DESC:TECHNICAL FIELD
The present invention relates to material science. In particular to a piezoelectric device developed from Titanium carbide-MXene. The invention provides a facile and economical method for rendering pristine Titanium carbide-MXene films to be piezoelectric; and applications of said piezoelectric device.

BACKGROUND
MXenes are a family of two-dimensional (2D) nanomaterials of metal carbides or nitrides first discovered in 2011. The first MXene compound discovered is 2D Titanium Carbide (Ti3C2-MXene). Since the invention of Ti3C2-MXene compound, its physical and chemical properties are being explored around the world by many research groups to adopt for various applications. The synthesis and processing of pristine Ti3C2-MXene films are well established and have been extensively used in the prior art patent documents US 10,683,208; and US 10,573,768. The Ti3C2-MXene films exhibiting piezoresistive property have been demonstrated in prior art and their use for several applications have also been provided in literature. However, degradation of physical properties and lack of stability poses a challenge for long term applications and for adoption in technology according to the current trend in mechanical, electronics and communication devices.

The present invention aims to provide piezoelectric Titanium carbide-MXene device, a method for rendering the MXene films to be stable and piezoelectric in nature and adopt said piezoelectric MXene device in various applications.

SUMMARY OF INVENTION
The present invention is in relation to piezoelectric MXene Titanium carbide.
A method of preparation of piezoelectric Titanium carbide MXene, said method comprising acts of- (a) preparing and patterning Titanium carbide MXene film; and (b) encapsulating the patterned film by laminating between polymer sheetsat a temperature ranging from 60ºC to 180ºC, pressure of 2 bar to 4 bar for a period of 10s to 60s to obtain piezoelectric Titanium carbide MXene.
A piezoelectric Titanium carbide MXene device (A) comprising- Titanium carbide MXene (1) with electric leads (3) encapsulated between polymer sheets (2).
A method of fabrication of piezoelectric Titanium carbide MXene device (A) comprising- Titanium carbide MXene (1) with electric leads (3) encapsulated between polymer sheets (2); said method comprising acts of- (a) preparing and patterning Titanium carbide MXene film (1); applying electric lead (3) to the patterned Titanium carbide MXene film (1); and (c) encapsulating the patterned film (1) with electric leads (3) by laminating between polymer sheets at a temperature ranging from 60ºC to 180ºC, pressure of 2 bar to 4 bar for a period of 10s to 60s to obtain piezoelectric Titanium carbide MXene device (A).

BRIEF DESCRIPTION OF FIGURES
The features of the present invention can be understood in detail with the aid of appended figures. It is to be noted however, that the appended figures illustrate only typical embodiments of invention and are therefore not to be considered limiting of its scope for the invention.
Figure 1: shows (a) schematic of piezoelectric Ti3C2-MXene encapsulated in polymer sheets (b) schematic of Ti3C2-MXene Piezoelectric device (as shown in A), (c) specific sample of Ti3C2-MXene of present invention and tested; and (d) electrical resistance exhibited by the Ti3C2-MXene sample.
Figure 2: shows the piezoelectric response of Ti3C2-MXene.
Figure 3: shows the photograph of commercially available, table-top Shocktube system.
Figure 4: shows the schematic diagram of shock tube system.
Figure 5: shows the output display (Voltage vs Time) from the oscilloscope for a standard commercial sensor, wherein the experiment is conducted by manual air compression.
Figure 6: shows the reference signal from standard commercial sensor, wherein the experiment is conducted by manual air compression.
Figure 7: shows the output display (Voltage vs Time) from the oscilloscope for a standard commercial sensor, wherein the experiment is conducted by piped air compression.
Figure 8: shows the reference signal from the standard commercial sensor, wherein the experiment is conducted by piped air compression.
Figure 9: shows the results of experimentation carried out with piezoelectric Titanium carbide-MXene of present invention after its fabrication; (a) without Wheatstone bridge and (b) with Wheatstone bridge.
Figure 10: shows the results of experimentation carried out with piezoelectric Titanium carbide-MXene of present invention after 6 months period of fabrication; (a) without Wheatstone bridge; and (b) with Wheatstone bridge.
Figure 11: shows the analysis of performance of fabricated device (A) for time response during first month of its fabrication (without Wheatstone bridge signal processing).
Figure 12: shows the analysis of performance of fabricated device (A) for time response in the 8th month of its fabrication (without Wheatstone bridge signal processing).

