Citation: Yang, Y.; Yi, T.; Liu, Y.;
Zhao, H.; Liang, C. Design of a
Highly Sensitive Reduced Graphene
Oxide/Graphene Oxide@Cellulose
Acetate/Thermoplastic Polyurethane
Flexible Sensor. Sensors 2022, 22, 3281.
https://doi.org/10.3390/s22093281
Academic Editor: Antonio Di
Bartolomeo
Received: 2 March 2022
Accepted: 22 April 2022
Published: 25 April 2022
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Article
Design of a Highly Sensitive Reduced Graphene
Oxide/Graphene Oxide@Cellulose Acetate/Thermoplastic
Polyurethane Flexible Sensor
Yujie Yang
1
, Tan Yi
1
, Yang Liu
1,2,3,
* , Hui Zhao
1,2
and Chen Liang
1,2
1
College of Light Industry and Food Engineering, Guangxi University, Nanning 530004, China;
yangyujie0985@163.com (Y.Y.); yitansysu@163.com (T.Y.); zhh@gxu.edu.cn (H.Z.);
liangchen@gxu.edu.cn (C.L.)
2
Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, Guangxi University,
Nanning 530004, China
3
Guangxi Bossco Environmental Protection Technology Co., Ltd., Nanning 530000, China
* Correspondence: xiaobai@gxu.edu.cn; Tel.: +86-155-7832-3385; Fax: +86-0771-3237309
Abstract:
As a substitute for rigid sensors, flexible sensing materials have been greatly developed
in recent years, but maintaining the stability of conductive fillers and the stability of micro-strain
sensing is still a major challenge. In this experiment, we innovatively prepared a polyurethane-based
cellulose acetate composite membrane (CA/TPU) with abundant mesopores through electrospinning.
Then, we reduced graphene oxide (rGO)—as a conductive filler—and graphene oxide (GO)—as an
insulating layer—which were successively and firmly anchored on the CA/TPU nanofiber membrane
with the ultrasonic impregnation method, to obtain an rGO/GO@CA/TPU sensor with a GF of 3.006
under a very small strain of 0.5%. The flexibility of the film and its high sensitivity under extremely
low strains enables the detection of subtle human motions (such as finger bending, joint motion, etc.),
making it suitable for potential application in wearable electronic devices.
Keywords: electrospinning; porous fiber; flexible strain sensor; high sensitivity
1. Introduction
In recent years, with the rapid development of fields within electronic technology,
such as intelligent robots, flexible wearable devices, mobile intelligence, and electronic
skin, the research and development of functional flexible sensors has attracted increasing
levels of attention [
1
–
4
]. Due to the narrow strain range and easy plastic deformation of
rigid sensors, such as traditional metal foil and semiconductor strain sensors, which have
poor stretchability (
ε
< 5%) [
5
,
6
], it is increasingly difficult to meet the requirements of
new conductive materials for a high strain-sensing ranges and deformable sensing. More
importantly, the flexible sensor manufacturing process is simple, and such sensors have
a low cost and light weight. Flexible sensors can respond to external signals in real time
and in any form, and they can provide output in the form of electrical signals, which also
makes them better for applications as wearable devices, in device motion detection, as
health testing equipment, amongst other fields [
1
,
2
,
4
]. The response of a flexible sensor is
realized by the conductive unit, which forms a path, and regular changes in the conductive
unit due to external stimuli [
7
]. Except for a few structural self-conductive polymers,
most flexible sensors are realized primarily with composite conductive polymers that are
composed of non-conductive polymer materials mixed with conductive substances [
8
].
The electron transport mechanism of this type of composite conductive polymer is mainly
explained by three theories: the “conducting path”, “tunneling effect” and “field electron
emission” [9–11].
At present, there are many kinds of materials used for flexible sensors, such as poly-
dimethylsiloxane (PDMS) [
12
], thermoplastic polyurethane (TPU) [
13
,
14
], polyvinylidene
Sensors 2022, 22, 3281. https://doi.org/10.3390/s22093281 https://www.mdpi.com/journal/sensors
