Investigations on Structural, Optical and Dielectric properties of Cold Plasma Polymerized Polypyrrole Thin films for Soft Matter Applications

In the current and science & technology, the plasma – assisted polymerization techniques have been distinguished as promising and versatile to prepare polymer films with desired futuristic properties for potential industrial applications. It is noteworthy to mention that, plasma assisted thin film deposition is multi-disciplinary and involves knowledge, methods and approaches from materials science, the physics and chemistry of plasmas and gas discharge to various engineering subjects. Among the various physical vapor thin film deposition techniques, Cold plasma polymerization (CPP) is one of the plasma assisted polymerization technique and relatively simple single-step technique to deposit pinhole free, uniform and conformal organic thin films of conducting polymers consisting novel surface properties with wide functionalities. In the present study, Polypyrrole (PPy) thin films of thickness 250 nm, have been deposited on ITO coated glass substrates by Cold plasma polymerization technique. The micro-structural, optical, surface wetting and dielectric properties of grown PPy films, are investigated as a function of glow power by varying its value in the range 10 – 50 W. The presence of broad X-ray diffraction peak at 2θ = 23.5o reveals the amorphous nature of the films. The FTIR spectra demonstrated characteristic vibrational modes in the wave number regions 3300 – 3400 cm-1 and 1635 – 1700 cm-1, respectively and confirms the growth of Polypyrrole. The intensity of FTIR peaks is noticed to be increased slightly, which reveal the improvement in polymerization and the cross-linking during polymerization due to formation of free radicals by the presence of plasma. The surface morphology of grown films is analyzed by means of Atomic force microscopy (AFM) and observed enhancement of root mean square (rms) surface roughness of prepared samples with the increase of plasma power. Films deposited at lower plasma power of 10 W are demonstrated higher optical band value of 2.97 eV provided with higher refractive index value of 1.478 at the wavelength of 550 nm. The surface wettability studies revealed that, PPy films grown films at higher plasma power of 50 W are demonstrated better surface wetting properties. Dielectric measurements on as deposited PPy thin films were carried out in the frequency range from 1 mHz to 100 kHz in symmetrically aligned cells. Dielectric studies revealed that, films deposited at lower plasma power of 10 W are demonstrated better performance.