Citation: Turco, A.; Monteduro, A.G.;
Montagna, F.; Primiceri, E.; Frigione,
M.; Maruccio, G. Does Size Matter?
The Case of Piezoresistive Properties
of Carbon Nanotubes/Elastomer
Nanocomposite Synthesized through
Mechanochemistry. Nanomaterials
2022, 12, 3741. https://doi.org/
10.3390/nano12213741
Academic Editor: Ilaria Armentano
Received: 7 October 2022
Accepted: 21 October 2022
Published: 25 October 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
Does Size Matter? The Case of Piezoresistive Properties of
Carbon Nanotubes/Elastomer Nanocomposite Synthesized
through Mechanochemistry
Antonio Turco
1,
* , Anna Grazia Monteduro
1,2
, Francesco Montagna
3
, Elisabetta Primiceri
1
,
Mariaenrica Frigione
3
and Giuseppe Maruccio
1,2,
*
1
CNR Nanotec Institute of Nanotechnology, Via Monteroni, 73100 Lecce, Italy
2
Omnics Research Group, Department of Mathematics and Physics “Ennio De Giorgi”, University of Salento,
Via per Monteroni, 73100 Lecce, Italy
3
Department of Innovation Engineering, University of Salento, Prov.le Lecce-Monteroni, 73100 Lecce, Italy
* Correspondence: antonio.turco@nanotec.cnr.it (A.T.); giuseppe.maruccio@unisalento.it (G.M.)
Abstract:
The growing interest in piezoresistive sensors has favored the development of numerous
approaches and materials for their fabrication. Within this framework, carbon nanotubes (CNTs)
are often employed. However, CNTs are a heterogeneous material with different morphological
characteristics in terms of length and diameter, and, so far, experimental studies have not usually
considered the effect of these parameters on the final sensor performances. Here, we observe
how, by simply changing the CNTs length in a solvent-free mechanochemistry fabrication method,
different porous 3D elastomeric nanocomposites with different electrical and mechanical properties
can be obtained. In particular, the use of longer carbon nanotubes allows the synthesis of porous
nanocomposites with better mechanical stability and conductivity, and with a nine-times-lower limit
of detection (namely 0.2 Pa) when used as a piezoresistive sensor. Moreover, the material prepared
with longer carbon nanotubes evidenced a faster recovery of its shape and electrical properties
during press/release cycles, thus allowing faster response at different pressures. These results
provide evidence as to how CNTs length can be a key aspect in obtaining piezoresistive sensors with
better properties.
Keywords:
electrical properties; carbon nanotubes; nano composites; mechanical properties; flexible
composites
1. Introduction
The future generations of portable and foldable devices such as wearable flexible
electronics, medical implants and electronic skins will require the development of highly
sensitive, stretchable and low-cost pressure sensors [
1
–
3
]. For example, an electronic skin
could generate signals able to reflect the strength and the location of an external pressure,
but a stability of the sensing materials of up to 55% strain is necessary [
4
]. Under this view,
different strategies have been proposed, e.g., relying on transistor [
5
], piezoelectric [
6
],
capacitive [
7
] and piezoresistive sensing [
8
]. Among them, piezoresistive transducers have
attracted researcher interest, due to the relative simplicity of signal collection and the
possibility of preparing highly flexible materials. The first approaches proposed the use of
a polymer streamer with metal layers on the surface. However, these devices were usually
able to detect only small strains (~5%) with relatively low sensitivity, due to problems such
as the cracking of the materials [
9
], which can affect the sensor reproducibility and stability
and could cause environmental and health concerns [
10
,
11
]. Another strategy is to prepare
polymeric 2D films mixed with conductive (nano)materials for the fabrication of the sensors.
However, the application of these materials is limited, due to the difficulties in dispersing
conductive nanomaterials [
12
], low sensitivity, instability and the impossibility of detecting
Nanomaterials 2022, 12, 3741. https://doi.org/10.3390/nano12213741 https://www.mdpi.com/journal/nanomaterials
