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Tuning Mechanical Properties of Mesoporous Silicas Using Associating Homopolymers/Block Copolymer Blends as Templates

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journal contribution
posted on 10.01.2008 by Xinxin Li, Lingyan Song, Bryan D. Vogt
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.