Claims:1. A method (10) for preparing a polymer - ceramic nano composite film, wherein the method comprises:
mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)) in a pre-defined ratio, in a magnetic stirrer upon adding distilled water, for a pre-defined amount of time; (20)
mixing a pre-defined amount of concentrated nitric acid (HNO3) for obtaining a mixture solution, wherein the pre-defined amount of concentrated nitric acid (HNO3) depends on nature of the solution obtained upon mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)); (30)
mixing a pre-defined amount Sodium Hydroxide (NaOH) (Sigma Aldrich) solution to the obtained mixture solution for preventing agglomeration for obtaining a final mixture; (40)
drying the obtained final mixture at about 60 degrees Celsius for about two hours for obtaining fine brown powder; (50)
grinding calcined powder upon subjecting the obtained fine brown powder for calcination process at about 650 degrees Celsius, for obtaining powder in a pure phase; (60)
segregating Bismuth ferrite (BFO) ceramic nano particles with varying weight percentage and N-Methyl-2-pyrrolidone (NMP) solvent from the obtained powder for subjecting segregated particles to ultra-sonification; (70)
adding polyvinylidene fluoride (PVDF) polymer powder to the Bismuth ferrite (BFO) nano particles in a magnetic stirrer for obtaining a mixture; (80)
subjecting the mixture to ultra-sonification and magnetic stirring in an iterative manner until a homogeneous solution of polymer – ceramic is obtained; and (90)
casting the homogeneous solution into one or more films on one of a glass slide or a metal sheet and baking casted homogeneous solution at a pre-defined temperature for obtaining the polymer- ceramic nano composite film, wherein the polymer – ceramic nano composite film corresponds to polyvinylidene fluoride (PVDF) - Bismuth ferrite (BFO). (100)
2. The method (10) as claimed in claim 1, wherein mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)) for a pre-defined amount of time comprises mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)) for about 45 minutes at about 25 degrees Celsius.
3. The method (10) as claimed in claim 1, wherein mixing the pre-defined amount Sodium Hydroxide (NaOH) (Sigma Aldrich) solution comprises mixing about 20-100 g/mL W/V% of the Sodium Hydroxide (NaOH) in a weight volume ration.
4. The method (10) as claimed in claim 1, wherein obtaining powder in the pure phase comprises obtaining the powder in one of an α-phase or a β-phase.
5. The method (10) as claimed in claim 1, wherein varying weight percentage comprises varying weight percentage between 0 -6wt.% of BFO.
6. The method (10) as claimed in claim 1, wherein casting the homogeneous solution comprises casting the homogeneous solution using a conventional doctor blade technique.
7. The method (10) as claimed in claim 1, wherein one or more casted films work on a principle of piezoelectric effect, wherein the one or more casted films is configured to detect pressure flow.
8. The method (10) as claimed in claim 6, wherein the one or more casted films is configured to generate electricity due to one or more detected vibrations due to gas flow.
9. The method (10) as claimed in claim 1, wherein baking casted homogeneous solution at the pre-defined temperature for obtaining the polymer- ceramic nano composite film comprises baking casted homogeneous solution at about 60 degrees Celsius for obtaining the polymer- ceramic nano composite film.

Dated this 29th day of July 2021

Signature

Harish Naidu
Patent Agent (IN/PA-2896)
Agent for the Applicant
, Description:FIELD OF INVENTION
Embodiments of the present disclosure relates to nano composite films, and more particularly, to a method for preparing a polymer - ceramic nano composite film.
BACKGROUND
In recent years organic ferroelectric polymers have received major attention due to their application in various fields such as sensors, actuators, energy harvesters, biomedical devices and other applications. One of the limitations of ferroelectric polymer in their low piezoelectric coefficient (d33) in comparison to ceramics. There are ample studies on enhancing the β-phase of PVDF, one of such method is by adding nanofillers or composites. Nanofillers play a crucial role in the improvement and alteration of properties of polymer and/or polymer blend.
