Citation: Xing, F.; Li, M.; Wang, S.;
Gu, Y.; Zhang, W.; Wang, Y.
Temperature Dependence of
Electrical Resistance in Carbon
Nanotube Composite Film during
Curing Process. Nanomaterials 2022,
12, 3552. https://doi.org/10.3390/
nano12203552
Academic Editor: Dong-Joo Kim
Received: 8 September 2022
Accepted: 8 October 2022
Published: 11 October 2022
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Article
Temperature Dependence of Electrical Resistance in Carbon
Nanotube Composite Film during Curing Process
Fei Xing
1
, Min Li
1,
* , Shaokai Wang
1,
*, Yizhuo Gu
2
, Wei Zhang
2
and Yanjie Wang
2
1
Key Laboratory of Aerospace Advanced Materials and Performance (Ministry of Education),
School of Materials Science and Engineering, Beihang University, No. 37 Xueyuan Road, Haidian District,
Beijing 100191, China
2
Research Institute of Frontier Science, Beihang University, No. 37 Xueyuan Road, Haidian District,
Beijing 100191, China
* Correspondence: leemy@buaa.edu.cn (M.L.); wsk@buaa.edu.cn (S.W.)
Abstract:
Carbon nanotube (CNT) film possesses excellent mechanical and piezoresistivity, which
may act as a sensor for process monitoring and reinforcement of the final composite. This paper
prepared CNT/epoxy composite film via the solution dipping method and investigated the electrical
resistance variation (∆R/R
0
) of CNT/epoxy composite film during the curing process. The tempera-
ture dependence of electrical resistance was found to be closely related to resin rheological properties,
thermal expansion, and curing shrinkage. The results show that two opposing effects on electrical
resistivity occur at the initial heating stage, including thermal expansion and condensation caused
by the wetting tension of the liquid resin. The lower resin content causes more apparent secondary
impregnation and electrical resistivity change. When the resin viscosity remains steady during the
heating stage, the electrical resistance increases with an increase in temperature due to thermal
expansion. Approaching gel time, the electrical resistance drops due to the crosslink shrinkage of
epoxy resin. The internal stress caused by curing shrinkage at the high-temperature platform results
in an increase in electrical resistance. The temperature coefficient of resistance becomes larger with
an increase in resin content. At the isothermal stage, an increase in
∆
R/R
0
value becomes less obvious
with a decrease in resin content, and ∆R/R
0
even shows a decreasing tendency.
Keywords:
carbon nanotube composite film; process monitoring; temperature dependence; curing
shrinkage; thermal expansion
1. Introduction
Carbon nanotubes (CNTs) are promising materials to reinforce polymers due to their
superior mechanical properties and excellent physical properties. CNTs have been suc-
cessfully manipulated to form CNT fibers and films with high CNT concentrations. These
nanocomposites reinforced by CNT fibers or films even exhibit comparable mechanical
properties with traditional carbon fiber reinforced composites [
1
–
3
], which show great
potential as structural materials. For instance, CNT film has been successfully used in the
Juno spacecraft by hybridizing it with an M55J carbon fiber [
4
]. Meanwhile, the prominent
electromechanical properties of CNTs and the CNT network also impart the excellent
piezoresistive response of CNT composites, which could achieve the strain sensing and
structural health monitoring of polymer composites.
The fabrication of thermosetting composites involves complex physical and chemical
changes, including resin infiltration, resin curing, fiber densification, and so on. Effective
process quality control could avoid the formation of voids, delamination, and other de-
fects. Thereby, process monitoring has attracted more and more attention, and various
process monitoring approaches have been developed, such as optical fiber sensors [
5
],
dielectric/capacitance sensors [
6
], ultrasonic monitoring [
7
], thermocouples [
8
], pressure
sensors, and resistance sensors. These methods have been successfully used to monitor the
Nanomaterials 2022, 12, 3552. https://doi.org/10.3390/nano12203552 https://www.mdpi.com/journal/nanomaterials
