By employing polyamines and polypeptides as templates, bioinspired synthesis could lead to greener methods for production and purification of porous silica materials. For this to be achieved, it is essential to gain detailed... [ view full abstract ]
By employing polyamines and polypeptides as templates, bioinspired synthesis could lead to greener methods for production and purification of porous silica materials. For this to be achieved, it is essential to gain detailed knowledge of the synthesis mechanism, which involves multiple species in solution and multiple physical processes occurring at the same time. Because of this complexity, a complete understating solely based on experimental observations is very difficult to obtain.
In this work, molecular dynamics simulations at different length scales have been used to investigate the formation of bioinspired materials [1] as a function of pH. In a first step, all-atom (AA) simulations were performed to study the early stages of synthesis of the materials, revealing that structure formation is promoted by charge matching interactions between surfactant molecules and silica monomers. Our results shed light on the molecular-level mechanism for the formation of multilayered silica-surfactant structures at the initial stages of the synthesis process. The results obtained at the AA level were then used to develop coarse-grained (CG) models for surfactants and silicates based on the MARTINI framework [2]. This multi-scale approach allowed to explore longer time and length scales while maintaining chemical specificity. Results of the CG simulations indicate that silica dimers are necessary in order to promote long-range packing of surfactant mesostructures, although the structures observed appear to be significantly more disordered when compared to traditional periodic mesoporous silicas (e.g. MCM-41). Nonetheless, this observation is in agreement with the “worm-like” description of these materials in experimental studies [3]. Yet, contrary to what has been previously hypothesised, strong electrostatic interactions between charged species, rather than hydrogen bond interactions, guide the process of formation of these bioinspired porous materials. Our results open the possibility of controlling the pore structure of these materials by careful manipulation of the synthesis conditions, potentially allowing their properties to be tuned for particular applications.
[1] P. T. Tanev and T. J. Pinnavaia. ‘Mesoporous Silica Molecular Sieves Prepared by Ionic and Neutral Surfactant Templating: A Comparison of Physical Properties’. Chemistry of Materials; 8 (8) 1996, pp. 2068-2079.
[2] S. J. Marrink, H. J. Risselada, S. Yefimov, D. P. Tieleman and A. H. de Vries. ‘The MARTINI Force Field: a Coarse Grained Model for Biomolecular Simulations’. Journal of Physical Chemistry; 111 (27) 2007, pp. 7812-7824.
[3] W. Zhang,T. R. Pauly, and T. J. Pinnavaia. ‘Tailoring the Framework and Textural Mesopores of HMS Molecular Sieves through an Electrically Neutral (S°I°) Assembly Pathway’. Chemistry of Material; 9 (11) 1997, pp. 2491-2498.
