Effect of Molecular Weight and Layer Thickness on the Dielectric Breakdown Strength of Neat and Homopolymer Swollen Lamellar Block Copolymer Films

Abstract

Designing next-generation lightweight pulsed power devices hinges on understanding the factors influencing the energy storage performance of dielectric materials. Polymer dielectric films have a quadratic dependence of energy storage on the voltage breakdown strength, and strategies to enhance the breakdown strength are expected to yield a path toward high energy storage densities. Highly stratified lamellar block copolymer (L-BCP) films of model polystyrene-b-polymethylmethacrylate (PS-b-PMMA) exhibited as much as ∼50% enhancement in breakdown voltage (E BD) (225% increase in stored energy density, U ∼ E BD 2) compared to unordered as-cast L-BCP films. Such an energy density using amorphous polymer is on par with industry-standard semicrystalline biaxially oriented polypropylene (BOPP) and as such a notable development in the field. This work develops a deeper understanding of the molecular mechanisms of E BD enhancement in L-BCP films, relating E BD directly to molecular weight (M n), with interpretation to effects of chain-end density and distribution, interface formation, layer thickness, and their relative contributions. As-cast disordered L-BCP films show decreasing E BD with decreasing M n similar to homopolymer studies because of the increase of homogeneously distributed chain ends in the film. E BD increases significantly in parallel ordered L-BCP films because of the combination of interface formation and spatial isolation of the chain ends into segregated zones. We further confirm the role of chain ends in the breakdown process blending a low M n L-BCP with matched M n homopolymers to attain the same layer spacing as neat L-BCP of higher M n. E BD shows a significant decrease at low homopolymer fractions because of increased net chain-end density within swollen ordered L-BCP domains in wet-brush regime, followed by increased E BD because of layer thickness increase via segregated “interphase layer” formation by excess homopolymers. Notably, E BD of homopolymer swollen L-BCPs is always lower than that of neat L-BCPs of the same domain spacing because of overall adverse chain-end contribution from homopolymers. These findings provide important selection rules for L-BCPs for designing next-generation flexible electronics with high energy density solid-state BCP film capacitors.

Achieving Superior Energy Storage Properties of All-Organic Dielectric Polystyrene-Based Composites by Blending Rod–Coil Block Copolymers

“…To construct high-performance PS dielectrics, researchers have made great effort to increase ε r or U d by designing molecular structures and fabricating PS-based composites. , The former method is related to random copolymerization, , graft modification, , block copolymerization, , and so forth. In these ways, polar groups or polar polymers are introduced into the PS polymer chains.…”

Control of Phase Morphology of Binary Polymer Grafted Nanoparticle Blend Films via Direct Immersion Annealing

“…To overcome these issues, we apply a solvent-assisted annealing method termed direct immersion annealing to help control PGNPs blend morphologies. DIA is a facile solvent annealing technique that was developed recently to investigate rapid phase separation in block copolymer (BCP) films − and has shown comparable phase separation and self-assembly kinetics to the fastest block copolymer self-assembly techniques. ,− Unlike the traditional solvent vapor annealing (SVA), DIA involves direct immersion of the binary PGNP blend films into a tunable mixture of solvents to control the effective solvent quality, including a significant nonsolvent fraction to prevent the dissolution of either PGNPs into solution. To our knowledge, a controlled phase separation study of a binary PGNPs blend, including tests of reversibility from two-phase to one-phase state and progression in-between using direct immersion annealing, has not been previously reported.…”

Self‐Strengthening Dielectric Elastomer of Triblock Copolymer with Significantly Improved Electromechanical Performance under Low Voltage

“…As shown in Figure , with higher ellipticity, PS nanodomains would have higher specific interface area, leading to higher blocking effectiveness, that is, higher dielectric strength. [ 53 ]…”