Polymer Engineering Faculty Research


Effect of Porogen Molecular Architecture and Loading on Structure of Porous Thin Films

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Publication Date

Fall 2008


The effects of molecular architecture and loading of a porogen material on the structural characteristics of methylsilsesquioxane (MSQ)-based porous films are examined using X-ray porosimetry (XRP) and small-angle neutron scattering (SANS). Either linear (NG) or star-shaped (TP) polymers are used as the porogen here and blended with the MSQ material at loadings from 20 to 50% by mass, resulting in porosities between 30 and 60% by volume, regardless of porogen architecture. This indicates that the MSQ matrix material contains approximately 10% by volume inherent microporosity. The average pore size increases with increased porogen loadings in a way that depends on the porogen architecture. The NG porogen tends to aggregate, more than tripling the average pore size as the porogen loading increases from 20 to 50% by mass (22 to 76 Å in diameter). By contrast, the TP porogen has less propensity to aggregate, leading to a smaller increase in terms of percent change in the average pore size for the same porogen loading range (76 to 132 Å in diameter). Changes in the porogen type or loading do not influence the wall density (1.47 ± 0.01) g/cm3 of the material between the pores, whereas the coefficient of thermal expansion (CTE) is approximately 1.5 times greater for the NG samples than for the TP samples at all porogen loadings.



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