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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