Structural Design And Properties Of Polyvinylidene Fluoride/Ionic Liquid/Nanomontmorillonite Composites

In the past two decades,montmorillonite(MMT)modified polyvinylidene fluoride(PVDF)nanocomposites have been widely studied.The research of PVDF/Na⁺MMT nanocomposites mainly focused on crystallization characteristics,electrical activity,energy storage,transparency,mechanical properties and so on.In order to obtain excellent properties,the effective stripping and uniform dispersion of montmorillonite in PVDF matrix is very important for PVDF nanocomposites.Because MMT is hydrophilic and PVDF is hydrophobic,it is necessary to prepare organic montmorillonite(OMMT)by organic modification to increase its affinity with PVDF,so that OMMT has a good intercalation/exfoliation morphology in PVDF matrix.In the previous work,it was found that the synergistic effect of ionic liquid(IL)and Na⁺MMT could improve the dispersion of Na⁺MMT in the matrix and improve the dielectric,mechanical and thermodynamic properties of PVDF.Therefore,taking PVDF as the matrix and Na⁺-MMT as inorganic nano materials,this paper uses ionic liquids with different properties to regulate the modification effect of Na⁺MMT on PVDF,and explores the effects of different IL on PVDF crystal transformation,thermodynamic properties,dielectric properties,energy storage properties,light transmittance and mechanical properties:(1)The mass fraction of Na⁺MMT was fixed at 1wt%,the anion of ionic liquid was fixed as[Cl]ion,and the molar mass fraction of IL was changed.The effects of imidazole IL with different cationic chain length on PVDF composites were studied.The effect of IL with different cationic chain length on the crystal transformation of PVDF was studied by FTIR and XDR.The results showed that the crystal transformation of PVDF occurred when the contents of[C₄MIM][Cl]and[C₈MIM][Cl]were both 0.12%;When[C₁₂MIM][Cl]and[C₁₆MIM][Cl]were both at 0.05%,PVDF had a complete conversion from non-polar crystal to polar crystal,so as to achieve the effect of"low content,high conversion",indicating that the IL of long cation chain is conducive to promoting the crystal form conversion of PVDF.In melt blending,IL and Na⁺MMT will exchange ions,and the cations of IL are fixed on the Na⁺MMT sheet.The stripped Na⁺MMT sheet increases the barrier of electric field,reduces the dielectric loss and leakage current,and increases the dielectric and energy storage properties.NC-IL16-0.1%has the highest discharge energy density,reaching 5.17 Jcm^-3.(2)The mass fraction of Na⁺-MMT was fixed at 1wt%,and the ionic liquid cation was fixed as[C₁₆MIM]ion.The molar mass fraction of IL was changed to explore the effect of imidazole IL with different anions on PVDF composites.The results showed that IL with large anion was conducive to the improvement of Na⁺MMT stripping,crystallinity,mechanics,dielectric and energy storage properties.The size of IL anion had little effect on the crystal form transformation of PVDF,but the crystallinity of PVDF modified by IL with large anion volume was relatively high.At the same time,the mechanical properties of PVDF/IL/Na⁺MMT composites were significantly increased because of the long chain length,large flexibility and increased plasticization of IL.The ionic properties of ILs could improve the conductivity of nanocomposites,resulting in the increase of dielectric loss and leakage current.The ionic liquid with larger anion volume behaved weaker migration ability of IL and lower dielectric loss,which was conducive to improve the energy storage of PVDF.