Tunable microcellular morphologies from poly (ferrocenylsilane) ceramic precursors foamed in supercritical CO2

摘要

Poly(ferrocenylmethylphenylsilane) (PFMPS) and polyferrocenylmethyl(phenylacetylido)silane (PFM-PAS) homopolymers are organometallic polymers that can serve as precursors to magnetically-active ceramics. In this work, PFMPS and PFMPAS films ranging in thickness from 30 to 220 pm have been exposed to scCO(2) over a broad range of saturation pressures, temperatures and times to produce surface-constrained microcellular polymeric foams. Electron microscopy identifies viable foaming windows and reveals that foams with submicron cell sizes can be generated by judicious selection of exposure conditions. Cell shape anisotropy can likewise be varied from being nearly spherical to vertically elongated. Curvature in the films and non-negligible surface roughness create paths that facilitate CO2 diffusion, resulting in the formation of "V-directional" cells oriented at approximately 30degrees to the film surface. The development of bimodal cell size distributions is attributed to temperature variation during depressurization and/or step-wise homogeneous and heterogeneous nucleation. These results are prerequisite for the production of magneticallyactive porous ceramics from pyrolyzed PFS foams.