Effect of organic additives on the formation of alkylsiloxane mesophases

The effects of organic additives (1,3,5-trialkylbenzenes, n-alkanes, and n-alkyl alcohols) on the formation of hybrid siloxane–organic mesophases from alkoxylated precursors (CnH2n+1Si(OSi(OMe)3)3, 1Cn, n = 6, 10, and 16) have been investigated. These precursors become amphiphilic upon hydrolysis of the alkoxy groups, thus forming two-dimensional (2D) hexagonal phase (n = 6 and 10) and lamellar phase (n = 16) by evaporation-induced self-assembly followed by polycondensation. The addition of 1,3,5-trialkylbenzenes or n-alkanes to the 1C10 system leads to swollen 2D hexagonal phases, thereby achieving pore-size expansion of the calcined samples from 2.0 nm up to 3.8 nm in diameter. The effect of these organic additives depends largely on the alkyl chain length of 1Cn; the 2D hexagonal structure (n = 6) undergoes structural disordering, while the lamellar structure (n = 16) remains unchanged. On the other hand, the addition of alkyl alcohols to the 1C10 system causes a drastic change in the mesostructure from 2D hexagonal to lamellar, which can be attributed to possible interactions between alcohol molecules and silanol groups of hydrolyzed 1C10. These results provide a facile approach to the fine structural control of nanohybrid materials assembled from single siloxane-based molecules.

The organic additives such as 1,3,5-trialkylbenzenes, n-alkanes, and n-alkyl alcohols caused the swelling or phase change of alkylsiloxane mesophases, leading to the structural control of silica-based nanohybrid materials.Figure optionsDownload high-quality image (50 K)Download as PowerPoint slideResearch highlights
► Effects of organic additives on alkylsiloxane mesphases are described for the first time.
► Swollen 2D hexagonal phases are formed by adding 1,3,5-trialkylbenzenes and alkanes.
► Pore size control of calcined products can be achieved.
► Lamellar phases are formed by adding alkyl alcohols.