Effect of TiO2 nano particles on Structural and Optical Properties of Poly Pyrrole - Poly Vinyl Alcohol Polymer Blend Thin Films

Introduction

Conducting polymers, Polymer blends, and their nano composites have become very popular in the recent past due to their exceptional properties which are not exhibited by individual constituents present in them ^1-11. Review of research literature shows that they find numerous applications in electronics, photonics, biotechnology, bio-medical sciences, aerospace, food industry ^12-16. PPY has extended conjugation of delocalized π- electrons, highly mobile charge carriers, across the polymer chains. PPY has wide range of applications in rechargeable batteries, sensors, anticorrosive coatings, actuators, light emitting diodes, supercapacitors, etc., ^17-25 due to its several noted chemical, and electrochemical properties. Poly (vinyl alcohol) (PVA) is an ecological synthetic polymer, grabbed distinct attention because of its high transparency, flexibility, anti-electrostatic, luster, chemical resistance, and wide commercial availability. Polymer blends of conducting PPY, PVA have drawn the attention of researchers, and motivated them to take up the research study on effect of dopants on physical, mechanical, and conducting characteristics due to their various applications in electric nanodevices ^{26 – 31}. The properties of PPY, and its composites can be easily modified suitably to requirement of desired applications by varying size, shape, and distribution of dopant particles. TiO₂ nano particles show large surface area to volume ratio, that can significantly enhance the sensors sensing property and response time ³². Motivated by the remarkable features of PPY-PVA polymer blends as multifunctional composite thin film with suitable conductivities and superior physical properties, the authors taken up this work to study the pure PVA-PPY blend, and effect of TiO₂ nano powder as a dopant on PVA-PPY blend composites.

Experimental

Materials

Poly Vinyl Alcohol (Degree of polymerization 1700-1800), FeCl₃ & Acetone were purchased from Research lab Fine Chem Industries, Mumbai. 99.9% of pure Pyrrole monomer and TiO₂ nano powder were purchased from Sigma Aldrich Laboratory. In this study, the authors have adopted in-situ chemical oxidative polymerization method ^33-34 to synthesize composite thin films of poly pyrrole (PPY) – poly viny alcohol (PVA), and PPY – PVA blends doped with TiO₂ nano powder.

Preparation of thin films

Pyrrole solution (aqueous) was obtained by dissolving 0.85 mL in 25 mL of distilled water taken a in a beaker under constant stirring for about two hours at room temperature. The obtained aqueous solution of Pyrrole and 20 mL of already prepared 4% PVA solution were mixed thoroughly under constant stirring for 4 hours. The drop wise addition of freshly prepared aqueous solution of FeCl₃ (about 2 gr/25 mL of distilled water) to the above reaction mixture by thorough mixing for 4 hours yielded a black colored solution of PPY-PVA, and a thin film was obtained upon drying the yielded solution. About 10 mg of TiO₂ nano powder is mixed with Pyrrole aqueous solution prepared as shown in the above step, and stirred it for about two hours followed by the addition of 20 mL of PVA solution under constant stirring for about two hours. Freshly FeCl₃ solution was added drop wise to the above reaction mixture by thorough mixing. Thin film of PPY-PVA-TiO₂ black in color was obtained after evaporating excess water. Set of different films were prepared by the same procedure by varying concentration (like 20 mg, 30 mg, and 40 mg) of TiO₂. All the films prepared were analyzed by UV, XRD, SEM, and FTIR techniques.

Results and Discussion

Structural Studies

XRD is a promising technique which reveals the information of materials to understand their structural properties such as size, nature, etc. The films of PPY-PVA, and PPY-PVA-TiO₂ were characterized by XRD in the range of 10⁰-60⁰. XRD spectra (Fig.1(a)) of PPY-PVA thin film shows that the increase in the broadness and decrease in the strength of peaks might be attributed to its amorphous nature of thin films.

