Role of ionic liquid [BMIMPF6] in modifying the crystallization kinetics behavior of the polymer electrolyte PEO-LiClO4

Abstract

We report on the modification in crystallization kinetics behavior of PEO + 10 wt% LiClO₄ polymer electrolyte by the addition of an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆). Three techniques have been used for studying crystallization kinetics, viz., (i) isothermal crystallization technique using DSC, (ii) non-isothermal crystallization technique using DSC, and (iii) by monitoring the growth of spherulites with time in the polymer electrolyte films using a polarizing optical microscope (POM). Results from all the three techniques show that the presence of ionic liquid BMIMPF₆ suppresses the crystallization rate due to its plasticization effect. Isothermal crystallization data was well described by the Avrami equation, and Avrami exponent n lies in the range of 1 to 2, which signifies 2D crystal growth geometry occurring in these polymer electrolytes under the investigated temperature range. However, the Avrami crystallization rate constant ‘K’ increases exponentially with crystallization temperature and ionic liquid content as well. However, the non-isothermal crystallization kinetics of these polymer electrolytes is discussed in terms of three different models (Jeziorny's, Ozawa's and Mo's method), and it is found that Mo's method better explains the non-isothermal crystallization data. In addition, crystalline morphology and spherulite growth were studied by POM, which shows the suppression in crystallization in the presence of ionic liquid, as confirmed by spherulite growth rate (G_s) analysis.