L. Zhanshayeva, V. Favaron, and G. Lubineau, Macroscopic modeling of water uptake behavior of PEDOT:PSS films； ACS Omega，accepted(2019)
Abstract:
Poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) is a widely used conductive polymer (CP) for applications in electronic devices. In the context of transparent electrodes or soft actuators, the uptake of water by PEDOT:PSS is an essential element in the performance of the physical system. We studied water uptake of pure films and films treated with ethylene glycol (EG, that is commonly used to enhance the electrical properties of PEDOT/PSS). Gravimetric analysis was used to investigate water sorption-desorption of CP and its change with the EG treatment for a wide range of configurations (thickness, temperature and relative humidity). We demonstrate that a simple Fickian model cannot represent correctly the experimental results and introduce a fully-coupled reaction-diffusion scheme. This model describes the transport of diffusing molecules into the polymer film taking into account, on top of the classical diffusion mechanism, the reaction between the reactive sites of the polymer network and the water molecules. We demonstrate that solvent treatments have a direct influence on water uptake kinetics of PEDOT:PSS film in terms of diffusivity, solubility and rate of reaction. The proposed model can be used to predict accurately the water uptake of CP films in case of complex three dimensional configurations, that is needed for the design of complex actuators.
