14.21 W m-1 K-1 and a through-plane thermal conductivity of 7.29 W m-1 K-1 . Additionally, the thermal conductive anisotropic constants of the as-obtained PVA/(CNC/PA-BNNS) films are in the range of 1 to 4 when the h-BNNS contents change from 0 to 60wt%, exhibiting quasi-isotropic thermal conductivity. More importantly, the PVA/(CNC/PA-BNNS) films exhibit excellent transparency, super flexibility, outstanding mechanical strength, and electric insulation, making them very promising as TIMs for highly efficient heat dissipation of diverse electronic devices.

A Novel Branched Al2O3/Silicon Rubber Composite with Improved Thermal Conductivity and Excellent Electrical Insulation Performance.

In this paper, we report a thermal conductive polymer composite that consists of silicone rubber (SR) and branched Al2O3 (B-Al2O3). Owing to the unique two-dimensional branched structure, B-Al2O3 particles form a continuous three-dimensional network structure by overlapping each other in the matrix, serving as a continuous heat conductive pathway. As a result, the polymer composite with a 70 wt% filler achieves a maximum thermal conductivity of 1.242 Wm−1 K−1, which is equivalent to a significant enhancement of 521% compared to that of a pure matrix. In addition, the composite maintains a high volume resistivity of 7.94 × 1014 Ω·cm with the loading of 70 wt%, indicating that it meets the requirements in the field of electrical insulation. Moreover, B-Al2O3 fillers are well dispersed (no large agglomerates) and form a strong interfacial adhesion with the matrix. Therefore, the thermal decomposition temperature, residual mass, tensile strength, modulus and modulus of toughness of composites are significantly improved simultaneously. This strategy provides new insights for the design of high-performance polymer composites with potential application in advanced thermal management in modern electronics.

Microscopic ordered structure compactness and intrinsic thermal conductivity improvement of dispersed liquid crystal films of flexible epoxy-thiol polymers

Flexible epoxy-thiol polymers were fabricated by the reaction between N, N-Diglycidyl-4-glycidyloxyaniline (NDGA), poly (propylene glycol) diglycidyl ether (PGDE) and thiol curing agent with different functionality including 3,6-dioxa-1,8-octanedithiol (DET), pentaerythritol tetra(3-mercaptopropionate) (PETMP) and trimethylolpropane tris(3-mercaptopropionate) (TTMP). Liquid crystal monomer (LCM) was uniformly dispersed into epoxy-thiol polymers to prepare dispersed liquid crystal films of flexible epoxy-thiol polymers (E-PDLC films). The elongation at break and tensile strength of E-PDLC films increased to 195.9% and 25 MPa respectively. LCM showed favorable dispersibility and maintain ordered orientation of liquid crystal in E-PDLC films. The degree of order in molecular chain of epoxy-thiol polymers was increased, and chain interaction of epoxy-thiol polymers and LCM was enhanced by hydrogen-bonding. In E-PDLC films, with different thiol curing agent and LCM addition，different microscopic-ordered structure formed: ordered-layered structures and denser squamous ordered structures. Both of these two microscopic-ordered structures formed by different thiol curing agent and the addition of LCM, and afforded continuous phonon transfer paths. The thermal conductivity of E-PDLC films is up to 0.70 W m−1 K−1. This work offered a new way to design flexible epoxy resin and intrinsic thermal conductive polymers.

Improving Some Mechanical Properties and Thermal conductivity of PMMA Polymer by using Environmental Waste

This study was achieved to satisfy two goals, the first of which is to treat an environmental problem represented by the disposal of date seeds, and the second is the use of these wastes to improve some mechanical and thermal properties of poly methyl methacrylate PMMA through strengthening different proportions of the powder of date seeds.
 Particles of date seeds were used as a natural strengthening material for PMMA polymer, by mixing the matrix material (resin) with the hardener while still stirring continuously for a period of 10 min. After that, the samples of the reinforced material were prepared by adding the powder of date seeds, which is the reinforcing substance, with different percentages of weight fraction (0, 0.5, 1, 2, 3, 5 wt. %) and a grain size of <75 µm, while continuing to stir (10 min) for a second time. The composite samples were prepared by the Hand-Lay-up method and cut according to the standard ASTM. Thermal conductivity and some mechanical properties, such as impact strength, tensile strength, compressive strength, flexural strength, and hardness, were studied. An improvement was found in all properties at the reinforcement rate of 1-2 wt. %.