Figure 1: XRD spectra of (a) PPY-PVA, (b) PPY-PVA-10 mg TiO2, (c) PPY-PVA-20 mg TiO2 , (d) PPY-PVA- 30 mg TiO2, (e) PPY-PVA-40 mg TiO2 Click here to View figure

XRD results (Fig.1 (b), (c)) of PPY-PVA films doped with TiO₂ showed significant change in structure of composite thin films which could be due to the TiO₂ nano particle dispersion in PPY-PVA polymer blend matrix. It was also observed that, as % TiO₂ dopant increased in the polymer matrix the peak intensity was also increased which might be due to lack of lattice disorder and stress of high amount of TiO₂ dopant. The sharp peaks (Fig.1 (d), (e)) appeared in the XRD spectra of PPY-PVA-TiO₂ at higher concentration of dopant could be due to crystalline nature of the composite thin films. It also was observed that peaks have been shifted slightly towards higher angle of diffraction.

Morphological Studies

SEM is an effective technique that provides high-resolution images which revels morphology of surface of the materials.  SEM image (Fig. 2(a)) of PPY-PVA revealed that the surface of film was very smooth and good miscibility of polymers PPY and PVA. The Pyrrole monomer was dispersed uniformly in PVA polymer matrix, and PVA is purely responsible for improved order and reduction in agglomeration of PPY which strongly affects morphology of PPY-PVA thin film. Due to large surface of TiO₂ doped nano composite films may promote adsorption of gasses.

Figure 2: SEM Images Of (A) PPY-PVA, (B) PPY-PVA-10 Mg Tio2 , (C) PPY-PVA-20 Mg Tio2, (D) PPY-PVA-30 Mg Tio2 , (E) PPY-PVA-40 Mg Tio2 Click here to View figure

FITR

One of the best techniques to identify the functional groups present in a sample is FTIR spectroscopy. The thin films of PPY-PVA and nano TiO₂ doped PPY-PVA were characterized by FTIR technique. 

Figure 3: FTIR spectra of (a) PPY-PVA, (b) PPY-PVA10 mg TiO2, (c) PPY-PVA-20 mg TiO2 , (d) PPY-PVA-30 mg TiO2, (e) PPY-PVA-40 mg TiO2 Click here to View figure

IR spectra (fig.3 (a)) of PPY-PVA and the broad peaks appeared in the range of 3350 – 3240 cm^-1, around 1050 cm^-1 are attributed to O-H and N-H stretching, and C-H and N-H in-plane deformation in PVA and PPY respectively. The peaks between 1626-1628 cm^-1 may be attributed to functional groups to C=O stretching frequency of PVA in PPY-PVA polymer thin film. The slight shift in wavenumber higher side has been observed at around 1640 cm^-1 which may be due to the addition TiO₂ nano powder to PPY-PVA thin films. The peaks (fig.3. (a-c)) which were observed between 1000 -800 cm^-1 in PPY-PVA thin films almost disappeared in case of PPY -PVA -TiO₂ (fig 3. (c-d)) which might be due to interactions of TiO₂ at moderate to high concentration with PPY-PVA thin films.

UV studies

Electronic spectroscopy is one of the significant spectroscopic techniques used to determine optical constants i.e., transmittance, absorbance, and reflectance of polymer films. Table-1 shows direct optical energy band gap values of PPY-PVA and nano TiO₂ embedded composite thin films which were calculated by plotting (αhʋ)² verses (hʋ). The decrease in the direct optical energy band gap obtained may indicate role of the dopant in PPY-PVA blend polymer matrix. The increase in concentration of TiO₂ dopant causes formation of crystal imperfections which involves modification of electronic energy states and overlap of electronic energy bands in composite thin films. Concentration TiO₂ nano particles found to proportional the population density of localized energy states ³⁵. The decreasing order of optical energy band gap values as the concentration of TiO₂ nano particles in PPY -PVA thin films suggest increase in conductivity levels.

Table 1: Energy band gap values of PPY-PVA and PPY-PVA-TiO₂ thin films.

