Experimental determination of the coefficient of thermal expansion of flexible, binder-free single wall carbon nanotube membranes

Open Access
Author:
Shetty, Pralav P
Area of Honors:
Mechanical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • John Michael Cimbala, Thesis Supervisor
  • Sean N Brennan, Honors Advisor
  • Kofi W Adu, Faculty Reader
Keywords:
  • carbon nanotube
  • membrane
  • coefficient of thermal expansion
  • optical profilometry
  • thermal cell
Abstract:
The current literature reporting on the thermophysical properties of single-wall carbon nanotube (SWCNT) materials (individual tubes, bundles, and films/mats) reveals disparities in both experimental and theoretical results. Various theoretical models and simulations for predicting the thermophysical characteristics of individual/bundles of SWCNTs have established general trends in these properties. Yet, there is significant variation in the results and these discrepancies need to be resolved. The thermophysical behavior of SWCNTs is influenced by the structural properties (chiral, armchair, zigzag), nanotube length and diameter, sample history (synthesis, processing and purification methods), defects, thermal contact between tubes, and the uncertainty in the unconventional techniques being used to probe the samples. Furthermore, there are relatively few reports on the thermophysical properties of large-scale SWCNT mats and films. In this study, a simple, but novel non-contact and nondestructive optical profilometry technique has been employed to measure the out-of-plane, temperature-dependent coefficient of thermal expansion (CTE). A thermal cell was designed to accomodate the 10x objective lens of a Zygo Optical Profilometer for the purpose of measuring the CTE of the SWCNT films. This cell has an internal resistance of around 12 Ω and can be used to generate temperatures ranging from room temperature to 373 K. The Zygo NewView 7300 Optical Profilometer was used to measure the out-of-plane CTE of 1mm x 1mm SWCNT films over the range of temperatures between room temperature and 353 K. The CTE was found to be as low as -4.96 . 10-3 K-1 and went up to 5.14 . 10-3 K-1 for temperature changes of 20 K from room temperature to 353 K for sample #1. Other representative samples showed similar variations in their CTE. Though the results seem counterintuitive at first due to the both positive and negative CTE’s measured for the samples, specifically because individual SWCNTs are reported to have a negative CTE at temperatures below 400 K. The variation might be due to shrinkage in certain areas of the films with an increase in temperature causing micro-buckling in other regions of the films due to their macroscopic nature which consequently gives a positive CTE reading for these other areas. However, further investigations are needed to delineate the factors that could lead to the observed variation.