Also, a ceramic compound BFO, the ferroelectricity in BFO is primarily due to the stereo-chemically-active 6s2 lone pair of Bi3+. However, there are device related drawbacks for BFO such as high leakage current, a tendency to fatigue, and thermal decomposition near the coercive field. There have been attempts to address these issues by doping BFO with various materials. Due the exceptional ferroelectric properties, multiferroic nature, and its lead-free character, BFO remains a potential candidate for multifunctional device applications.
Therefore, there is a need in the art to prepare a polymer - ceramic nano composite film using polyvinylidene fluoride (PVDF) - Bismuth ferrite (BFO) particles.
Hence, there is a need for an improved method for preparing a polymer - ceramic nano composite film to address the aforementioned issues.
BRIEF DESCRIPTION
In accordance with the present disclosure, a method for preparing a polymer - ceramic nano composite film is provided. The method includes mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)) in a pre-defined ratio, in a magnetic stirrer upon adding distilled water, for a pre-defined amount of time. The method also includes mixing a pre-defined amount of concentrated nitric acid (HNO3) for obtaining a mixture solution. The method also includes mixing a pre-defined amount Sodium Hydroxide (NaOH) (Sigma Aldrich) solution to the obtained mixture solution for preventing agglomeration for obtaining a final mixture. The method also includes drying the obtained final mixture at about 60 degrees Celsius for about two hours for obtaining fine brown powder. The method also includes grinding calcined powder upon subjecting the obtained fine brown powder for calcination process at about 650 degrees Celsius, for obtaining powder in a pure phase. The method also includes segregating Bismuth ferrite (BFO) ceramic nano particles with varying weight percentage and N-Methyl-2-pyrrolidone (NMP) solvent from the obtained powder for subjecting segregated particles to ultra-sonification.
Furthermore, the method also includes adding polyvinylidene fluoride (PVDF) polymer powder to the Bismuth ferrite (BFO) nano particles in a magnetic stirrer for obtaining a mixture. The method also includes subjecting the mixture to ultra-sonification and magnetic stirring in an iterative manner until a homogeneous solution of polymer – ceramic is obtained. The method also includes casting the homogeneous solution into one or more films on one of a glass slide or a metal sheet and baking casted homogeneous solution at a pre-defined temperature for obtaining the polymer- ceramic nano composite film, wherein the polymer – ceramic nano composite film corresponds to polyvinylidene fluoride (PVDF) - Bismuth ferrite (BFO). Furthermore, the method includes subjecting the films for annealing at pre-defined which is about 90-degree Celsius temperature to attain desired β phase of PVDF.
To further clarify the advantages and features of the present disclosure, a more particular description of the disclosure will follow by reference to specific embodiments thereof, which are illustrated in the appended figures. It is to be appreciated that these figures depict only typical embodiments of the disclosure and are therefore not to be considered limiting in scope. The disclosure will be described and explained with additional specificity and detail with the appended figures.
BRIEF DESCRIPTION OF DRAWINGS
The disclosure will be described and explained with additional specificity and detail with the accompanying figures in which:
FIGs. 1a and 1b are flow chart representing steps involved in a method for preparing a polymer - ceramic nano composite film in accordance with an embodiment of the present disclosure;
FIG. 2a is a graphical representation of an exemplary embodiment of an X-ray diffraction pattern of PVDF-BFO thin film of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure;
FIG. 2b is a graphical representation of an exemplary embodiment of Raman spectra of 0 and 2 weight percentage PVDF-BFO composite thin film of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure;
FIG. 2c is a graphical representation of an exemplary embodiment of FTIR spectra of 0, 2, 4wt.% PVDF/BFO composite film of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure;
FIGs. 3a-3e are graphical representation of an exemplary embodiment representing PFM images of PVDF-BFO samples Morphology, In-Plane (IP) Amplitude, In-Plane Phase, Out-of-Plane (OP) Amplitude and Out-of-Plane Phase (IP) respectively of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure; and
FIGs. 4a-4b are graphical representation of an exemplary embodiment representing Piezoelectric coefficient from sample with various BFO weight percentage and Output voltage for 0, 2, 4, 6 wt.% PVDF-BFO nano composites based energy harvester respectively of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure.
