High thermal conductivity of chain-oriented amorphous polythiophene

Singh, Virendra; Bougher, Thomas L.; Weathers, Annie; Cai, Yuanqiang; Bi, Kedong; Pettes, Michael T.; McMenamin, Sally A.; Lv, Wei; Resler, Daniel P.; Gattuso, T. R.; Altman, David; Sandhage, Kenneth H.; Shi, Li; Henry, Asegun; Cola, Baratunde A.

doi:10.1038/nnano.2014.44

Cited by 345 publications

(338 citation statements)

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“…correlated scattering events) are most responsible. In this study we address the four aforementioned questions, using the following approach: To address question (1) we simulated a different polymer, polythiophene (Pth), which was a polymer of interest for high conductance thermal interface materials 4 , that has greater inhomogeneity in stereochemistry (e.g., a more complicated unit cell). To address question (2) we used a different potential, namely the ReaxFF potential 53 .…”

Section: Non-ergodic Behaviormentioning

confidence: 99%

Understanding Divergent Thermal Conductivity in Single Polythiophene Chains Using Green–Kubo Modal Analysis and Sonification

Winters

DeAngelis

et al. 2017

J. Phys. Chem. A

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Abstract:We used molecular dynamics simulations, the Green-Kubo Modal Analysis (GKMA) method and sonification to study the modal contributions to thermal conductivity in individual polythiophene chains. The simulations suggest that it is possible to achieve divergent thermal conductivity and the GKMA method allowed for exact pinpointing of the modes responsible for the anomalous behavior. The analysis showed that transverse vibrations in the plane of the aromatic rings at low frequencies ~ 0.05 THz are primarily responsible. Further investigation showed that the divergence arises from persistent correlation between the three lowest frequency modes on chains. Sonification of the mode heat fluxes revealed regions where the heat flux amplitude yields a somewhat sinusoidal envelope with a long period similar to the relaxation time. This characteristic in the divergent mode heat fluxes gives rise to the overall thermal conductivity divergence, which strongly supports earlier hypotheses that attribute the divergence to correlated phonon-phonon scattering/interactions. Main text:In all substances, energy/heat is transferred through atomic motions. In electrically conductive materials, electrons can become the primary heat carriers, but in all phases of matter, atomic motions are always present and contribute to the thermal conductivity of every object. Here, we use the term "object" instead of "material" to emphasize that thermal conductivity is highly dependent on the actual structure of an object, that is, its internal atomic level structure and its larger nanoscale or microscale geometry [1][2][3][4][5][6] . In studying the physics of thermal conductivity, tremendous progress has been made over the last 20 years toward understanding various mechanisms that allow one to reduce thermal conductivity in solids 1,7 . This reduction is generally measured relative to a theoretical upper limiting maximum value that arises solely from the intrinsic anharmonicity within the interactions between atoms.In the limiting case, where the atomic interactions are perfectly harmonic, thermal conductivity tends to infinity because the normal modes of vibration do not interact, thus yielding effectively infinite phonon mean free paths and thermal conductivity. As a result, the notion of anharmonicity is critical, and perfectly harmonic interactions between atoms are physically unreasonable. This is because an asymmetry in the energetic well between atoms is an inherent consequence of finite bonding energy (e.g., at some point, the potential energy surface must become concave down). Although one can approach the harmonic limit at cryogenic temperatures, the notion that divergent thermal conductivity (e.g., anomalous thermal conductivity) might be realizable in a real material at room temperature seems theoretically impossible. However, in 1955 Fermi, Pasta, and Ulam (FPU) 8 made a "shocking little discovery" that even an anharmonic system can exhibit infinite thermal conductivity.FPU conducted a numerical experiment with a one-dimensio...

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Section: Non-ergodic Behaviormentioning

confidence: 99%

Understanding Divergent Thermal Conductivity in Single Polythiophene Chains Using Green–Kubo Modal Analysis and Sonification

Winters

DeAngelis

et al. 2017

J. Phys. Chem. A

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“…For instance, reports of thermal conductivity of polyethylene obtained by classical molecular dynamics with different potentials vary from ∼45 [14] to 310 AE 190 W m −1 K −1 [15]. As a result, a rigorous upper bound for the thermal conductivity of molecular crystals such as polyethylene is lacking.In addition to this challenge, most prior molecular dynamics simulations use a finite temperature description based on classical statistics of the nuclei motion [9,11]. This assumption is valid as long as zero-point motion can be neglected.…”

mentioning

confidence: 99%

“…In addition to this challenge, most prior molecular dynamics simulations use a finite temperature description based on classical statistics of the nuclei motion [9,11]. This assumption is valid as long as zero-point motion can be neglected.…”

mentioning

confidence: 99%

“…Wang et al [10] used an optical method to study heat transport along polymer fibers, reporting thermal conductivity on the order of tens of W m −1 K −1 for polymers such as crystalline polyethylene and poly (p-phenylene benzobisoxazole). Singh et al [11] reported amorphous aligned polythiophene fibers with a thermal conductivity of around 4 W m −1 K −1 , a factor of 20 increase over that of the unaligned fibers.…”

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Lattice Thermal Conductivity of Polyethylene Molecular Crystals from First-Principles Including Nuclear Quantum Effects