DETAILED DESCRIPTION OF INVENTION
The present invention is related to a method for inducing piezoelectricity in pristine MXene films; beget piezoelectric MXene device (A) and its adoption for various applications.
The foregoing description of the embodiments of the invention is presented for the purpose of illustration. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, as many modifications and variations are possible in light of this disclosure for a person skilled in the art in view of the figures, description and claims. It may further be noted that as used herein, the singular “a” “an” and “the” include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by a person skilled in the art.
The present invention provides a method for preparation of piezoelectric MXene comprising acts of–(a) patterning the MXene film (1); and (b) encapsulating the patterned film between polymer sheets (2) under distinct temperature and pressure.
In an embodiment of present invention, the Titanium carbide- MXene films are of thickness ranging from about 2 µm to about 10 µm.
In still another embodiment of present invention, the MXene films are cut into different polygonal or circular shapes of different dimensions and patterned by laser or physical methods like using scissor, cutter.
In another embodiment of present invention, the polygonal shapes of MXene films are preferably rectangular strips of millimeter lateral dimensions, ranging from millimeters (mm) to centimeters (cm) preferably (but not limited to) 1cm in length and 2 mm width.
In another embodiment of the present invention, the polymer is non-porous, water resistant, humidity and oxidation resistant, selected from a group comprising Polyethylene Terephthalate (PET), Ethylene-Vinyl Acetate (EVA), Nylon -6, Polypropylene (BOPP), and the like.
In another embodiment of the present invention the thickness of the polymer film is ranging from about 70 microns to about 300 microns.
In another embodiment of present invention, the encapsulation of the film is by lamination.
In still another embodiment of present invention, the lamination is carried out by heat treatment at a temperature ranging from about 60ºC to 180ºC, pressure of about 2 bar to about 4 bar for a period of about 10s to about 60s.
In yet another embodiment of present invention, the heat treatment is carried out by a method selected from hot compression rollers, hot air impingement, hot press and the like.
In another embodiment, the piezoelectric Titanium carbide MXene can be adopted with suitable electric leads as a piezoelectric device for various applications.
The present invention provides a piezoelectric Titanium carbide MXene device (A) comprising a piezoelectricity induced Titanium carbide MXene film (1) with electric leads (3) sandwiched between sheets of polymers (2).
In another embodiment of present invention, the electrical leads are selected from a group comprising silver epoxy paste, electrical conducting paste or terminal.
In an embodiment of present invention, the piezoelectric Titanium carbide MXene device (A) is fabricated by a method comprising acts of – a) patterning the MXene film (1); b) connecting the patterned film with electrical leads (3); and c) encapsulating the patterned film (1) with electrical leads (3) between polymer sheets (2) under high temperature and pressure to obtain the piezoelectric Titanium carbide MXene device (A).
In another embodiment of present invention, the encapsulation is through lamination by heat treatment at a temperature ranging from about 60ºC to 180ºC, pressure of about 2 bar to about 4 bar for a period of about 10s to about 60s.
The flow chart-A provides the schematic representation of the detailed process of preparation of the piezoelectric Ti3C2-MXene films and figure 1 (a) schematic of piezoelectric Ti3C2-MXene encapsulated in polymer sheets, (b) schematic of Ti3C2-MXene Piezoelectric device (A), (c) specific sample of Ti3C2-MXene of present invention and tested; and (d) electrical resistance exhibited by the Ti3C2-MXene sample.

Flowchart-A
In another embodiment of present invention, the piezoelectric MXene device (A) is checked for its voltage output. It is connected to a digital storage oscilloscope to display the voltage output when subjected to physical forces or pressure. It is demonstrated that when MXene device (A) provides a voltage output without any power supply when it is subjected to pressure wave in a pressure tube. The post-processed results are provided in figure 2. The voltage response to the applied pressure load resulting in the piezoelectric effect demonstrates the piezoelectric effect of the MXene device (A).
In another embodiment of present invention, the piezoelectric Titanium carbide MXene device (A) has a time response of about 0.8 µS to 1.5µS.
In another embodiment of present invention, the piezoelectric Titanium carbide MXene device (A) is stable for a period of more than 10 months.