Further, those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figures may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the figures with details that will be readily apparent to those skilled in the art having the benefit of the description herein.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the figures and specific language will be used to describe them. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as would normally occur to those skilled in the art are to be construed as being within the scope of the present invention.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such a process or method. Similarly, one or more devices or sub-systems or elements or structures or components preceded by "comprises... a" does not, without more constraints, preclude the existence of other devices, sub-systems, elements, structures, components, additional devices, additional sub-systems, additional elements, additional structures or additional components. Appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but not necessarily do, all refer to the same embodiment.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. The system, methods, and examples provided herein are only illustrative and not intended to be limiting.
Embodiments of the present disclosure relates to method for preparing a polymer - ceramic nano composite film. As used herein, polymer is a substance which has a molecular structure built up chiefly or completely from a large number of similar units bonded together. Also, the term ceramic is any non-metallic solid which remains hard when heated.
FIGs. 1a and 1b are flow chart representing steps involved in a method (10) for preparing a ceramic and polymer - ceramic nano composite film in accordance with an embodiment of the present disclosure. The method includes mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)) in a pre-defined ratio, in a magnetic stirrer upon adding distilled water, for a pre-defined amount of time in step 20. In one embodiment, the pre-defined ration may be 1: 1. In one exemplary embodiment, mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)) for a pre-defined amount of time may include mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)) for about 45 minutes at about 25 degrees Celsius.
The method (10) also includes mixing a pre-defined amount of concentrated nitric acid (HNO3) for obtaining a mixture solution in step 30. The method (10) further includes mixing a pre-defined amount Sodium Hydroxide (NaOH) (Sigma Aldrich) solution to the obtained mixture solution for preventing agglomeration for obtaining a final mixture in step 40. In one specific embodiment, the pre-defined amount of concentrated nitric acid (HNO3) depends on nature of the solution obtained upon mixing Bismuth Nitrate (Bi (NO3)) and Iron Nitrate (Fe (NO3)). In one exemplary embodiment, mixing the pre-defined amount Sodium Hydroxide (NaOH) (Sigma Aldrich) solution may include mixing about 20-100 g/mL W/V% of the Sodium Hydroxide (NaOH) in a weight volume ratio.
Furthermore, the method (10) includes drying the obtained final mixture at about 60 degrees Celsius for about two hours for obtaining fine brown powder in step 50. The method (10) also includes grinding calcined powder upon subjecting the obtained fine brown powder for calcination process at about 650 degrees Celsius, for obtaining powder in a pure phase in step 60.
The method (10) also includes segregating Bismuth ferrite (BFO) ceramic nano particles with varying weight percentage and N-Methyl-2-pyrrolidone (NMP) solvent from the obtained powder for subjecting segregated particles to ultra-sonification in step 70. In one embodiment, varying weight percentage may include varying weight percentage between 0 -6wt.% of BFO.
The method (10) also includes adding polyvinylidene fluoride (PVDF) polymer powder to the Bismuth ferrite (BFO) nano particles in a magnetic stirrer for obtaining a mixture in step 80. Furthermore, the method (10) includes subjecting the mixture to ultra-sonification and magnetic stirring in an iterative manner until a homogeneous solution of polymer – ceramic is obtained.
The method (10) also includes casting the homogeneous solution into one or more films on one of a glass slide or a metal sheet and baking casted homogeneous solution at a pre-defined temperature for obtaining the polymer- ceramic nano composite film in step 100. The polymer – ceramic nano composite film corresponds to polyvinylidene fluoride (PVDF) - Bismuth ferrite (BFO). In one embodiment, casting the homogeneous solution may include casting the homogeneous solution using a conventional doctor blade technique. In such embodiment, each of the one or more casted films work on a principle of piezoelectric effect, wherein the one or more casted films is configured to detect one or more vibrations associated to pressure flow. In one exemplary embodiment, Pressure flow of argon gas may be achieved at pressure of about 50kPa and above. Further, the one or more casted films is configured to generate electricity due to one or more detected vibrations. In one embodiment, baking casted homogeneous solution at the pre-defined temperature for obtaining the polymer- ceramic nano composite film may include baking casted homogeneous solution at about 60 degrees Celsius for obtaining the polymer- ceramic nano composite film. Furthermore, the films are annealed at 90 degrees Celsius to obtain the required β phase.

