Self-assembly of condensable "bola-amphiphiles" in water/tetraethoxysilane mixtures for the elaboration of mesostructured hybrid materials

Abstract

The self-assembly of condensable amphiphile molecules in water is an attractive approach for the synthesis of mesostructured hybrid materials. In this article, we focus on aminoundecyltriethoxysilane (AUT), a condensable "bola-amphiphile", i.e., an amphiphilic molecule possessing two polar heads on both sides of an aliphatic chain. In the present case, one side is a condensable triethoxysilane, and the other side is an amino group. We report on the self-assembly of AUT in mixtures of water and tetraethoxysilane (TEOS). In situ small-angle X-ray scattering (SAXS) measurements allowed us to follow the evolution of the structure from the liquid state up to the solid material formed upon catalytic polycondensation. Depending on the medium composition, hexagonal or lamellar structures can be observed in the final material. These observations allowed us to propose a model for the self-assembly of AUT in water/TEOS mixtures that we were able to validate by simulations of the SAXS profiles. By taking advantage of the modularity of such a system, it proves possible to prepare in a simple way various structured hybrid materials possessing a high number of available organic functions without using sacrificial surfactant molecules.