Large scale processing of dielectric electroactive polymers

Efficient processing techniques are vital to the success of any manufacturing industry. The processing techniques determine the quality of the products and thus to a large extent the performance and reliability of the products that are manufactured. The dielectric electroactive polymer (DEAP) technology is relatively new and is in the initial stages of development with no established large scale manufacturing techniques.

Danfoss Polypower A/S has set up a large scale manufacture process to make thin film DEAP transducers. The DEAP transducers developed by Danfoss Polypower consist of microstructured elastomer surfaces on which the compliant metallic electrodes are sputtered thus enabling large strains of non-stretchable metal electrode.

Thin microstructured polydimethlysiloxane (PDMS) films are quintessential in DEAP technology due to scaling of their actuation strain with the reciprocal of square of films’ thickness. Production of thin elastomer films with microstructures on one or both surfaces is therefore the crucial step in the manufacturing.

The manufacture process is still not perfect and further optimization is required. Smart processing techniques are required at Danfoss Polypower to solve production issues in DEAP film manufacture. The primary issue in the processing is the release of thin PDMS films from a corrugated substrate on which the films are cured.

The films are weak owing to their small thickness and low Young’s modulus. The process of peeling the films from the substrate either induces pre strain or tears the films leading to a total shut down of the manufacturing. Further problem arises in the lamination step of the manufacturing process. The thin films manufactured in the industry with the current process have only one microstructured surface.

The complaint electrode is sputtered on the microstructured surface of the film. Two such films are laminated to make a single DEAP laminate with two microstructured surfaces. The lamination process introduces two problems: 1) it may entrap air bubbles and dust at the interface which will cause the films to breakdown at the operating voltages and 2) after lamination the thickness of the elastomer is double that of the single film and as thickness of the elastomer between the electrodes increases, higher voltages are required to produce a desired strain.

The objective of this research work is to find suitable solutions to the above discussed technical hitches. To facilitate easy release of the films from substrates, following three approaches are investigated: 1) chemical modification of the elastomer film by adding surface active block copolymers to reduce its surface energy, 2) use of surfactants as release agents and 3) compounding a silicone resin with the elastomer matrix.

An alternate process of making microstructured films by hot embossing has been established in this research. From our experiments it has been learnt that addition curing PDMS elastomer has the unique property to retain an imprint made on it at gel point. With hot embossing technique the microstructures can be imprinted directly on the films at gel point.

Thus, films can be made on a flat substrate and embossed instead of making the films on a corrugated substrate. Releasing the films from a flat substrate is easier compared to the corrugated substrate. To address the lamination problem, bilaterally microstructured films can be made by combining the hot embossing method with the existing manufacturing process eliminating the lamination step.

The bilaterally corrugated monolithic films have lower thickness than the laminated films made with conventional manufacture process. This new technique developed on a lab scale is quick, economical, easy and can be implemented on a large scale. The results of all our experiments and the hot embossing technique have been discussed.