(574a) Multi-Scale Engineering of Polyimide-Derived Carbon Molecular Sieves

Applications as diverse as catalysis, membrane separations, energy storage, and drug delivery require multi-scale control over the structure of porous materials in order to tailor function (microstructure, microporosity), accessibility and transport (mesoporosity, macroporosity), as well as morphology (powder, thin films).¹ We have previously demonstrated the ability to hard-template extended carbon molecular sieve films² comprised of ultra-thin (ca. 50 nm) continuous carbon layers self-supported on three-dimensionally ordered mesoporous (3DOm) supports. The resulting mesostructure offers pathways for facile molecular transport and ease of access to microstructure, which we have shown can translate to improved properties in the context of electrolyte infiltration and charge transport for electrode and supercapacitor applications.³ While the hard templating strategy offers a clear approach for volumetric templating of ordered mesoporosity, the ability to simultaneously tailor the microstructure of these carbonaceous materials (i.e., alignment of graphitic planes, microporosity) can require high temperatures and metal catalysts.⁴

Motivated by substrate-mediated molecular orientation effects identified for ~50-100 µm poly (pyromellitic dianhydride-co-4,4’-oxydianiline) (PAA) films under similar processing conditions,^5,6 the large area associated with the template-replica interface in our 3DOm carbon films offers an unexploited handle for possibly simultaneously tailoring microstructure of the replica phase. In this talk, we will show how template-replica interfacial effects and interfacial surface chemistry alone can be employed to tailor replica carbon microstructure under mild carbonization conditions (600-900 ⁰C) and in the absence of specific metal catalysts when replica dimensions (i.e., distances from the silica template interface) are reduced by orders of magnitude (i.e., from ca. 100 µm to 1-10 nm scales). Specifically, we will show how temperature-tunable silanol surface chemistry of the template can be used to tailor the graphitic character (e.g., graphitic content relative to turbostratic carbon) of CMS replicas. The interfacial origin of this effect is confirmed through studies showing a decrease in graphitic character with increasing film thickness. Studies also show enhancement of graphitic character in thin carbon films as compared with untemplated carbon molecular sieves, with maximum sensitivity near the beginning of the carbonization process (around 600^oC). We hypothesize that the interface-mediated tunability of the replica graphitic character derives from adsorption-induced orientation of PAA molecules once the surface silanol density is reduced to the point of approximate registry with PAA molecular dimensions. Taken together, this templating approach offers a strategy for multi-scale control over film structure.

References

[1] M. A. Snyder, MRS Bulletin, 41 (2016), 683.

[2] M. Sharma, M. A. Snyder, in preparation.

[3] Z. Tian, M. A. Snyder, Langmuir, 30 (2014), 12411.

[4] M. Inagaki, New Carbons, Elsevier, (2014).

[5] H. Hatori et al. Carbon 30 (1992), 763.

[6] D. H. Zhong et al. Carbon 38 (2000), 2161.