Controllable Preparation And Application Of Free-standing PEDOT:PSS Conductive Film

Poly（3,4-ethylenedioxythiophene）:polystyrene sulfonate（PEDOT:PSS）is currently one of the most commercially available conductive polymers.It possesses enormous potential in the field of flexible electronics owning to the advantages such as:adjustable conductivity,solution processability,good environmental stability and etc.However,the conductivity of untreated PEDOT:PSS is extremely low,and the mechanical properties are poor after film formation.In addition,the preparation of PEDOT:PSS films is mainly achieved via flat coating,spin coating,and blade coating.These methods require attachment to a substrate,which will limit its application in the field of flexible electronics.To address the above issues,this paper prepares PEDOT:PSS free standing films by vacuum filtration,and improves the electrical conductivity and mechanical properties of the films by CNF doping,phosphoric acid post-treatment and polar solvent vapor bath orientation treatment,respectively,and investigates the electromagnetic shielding and thermoelectric properties of the films.The main research contents are as follows:In this work,PEDOT:PSS free-standing conductive films with high electrical conductivity and excellent mechanical properties is developed,and the film achieves an electrical conductivity of 3508 S/cm and an elongation at break of 3.75%.Further studies have shown that the improvement in the conductivity of the film is achieved by the synergistic effect of cellulose nanofibers（CNF）and phosphoric acid.PEDOT grains grow and stack orderly along the CNF,forming a highly ordered long-range conductive path.The phosphoric acid immersion process removes insulating CNF and PSS,resulting in a dense layered stacked structure of the film.In addition,the film showed excellent electromagnetic interference shielding effectiveness of 49 d B in the X-band（8.2-12.4 GHz）.In addition,PEDOT:PSS film has excellent stability and bending resistance,and this free-standing conductive film will have a broad application prospect in the field of electromagnetic shielding for portable and wearable smart electronics.A method of treated the PEDOT:PSS free-standing films with an orientated polar solvent vapor was developed.The influence of polar solvents with different dielectric constants on the microstructure and properties of the PEDOT:PSS free-standing film was explored.On the one hand,the high dielectric constant of the polar solvent could weaken the interaction between PEDOT and PSS,so that the PSS can be easier to be removed.On the other hand,the orientated evaporation of the solvent vapor had a similar effect on the film as the solution shear,inducing an ordered crystallization of PEDOT fragment.Therefore,the treated PEDOT:PSS free-standing film had a magnitude of increase in electrical conductivity and a significant improvement in the thermoelectric power factor compared to the pristine film.In particular,the conductivity of the PEDOT:PSS free-standing film treated with dimethyl sulfoxide（DMSO）reached 2947 S/cm,and the a power factor reached 72.46μW m^-1 K^-2.On this basis,the assembled flexible wearable thermoelectric device can generate an output voltage of 1 m V using the temperature difference between the arm and the environment.In summary,this paper prepared pure PEDOT:PSS free-standing films by a vacuum filtration process.The electrical conductivity and mechanical properties of the films were further improved by introducing CNFs and post-treatment with phosphoric acid.The modified film exhibits excellent electromagnetic shielding effectiveness in the X-band.In addition,the solvents with different polarities were employed to control the molecules arrangement in PEDOT:PSS free-standing films through a directional solvent vapor treatment,the thermoelectric performance of the film is thus significantly improved.The improvement of electromagnetic shielding and thermoelectric properties makes the films promising for wearable electromagnetic shielding and thermoelectric applications.