Effect of carbon nanotube diameter on thermal interfacial resistance through the analysis of vibrational mismatch: a molecular dynamics approach

Abstract

Carbon nanotube (CNT) have been known to increase the heat transfer at the solid-liquid interfaces, but have a limitation due to the interfacial thermal resistance. Vibrational mismatch at the interface leads to the interfacial thermal resistance, which plays an important role in energy transfer at the boundary. Negligible work has been reported on the influence of CNT diameter on the resistance through the vibrational mismatch study. Molecular dynamics simulations have been performed to investigate the effect of CNT diameter on interfacial resistance between CNT and water molecules. This work is an effort to understand the heat transfer phenomenon at the interface by quantifying the overlapping ratio, which is a measure of the vibrational mismatch. Analysis of the vibrational spectra of CNT and water molecules is done to study the effect of CNT diameter on interfacial resistance. Simulations are carried out using armchair CNTs having chiral indices (5,5), (10,10) and (15,15). Starting with the initial configuration, and equilibrating the system of CNT and water molecules at 300 K and 1 atm, the CNT temperature is raised to 700 K by velocity rescaling. This system is allowed to relax as a micro-canonical ensemble. Based on the lumped capacitance analysis, the time constant of the CNT temperature response is determined, which is used to compute the interfacial thermal resistance. The interfacial thermal resistance is observed to be relatively higher for the smaller diameter nanotube. This is attributed to the high vibrational mismatch existing for smaller diameter CNT as a result of low overlapping region between vibrational density states of CNT and water molecules. For larger diameter CNT, the interfacial thermal resistance is low which results in the efficient heat transfer at the interface thus, emphasizing the indispensable role of larger diameter CNTs in the cooling applications.