I certify that the manuscript entitled “Fabrication of Highly Flexible Strain Sensor Based on Elastomeric MXene” is the result of my original work, with the exception of. Flexible strain sensor has gained popularity in recent years due to high demand in modern applications such as flexible electronics, IoT, human-machine interactions, human motion detection and structural health monitoring. Nevertheless, they are often made of non-extensible substrates, they have a limited ability to be elongated at high loads; therefore, they are not durable at large load ranges and are susceptible to mechanical failure.
In the present work, we investigate the fabrication of a highly flexible strain sensor based on ternary composites;. Alhamdulillah, I would like to begin by conveying my heartfelt thanks and gratitude to my supervisor, Assistant Professor Sherif Araby Gouda, and my co-supervisor, Assistant Professor Gulnur Kalimuldina, for their unwavering and consistent support and motivation throughout my academic journey and research. I express my sincere appreciation to Professor Essam Shehab, who serves as the head of our department, and Assistant Professor Md Hazrat Ali for their encouraging words and insightful guidance during my study period.
In addition, I would like to acknowledge and thank my colleagues and senior researchers at the Department of Mechanical and Aerospace Engineering and assistant professor Gulnur Kalimuldina's research team for their continued support and guidance. Finally, I would like to express my sincere appreciation to my family members and friend who have given me support and motivation throughout my academic journey.
Motivation and Problem Statement
Research Aims and Objectives
MXene: New 2D Material
Strain Sensors based on MXene/Polymer nanocomposites
47] developed versatile strain sensor based on an MXene matrix structure incorporated with polyurethane coating. Figure 2 (a‒d) shows the preparation of the polyurethane/MXene strain sensor, the digital image of the polyurethane/MXene strain sensor, the SEM micrographs of the cross-linked polyurethane/MXene structure, and the shrunken structure, respectively. To fabricate the strain sensor, the MXene conductive sheet was attached to the P-structured matrix using electrostatic contact. A strain sensor  fabricated by modifying Ti3C2 MXenet and aminopoly(dimethyl siloxane) using small biological molecules through the esterification process.
Due to the homogeneous distribution of the modified MXene, the composite showed good electrical conductivity, remarkable tensile properties, because various chemical bonds and amine bonds are reversible, high efficient self-healing can occur without the requirement for external stimulus. An experiment  demonstrated the construction of a self-healing nanostructure MXene embedded with rubber-based elastomer for strain sensing. 50] fabricated Ti3C2TX-MXene/polyurethane strain sensor by a wet-spinning technique using acetic acid and isopropanol as coagulants.
The obtained MXene/polyurethane strain sensor showed high electrical conductivity of MXene and satisfactory stretchability of polyurethane. High performance polymer/MXene nanocomposites require the use of functional MXenes in combination with the polymers for further improved physical properties . In recent years it has been shown that hybridizing nanofillers result in synergy in the desired properties of the end product. At this point, 2D nanomaterials tend to re-stack in the polymeric matrix due to the van der Waals forces resulting from their large surface area.
After adding another geometrical nanofiller, such as 0D and 1 D, into the polymer/2D material, it improves the dispersion quality and improves the functional and mechanical properties of the final composite materials . In this paragraph, we focus on carbon nanotubes as a synergistic 1D nanofiller for MXenes, as they are one of the most well-known and common allotropes of carbon. CNTs, being a highly conductive 1D material, not only provide the flexibility of the MXene sheets, but also inhibit refolding and facilitate ion transport within the MXene flakes. In addition, the insertion of CNTs into rolled film electrodes of layered Ti3C2 MXene has been shown to improve the capacitance performance in the electrolyte .
These characteristics of conductive polymers and CNTs prove suitable for fabricating flexible strain sensors and supercapacitors, as discussed below. The delaminated Ti3C2TX MXene flake suspension was spray coated onto the latex to form a thin, continuous layer of MXene flakes, which was dried using a nitrogen gas gun. Moreover, Figure 3(c,d) shows the transmission electron microscope (TEM) images of MXene flakes and water-soluble SWCNTs.
