Nanoporous Organosilicate Films Prepared in Acidic Conditions Using Tetraalkylammonium Bromide Porogens

Abstract

Organosilicate films with narrow pore size distribution tunable in the range of 1–3.4 nm were prepared by spin‐coating of silicon wafers with sols prepared in acidic conditions using tetraethyl orthosilicate, methyltrimethoxysilane, and tetraalkylammonium bromide (TAABr) porogen. The pore size was defined by the alkyl chain length of the quaternary ammonium molecule and the porogen concentration. The pore network in the films and the hydrophobicity of the pore surfaces were characterized using ellipsometric porosimetry with toluene and water adsorbates. In the absence of TAABr, the pore volume was 9 vol% and the pore size 1 nm. By using TAABr porogens, monomodal pore size distributions were obtained in the range of 1.2–3.5 nm. The pore volume was in the range from 18 vol% at 1.2 nm pore diameter up to 54 vol% at 3.5 nm diameter. The hydrophobicity of the pores was dependent on the pore diameter, with smaller pores being the least hydrophobic. The increase of hydrophobicity with pore size was explained by an increased distance between silanol groups on the curved pore surfaces. The mechanical properties and dielectric constant of these films were comparable to reference materials prepared using more sophisticated porogens reported in the literature.

Effects of Silica Sources on Nanoporous Organosilicate Films Templated with Tetraalkylammonium Cations

“…[5] Films prepared from higher MTMS fraction had higher IR absorption related to SiCH 3 groups (~2980, ~1270, and 850-750 cm -1 ). [5] The broadening is attributed to the presence of Si-O-Si angles smaller than 144º caused by the linkage of CH 3 groups to one of the Si atoms. Finally, films prepared from higher MTMS content showed a Si-O-Si antisymmetric stretching (AS) with a more pronounced shoulder at higher frequencies (centered at ~1140 cm -1 ) as well a broadening of the AS at 1030-1080 cm -1 towards lower frequencies.…”

“…An organosilicate sol was prepared following same recipe described in [5] , in which tetraethyl orthosilicate (TEOS, 98% purity, Acros Organics) and methyltrimethoxy silane (MTMS, 98%, Fluka) were partially hydrolyzed and condensed under stirring at 60 ºC for 90 min. in presence of ethanol (EtOH), doubly deionized (DDI) water, and HCl.…”

“…The pore network and the matrix composition are crucially important for the final film properties. [5] This was demonstrated by using TAABr molecules as porogens in the spin coating of organosilicate sols prepared from an equimolar quantity of tetraethyl orthosilicate (TEOS) and methyltrimethoxysilane (MTMS) in acid conditions. [1][2][3][4] Recently, we have shown that tetraalkylammonium bromides (TAABr) of different alkyl chain length outperform other porogen molecules in terms of porosity results.…”

“…[1][2][3][4] Recently, we have shown that tetraalkylammonium bromides (TAABr) of different alkyl chain length outperform other porogen molecules in terms of porosity results. [5,6] In this work, we contribute to the study on the organosilicate films nanocasted with TAABr porogens. The alkyl chain length of the TAABr and the porogen concentration defined the final pore network.…”

Hydrophobic micro/mesoporous silica spheres assembled from zeolite precursors in acidic media for aromatics adsorption

“…On the other hand, with the increase in pore size, an increased a Obtained using the volume blocked by n-nonane. distance between silanol groups on the curved pore surfaces would improve the hydrophobicity [46]. The strong curvature of the small pore size favors hydrogen bonding of the surface hydroxyls.…”