Tuning the Triboelectric Polarity of PDMS Film through Thermal Treatment

The triboelectric effect is utilized in energy generators to convert ambient mechanical energy to electrical energy with potential to enable self-powered electronics. However, the fundamental mechanism behind the triboelectric effect is still unclear making it difficult to optimize the properties of the material pairs in the generator. In order to maximize the performance of triboelectric generators, the relationship between the triboelectric output and the mechanical properties of materials is investigated using polydimethylsiloxane (PDMS) as a model material. The bulk mechanical properties of PDMS were tuned by varying thermal treatment. Specifically, the tensile and compressive elastic modulus of PDMS heated for 48 hours increased by 4.4 folds and 2 folds respectively compared to PDMS without additional thermal treatment. In addition, the contacting surface of the PDMS samples were examined by measuring the surface roughness and contact angle. The results showed that the effect of thermal treatment on the mechanical properties is more significant than on the surface roughness. Interestingly, the triboelectric output polarity of the thermally treated PDMS samples is different from that of the PDMS without thermal treatment. The reversal of triboelectric polarity is surmised to result from bond breaking, and thus material transfer, between the two contacting materials. These findings confirm that the triboelectric output is not only affected by the chemical composition of the material, but also by the mechanical properties, which should be considered in the design and development of triboelectric devices.