Polymer-based dielectric capacitors are indispensable in advanced pulsed power and electronic systems owing to their ultrafast charge-discharge capability and superior reliability. However, state-of-the-art relaxor ferroelectric polymers such as PVDF-TrFE-CTFE suffer from an inherent contradiction: achieving high polarization requires strong ferroelectric ordering, yet strong ordering inevitably produces large hysteresis loss under high electric fields, severely compromising charge-discharge efficiency. Conventional approaches have invariably failed to simultaneously satisfy the three critical requirements of high dielectric constant, high breakdown strength, and low high-field loss. In particular, incorporating high-permittivity inorganic fillers (e.g., BaTiO3, TiO2) into ferroelectric polymers typically introduces severe interfacial charge accumulation and increased conduction loss, degrading energy storage efficiency rather than improving it. The work aims to experimentally validate a structurally rational dual synergistic strategy that integrates rigid amorphous aromatic polythiourea (ArPTU) with dopamine-modified SnO2 nanoparticles (SnO2@DA) to synergistically regulate the microstructure, ferroelectric domain architecture, and interfacial charge transport of a PVDF-TrFE-CTFE matrix. The central innovation lies in recognizing that the two major loss mechanisms in polymer dielectrics—ferroelectric phase-transition hysteresis and interfacial conduction loss—require distinct material solutions: the former demands disruption of long-range crystalline ordering, while the latter necessitates elimination of charge leakage pathways at the filler-polymer interface. ArPTU, synthesized via step-addition polycondensation of 4,4’-diaminodiphenylmethane and p-phenylenediisothiocyanate, is a fully amorphous polymer with a rigid aromatic backbone and intrinsic low dielectric loss (~0.05). The SnO2 nanoparticles (~100 nm) were surface-modified through a dopamine coating process. This procedure yielded a uniform and continuous amorphous polydopamine shell with a precisely controlled thickness of approximately 5 nm, as confirmed by transmission electron microscopy (TEM). Ternary composites with SnO2@DA loadings of 5, 10, and 15wt.% (ArPTU fixed at 10wt.%) were fabricated via solution blending and hot pressing at 195 ℃ under 10 tons pressure. SnO2@DA nanoparticles were homogeneously distributed throughout the matrix without observable aggregation, even at 15wt.% loading, in contrast to unmodified SnO2, which exhibited severe agglomeration at the same loading. This homogeneous dispersion was attributed to the dopamine shell, which reduced the high surface energy of inorganic nanoparticles and established strong interfacial adhesion through hydrogen bonding with both PVDF-TrFE-CTFE. X-ray diffraction (XRD) combined with Scherrer analysis revealed that the addition of SnO2@DA progressively refined the crystalline domain size of the polymer matrix from 30.9 nm (pure polymer) to 28.6 nm (5wt.% SnO2@DA), fundamentally transforming the ferroelectric domain architecture from macroscopic domains into nanoscale polar regions with significantly reduced switching barriers. Dielectric spectroscopy measurements demonstrated that the dielectric constant of the ternary composites increased monotonically with SnO2@DA content, reaching a maximum value of 74. Remarkably, the dielectric loss tangent at low filler loading (≤10wt.%) was substantially lower than that of the pure polymer across the entire measured frequency range (102-107 Hz), a counterintuitive finding attributed to the synergistic dual mechanism: the dense interfacial polymer layer constrained by dopamine suppressed the β-relaxation loss dominant in PVDF-based ferroelectrets, while the amorphous ArPTU diluted the high-loss PVDF phase and disrupted long-range carrier migration pathways. Weibull statistical analysis of breakdown strength revealed a characteristic breakdown strength of 700.3, 620.3, and 553.9 MV/m at 5, 10, and 15wt.% SnO2@DA loading, respectively, all significantly exceeding the 530.3 MV/m of the pure polymer matrix. The ferroelectric hysteresis (D-E) loops provided the most compelling evidence for the dual synergistic effect: the ternary composites evolved from the characteristic relaxor ferroelectric shape of pure PVDF-TrFE-CTFE into nearly linear dielectric responses with dramatically narrowed loop widths. At a SnO2@DA loading of 10wt.%, the composite achieved a discharged energy density of 24.3 J/cm3 under 600 MV/m, while simultaneously maintaining a charge-discharge efficiency exceeding 80%.
Key words
dopamine /
tin dioxide /
poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) /
aromatic polythiourea /
surface modification /
dielectric properties
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