A Fast and Room-temperature Self-healing Thermal Conductive Polymer Composite

A Fast and Room-temperature Self-healing Thermal Conductive Polymer Composite

Thermal conductivity of amorphous polymers and its dependence on molecular weight

Thermal conductivity is an important transport property governing the performance of polymers in non-isothermal conditions. Nevertheless, its dependence on molecular weight M has not been the subject of as much attention as other properties of polymeric materials. We determine the thermal conductivity of polystyrene and polyisobutylene for a wide range of molecular weight by measuring the density, heat capacity and thermal diffusivity. Using coarse-graining and reverse mapping methods, we were able to produce molecular melts to study the thermal conductivity of polystyrene using molecular dynamics simulations over a similar range of molecular weight. We find satisfactory agreement between the experimental and simulation results. However, all of our results show that thermal conductivity depends only slightly on molecular weight up the entanglement limit and it is independent thereafter. Our results put into question the few previous experimental studies on this topic by showing that the previously accepted proportionality to M does not hold. Our findings could have significant implications for the understanding of complex phenomena such as anisotropic thermal conductivity in polymers subjected to flow.

Enhanced Effective Thermal Conductivity of Composite Materials by Incorporating Constructal Fillers

It is a feasible way to use constructal filler to increase the effective thermal conductivity of polymer. However, the combined effect of filler constructal-shape, contact, anisotropy and interface thermal resistance on the effective thermal conductivity of the composites has not been considered, and the heat transfer mechanisms remain unclear. In this study, these effects are evaluated at the same time. The results show that the filler contact is a key factor in increasing the effective thermal conductivity of composite. The constructal fillers are easy to contact and form heat conduction network than common filler. The filler content of 5 % is the percolation threshold of constructal filler. It is lower than common filler and previous reports. The enhanced heat transfer performance of constructal filler is insensitive to directional angle and has no significant anisotropy. The composite with constructal filler has high effective thermal conductivity in different directions. Series numerical models are proposed to predict the effective thermal conductivity of composite. These models have high accuracy and reliability, the deviations with experiment results is in an acceptable range. The interface thermal resistance should be considered in predicting the effective thermal conductivity of composite with nano-fillers.

Mesoscale computational prediction of lightweight, thermally conductive polymer nanocomposites containing graphene-wrapped hollow particle fillers

Heat removal has become an increasingly crucial issue for microelectronic chips due to increasingly high speed and high performance. One solution is to increase the thermal conductivity of the corresponding dielectrics. However, traditional approach to adding solid heat conductive nanoparticles to polymer dielectrics led to a significant weight increase. Here we propose a dielectric polymer filled with heat conductive hollow nanoparticles to mitigate the weight gain. Our mesoscale simulation of heat conduction through this dielectric polymer composite microstructure using the phase-field spectral iterative perturbation method demonstrates the simultaneous achievement of enhanced effective thermal conductivity and the low density. It is shown that additional heat conductivity enhancement can be achieved by wrapping the hollow nanoparticles with graphene layers. The underlying mesoscale mechanism of such a microstructure design and the quantitative effect of interfacial thermal resistance will be discussed. This work is expected to stimulate future efforts to develop light-weight thermal conductive polymer nanocomposites.

Research progress in manufacturing multifunctional polymer composite materials based on fused deposition modeling technology

3D printing technology, also known as additive manufacturing technology, is based on materials, mechanical control, computer-assisted design and other multi-cross disciplines. 3D printing enables fabrication of complex structure materials which cannot be fabricated by traditional methods. Fused deposition modeling (FDM) is one of the most well-known 3D printing technologies due to its merits like cost-effectiveness, simple in equipment and ease of operation, which has been widely used in aerospace, medical and auto industry. This review introduced the overall layout, development and planning of 3D printing technologies. This review also systematically summarized the characteristics and classifications of common 3D printing technologies, and mainly focused on the principles, advantages and requirements for the FDM technology. Especially, we aim to outline the basic requirements of polymer that suitable for FDM printing and introduce the applications of carbon-based polymer composite materials in the FDM manufacturing process. In addition, recent advances of FDM printing in fabrication of functional polymer composite materials and parts, including biomedical, electrical and thermal conductive polymer composites are reviewed in detail. The prospects for the research and applications of FDM towards manufacturing of high-performance and multifunctional polymer composite materials are proposed. At last, the challenges and key problems that need to be solved in FDM processing are considered and prospected.

Facile fabrication of three-dimensional thermal conductive composites with synergistic effect of multidimensional fillers

Thermal conductive polymer composites are promising in the application of rapidly developing modern technology. Here, a facile method to fabricate three-dimensional thermal conductive composites with multidimensional fillers was reported. One-dimensional AgNW were used to bridge the randomly dispersing two-dimensional BNNS together in poly(dimethylsiloxane) (PDMS) to form thermal conductive networks. The through-plane thermal conductivity (0.64 W m−1 K−1) of composite 2wt%AgNW/20wt%BNNS/PDMS was 237% higher than that of matrix PDMS (0.19 W m−1 K−1), while the composites still maintained good electrically insulating. A series of theoretical models were used to describe the thermal conductivity as a function of BNNS contents with or without the presence of AgNW. The synergistic effect between BNNS and AgNW was verified from the calculation of interfacial thermal resistance, which decreases from 1.06 × 10–6 m2 K W−1 for system without AgNW to 6.14 × 10–9 m2 K W−1 for system with 2 wt% AgNW. This synergistic strategy via multidimensional fillers supported the methodological possibility of returning to simplicity from various template approaches which were limited in shape and size. It was expected to extend the understanding of available theory and predict the potential formation of 3D thermal conductive networks in other systems with multidimensional fillers.

Dielectric BN nanosheet / PVDF composites with high thermal conductivity

With the development of electronic devices, high thermal conductivity polymer will become an ideal electronic packaging material. Therefore, Polyvinylidene fluoride (PVDF) nanocomposite was prepared doped with boron nitride nanosheet (BNNS), which has significantly improved thermal conductivity, excellent electrical insulation and outstanding flexibility. These nanocomposite films were prepared by mixing BNNS/PVDF in organic solution, drying, slicing, and then hot-pressing. Compared with the pristine polymers, the nanocomposite films have excellent thermal conduction, which indicates that new high-performance thermal conductivity materials will play an important role in high-power density electronic devices.

Through-plane high thermal conducting networks via incorporation of graphene nanoplatelets in nanocomposite film under electric field and avoiding breakdown voltage

Electric field inducement technology is one of the most efficient and straightforward way to direct and form a percolation network of conducting fillers in a polymer without necessitating chemical functionalization. However, extended application is very restricted due to the initiation of electrical breakdown of conducting fillers in polymers. Herein, thermal conductive polymer nanocomposites are fabricated using graphene nanoplatelets (GNP) as a conducting filler under application of electric field that avoids electric breakdown. An electrode surface is coated with fuluoacrylate of nano-to-micro-dimensional thickness, which is applied as insulating electrodes to inhibit electric spark under application of electric current. Two different kinds of electric fields; direct current (DC) and switching DC (SWDC), were applied to envisage the enhancement of filler assembly. Analysis showed that an insulating layer with approximately 0.35–18 μm of thickness was successfully coated on the electrodes, which enabled increased formation of through-plane thermal conducting networks as well as enhanced thermal conductivity compared to composites with random filler distribution. The intensity of the available electric field could be increased over 30 times without breakdown with the insulating layer. Moreover, the field-induced GNP assembly generated by SWDC improved the thermal conductivity of the composite of over 112% compared to composite with random GNP distribution. This technique has the potential to control the linear assembly of conducting fillers an under electric field without electric breakdown.

