Structural, Thermal and Optical Properties of PMMA, PEO and PMMA/PEO/LiClO4 Polymer Electrolyte Blends

This paper is a report of a study conducted on Structural, thermal and optical Properties of pure PMMA, pure PEO and PMMA-PEO-LiClO4 polymer blend electrolyte thin films. These films were prepared using solution casting technique and characterized by X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). XRD analysis Observations confirmed that amorphous, crystalline and semi crystalline nature of pure PMMA, pure PEO and PMMAPEO-LiClO4 polymer blend electrolyte thin films the SEM micrographs suggest that the surface morphology of pure PEO changes from smooth to rough when PMMA and LiClO4 added to PEO polymer, which shows the interaction/ interface between the two polymers and polymer blend electrolyte due to cross – linking. Glass transition (Tg) and melting temperatures (Tm) of pure PMMA, pure PEO and PMMA-PEO-LiClO4 polymer blend electrolyte thin films were confirmed by DSC analysis. FTIR spectra confirmed that complex formation and interaction among PMMA, PEO polymers and LiClO4 salt. Article history Received: 21 October 2017 Accepted: 3 November 2017


introduction
Polymer electrolytes are becoming increasingly important because of their potential use in several electrochemical devices: "smart" windows, displays, sensors, and more importantly, rechargeable solidstate lithium batteries 1 .Most of the polymer blends are immiscible and shows morphological structure.
Themorphology of polymer blends change the final properties of polymers.Over the past few decades, polymers like PEO, PMMA, PAN, PVA, PVDF, etc.. have been widely investigated.Among these, the PEO shows flexible chain structure and considerable conductivity at room temperature.However, low strength and low modulus limit the use of PEO.
PMMA is one of the most widely studied polymer due to it having approximately 96% amorphous content at ambient temperature and also due to its promising mechanical and chemicophysical properties 2 .The polymer blending method is one of the suitable approaches in over coming this limitation.Therefore, instead of using a single polymer, blended PMMA and PEO polymers provides the required valuable properties.In addition to this blend, polymer electrolytes like Na+, Li+, Ag+, Mg+, etc.. also help to increase ionic transport in the blends.Li saltbased systems are most studied because Li+ ion is the most electropositive, which gives up electrons to form a positive Li+ with small ionic radii (0.6Å), which can easily find path for transportation in polymer matrix 3 .In the present study, LiClO 4 salt is added to PMMA and PEO polymer blend to carry out structural, thermal and optical properties.

Materials and Methods
Poly(methyl methacrylate) (PMMA) (M.W~15000), poly(ethylene oxide) PEO(M.W. 2 × 10 5 ) and LiClO 4 salt(purity 96%) were purchased from Sigma Aldrich.The polymer blend thin films were prepared using the solution casting technique.Thin films of pure PMMA and pure PEO were prepared separately using THF (Tetra Hydro Furan) as solvent.Appropriate amount of PMMA, PEO and LiClO 4 salt were separately dissolved together in THF (Tetra Hydro Furan) and stirred by using a magnetic stirrer for 24-36 hours at room temperature.Later obtained homogeneous solution was poured in a glass Petridis and then left to evaporate solvent at room temperature for several days to obtain dried blend films.The obtained films stored in a desiccator to complete dryness before characterization studies.The thickness of dried pure PMMA, pure PEO and polymer electrolyte blend thin films are around 1mm.
The XRD patterns of the polymer thin films were recorded using an X-ray Diffractometer.The diffraction data were taken at room temperature with the Bragg's angles (2θ) varying from 10 to 80 degrees.SEM micrographs of pure PMMA, pure PEO and PMMA/ PEO/LiClO 4 blend films were taken by using the ZEISS instrument.The differential scanning calorimetry (DSC) of the different polymer electrolyte blend thin films were carried out using DSCQ20 instrument.About 12 mg of each sample was heated for the temperature range varying from 0 o C to 200 o C at a heating rate of 10 o C.min -1 .FTIR Spectroscopy measurements of pure PMMA, pure PEO and PMMA/PEO/LiClO 4 blend films were recorded with the help of Spectrophotometer-Series II.adding 10 wt.% of LiClO 4 salt to PMMA+PEO (90:10) blend polymer, surface morphology of electrolyte blend film becomes smooth to rough.This indicates amorphous morphology changes to semi crystalline and which increases ionic conductivity, and depends on the segmental motion of the blended polymers and solvated carrier ions.

FTiR
Infrared spectroscopy has been proven a highly effective means of investigating specific interactions between polymers.This tool can be used to study the mechanism of interpolymer miscibility through the formation of hydrogen bonding both qualitatively and quantitatively 7 .FTIR is also a useful technique to characterize the organic, inorganic and composite materials 8 .FTIR spectra of PMMA, PEO, PMMA+PEO (90:10) and PMMA+PEO+LiClO 4 (90:10:10) blend films are shown in Fig. 3  ) decreases and it is also observed that some peaks disappear, some are shifted towards lower wave number and some new peaks appear in the complexes indicating that there is a complex formation and interaction among PMMA, PEO polymers and LiClO 4 salt.

Conclusions
Amorphous, crystalline and semi crystalline nature of pure PMMA, pure PEO and PMMA-PEO-LiClO 4 polymer blend electrolyte thin films have been confirmed by XRD analysis.The SEM images indicate that the interaction/interface between the polymers and LiClO4 salt due to cross-linking.Glass transition (T g ) and melting temperatures (T m ) of polymer blend electrolyte thin films were confirmed by DSC analysis.FTIR spectra confirmed that complex formation and interaction among PMMA, PEO polymers and LiClO 4 salt.