This review summarizes the current state of polymer composites used as dielectric materials for energy storage. The particular focus is on materials: polymers serving as the matrix, inorganic fillers used to increase the effective dielectric constant, and various recent investigations of functionalization of metal oxide fillers to improve compatibility with polymers. We review the recent literature focused on the dielectric characterization of composites, specifically the measurement of dielectric permittivity and breakdown field strength. Special attention is given to the analysis of the energy density of polymer composite materials and how the functionalization of the inorganic filler affects the energy density of polymer composite dielectric materials.
We report the preparation of new polymer composite dielectric materials for energy storage applications. New layered 1:1 mixed A+2/Ti4+ metal phenylphosphonates, ATi(O3PC6H5)3, A=Mg, Ca, Sr, Ba, and Pb, have been prepared via a melt route, in which mixed metal oxides, ATiO3, were reacted with molten phenyl phosphonic acid. The mixed-metal phosphonates were combined with polystyrene (PS) via a solution route and cast as thin films for dielectric permittivity measurements. The ATi(O3PC6H5)3-PS composites exhibit a substantial enhancement in the dielectric permittivity as a function of weight loading relative to the parent ATiO3-PS composites. For both ATiO3-PS and ATi(O3PC6H5)3-PS, the composites' dielectric permittivity increases with A cation polarizability. Unusually large increases for 40 wt% ATi(O3PC6H5)3-PS composites (A=Sr, Ba, and Pb) indicate permittivity enhancement that goes beyond the effect of varying filler composition.
New layered 1:1 mixed Ba 2+ /Ti 4+ metal phosphonates, BaTi(O 3 PC 6 H 5 ) 3 and SrTi(O 3 PC 6 H 5 ) 3 , have been prepared via a hydrothermal route, in which mixed metal oxides, BaTiO 3 and SrTiO 3 , were reacted with phenyl phosphonic acid. The mixed-metal phosphonates were combined with polystyrene (PS) via a solution route and cast as thin films for dielectric permittivity measurements. The composites exhibit an enhancement in the dielectric permittivity as a function of weight loading relative to the parent mixed metal oxide-PS composites.
This study used in situ polymerization to prepare polyethylene terephthalate (PET) nanocomposites incorporating Ethoquad-modified montmorillonite (eMMT), unmodified hectorite (HCT), or phenyl hectorite (phHCT) particles to study the impact of platelet surface chemistry and loading on thermal, mechanical, and gas barrier properties. eMMT platelets reduced the PET crystallization rate without altering the ultimate degree of crystallinity. In contrast, HCT and phHCT platelets accelerated the polymer's crystallization rate and increased its crystallinity. DMA results for thermallyquenched samples showed that as T increased past glass transition temperature (T g ), HCT and phHCT nanocomposites (and control PET) manifested precipitous drops in G 0 followed by increasing G 0 due to cold crystallization; in contrast, eMMT nanocomposites had much higher G 0 values around T g . This provides direct evidence of eMMT reinforcement in thermallyquenched eMMT nanocomposites. These results suggest that eMMT has a strong, favorable interaction with PET, possibly through Ethoquad-PET entanglement. HCT and phHCT have a fundamentally different interaction with PET that increases crystallization rate and T g by 11 to 178C. Water barrier improvement in eMMT nanocomposites agrees with previously published oxygen barrier results and can be rationalized in terms of a tortuous path gas barrier model. POLYM. ENG. FIG. 5. Crystallization peak temperature (T c ) as a function of platelet weight loading for CPET and PET nanocomposites. Curves are drawn to guide the eye. FIG. 6. Percent crystallinity as a function of platelet weight loading for CPET and PET nanocomposites. Curves are drawn to guide the eye.
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