Anomalous Enhancement of Dielectric Strength in Polymer Thin Films

This study explores the effects of polymer morphology, specifically film thickness and crosslinking density, on dielectric behavior. Polydimethylsiloxane (PDMS) is selected as the model system as it has widespread applications as a dielectric elastomer actuator (DEA), where performance is strongly influenced by its dielectric constant (k) and the square of the applied electric field (E). In today's rapidly advancing world, the trend toward miniaturizing electronics is increasingly important, as smaller, more efficient components are crucial for modern devices. Thin films, like PDMS, play a vital role in this miniaturization process, offering the potential to maintain high-performance standards while reducing size. Additionally, PDMS-based DEAs show immense promise in fields like robotics and therapeutic devices, including stroke rehabilitation, where they could mimic muscle movements by applying controlled forces, thereby enabling more natural interactions in these applications. However, PDMS use in DEAs is limited by the high electric fields required for operation, which presents significant safety risks. Our research aims to address these concerns by enhancing the dielectric breakdown strength (Eb) of polymers without compromising its other key properties.
Our findings demonstrate that increasing the crosslinking density, achieved by adjusting the proportion of the curing agent, results in a decrease in the dielectric constant. This reduction is likely due to a lower silica filler content, a trend that typically hampers electromechanical performance. However, despite this reduction in k, we discovered that modifying the crosslinking density allowed us to achieve desirable mechanical and dielectric properties simultaneously.
A pivotal discovery in our study pertains to the effect of film thickness on dielectric breakdown strength. For thicker PDMS films (~40 µm), we measured an average Weibull breakdown strength of 188.8 MV/m. Remarkably, when the film thickness was reduced to 15 nm, we observed a dramatic increase in breakdown strength, reaching an average of 20,000 MV/m, an increase of approximately 10,443%. This extraordinary enhancement in breakdown strength is attributed to lateral chain stretching in sub-micron films and proportional decay in the polarizability of the polymer.
The implications of our research suggest that by manipulating the crosslinking density and film thickness, we can engineer polymer films with enhanced dielectric properties, making them ideal for miniaturized electronics and improving their safety and viability in high-power density applications. These insights also contribute to the development of robust and efficient DEAs for use in advanced fields such as robotics and therapeutic devices, enabling potential breakthroughs in stroke rehabilitation and similar areas where muscle-mimicking movements through controlled forces are essential.