Abstract
In this work the role of phase transition of PEO from crystalline to amorphous phases on DC conductivity enhancement in chitosan-based polymer electrolyte was discussed. Silver ion-conducting polymer electrolytes based on chitosan (CS) incorporated with silver nitrate (AgNt) is prepared via solution cast technique. Various amounts of polyethylene oxide (PEO) are added to the CS:AgNt system to prepare blend polymer electrolytes. Ultraviolet-visible (UV-vis) spectrophotometry is used to confirm that the blended samples containing AgNt salt exhibit a broad absorption peak. From optical micrograph images it is apparent that small white specs appear on the surface of the samples. The SEM results clearly show the aggregated silver nanoparticles. The enlargement of the crystalline area was observed from the morphological emergence and impedance plots. The phase separation in SEM images was observed at high PEO concentration. The XRD consequences support the morphological manifestation. In this study a new approach is offered to explore the microstructures existing in the blend electrolytes. The width of the semicircle linked to crystalline phase in impedance spectra was found to be increased with the increase of PEO concentration. A slow increase of DC conductivity was observed at low temperatures while above 333 K an immediate change in DC conductivity was obtained. The rapid rise of DC conductivity at high temperatures is correlated with the DSC results and impedance studies at high temperatures.
Highlights
Silver ions to silver particles and complexation[12]
The result was further supported by optical microscopy (OM), scanning electron micrograph (SEM) and EDX analysis
The spherulites observed in OM micrographs and phase divisions emerged in SEM images are ascribed to crystalline phases of polyethylene oxide (PEO) polymer
Summary
Silver ions to silver particles and complexation[12]. In our previous works we observed that chitosan incorporated with silver salts exhibits an almost amorphous phase[7,11]. One of the most promising alternate choices of enhancing the amorphous phase and increase of ionic conductivity in PEO based electrolyte systems is blending of PEO with a suitable higher amorphous polymer[19,20]. The melting temperature (Tm) is the temperature at which transformation of phase takes place in PEO based electrolytes and a steep increase of ionic conductivity may be observed from the plots of DC conductivity versus 1000/T. In former studies, a rapid increase of DC conductivity over 60 °C in PEO based solid polymer electrolytes has not been observed[23,26,27,28,29]. An obvious increase of crystalline phase as a consequence of an increase of various amounts of PEO to CS-based electrolyte has predicted from the impedance plots. To support the electrochemical impedance results and sudden increase in DC conductivity, various techniques, such as UV-vis, OM, SEM, XRD and DSC, were used
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