Enhancing flexoelectricity in PEDOT:PSS polymer films with soft treatments

Abstract

We report the use of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as a transducing material in the fabrication of mechanical-to-electrical conversion devices based on the flexoelectric-like response of this polymer. Devices are made in a cantilever-based three-layer stainless-steel/PEDOT:PSS/top metal electrode configuration to assess the effective transverse flexoelectric coefficient μ12′. We investigated the influence of the nature of the top electrode in the flexoelectric response comparing samples with gold and aluminum top electrodes and demonstrated the huge impact of adding a small fraction of a second dopant such as xylitol to the PEDOT:PSS polymer blend and the benefits of a post-treatment of the polymer film with ethanol and methanol on the flexoelectric coefficient. The combination of xylitol addition and the rinsing of the polymer films with ethanol and methanol, along with the use of gold as a top electrode, led to a significant improvement of μ12′ to ca. 24 μC m−1, which is in the range of those reported for high permittivity oxide materials. These findings support the use of conjugated polymers as an alternative to inorganic materials in flexoelectric-based applications, where large flexibility is required.

Large Curvature Sensors Based on Flexoelectric Effect in PEDOT:PSS Polymer Films

“…We observed an increase in roughness on the matte surfaces of the freestanding films (surface in contact with the Teflon substrate during deposition) for both solutions of PEDOT:PSS (1:6 and 1:2.5 ratio). The matte surfaces of the films show a more granular distribution of the polymer material on the surface (Figure b) and PEDOT:PSS (1:2.5 ratio) (Figure d), which may indicate a depletion of PSS from the film surface . And conversely, glossy surfaces are systematically smoother, as we observed for both PEDOT:PSS (1:6 ratio) samples (Figure a) and PEDOT:PSS (1:2.5 ratio) (Figure c).…”

“…PH1000, OSSILA) was used to which xylitol 99+% [C 5 H 12 O 5 ] (Acros Organics) was added 0.3% by weight to form the precursor solution. This additive favors softening the PEDOT:PSS film (plasticizing effect) and also decreases the electrostatic interaction PEDOT + chains and PSS – chains via the hydrogen bonds they impose, thus increasing the mobility of charge carriers in the polymer …”

“…They obtained a large flexoelectric coefficient of ∼3.4 μC/m, which was attributed to the overall high polarizability of PEDOT:PSS induced by the electrical double layer formed between the positively charged oligomer of PEDOT + and negatively charged chains of PSS – . The same group notably improved the flexoelectric coefficient (24 μC/m) by a soft treatment of the polymer surface . However, the use of a stainless steel substrate makes the device hard, which limits its deformation.…”

The emancipation of flexoelectricity

“…Possible approaches of enhancing flexoelectric properties are discussed in polymers, 51,52,44,53 ceramics, [54][55][56][57] ferroelectrics, [58][59][60][61][62] and two-dimensional (2D) materials. 63,62 There is also an intriguing proposal regarding flexoelectricity in metals.…”