Finite-size effects on capacitive energy storage in ultra-thin polymer and block copolymer films

Ultrathin polymer films present unique opportunities to understand the physics and properties of polymers at the nanoscale when the film thicknesses become comparable to the polymer dimensions. In this work, we demonstrate that ultrathin glassy polymer films (~100 nm) show an order of magnitude higher dielectric strength (E_BD) and capacitive energy density (U_max ∝ E_BD²) of ~27 J/cm³ as compared to the bulk polymer films when used as dielectric capacitors. We believe that the enhancement of the dielectric strength and capacitive energy density is due to the tighter chain packing of polymers in ultrathin films. We test the density of thin polymer films by optical measurements and observe that the ultrathin films show higher densities as compared to their bulk counterparts, which might be a governing factor for the enhancement of the dielectric strength. Furthermore, the ultrathin films of polymers having sub-room temperature glass transition don’t show ultra-high dielectric strength and capacitive energy density. More recently, we have shown that the introduction of 2D sheet-like nanoparticles can greatly enhance the dielectric constant in addition to the thin film effect for capacitive energy density (U_max ∝ E_BD²) of ~76 J/cm³ which is significantly higher than the highest energy density reported to date of ~36 J/ cm³ using a blending approach. Thus, multilayered hybrid inorganic/organic polymer thin films have much potential for applications as high-energy density storage media. Work funded by NSF-DMR.