EXPERIMENTAL RESULTS
Referring to FIGs. 2a-2c, FIG. 2a is a graphical representation (110) of an exemplary embodiment of an X-ray diffraction pattern of PVDF-BFO thin film of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure. The FIG. 2a (110) represents the X-ray diffraction pattern of PVDF-BFO thin film of 0, 2 weight percentage synthesized from a precursor solution. The graph (110) is obtain by plotting the reading having degree along X-axis. The peak at 2θ = 20·2° for pure PVDF films (0 wt.%) and peak at 2θ = 20.6° for 2 wt.%. PVDF-BFO film, which is relative to the sum of diffraction from the plane points 200 and 110 confirms the dominant presence of β-phase, however fractions of  phase was also detected in pure PVDF films, which disappears with introduction of BFO content above 2wt.%. Further, the presence of peaks for PVDF-BFO films at 2θ = 22.3° correspond to a plane point 012 and split peak at 2θ = 32° corresponds to plane points 104 and 110, confirming rhombohedral distorted perovskite structure of BFO. The addition of BFO filler at 2wt.% enhances the peak intensity of β-phase with respect to pure PVDF, however higher percentage of PVDF-BFO leads to reduction of β-phase peak and thereafter disappearance of the peak.
FIG. 2b is a graphical representation (120) of an exemplary embodiment of Raman spectra of 0 and 2 weight percentage PVDF-BFO composite thin film of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure. The Raman spectra is dominated by a band at 839 cm–1. The high intensity peak at 839cm–1 confirms the high percentage β-phase for all PVDF-BFO annealed films. The Raman bands at 812 cm-1, 1426 cm-1 corresponds to γ phase, α phase and the peak at 882 cm-1 corresponds to the mixed phase of PVDF. The overall piezoelectric phase enhances due to addition of BFO fillers can be observed, however as the filler content exceeds 6 wt.% the α-phase becomes more prominent and β, γ-phase reduces. The inset represents graph for phase fraction of β to γ and β to α which shows that with PVDF-BFO films with 2 wt.% exhibit highest value in both the phase fraction ratios.
FIG. 2c is a graphical representation (130) of an exemplary embodiment of FTIR spectra of 0, 2, 4wt.% PVDF-BFO composite film of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure. The peak at 875cm-1 and 1400cm-1 represents the β phase and α phase respectively, Whereas the peaks at 833cm-1 and 1232cm-1 confirm the presence of γ phase. The presence of peaks at 1067 cm-1 and 1167 cm-1 indicates mixed phases. The solution casting method often gives rise to mixed phases and also agglomeration of BFO nanoparticles, which is evident from the experimental results. Based on above results it can be concluded that the composite film with 2wt.% possessed a predominant β-phase whereas, further increment of BFO content reduces the β-phase of PVDF.
The PFM studies of the ferroelectrics include domain imaging, polarization switching and various other local spectroscopic studies. In PFM, a ferroelectric sample is placed between a bottom electrode and a PFM tip, which act as a top electrode during the measurements. Measurements may be carried out in the contact mode to gather surface response information normal and parallel to the film plane. The PFM scan gives the information regarding morphology, amplitude and phase which corresponds to topography, piezoelectric coefficient (d33) and the orientations of the polarization field relative to one or more plane of the corresponding one or more films.