Effect of Aromatic/Aliphatic Structure and Cross-Linking Density on the Thermal Conductivity of Epoxy Resins

High thermal conductivity polymers are in great demand as thermal management materials. However, the thermal conductivity of polymers is typically low, ∼0.2 W/(m K), and a predictive understanding of the relationship between the thermal conductivity and the molecular structure of polymers is not yet established. In this work, 14 epoxy resin thermosets are synthesized from one aliphatic epoxide and one aromatic epoxide with seven amine hardeners. These thermosets are used to systematically examine the dependence of the thermal conductivity on the molecular structure of the epoxide and the hardener. In general, aromatic structures have a higher thermal conductivity than aliphatic structures. Moreover, naphthalene-based hardeners provide the highest thermal conductivity, 0.34 W/(m K), 230% higher than the lowest thermal conductivity among the 14 epoxy resin thermosets. The cross-linking density is controlled by mixing different molar ratios of diamine and triamine and does not influence the thermal conductivity, volumetric heat capacity, density, or longitudinal speed of sound. Measured thermal conductivities of 14 epoxy resins lie between 50 and 115% of the prediction of the minimum thermal conductivity model.

Hypergravity-Induced Accumulation: A New, Efficient, and Simple Strategy to Improve the Thermal Conductivity of Boron Nitride Filled Polymer Composites.

Thermal conductive polymer composites (filled type) consisting of thermal conductive fillers and a polymer matrix have been widely used in a range of areas. More than 10 strategies have been developed to improve the thermal conductivity of polymer composites. Here we report a new “hypergravity accumulation” strategy. Raw material mixtures of boron nitride/silicone rubber composites were treated in hypergravity fields (800–20,000 g, relative gravity acceleration) before heat-curing. A series of comparison studies were made. It was found that hypergravity treatments could efficiently improve the microstructures and thermal conductivity of the composites. When the hypergravity was about 20,000 g (relative gravity acceleration), the obtained spherical boron nitride/silicone rubber composites had highly compacted microstructures and high and isotropic thermal conductivity. The highest thermal conductivity reached 4.0 W/mK. Thermal interface application study showed that the composites could help to decrease the temperature on a light-emitting diode (LED) chip by 5 °C. The mechanism of the improved microstructure increased thermal conductivity, and the high viscosity problem in the preparation of boron nitride/silicone rubber composites, and the advantages and disadvantages of the hypergravity accumulation strategy, were discussed. Overall, this work has provided a new, efficient, and simple strategy to improve the thermal conductivity of boron nitride/silicone rubber and other polymer composites (filled type).

Liquid crystalline texture and hydrogen bond on the thermal conductivities of intrinsic thermal conductive polymer films

Polymer-dispersed liquid crystal (PDLC) films comprising polyvinyl alcohol (PVA) and liquid crystal monomer (LCM) were successfully obtained by the method of solution casting & thermal compressing. LCM was distributed orderly in PVA matrix by hydrogen bond interaction, to form PVA-LCM interpenetrating-layered networks. When the mass fraction of LCM was up to 35 wt%, the corresponding in-plane thermal conductivity coefficient (λ//) of PDLC film was significantly increased to 1.41 W m−1 K−1, about 10.8 times that of neat PVA (0.13 W m−1 K−1). High intrinsic λ// values of PDLC films were mainly attributed to the formed microscopic-ordered structures from ordered stacking of LCM, ordered arrangement of PVA chains, and their hydrogen bond interaction. This work would offer a new way to design and prepare novel intrinsic high thermal conductive polymers.

Thermal and Electrical behaviors of Boron Nitride/Epoxy reinforced polymer matrix composite—A review

AbstractIn electronic and electric instruments, heat dissipation is one of the major issues that degrade performance and efficiency. Polymer material has high specific strength and modulus, and it is mainly used in electrical insulation materials due to easy processability and light in weight with great flexibility but has low thermal conductivity. This paper examines the recent developments in highly thermal conductive epoxy‐based polymer composites. First, the composite materials, with applications, are briefly introduced. Second, the thermally conductive polymer types with their thermal conductivity are summarized. Third, the thermal and electric properties of different boron nitride (BN) with epoxy‐filled composite are listed. It also focuses on enhancement in thermal conductivity and electrical insulation, which are mainly influenced by the microstructure and amount of filler content. Some highly thermal conductive BN polymer based composites are reviewed. Fourth, various thermal conductivity measurement techniques are listed with their drawbacks. Finally, the review gives current scenario on thermal conductive polymer materials and developments needed with challenges in this area.