resumo
Molecular dynamics simulations of a coarse-grained model are used to study the formation mechanism of periodic mesoporous silica over a wide range of cationic surfactant concentrations. This follows up on an earlier study of systems with low surfactant concentrations. We started by studying the phase diagram of the surfactant-water system and found that our model shows good qualitative agreement with experiments with respect to the surfactant concentrations where various phases appear. We then considered the impact of silicate species upon the morphologies formed. We have found that even in concentrated surfactant systems-in the concentration range where pure surfactant solutions yield a liquid crystal phase-the liquid-crystal templating mechanism is not viable because the preformed liquid crystal collapses as silica monomers are added into the solution. Upon the addition of silica dimers, a new phase separated hexagonal array is formed. The preformed liquid crystals were found to be unstable in the presence of monomeric silicates. In addition, the silica dimer is found to be essential for mesoscale ordering at both low and high surfactant concentrations. Our results support the view that a cooperative interaction of anionic silica oligomers and cationic surfactants determines the mesostructure formation in the M41S family of materials.
palavras-chave
MONTE-CARLO-SIMULATION; COARSE-GRAINED MODEL; TEMPLATED SYNTHESIS; DYNAMICS; MCM-41; SIEVES; WATER; MESOSTRUCTURES; MESOPHASES; MECHANISM
categoria
Chemistry; Science & Technology - Other Topics; Materials Science
autores
Chien, SC; Perez-Sanchez, G; Gomes, JRB; Cordeiro, MNDS; Jorge, M; Auerbach, SM; Monson, PA
nossos autores
Germán Pérez-Sánchez
Investigador Júnior
José R. B. Gomes
Investigador PrincipalProjectos
agradecimentos
P.A.M., S.M.A., and S.-C.C. acknowledge a grant from the U.S. Department of Energy (Contract No. DE-FG02-07ER46466) and the computational resources provided by the Massachusetts Green High-Performance Computing Center (MGHPCC). G.P.-S., M.J., and J.R.B.G. thank the financial support of the PTDC/QUI-QUI/109914/2009 project. This work was developed within the scope of the projects CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT UID/CTM/50011/2013), LAQV@REQUIMTE, POCI/01/0145/FEDER/007265, (FCT UID/QUI/50006/2013 and NORTE-01-0145-FEDER-000011), and LSRE (FCT UID/EQU/500230/2013), financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. G.P.-S. acknowledges CICECO-UID/CTM/50011/2013 for grant ref. BI/U189/7145/2015. M.J. acknowledges funding from the EPSRC UK Project Grant EP/L014297/1. Results were partially obtained using the EPSRC funded ARCHIE-WeSt High Performance Computing Centre (www.archie-west.ac.uk and EPSRC Grant EP/K000586/1). This work was produced with the support of the Portuguese National Distributed Computing Infrastructure (INGRID). More information in http://www.incd.pt.