Tuning mechanical properties and pore size distribution of mesoporous silicas using associating homopolymer/block copolymer blends as templates
Ordered mesoporous films are synthesized from the vapor-phase condensation of tetraethyl orthosilicate within preformed amphiphilic template films consisting of a blend of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic F127) and poly(4-hydroxystyrene) (PHOSt). By modification of the Pluronic F127:PHOSt ratio in the template film, the long range order of the synthesized mesoporous silica can be tuned with the largest grains observed at approximately 15 wt % PHOSt. This increase in ordering and orientation of the mesopores is accompanied by a narrowing of the pore size distribution, a slight increase in the average mesopore radius, and a substantial increase in the Young's modulus of the film. Deviations from this 15 wt % PHOSt composition to higher or lower PHOSt loadings result in a decay in the long range ordering and subsequently a decrease in the film modulus. The modulation in the mechanical properties through modification in the PHOSt concentration (1−50 wt %) is nearly 1 order of magnitude without significantly altering the porosity. Moreover, samples with nearly indistinguishable morphology as determined through TEM micrographs can exhibit a difference in modulus by a factor of 3. This work demonstrates the importance of long range order for fabricating mechanically robust porous films.
Vogt, Bryan, "Tuning mechanical properties and pore size distribution of mesoporous silicas using associating homopolymer/block copolymer blends as templates" (2008). Polymer Engineering Faculty Research. 1024.