Thermal Transport through Polymer-Linked Gold Nanoparticles

Abstract

Polymer–nanoparticle networks have potential applications in molecular electronics and nanophononics. In this work, we use all-atom molecular dynamics to reveal the fundamental mechanisms of thermal transport in polymer-linked gold nanoparticle (AuNP) dimers at the molecular level. Attachment of the polymers to AuNPs of varying sizes allows the determination of effects from the flexibility of the chains when their ends are not held fixed. We report heat conductance (G) values for six polymersviz. polyethylene, poly(p-phenylene), polyacene, polyacetylene, polythiophene, and poly(3,4-ethylenedioxythiophene)that represent a broad range of stiffness. We address the multimode effects of polymer type, AuNP size, polymer chain length, polymer conformation, system temperature, and number of linking polymers on G. The combination of the mechanisms for phonon boundary scattering and intrinsic phonon scattering has a strong effect on G. We find that the values of G are larger for conjugated polymers because of the stiffness in their backbones. They are also larger in the low-temperature region for all polymers owing to the quenching of segmental rotations at low temperature. Our simulations also suggest that the total G is additive as the number of linking polymers in the AuNP dimer increases from 1 to 2 to 3.

Heat Transfer Enhancement in Tree-Structured Polymer Linked Gold Nanoparticle Networks

“…The tree polymers in these systems are unstretched; see schemes in Figure a,b. Previously, we had found that unstretched polymers have converged heat flux values, ,, and thus they are sufficient to reveal the tree structure effect on heat transfer. After the relaxation step, the nonequilibrium MD simulation method is applied to calculate the heat flux through the tree networks.…”

“…In determining heat fluxes, we calculate the heat conductance , G and not the conventional thermal conductivity κ because the heat transfer mechanism is not diffusiveas might be required for the latterat the nanoscale. In our previous work, we found that heat conductance ( G ) of a linear PE chain with 100 carbons C100 is 24.8 ± 2.4 pW/K . Though not shown, we converted our results from G to κ and confirmed agreement with Zhang and Luo for unstretched unbranched PE chains.…”

“…For example, in prior work, − we demonstrated that polymer linked nanoparticle networks can be used as primitives for data storage and computing. Dendrons and dendrimers are popular choices for tree-structured polymerswhich are in turn regarded as unique building blocks for nanoscale materials engineering,and have been useful in applications for drug delivery, gene transfection, and biomedical imaging. − A system with digital dendrimersdistinctly mapped into two types of subunits identifiable as 0 or 1 in a binary codewere seen to exhibit high capacity for data storage. , Polymeric materials are also popular in energy management; for example, the thermal conductivity of polymer composites can be engineered by functionalizing the filler and polymer matrix with different chemical groups. − In polymers, thermal conductivity is a result of the complex relationship between chemical structure, chain conformation, length, and stiffness. − Specifically, in polymer linked nanoparticle systems, the internal connection and the polymer network structure determine the heat transfer mechanism and rate. − The heat conductance in polyethylene (PE) molecular junctions has been seen to increase with increasing PE chain length from 2 to 10 CH 2 units in alkanedithiol molecules . We also found that the heat flux through polymer linked dimers is related to the polymer stiffness and the number of polymer linkers between two gold nanoparticles (AuNPs) …”

“…The reduced heat conductance in the intrinsic phonon scattering mechanism is due to the collision of short-wavelength phonons inside of a polymer chain. Earlier, we reported that in linear PPP with chain length C50–C200 G ≈ 40 pW/K . Here, we find that the level 1 PPP tree drops to G ≈ 34 pW/K at a chain length of 96 carbons; see Figure c.…”

“…In our previous work, we found that heat conductance (G) of a linear PE chain with 100 carbons C100 is 24.8 ± 2.4 pW/K. 39 Though not shown, we converted our results 39 from G to κ and confirmed agreement with Zhang and Luo 42 for unstretched unbranched PE chains. If we branch a chain in the middle to obtain the level 1 tree, we find an increased conductance of G = 33.1 ± 3.9 pW/K, as indicated in Figure 2a.…”