PVDF-ionic liquid modified clay nanocomposites: Phase changes and shish-kebab structure

•First report on interplay of phase change and molecular orientation in PVDF-ionic liquid modified clay composites.•This is an unprecedented method to produce self reinforced shish kebab structures in PVDF by varying only the alkyl chain length of organic modifier in the clay fillers.•Phase change from α to β increased with alkyl chain length of the filler; 1-alkyl-3-methylimidazolium clay.•99% β-phase in PVDF-1-hexadecyl-3-methylimidazolium modified clay composite with 2% loading.

Crystalline behaviour of PVDF nanocomposite with 1-alkyl-3-methylimidazolium modified montmorillonite clay was analyzed. The phase change from α to β increased with alkyl chain length of the organic modifier in the filler; 1-alkyl-3-methylimidazolium clay and maximum conversion (99%) was observed for PVDF-1-hexadecyl-3-methylimidazolium modified clay composite with 2% loading. The phase conversion was evident from X-ray diffraction, DSC analysis and improved electrical properties. AFM analysis of PVDF-1-butyl-3-methylimidazolium montmorillonite clay composite (PVDF-C4) showed a shish-kebab structure while pristine PVDF and all other composites showed spherulite structures. Computational studies revealed that the extended chain α-phase forms the 'shish', the back bone and folded chain β-phase forms the 'kebab'. This was further supported by the superior mechanical properties for PVDF-C4 composite. Present work shows that introducing ionic liquid modified MMT-clay within the PVDF matrix enables nucleation of electroactive β phase and the presence of equal content of α and β phases can lead to the formation of self reinforced shish-kebab structures in PVDF.

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