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Title: Molecular Simulations of the Synthesis of Periodic Mesoporous Silica Phases at High Surfactant Concentrations

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.
Authors:
ORCiD logo ;  [1] ; ORCiD logo [2] ;  [3] ; ORCiD logo [4] ; ;
  1. CICECO-Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal; LAQV@REQUIMTE, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Rua Campo Alegre 687, 4169-007 Porto, Portugal
  2. CICECO-Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
  3. LAQV@REQUIMTE, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Rua Campo Alegre 687, 4169-007 Porto, Portugal
  4. Department of Chemical and Process Engineering, University of Strathclyde, 75 Montrose Street, Glasgow G1 1XJ, United Kingdom
Publication Date:
Grant/Contract Number:
FG02-07ER46466
Type:
Published Article
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 8; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Univ. of Massachusetts, Amherst, MA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1352290
Alternate Identifier(s):
OSTI ID: 1423812; OSTI ID: 1423813

Chien, Szu-Chia, Pérez-Sánchez, Germán, Gomes, José R. B., Cordeiro, M. Natália D. S., Jorge, Miguel, Auerbach, Scott M., and Monson, Peter A.. Molecular Simulations of the Synthesis of Periodic Mesoporous Silica Phases at High Surfactant Concentrations. United States: N. p., Web. doi:10.1021/acs.jpcc.6b09429.
Chien, Szu-Chia, Pérez-Sánchez, Germán, Gomes, José R. B., Cordeiro, M. Natália D. S., Jorge, Miguel, Auerbach, Scott M., & Monson, Peter A.. Molecular Simulations of the Synthesis of Periodic Mesoporous Silica Phases at High Surfactant Concentrations. United States. doi:10.1021/acs.jpcc.6b09429.
Chien, Szu-Chia, Pérez-Sánchez, Germán, Gomes, José R. B., Cordeiro, M. Natália D. S., Jorge, Miguel, Auerbach, Scott M., and Monson, Peter A.. 2017. "Molecular Simulations of the Synthesis of Periodic Mesoporous Silica Phases at High Surfactant Concentrations". United States. doi:10.1021/acs.jpcc.6b09429.
@article{osti_1352290,
title = {Molecular Simulations of the Synthesis of Periodic Mesoporous Silica Phases at High Surfactant Concentrations},
author = {Chien, Szu-Chia and Pérez-Sánchez, Germán and Gomes, José R. B. and Cordeiro, M. Natália D. S. and Jorge, Miguel and Auerbach, Scott M. and Monson, Peter A.},
abstractNote = {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.},
doi = {10.1021/acs.jpcc.6b09429},
journal = {Journal of Physical Chemistry. C},
number = 8,
volume = 121,
place = {United States},
year = {2017},
month = {2}
}