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Nanoprobing on conducting PEDOT:PSS gels

Porous conducting polymers have high porosity and surface area that could be useful for supercapacitors, thermoelectrics, solar cells, solar steam generators or ion diffusion membranes.

PEDOT:PSS, or poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) is one of such polymers that can form conducting gels. There is a lot of active research on how to control PEDOT:PSS gel formation so it has specific pore size, morphology and directionality, which all define its thermal and electrical properties.

Quentin Weinbach, Laure Biniek and their colleagues from ICPEES, University of Strasbourg, developed ice-templating or “freeze-casting” approach to tailor the macroporous structure in PEDOT:PSS. In ice-templating, ice-crystals are grown in the gel mixture and then sublimated, leaving pores in their place. In their recent work, the researchers showed controlled directionality of freezing. This directionality, in turn, produced anisotropy the resulting porous gel's electrical properties.

Study collaborators from Institut de Science des Matériaux de Mulhouse led by Laurent Simon used our nanoprobers to assess conductivity and anisotropy of charge transport of individual pore walls. The four probes contacted the pore wall at equal distances, either along the freezing direction, or perpendicular to it. These measurements showed that the cryogel formation by ice-templating preserves the electrical characteristics of the PEDOT:PSS and that electrical conductivity is anisotropic within the pore wall.

This study is an important step towards a well-controlled process to produce electrically conducting and thermally insulating PEDOT:PSS samples with a well-defined macroporous structure on cm scale.

Tailoring the 3D porous structure of conducting PEDOT:PSS gels via ice-templating
A scanning electron microscope image shows a defective spot in an insulating layer of a capacitor, found by resistive contrast imaging.