- Synthesis of MXene
- Modification of MWCNTs and preparation of Ti 3 C 2 T x -MXene/m-MWCNTs
- Fabrications of m-MWCNT/MXene/Ecoflex composite strain sensor
The mixture was sonicated in a water bath for 1 h under room temperature to produce modified m-MWCNTs. Then, MXene solution was prepared by dispersing MXene powder in 10 mL of deionized water and sonicated for 1 h. The m-MWCNTs suspension and MXene solution were mixed and sonicated for 1 h together with different weight ratios.
Two parts (A and B) of Ecoflex were mixed together in a mass ratio of 1:1, with a total mass of 10 g, and mixed for 5 minutes. Next, 0.4 g of MXene was directly dispersed into the Ecoflex mixture and mixed well for about 10 minutes until it was completely homogenized. Air bubbles were removed by placing the solution under vacuum until the solution was completely degassed (10 min).
One method involved using a mold with dimensions of 3 cm × 1.5 cm × 2 cm to pour the solution into the mold while wire electrodes were attached to both sides. The composite was left for 4 hours at room temperature until fully cured and then peeled from the mold. The composite was poured onto a casting glass and a squeegee was used to spread it and form a film.
The prepared composite is then allowed to dry at room temperature for 4 hours until completely dry. The desired size was cut and the wire electrodes were attached to both sides with the help of silver paste. Whereas, the two parts (A and B) of Ecoflex are mixed together in a mass ratio of 1:1, with a total mass of 10 g.
- Chemical morphology and microstructure
- Mechanical measurements
- Electromechanical performance of MXene-based composites
- Real-Time Application human movement
This suggests that the breaking load and elongation increase as the content of MXene/m-MWCNT increases, until the amount reaches a certain destructive level of the Ecoflex. The value ε indicates the applied stress; ΔL represents the variation in the length of the material under load; and Lo represents the initial or original length of a material. The strain sensor was clamped between the stationary rod and the horizontal movable part of the linear motor device.
The two electrode leads of the load sensor were then connected to the Keithley source meter integrated with triple current source. To study the sensitivity and stretchability performance of MXene and m-MWCNTs strain sensors, two different samples with (MXene and MXene /m-MWCNTs) were fabricated and tested within the strain range of 0–60% as shown in Figure 14. resistance-strain curve for MXene/m-MWCNT's strain sensor indicates that it has a wide and adjustable sensitivity range with.
This aspect facilitates their alignment with the direction of the applied voltage, producing a more pronounced change in electrical resistance per unit voltage, ultimately resulting in a higher gauge factor. MXenes, on the other hand, are more susceptible to cracking under load due to their brittle nature, which can adversely affect strain sensor performance. Thus, the amplitude modulation of the electrical signal was almost proportional to the increase in frequency.
This indicates that the sensor response remained constant regardless of the displacement change. Deformation values of 15%, 30% and 45%. To evaluate the durability and electromechanical response of the MXene/m-MWCNT strain sensor, data were acquired by subjecting it to a 10% strain for 1000 cycles of stretch and release at a frequency of 1 Hz. The resistance remained constant with good reproducibility over the first 5 cycles, indicating excellent fatigue resistance of the sensor.
The MXene/m-MWCNTs strain sensor exhibits excellent sensing performance, including good sensitivity, a wide sensing range, an extremely fast response, and outstanding cycle stability. This makes it possible to use the sensor as a wearable device to instantly monitor various movements of the human body. Furthermore, when the sensor was mounted on the hand, wrist, and knee joints, it immediately displayed reliable electrical signals for joint flexion movements as shown in Figure 17c, d, e, and f, with corresponding digital photographs.
This shows the great potential of the MXene/m-MWCNT sensor for use in human health assessment. Human body motion detection using MXene /m-MWCNTs strain sensor: (a) Digital photograph of finger flexion; (b) Finger flexion graph, (c) Wrist motion digital photograph, (d) Wrist motion graph, (e) Knee flexion digital photograph, (f) Flexion graph of the knee.
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