Wall Thickness Prediction in Precipitated Precursors of Mesoporous Materials

We describe a parameter-free analytical model based on molecular force balance to quantitatively explain the wall thickness of silica-based mesoporous materials obtained by a sol gel route. Simple synthesis routes were proposed 20 years ago that led to a well-developed class of porous materials with mesoscale pores (i.e., between 2 and 50 nm). The general route is a micelle-templated precipitation of silicate-based polymers. To optimize thermal stability and efficient resistance to leaching, the wall thickness must be as large as possible, whereas the microporosity has to be as low as possible. Experimental attempts to control wall thickness have appeared in more than 100 publications, but a clear general predictive model is not yet available. Here, we propose a rational evaluation of wall thickness based on molecular force balance that minimizes the free energy between adjacent micelles. The force balance takes into account the following three main uncoupled driving forces: repulsive electrostatic, repulsive hydration, and attractive van der Waals. We argue that our predictive model is an efficient guide for mesoporous material formulations.