Phase behavior of hierarchical mesoporous silicas prepared using ABC triblock copolymers as single templates

Abstract

In this study we found that complicated mesostructures featuring bimodal mesopore distributions could be fabricated through simple evaporation-induced self-assembly when employing lab-made poly(ethylene-b-ethylene oxide-b-ε-caprolactone) (PE-PEO-PCL) triblock copolymers as single templates without any other additives. Using this approach, we produced two kinds of ultra-complicated hierarchical mesoporous silica samples as a result of the unusual composition of the ABC-type triblock copolymer: hydrophobic segments at the termini and a hydrophilic segment in the middle. Notably, by adjusting the amount of tetraethyl orthosilicate (TEOS) in the reaction medium, we obtained a series of silica samples with well-defined morphologies and two types of well-ordered hierarchical mesostructures, namely “alternate body-centered cubic” and “tetragonal cylinder alternated with face-centered cubic.” Using small-angle X-ray spectroscopy, transmission electron microscopy, and isothermal N₂ adsorption–desorption experiments, we studied the phase behavior of the mesoporous silica samples templated by a series of PE-PEO-PCL triblock copolymers at various TEOS-to-PE-PEO-PCL-to-HCl weight ratios. Notably, we report the first example of the fabrication and characterization of the special “alternate body-centered cubic” mesostructure (E1T40).