Homopolymer induced phase evolution in mesoporous silica from evaporation induced self-assembly process

In this paper, we report the experimental findings on the phase evolution of mesoporous silica in an evaporation induced self-assembly (EISA) approach by using low molecular weight homopolymer poly(propylene oxide) (M_n = 400, PPO400) as an additive. It is found that the addition of PPO400 can cause hydrotropic curvature-reducing effect on the mesostructures. Upon the increase of PPO400 addition amount, the structures of the obtained mesoporous silicas gradually evolve from three-dimensional (3-D) cubic Im over(3, ̄) m to quasi-p6m, to hexagonal p6m, and to mixed structures consisting of lamellar and reversed cylindrical structure. The quasi-p6m mesoporous silica structure has the buckled cylindrical mesopores with intermediate curvature and acts as the metastable structure during the phase evolution from Im over(3, ̄) m to p6m structure. We ascribe this curvature-reducing effect to the relatively weak hydrophobicity and good compatibility of PPO400 homopolymer. Moreover, the condition with larger homopolymer PPO4000 (M_n = 4000) as the additive has been also investigated and discussed.