EXPERIMENTAL
Materials used
Titanium Aluminium Carbide (Ti3AlC2; Carbon-Ukraine Ltd.); Hydrochloric acid (HCl; Sigma Aldrich); and Lithium fluoride (LiF; Sigma Aldrich); Polyethylene Terphtahalate (PET; commercially available by local supplier); Silver epoxy paste (local supplier at Bangalore, Siltech); copper thin wire (100-150 micron, local supplier from Bangalore) as an electrical lead.
Preparation of Titanium carbide-MXene film
2 g of Titanium Aluminium Carbide (Ti3AlC2) is added gradually into etchant solution comprising 6 M HCl and 1.5 g amount of LiF and continuously stirred for 24 h. Thereafter, the solution is washed with water until the pH is greater than or equal to 6. The product obtained after washing, is collected, and sonicated for 1 hat 40 KHz in a water bath sonication. The resultant black colour solution is filtered under vacuum (vacuum-assisted filtration process) to form Titanium Carbide (Ti3C2) films. The obtained MXene free standing film are of thickness ranging from about 2 µm to 10 µm.

Fabrication of piezoelectric Titanium carbide-MXene device (A).
General method: The Titanium carbide-MXene films are dimensionally cut into desirable shape of rectangular strips and the like. The freestanding films are patterned and electrical nodes are attached on the patterned MXene at the edges for connecting oscilloscope for output signal processing and recording. Said MXene film is sandwiched between two polymer sheets of thickness of about 70µm thick by hot press lamination process at temperature of about ~ 100ºC, Pressure of about 3bar for a period of 40 sec to obtain the piezoelectric MXene device (A).
Pattering process: Laser patterning process is adopted to cut the MXene film into specific dimension. Various polygonal shapes are possible to be patterned. The process would use laser beam for cutting process.
Example 1: The Ti3C2-MXene films are cut to rectangular strips of 10 mm length, and 2 mm width. The free standing films are patterned by pulse laser. Silver epoxy paste is applied on the patterned Ti3C2-MXene at the edges for connecting oscilloscope for output signal processing and recording. Said Ti3C2-MXene film is sandwiched between two polyethylene terephthalate (PET) polymer sheets of thickness of about 70µm thick by hot press lamination process at a temperature of 100ºC, Pressure of about 3bar for a period of 40 sec to obtain the piezoelectric Titanium carbide-MXene device (A).

c. Demonstration of piezoelectric effect of Titanium carbide-MXene device (A).
A Shocktube system is used to provide dynamic pressure input (Shockwaves) for measurement of piezoelectric behaviour of fabricated device (A).
Commercially available, table-top Shocktube system known as ‘Reddy Tube’ (Figure 3.) is adopted. Typically, the system consists of a Driver section (5) and a Driven section (6) separated by a Diaphragm (4) (Figure 4). The Driver section (5) is pressurized using gas cylinder pressure lines or by manually pushing a plunger and compressing the gas up to a desired pressure (preferably 2-3 bar). When the diaphragm (7) ruptures (detected using burst sensor (9), a Shockwave (8) is produced and propagates at supersonic velocity in the Driven section (6). The properties- pressure, temperature, and density of the gas vary instantaneously along its path of propagation. On reaching the end of the driven section, the shockwave reflect and propagate backwards further changing the gas properties. The property is measured with commercially available Piezoresistive sensors (Axial 6-SIP MPX5700A; Make: NXP Semiconductors USA Inc.) and compared with the performance of device (A) of present invention. The time duration of the shock wave application on the films are in few hundred to thousands of microseconds.

The output signals with experimental parameters as given below are checked for pressure and velocity.
a) Gas used – Air (4)
b) Pressure of air in the Driver section to rupture the Diaphragm (P4) = 2.8 to 3 bar
c) Same diaphragm material (tracing paper; 90 gsm, 50 µm) is used in all experiments and the value of Rupture pressure (P4) remained the same.
d) Sensitivity - 6.4 mV/kPa
e) Local velocity of Sound (a)
a = v("?" RT) = v("1.4*287*298(lab)" )=346 ms-1
? ?Ratio of specific heat of the gas. For air ? = 1.4
R ?Characteristic Gas Constant. For air R = 287 J/kg-K
T? Room Temperature. T1 = 298 K
Experiment by manual compression:
The experiments are performed for Manual Operation by manually compressing Air (4) in the Driver section (5) (figure 5) wherein, distance between sensors (S1 (10) and S2 (11)) is 15cm and the time for shock wave (8) to propagate between from S1 (10) to S2 (11) is 326 µs. The velocity of shock wave (8) is observed as 460ms-1. The Mach Number of Shockwaves is calculated as -
Mshock = Vshock/a=552.14 ms"-1 " /346.03 ms"-1 " =1.3(rounded off to one decimal place)

