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C: Surfaces, Interfaces, Porous Materials, and Catalysis
Implications of the Interface Modelling Approach on the Heat Transfer across Graphite-Water Interfaces C. Ulises Gonzalez-Valle, Luis Enrique Paniagua-Guerra, and Bladimir Ramos-Alvarado J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b05680 • Publication Date (Web): 13 Aug 2019 Downloaded from pubs.acs.org on August 13, 2019
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The Journal of Physical Chemistry
Implications of the Interface Modelling Approach on the Heat Transfer across Graphite-Water Interfaces C. Ulises Gonzalez-Vallea, Luis E. Paniagua-Guerraa, and Bladimir Ramos-Alvaradoa* aDepartment
of Mechanical Engineering, The Pennsylvania State University, University Park,
Pennsylvania, 16802, United States. * Corresponding author:
[email protected] ABSTRACT In this investigation, the thermal transport across graphite-water interfaces was studied by means of nonequilibrium classical molecular dynamics (NEMD) simulations. The main focus of this work was the assessment of the interface modeling approach of the non-bonded interactions, where empirical models optimized for predicting an experimental wetting condition were compared against interface models derived from multi-body electronic structure methods. To understand the mechanisms involved in the interfacial heat transfer, spectral heat flux mapping and phonon dynamics (spectral energy density) analyses were implemented to query the vibrational composition of interfacial heat transfer. Aside from the NEMD formulation, a modified acoustic mismatch model including interfacial interactions was utilized. The results obtained from this
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investigation are twofold. (i) The minimum of the adsorption energy curve (binding energy) can be used to fully describe the wetting response of an atomically dense surface, such as graphene/graphite, as irrespective of the interface modeling approach, a linear relationship exists between the work of adhesion and the binding energy. (ii) The sole effect of the solid-liquid affinity, characterized by wetting behavior, does not provide a conclusive description of the interfacial heat transfer when different interface models are used, which is consistent with recent experimental reports. Alternatively, the interfacial liquid depletion provided a sound explanation of the non-conclusive observations derived from correlating wetting behavior to thermal transport. Furthermore, it has been brought to light the critical impact that the modelling techniques have in the description of heat transfer across solid-liquid interfaces. These findings call to review the modelling efforts of interfacial heat transfer when using empirical mixing rules or matching wetting behavior to model solid-liquid interfaces.
1. INTRODUCTION The rapid pace of the technological advancements and the manufacturing procedures has permitted the miniaturization of high-density power electronic packages. The small sizes and highpower requirements pose a challenge for the adequate thermal management of these devices1. Several investigations have reported the particularly high thermal conductivity of graphene, making it a desirable material for thermal management purposes2-10. However, it has been indicated that for a composite material (e.g., nanofluids) the tremendous energy transport capabilities of graphene are limited by the thermal resistance imposed by solid-liquid interfaces, or its reciprocal, the thermal boundary conductance (TBC)11. Thus, a fundamental understanding of the energy transport across solid-liquid interfaces is necessary to exploit the features found in such materials.
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The Journal of Physical Chemistry
When a solid is in contact with a liquid, the organized structure of the solid atoms will induce ordering and the presence of high-density zones in the interfacial liquid12-16. This highly ordered water film has been related to the thermal transport mechanisms with a notable impact on the TBC14, 16-18. As reported in Ref. 16, the TBC of a hard-soft interface is strongly related to the density peak of the first hydration water layer; however, both the location and magnitude of the density peak within the aforementioned hydration layer could be strongly affected depending on different factors e.g., the surface wettability or the pressure14, 16, 18. It is noteworthy that the highly ordered structures can be found within one nanometer from the solid surface, posing a challenge to experimental probing. From the theoretical perspective, two main models have been extensively used to describe the TBC, the acoustic and the diffusive mismatch models19-20, AMM and DMM, respectively; however, none of these models include effects such as the interfacial roughness, the formation of the hydration layer, and the high density zones. Alternatively, atomistic level simulations provide detailed information of the interfacial properties and features. Among the atomistic level computational approaches, classical molecular dynamics (MD) simulations are preferred over quantum mechanical methods due to their relatively low computational cost and the large number of atoms that can be used, as contrasted with electronic structure methods (e.g., DFT, Hartree-Fock, or RPA). Nonetheless, MD simulations rely on empirical descriptions of the quantum-level atomic interactions. Thus, a proper characterization of the solid-liquid interactions is fundamental for any investigation on interfacial transport. Commonly, solid-liquid interfaces are modelled by means of a 12-6 Lennard-Jones (LJ) potential; thus, the interface model is reduced to find a proper set of parameters to reproduce a property of interest. Ramos-Alvarado et al.21 reported the optimized parameters for the LJ potential to obtain a contact angle (θ) of 64.4º for water on pristine graphite. Wu and Aluru22 obtained
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graphene-water interaction parameters using data from adsorption energy curves of water on graphene using quantum-level calculations. The adsorption curves were obtained by implementing four different methods, namely, Møller−Plesset perturbation theory of the second order (MP2)22, random-phase approximation (RPA)23, density functional theory-symmetry-adapted perturbation theory (DFT-SAPT)24, and coupled cluster treatment with single and double excitations and perturbative triples (CCSD(T))25. The θ for water on graphite were 10.3°, 34.2°, 42.4°, and
