Abstract
Small-Angle X-ray scattering (SAXS) and TEM were used to investigate the structural properties of mesoporous silica materials prepared by condensation of tetramethyl orthosilicate on the zwitterionic bicelle, cationic bicelle, anionic bicelle and cationic bicelle-DNA complex. Using zwitterionic bicelles (mixing DPPC and diC7PC at a ratio of 3:1), thread-like structure formed by one-dimensionally stacked discs ( Å-1) as well as lamellar structure ( Å-1) would be formed in coexistence. The lamellar structure was formed with fused bicelles that have a thinner bilayer thickness. With the doping of cationic lipids above about 10%, only isolated discs were formed with a coating of silicate layer. The hydrolyzed TMOS molecules are adsorbed to single cationic bicelle due to the strong attraction of the positive charges on the cationic bicelle surface. However, with the presence of NH4F which could accelerate the hydrolysis of TMOS, thread-like structure was formed by stacking discs into long thread. With the doping of 5% DPPG, which is a negatively charged lipid, bundles of stacking disc threads were formed. With 10 % and 30% DPPG, isolated threads were formed by stacking discs. However, with 15% DPPG, irregular stacking of the discs would be formed with different d-spacings ( and 0.107 Å-1). At low pH, such as pH 2, both the hydrolysis rate and condensation rate of TMOS becomes much lower, other than stacking on the disc face, the discs are also connected side-by-side to form bundles of long structure. Increasing the pH higher than 2, the side-to-side disc connection are significantly reduced.