Peak Voltage – 1.75 Volts
Sensitivity – 6.4 mV/kPa
Peak -pressure of the Shockwave (P5) - (1.75 V)/(6.4 mV/kPa)?270 kPa = 2.7 bar

The value 1200 mm indicated in figure 6 is the distance shockwave (8) travels between 2 successive reflections inside the tube. For manual operation the piston stops at the end of Driver section. Thus, the shockwave after 1st reflection (1st Peak), travels 600 mm and reflects from the piston face to travel back 600 mm in a total time of ~ 4 ms. This acts as a reference for specimen sensor’s response (at same location) at specific time points.
(ii) Experiment with external pressure using pressure line:
Parallely the experiment is performed involving external pressure using pressure lines compressing air (4) in the Driver section (5) (figure 7) wherein, distance between sensors (S1(10) and S2(11)) is 30cm and the time for shock wave (8) to propagate between from S1(10) to S2(11) is 630 µs. The velocity of shock wave (8) is observed as 476ms-1. The Mach Number of Shockwaves is calculated as -
Mach Number of Shockwave
Mshock = Vshock/a=476.19 ms"-1 " /346.03 ms"-1 " =1.4 (rounded off to one decimal place)

For external pressure operation, the shockwave after 1st reflection (1st Peak), travels 1000 mm and reflects from the front (inlet face) to travel back 1000 mm in a total time of approximately 6 ms. This acts as a reference for Specimen sensor’s response (at same location) at specific time points (figure 8).

The device (A) of MXene Ti3C2 of present invention is placed inside the driven section (6) by means of a specially designed Sensor port (12) and subjected to the Shockwaves (8). As shown in the schematic diagram, the device is attached to the end flange using a double-sided sticky tape. Lead wires of specimen are connected to the sensor port (12) which can send the electrical changes externally to an oscilloscope through output leads (13) & (14). It responds to the instantaneous increase in pressure in the form of a voltage output even without Wheat stone’s bridge. This confirms the piezoelectric behaviour of device (A).The output display (Voltage vs Time) from the oscilloscope consists of Voltage along Y-axis (in Volts) and Time along X-axis (in milliseconds). Additionally, sampling values are produced from Oscilloscope and recorded using USB drive. The data is plotted for comparative analysis. The events of the response of device (A) (Figure 9 and Figure 10) are compared to the events of standard sensors (Figure 7 and Figure 8). Piezo behaviour based on the Shockwave reflections are observed at same time point (~6 ms for external pressure and ~ 4 ms for manual pressure) as established in standard commercial piezo sensors.

The device (A) responds to sudden changes in microseconds and is able to record the changes as a signal output. Thus, it may be useful in areas of gas dynamics involving supersonic speeds like for example in blast studies, and supersonic flight.
(iii) Performance of device

Device aging: The performance of the device (A) is checked for a period of 8 months by conducting about 20 tests using shock tube to find out deterioration in piezoelectric effect if any.
The time response is found to be 1µS to 1.5µS in the first month, the figure 11 (a) shows the response captured at 10ms window, 11 (b) shows the response captured at 2.5 ms window in a subsequent trail and the resolution image of fig 11(b) to obtain rise time.
Subsequently, the figure 12 shows the time response of the device (A) in the eighth month it is observed to be 0.8 to 1.05 µS, indicating no significant deterioration. The device resistance change is in the range of 10 to 13 ohms over a period of 10 month. The experiment indicates the stability rendered to the Titanium carbide-MXene by the present method; which otherwise is known to be a highly unstable.

A comparison between the dynamic response of the piezoelectric pristine Ti3C2-MXene device (A) is carried out with other commercially available sensor is reported in Table 1.
Table 1: Comparison of piezoelectric pristine Ti3C2-MXene films with known sensor.
Material Characterization Method
(Material Behavior) Response time Reference
Pristine Ti3C2-MXene film Shock tube test
(Piezoelectric) 1.31 ± 0.45 µs Present invention
PVDF film Shock tube test
(Piezoelectric) ~ 21 µs Compared with present invention
Ceramic (Commercial sensor) Shock tube test
(Piezoelectric)
= 3 µs PCB PIEZOTRONICS:
Micro ICP® pressure sensor 132A series
(https://www.pcb.com/nx/search-results?q=132A)

The present invention can have application as-

-Vibration sensor: For sinusoidal, random level vibration testing of automobile, aerospace equipment.
-Skin friction sensor: During re-entry as well as take-off of rockets launch vehicle and the like.
-Dynamic pressure transducer in blast studies, aerospace studies and the like
-Microphone: To find the range of frequency for various microphone frequency limit and saturation level-to categorize microphone directionality.
-Shear sensor: For shear strength measurement as well as partial shear force measurement during breaking-damage and normal applications.
-Dynamic load/ Force sensor – Load cell: To find the frequency response of conventional as well as advanced technology-based load cell/force-Load cell and to find out the dynamic load on spring-mass system, diaphragm, bellows, springs, plated, column and the like.
-Energy harvester: Energy harvesting using piezo electric elements, thin film, nanomaterial-based harvester like ZnO, AlN, PVDF requires frequency domain for maximum energy transfer generation, which will yield better efficiency and reliability.

The present invention thus provides piezoelectric Titanium carbide-MXene that can be adopted for a number of applications effectively. The facile, scalable and economical fabrication method of piezoelectric Titanium Carbide-MXene device adds to the advantage of developing potential appliances including sensors cost effectively.
,CLAIMS:WE CLAIM
1. A method of preparation of piezoelectric Titanium carbide MXene, said method comprising acts of -
a) preparing and patterning Titanium carbide MXene film; and
b) encapsulating the patterned film by laminating between polymer sheets at a temperature ranging from 60ºC to 180ºC, pressure ranging from 2 bar to 4 bar for a period ranging from 10s to 60s to obtain piezoelectric Titanium carbide MXene.
2. The method of preparation as claimed in claim 1, wherein the MXene films are of thickness ranging from 2 µm to 10 µm.
3. The method of preparation as claimed in claim 1, wherein the MXene films are patterned by laser or physical methods with scissor or cutter.
4. The method of preparation as claimed in claim 1, wherein the polymer is selected from a group comprising of Polyethylene terephthalate (PET), Ethylene-Vinyl Acetate (EVA), Nylon -6, Polypropylene (BOPP) and the like.
5. The method of preparation as claimed in claim 1, wherein the polymer is of thickness ranging from 70 microns to 300 microns.
6. The method of preparation as claimed in claim 1, wherein the lamination is by a method selected from hot compression rolling, hot air impingement, hot press, and the like.
7. A piezoelectric Titanium carbide MXene device (A) comprising- piezoelectric Titanium carbide MXene (1) with electric leads (3) encapsulated between polymer sheets (2).
8. The piezoelectric Titanium carbide MXene device (A) as claimed in claim 7, wherein the electric leads (3) is selected from a group comprising silver epoxy paste, electrical conducting paste or terminal.
9. The piezoelectric Titanium carbide MXene device (A) as claimed in claim 7, wherein the device exhibit response within a period of 0.8 µS to 1.5 µS.
10. The piezoelectric Titanium carbide MXene device (A) as claimed in claim 7, wherein the device is stable for a period of 10 months.
11. A method of fabrication of piezoelectric Titanium carbide MXene device (A) comprising- piezoelectric Titanium carbide MXene (1) with electric leads (3) encapsulated between polymer sheets (2); said method comprising acts of-
a. preparing and patterning Titanium carbide MXene film (1);
b. applying electric leads (3) to the patterned Titanium carbide MXene film(1); and
c. encapsulating the patterned film (1) with electric leads (3) by laminating between polymer sheets at a temperature ranging from 60ºC to 180ºC, pressure of 2 bar to 4 bar for a period of 10s to 60s to obtain piezoelectric Titanium carbide MXene device (A).