Evolution of mechanical, optical and electrical properties of self-assembled mesostructured phenolic resins during carbonization

Ordered mesoporous polymer and carbon films are synthesized through the cooperative self-assembly of a phenol–formaldehyde resin with an amphiphilic block copolymer template, Pluronic F127. The processing temperature at which the template is removed and the resin is pyrolyzed dramatically impacts the mechanical, electrical and optical properties of the mesoporous film. There is a substantial increase in the hardness, modulus, conductivity and refractive index of the films as the pyrolysis temperature is increased from 400 to 800 °C. Upon further increasing the temperature to 1000 °C, there is no statistical change in the mechanical properties of the porous film, although the conductivity increases significantly from 18 to 74 S/cm. The modulus and hardness of the near surface are larger compared to the bulk of the film; this difference is more pronounced for the highly conductive films (carbonized at 800 and 1000 °C) and suggests a denser surface, which is consistent with low porosity calculated from ellipsometric porosimetry measurements that are surface sensitive. This work illustrates how the mechanical and electrical properties of mesoporous carbon films change with pyrolysis temperature. These mechanical and electronic properties are critical to the utility of these films in electronic or electrochemical applications.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Seven order of magnitude increase in electrical conductivity for pyrolysis between 600 and 800 °C. ► Young’s modulus more than triples by increasing pyrolysis temperature from 400 to 800 °C. ► Electrical conductivity doubles between 800 and 1000 °C, but no change in modulus. ► Conductivity and modulus for pyrolysis at 800 and 1000 °C appear to be sufficient for sensing apps.