Sample name	Concertation of TiO2	Direct optical band gap in eV
PPY-PVA	0	2.92
PPY-PVA-TiO2	10 mg	2.01
PPY-PVA-TiO2	20 mg	1.72
PPY-PVA-TiO2	30 mg	1.65
PPY-PVA-TiO2	40 mg	1.61

 

Figure 4: UV plots of PPY-PVA and nano TiO2 embedded PPY-PVA composite films. Click here to View figure

Conclusion

The authors adopted oxidative chemical polymerization (in-situ) technique to synthesize Poly Pyrrole-Poly Vinyl Alcohol and Poly Pyrrole-Poly Vinyl Alcohol -TiO₂ thin films, and the obtained samples (thin films) were analyzed by UV, SEM, XRD, and FTIR techniques. XRD studies suggest that increase in crystalline nature of PPY-PVA-TiO₂, as the concentration of TiO₂ nano particle increases. FTIR spectra of thin films shows that slight shift in wave number towards higher side, and almost disappearance of some peaks which supports the interactions between PPY-PVA with TiO₂ at moderate to high concentration. SEM results are evident that morphology of composite thin films have been modified significantly by the addition of TiO₂ dopant besides that it has also been observed the presence of pores in surface of composite thin films which may be suitable for detection leakage of certain gasses. The decrease in direct optical energy band gaps with increase in concentration of TiO₂ nano particles might suggest overlapping of electronic energy states in composite thin films and which indirectly hint the increase in conductivity levels of Poly Pyrrole-Poly Vinyl Alcohol -TiO₂ thin films. The Poly Pyrrole-Poly Vinyl Alcohol doped thin films have wide applications as electronic nano devices besides they may also be used as gas Sensors.

Acknowledgement

The authors acknowledged that principal, management of Maturi Venkata Subba Rao Engineering college and Head and BOS of Physics, Osmania University.

Conflicts of Interest

The authors declare that no conflict of interest.

Funding Sources

There is no funding source.