2017

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Molecular crystals such as polyethylene are of intense interest as flexible thermal conductors, yet their intrinsic upper limits of thermal conductivity remain unknown. Here, we report a study of the vibrational properties and lattice thermal conductivity of a polyethylene molecular crystal using an ab initio approach that rigorously incorporates nuclear quantum motion and finite temperature effects. We obtain a thermal conductivity along the chain direction of around 160 W m −1 K −1 at room temperature, providing a firm upper bound for the thermal conductivity of this molecular crystal. Furthermore, we show that the inclusion of quantum nuclear effects significantly impacts the thermal conductivity by altering the phase space for three-phonon scattering. Our computational approach paves the way for ab initio studies and computational material discovery of molecular solids free of any adjustable parameters. DOI: 10.1103/PhysRevLett.119.185901 Polymers have long been of interest for their potential as flexible thermal conductors in applications such as flexible electronics [1][2][3][4]. In bulk form, essentially all polymers are thermal insulators, with a thermal conductivity of less than 1 W m −1 K −1 , due to the random orientation of the molecular chains [5]. However, samples with highly aligned molecular chains may exhibit thermal conductivities as much as 2 orders of magnitude larger. Early work by Choy, Chen, and Luk [6] demonstrated that increasing the crystallinity in polymers drives an increase in thermal conductivity along the direction of the covalently bonded molecular chains. In low-density polyethylene, for instance, they reported increased thermal conductivity along the chain direction from 0.4 to 1.5 W m −1 K −1 when the polymers are stretched by a factor of 5. Other experiments on mechanically stretched bulk polyethylene [7,8] report thermal conductivities as high as ∼42 W m −1 K −1 along the stretching direction due to crystalline alignment of the chains.More recently, Shen et al.[9] reported a high thermal conductivity of around 100 W m −1 K −1 in high-quality ultradrawn polyethylene nanofibers. Wang et al.[10] used an optical method to study heat transport along polymer fibers, reporting thermal conductivity on the order of tens of W m −1 K −1 for polymers such as crystalline polyethylene and poly (p-phenylene benzobisoxazole). Singh et al.[11] reported amorphous aligned polythiophene fibers with a thermal conductivity of around 4 W m −1 K −1 , a factor of 20 increase over that of the unaligned fibers.Despite these experimental advances, the theoretical treatment of heat transport in molecular crystals remains less developed. Molecular dynamics has been used in many studies to examine heat transport in polymers such as stretched polyethylene [12] and polydimethylsiloxane [13]. However, the semiempirical potentials used in these studies restrict their predictive power, especially for the polymers for which experimental data are scarce or unavailable.Additionally, as with covalent crystals,...

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“…20 Further information regarding the PA measurement technique, model fitting parameters, and sample preparation can be found in the supplementary material and our previous publications. [21][22][23] As illustrated in Figure 1, the thermal conductivity does not significantly change as a function of laser irradiation, and a peak value of approximately 0.7 W/m-K is observed for foams fabricated at 4% duty cycle. Regardless, the LIG foam thermal conductivity is significantly larger than the PI thermal conductivity of 0.15 W/m-K reported by DuPont.…”

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confidence: 92%

Thermal conductivity enhancement of laser induced graphene foam upon P3HT infiltration

Smith

Luong

Bougher

et al. 2016

Applied Physics Letters

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Significant research has been dedicated to the exploration of high thermal conductivity polymer composite materials with conductive filler particles for use in heat transfer applications. However, poor particle dispersibility and interfacial phonon scattering have limited the effective composite thermal conductivity. Three-dimensional foams with high ligament thermal conductivity offer a potential solution to the two aforementioned problems but are traditionally fabricated through expensive and/or complex manufacturing methods. Here, laser induced graphene foams, fabricated through a simple and cost effective laser ablation method, are infiltrated with poly(3-hexylthiophene) in a step-wise fashion to demonstrate the impact of polymer on the thermal conductivity of the composite system. Surprisingly, the addition of polymer results in a drastic (250%) improvement in material thermal conductivity, enhancing the graphene foam's thermal conductivity from 0.68 W/m-K to 1.72 W/m-K for the fully infiltrated composite material. Graphene foam density measurements and theoretical models are utilized to estimate the effective ribbon thermal conductivity as a function of polymer filling. Here, it is proposed that the polymer solution acts as a binding material, which draws graphene ligaments together through elastocapillary coalescence and bonds these ligaments upon drying, resulting in greatly reduced contact resistance within the foam and an effective thermal conductivity improvement greater than what would be expected from the addition of polymer alone. Published by AIP Publishing. [http://dx

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High thermal conductivity of chain-oriented amorphous polythiophene

Cited by 345 publications

References 32 publications

Understanding Divergent Thermal Conductivity in Single Polythiophene Chains Using Green–Kubo Modal Analysis and Sonification

Understanding Divergent Thermal Conductivity in Single Polythiophene Chains Using Green–Kubo Modal Analysis and Sonification

Lattice Thermal Conductivity of Polyethylene Molecular Crystals from First-Principles Including Nuclear Quantum Effects

Thermal conductivity enhancement of laser induced graphene foam upon P3HT infiltration

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