Turning to FIGs. 3a-3e which are graphical representation of an exemplary embodiment representing PFM images of PVDF-BFO samples Morphology (140), In-Plane (IP) Amplitude (150), In-Plane Phase (160), Out-of-Plane (OP) Amplitude (170) and Out-of-Plane Phase (IP) (180) respectively of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure. BFO nanoparticle and PVDF as the intermediate region between them from the morphology image shown in FIG. 3a. The FIG. 3c represents the presence of dominant IP polarization components in the one or more films. The contrast evidently shows the presence of regions with opposite domain orientations. Similar IP dominant domains were reported for pure PVDF earlier, however domains were arranged in pair of opposite orientation. It is to be noted that a whole region of particle exhibits both the orientation of ferroelectric domain which can be attributed to agglomeration of several nanoparticles with different orientation. The polymer region which is in between the particles also showed presence of domain. It can be concluded that BFO particle helps in nucleating piezoelectric phase thus enhancing the crystallinity of the sample. This can be attributed to the enhancement of stiffness on addition of BFO particle. It is plausible that two individual or agglomerated BFO particles separated by polymer induces electrostatic field. This field might cause the polymer chains to orient themselves to attain crystalline piezoelectric phases. It is known in polymer’s that increase in the crystallinity leads to enhancement in Young’s modulus as a result stiffness of the sample increases. We also observe OP polarization component from the sample which indicate that BFO helps in enhancement of OP ferroelectric domains, however the IP polarization is more dominant than OP polarization.
FIGs. 4a-4b are graphical representation of an exemplary embodiment representing Piezoelectric coefficient from sample with various BFO weight percentage (190) and Output voltage for 0, 2, 4, 6 wt.% PVDF-BFO nano composites-based energy harvester (200) respectively of FIGs. 1a and 1b in accordance with an embodiment of the present disclosure. In FIG. 4b, an inset image (210) represents a schematic representation of the set up for energy harvester and Interdigitated Electrode pattern.
FIG. 4a shows the graph of d33 measured throughout the sample at different locations for films with varying content of BFO. The samples did not show much variation in the d33 but was oscillating between 3.5 to 7.5 pm/V. These variations are likely because of agglomeration of BFO particles. The agglomeration causes them to form particle clusters of various size and as a result the electrostatic force and stiffness effect on the composite varies, therefore resulting in varying d33.
In order to demonstrate the effect of BFO on the overall device performance, a harvester based on the composite film was fabricated. The planar harvester has electrodes over the same surface of the film. The harvesters are tested by subjecting them to gas flow. An inset in the FIG. 4a shows the setup made for measuring the device performance. Interdigitated electrode (IDE) pattern made of silver paste is utilized for harvesters. The harvester is suspended at a distance from the wall. Passing air from the nozzle with 100 kPa of pressure caused displacement of the harvester in the direction of air flow towards the wall. The impact with wall causes device, experience a force and as a result voltage response is observed.
It is noticed that for 0 and 2wt.% PVDF-BFO based harvesters have almost similar output voltage and thereafter it increases. Interestingly, maximum voltage of ~5V was generated by harvester based on 6wt.% PVDF-BFO samples which is suitable to drive a low powered device. This can be attributed to the increase in stiffness of sample due to introduction of BFO filler and making it more sensitive to deformation. It is also observed that the harvester from 0 and 2wt.% were able to resist any pressure below 100 kPa as a result, the required force during its impact with wall is not experienced and hence no piezoelectric response is generated. However, it is noticed that device based on 4 and 6wt.% PVDF-BFO sample, gives response for pressure below 100kPa. Hence, the fabricated device has significant sensitivity to detect minute pressure which can be ~2N of force and generate voltage, therefore can be utilized as micro energy harvester.
Various embodiments of the present disclosure generated an influence of BFO nanofiller on the crystalline phases of PVDF matrix as well as on the device performance. Furthermore, it was found that energy harvesting capability of hybrid composite PVDF-BFO based device is higher than pure PVDF. The addition of BFO filler leads to enhancement of crystallinity which in turn increases the stiffness of the sample. The stiffness improves the sensitivity and voltage generating efficiency of the thin film, thus giving a scope of utilizing it as pressure sensor and micro energy harvester.
While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person skilled in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.
The figures and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, the order of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts need to be necessarily performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples.