Session: Research Posters

Paper Number: 166522

Effect of Nanopatterning on Thermal Conductivity of Single-Wall Carbon Nanotube Thin Films 

The thermal transport properties of carbon nanotube (CNT) network material such as CNT films, veils, and vertically aligned arrays, determine their performance in various engineering applications, including thermal management and thermoelectric materials. While the intrinsic thermal conductivity of individual CNTs is exceptionally high, the effective thermal conductivity of CNT-based materials is heavily influenced by structural factors such as CNT arrangement, inter-tube interactions, and the presence of defects. In addition, the thermal transport properties of CNT materials can be tailored by introducing patterning in the form of trenches, voids, and cuts. Such patterning is required for CNT-based printable electronics. In thermoelectric energy conversion, patterning can be used to introduce structural defects to reduce the effective thermal conductivity of the material.

The goal of the present work is to numerically study the effect of patterning with various geometrical shapes on the reduction of the effective thermal transport properties of thin films composed of single-walled CNTs. Large-scale coarse-grained dynamic simulations are performed to generate computational samples composed of thousands of individual CNTs with a random structure of interconnected bundles of nanotubes.  In the coarse-grained mesoscopic modeling of CNT materials, each nanotube is represented by a chain of stretchable cylindrical segments. The potential mesoscopic force field accounts for stretching, bending, and bending buckling of individual CNTs, as well as van der Waals interaction between nanotubes. In the material samples with static networks of nanotubes, patterning in the form rectangular and circular cuts of varying sizes, orientations, densities, and distributions is introduced. Then the temperature fields and heat fluxes through these samples placed between two heat baths with different temperatures are calculated. The model of thermal transport accounts for the intrinsic thermal conductivity of individual nanotubes and inter-tube contact conductance.

The simulations clearly indicate that thermal transport in the patterned CNT films is not solely dictated by the absolute void fraction but is governed by the interplay between defect geometry, network connectivity, and heat conduction pathways. Large, continuous defects act as substantial barriers to heat flow, drastically reducing thermal conductivity. Conversely, segmented, or staggered defects with similar total blockage areas allow for partial heat percolation, leading to a less reduction in conductivity. The effects of defect spacing or density follow a non-monotonic trend, when closely spaced defects exhibit a compounded resistance effect, while at larger spacing, thermal conductivity partially recovers. Gate-like defects were also examined, where two rectangular defects originate from opposite sides of the sample and are gradually elongated toward the center. These defects act as physical barriers, forcing heat to take more convoluted paths through the remaining unblocked sections of the sample. However, even when these defects extend to create a total blockage area of 100%, thermal transport is not entirely halted. Instead, heat conduction persists through residual pathways within the CNT network. The results of simulations show that the patterning of CNT materials can be effectively used for on-demand tuning of their thermal transport properties.

This work was supported by the National Science Foundation (NSF), USA through award OIA-2148653 and UKRI Innovate UK (KiriTEG Project, Reference: 51868). A.N.V. also acknowledges the support from NSF through award CMMI-1554589.

Presenting Author: Saeed Siahtiri The University of Alabama

Presenting Author Biography: Saeed Siahtiri is a Ph.D. student in the Department of Mechanical Engineering at the University of Alabama, specializing in molecular dynamics and numerical simulations of phase-change phenomena, nano and micro materials, and heat transfer.

Authors:

Saeed Siahtiri The University of Alabama
Chongyang Zeng Imperial College London
Emiliano Bilotti Imperial College London
Alexey Volkov The University of Alabama