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

Published

July 31, 2020

Author(s)

Saumil Samant, Monali Basutkar, Maninderjeet Singh, Ali Masud, Christopher A. Grabowski, Kim Kisslinger, Joseph Strzalka, Guangcui Yuan, Sushil K. Satija, Ikeoluwa Apata, Dharmaraj Raghavan, Michael Durstock, Alamgir Karim

Abstract

Designing next generation light-weight pulsed power sources hinges on understanding the factors influencing the performance of high energy density storage materials. In prior work, we demonstrated the use of Cold Zone Annealing with Soft Shear (CZA-SS) as a processing strategy to fabricate highly stratified lamellar block copolymer (L-BCP) films which resulted in approximately equal} 50 % enhancement in breakdown voltage (E_BD) or approximately equal} 225 % increase in stored energy density (U), compared to unordered as-cast, or oven annealed ordered, though not-fully stratified parallel to substrate L-BCP films¹¹. Notably, low molecular weight (M_n) L-BCPs have low domain spacing, (d approximately equal} M_n^0.66, d = half L-BCP domain size) with a larger amount of chain ends compared to high M_n L-BCP films. This work reports interesting differences between increasing L-BCP layer thickness, d, that increases E_BD, versus increasing chain end density (ρc) within film layers that decreases E_BD, by acting as defect sites for promoting breakdown in polymer films. We delineate these effects by increasing d while decreasing ρc with increasing molecular weight (M_n) of L-BCP, versus adding homopolymer block components to a low molecular weight L-BCP that increases both d and ρc simultaneously. Neutron Reflectivity and X-ray scattering (GISAXS) measurements confirm stratified lamellar structure. Notably, E_BD was found to increase linearly with M_n of neat L-BCP. We hypothesize that the increase of E_BD with M_n is coupled to enhanced interfacial segregation of chain ends due to increase in χN. The high molecular weight films of amorphous L-BCP of PS-b-PMMA with layered morphology exhibited U of 4.8 J/cm³, comparable to the industry standard of semi-crystalline biaxially oriented polypropylene (BOPP) films of approximately equal} 5 J/cm³. In contrast, swelling L-BCP domains with homopolymers also increases E_BD with an increase of d, however, these values are approximately equal} 30 % lower than neat L-BCP films with same d due to an increased chain end density within domain from the added homopolymers. These findings can be vital in the selection of L-BCP for designing next generation high energy density solid-state polymer capacitors.

Citation

ACS Applied Polymer Materials

Volume

2

Issue

8

Pub Type

Journals

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DOI Link

Keywords

electrostatic capacitors, barrier effect, breakdown strength, block copolymers, directed self-assembly, cold zone annealing-soft shear

Citation

Samant, S. , Basutkar, M. , Singh, M. , Masud, A. , Grabowski, C. , Kisslinger, K. , Strzalka, J. , Yuan, G. , Satija, S. , Apata, I. , Raghavan, D. , Durstock, M. and Karim, A. (2020), Effect of Molecular Weight and Layer Thickness on the Dielectric Breakdown Strength of Neat and Homopolymer Swollen Lamellar Block Copolymer Films, ACS Applied Polymer Materials, [online], https://doi.org/10.1021/acsapm.0c00127 (Accessed April 25, 2024)