References

1. Sengwa, R. J.; Dhatarwal, P. J. Mater. Sci.: Mater. Electron. 2021, 13, 1.
2. Gahlout, P.; Choudhary, V. Synth. Metals. 2020, 266, 116414.
   CrossRef
3. Ramesan,M. T,; Greeshma, K. P,; Parvathi, K,; Anilkumar, T,. J. Vinyl Addit. Technol. 2020. 26, 187.
   CrossRef
4. Shanthala, V. S.; Shobha Devi, S. N.; Murugendrappa, M. V. Asian Ceram. Soc. 2017. 5, 227.
   CrossRef
5. Ramesan, M. T.; Jayakrishnan, P.; Anilkumar, T.; Mathew, G. J. Mater. Sci.: Mater. Electron.2018. 29. 1992.
   CrossRef
6. Ramesan, M. T.; Athira, V. K,;Jayakrishnan, P.; Gopinathan, C. J. Appl. Polym. Sci.2016. 133. 11.
   CrossRef
7. Yassin, A. Y.  J. Mater. Sci.: Mater. Electron.2020. 31, 19447.
   CrossRef
8.  Rajesh, K.; Crasta, V.; Rithin Kumar, N. B.; Shetty, G.; Rekha, P. D. J. Polym. Res.2019. 26. 1.
   CrossRef
9. Mohammed, Gh.; El Sayed, A. M.; Morsi, W. M. J. Phys. Chem. Solids.2018. 115. 238.
   CrossRef
10. Deshmukh, K.; Ahamed, M. B.; Polu, A. R.; Sadasivuni, K. K.; Pasha, S. K. K.; Ponnamma, D.; Al-Ali AlMaadeed, M.; Deshmukh, R. R.; Chidambaram, K. J. Mater. Sci.: Mater. Electron.2016. 27. 11410.
    CrossRef
11. Rajeswari, N.; Selvasekarapandian, S.; Sanjeeviraja, C.; Kawamura, J.; Asath Bahadur, S.  Polym. Bull.2014. 71. 1061.
    CrossRef
12. Shanthi, B.; Muruganand, S. Inter J SciEngAppl Sci. 2015. 1. 1105.
13.  El-Houssiny, A. S.; Ward, A. A. M.; Mansour, S. H.; AbdEl-Messieh, S. L. J. Appl. Polym. Sci.2012. 124. 3879.
    CrossRef
14. Choudhary, S.; Sengwa, R. J. Curr. Appl. Phys.2018. 18. 1041.
    CrossRef
15. Choudhary, S. J. Mater. Sci.: Mater. Electron.2018. 29. 10517.
    CrossRef
16. SushmaJha, ; VaishaliBhavsar, K. P.;  Sooraj, ; MukeshRanjan,; DeeptiTripathi. Adv. Dielect. 2021. 11. 2150020.
    CrossRef
17. Basavaraja, C.; Kim, E. A. Jo. B. S.;   Kim, D. G.; Huh, D. S. Macromolecular Research.2010. 11. 1037- 1044.
    CrossRef
18. Vernitskaya, T. V.; Efimov, O. N. Russian Chemical Reviews. 1997. 66 (5). 443-457.
    CrossRef
19. Bai, H.; Shi, G. Sensors.2007. 7(3). 267-307.
    CrossRef
20. Miasik, J. J.; Hooper, A.; Tofield, B. C. J. Chem. Soc., Faraday Trans.,1986. 82.  1117–1126.
    CrossRef
21. Hutchison, A. S.; Lewis, T. W.; Moulton, S. E.; Spinks, G. M.; Wallace, G. G. Synthetic Metals.2006. 113(1-2). 121–127.
    CrossRef
22. Annibaldi, V.; Rooney, A. D.; Breslin, C. B. Corrosion Science. 2012. 59. 179–185.
    CrossRef
23. Jurewicz, K.; Delpeux, S.; Bertagna, V.; Béguin, F.; Frackowiak, E. Chemical Physics Letters. 2001. 347(1-3). 36–40.
    CrossRef
24. Pomposo, J. A.; Rodrıguez, J.; Grande, H. Synthetic Metals. 1999. 104. 107–111.
    CrossRef
25. Nerkar, D. M.; et al. IJSRR. 2018. 7(1). 136-147.
    CrossRef
26. Adnan, R.; Razana, N. A.; Rahman, I. A.; Farrukh, M. A. J. Chin. Chem. Soc.  2010. 57. 222–2292.
    CrossRef
27. Zhu, J.; Tay, B.; Ma, Y. J. Mater. Lett.2006. 60. 1003.
    CrossRef
28. Peaker, A. R.; Horsley, B. Rev. Sci. Instrum.1971. 42. 1825–1827.
    CrossRef
29. Kumar, D. S.; Carbarrocas, P. R.; Siefert, J. M. Appl. Phys. Lett. 1989. 54. 2088.
    CrossRef
30. Pan, J.; Shen, H.; Mathur, S. J. Nanotechnol. 2012. 12. 12.
    CrossRef
31. Husain, J.; Reddy, N.; Anjum, R. Materials Today: Proceedings. https://doi.org/10.1016/j.matpr.2020.07.630.
    CrossRef
32. Ferreira, H. S.; Rangel, M. C. Quím. Nova, 2009, 32, 1860.
    CrossRef
33. Jyoti Srivastava,;Pawan Kumar Khanna,; Priyesh, V.; More Neha Singh. Advanced Materials Letters. 2017. 8(1). 42- 48.
    CrossRef
34. Manammel,;Thankappan,; Ramesan. Polymer-Plastics Technology and Engineering. 2012. 51. 1223–1229.
    CrossRef
35. Elkomy, G. M.; Mousa, S. M.; Abo Mostafa, H. Arabian Journal of Chemistry, 2016, 9, 786-792.
    CrossRef

---

This work is licensed under a Creative Commons Attribution 4.0 International License.