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Full-Text Articles in Engineering
Modeling Silicic Acid Polymerization Using A Low Coordination Lattice Model, Peter A. Monson, Scott M. Auerbach, Lin Jin
Modeling Silicic Acid Polymerization Using A Low Coordination Lattice Model, Peter A. Monson, Scott M. Auerbach, Lin Jin
Peter A. Monson
We present an atomic lattice model for studying the polymerization of silicic acid in sol-gel and related processes for synthesizing silica materials. Our model is based on Si and O atoms occupying the sites of a body-centered-cubic lattice, with all atoms arranged in SiO4 tetrahedra. This is the simplest model that allows for variation in the Si–O–Si angle, which is largely responsible for the versatility in silica polymorphs. The model describes the assembly of polymerized silica structures starting from a solution of silicic acid in water at a given concentration and pH. This model can simulate related materials—chalcogenides and clays—by …
Probing The Mechanism Of Silica Polymerization At Ambient Temperatures Using Monte Carlo Simulations, Peter A. Monson, Ateeque Malani, Scott M. Auerbach
Probing The Mechanism Of Silica Polymerization At Ambient Temperatures Using Monte Carlo Simulations, Peter A. Monson, Ateeque Malani, Scott M. Auerbach
Peter A. Monson
We have developed a model for silica polymerization at ambient temperatures and low densities and have studied this using reactive Monte Carlo simulations. The model focuses on SiO4 coordination with the energetics of hydrolysis and condensation reactions treated via the reaction ensemble. The simplicity of the model makes large system sizes accessible on a modest computation budget, although it is necessary to make additional assumptions in order to use the reactive Monte Carlo method as a simulation of the system dynamics. Excellent agreement for the evolution of the Qn distribution is obtained upon comparing the simulation results to experimental observations. …
Modeling Nanoparticle Formation During Early Stages Of Zeolite Growth: A Low-Coordination Lattice Model Of Template Penetration, Peter A. Monson, L. Jin, Scott M. Auerbach
Modeling Nanoparticle Formation During Early Stages Of Zeolite Growth: A Low-Coordination Lattice Model Of Template Penetration, Peter A. Monson, L. Jin, Scott M. Auerbach
Peter A. Monson
We present an extension of the simple-cubic lattice model developed by Jorge et al. [ J. Am. Chem. Soc. 2005, 127, 14388] of nanoparticle growth in the clear solution synthesis of silicalite-1 (MFI). We have implemented the model on a body-center cubic (bcc) lattice with second-neighbor repulsions, to generate a four-coordinate network that mimics the tetrahedral structure of silica. With this low-coordination lattice model we observe that the nanoparticles are metastable, possessing a core−shell structure with mostly silica in the core and templates forming a shell. Nanoparticle size is found to increase with temperature and decrease with solution pH, in …
Understanding Adsorption And Desorption Processes In Mesoporous Materials With Independent Disordered Channels, Peter A. Monson, Sergej Naumov, Rustem Valiullin, Jörg Kärger
Understanding Adsorption And Desorption Processes In Mesoporous Materials With Independent Disordered Channels, Peter A. Monson, Sergej Naumov, Rustem Valiullin, Jörg Kärger
Peter A. Monson
Using a lattice-gas model in mean-field theory, we discuss the problem of how adsorption and desorption of fluids in independent cylinderlike pores is influenced by variations in the pore diameter along the length of the pore, surface roughness of the pore walls, and chemical heterogeneity. We also consider the impact of contact with the bulk phase via the pore opening and the possibility of interactions between neighboring pores via a liquid film on the external surface of the material. We find that a combination of pore size variation along the length of the pore and surface roughness yields sorption hysteresis …
Modeling Relaxation Processes For Fluids In Porous Materials Using Dynamic Mean Field Theory: An Application To Partial Wetting, Peter A. Monson, John R. Edison
Modeling Relaxation Processes For Fluids In Porous Materials Using Dynamic Mean Field Theory: An Application To Partial Wetting, Peter A. Monson, John R. Edison
Peter A. Monson
We review a recently developed dynamic mean field theory for fluids confined in porous materials and apply it to a case where the solid-fluid interactions lead to partial wetting on a planar surface. The theory describes the evolution of the density distribution for a fluid in a pore that has contact with the bulk during a quench in the bulk chemical potential. In this way the dynamics of adsorption and desorption can be studied. By focusing on partial wetting situation we can investigate influence of a weaker surface field on the mechanisms of capillary condensation and desorption. We have studied …
Solid−Fluid And Solid−Solid Equilibrium In Hard Sphere United Atom Models Of N-Alkanes: Rotator Phase Stability, Peter A. Monson, M. Cao
Solid−Fluid And Solid−Solid Equilibrium In Hard Sphere United Atom Models Of N-Alkanes: Rotator Phase Stability, Peter A. Monson, M. Cao
Peter A. Monson
We present a study of the phase behavior for models of n-alkanes with chain lengths up to C21 based on hard sphere united atom models of methyl and methylene groups, with fixed bond lengths and C−C−C bond angles. We extend earlier work on such models of shorter alkanes by allowing for gauche conformations in the chains. We focus particularly on the orientational order about the chain axes in the solid phase near the melting point, and our model shows how the loss of this orientational order leads to the formation of rotator phases. We have made extensive calculations of the …
Mean Field Kinetic Theory For A Lattice Gas Model Of Fluids Confined In Porous Materials, Peter A. Monson
Mean Field Kinetic Theory For A Lattice Gas Model Of Fluids Confined In Porous Materials, Peter A. Monson
Peter A. Monson
We consider the mean field kinetic equations describing the relaxation dynamics of a lattice model of a fluid confined in a porous material. The dynamical theory embodied in these equations can be viewed as a mean field approximation to a Kawasaki dynamics Monte Carlo simulation of the system, as a theory of diffusion, or as a dynamical density functional theory. The solutions of the kinetic equations for long times coincide with the solutions of the static mean field equations for the inhomogeneous lattice gas. The approach is applied to a lattice gas model of a fluid confined in a finite …
Understanding Capillary Condensation And Hysteresis In Porous Silicon: Network Effects Within Independent Pores, Peter A. Monson, Sergej Naumov, Alexey Khokhlov, Rustem Valiullin, Jörg Kärger
Understanding Capillary Condensation And Hysteresis In Porous Silicon: Network Effects Within Independent Pores, Peter A. Monson, Sergej Naumov, Alexey Khokhlov, Rustem Valiullin, Jörg Kärger
Peter A. Monson
The ability to exert a significant degree of pore structure control in porous silicon materials has made them attractive materials for the experimental investigation of the relationship between pore structure, capillary condensation, and hysteresis phenomena. Using both experimental measurements and a lattice gas model in mean field theory, we have investigated the role of pore size inhomogeneities and surface roughness on capillary condensation of N2 at 77 K in porous silicon with linear pores. Our results resolve some puzzling features of earlier experimental work. We find that this material has more in common with disordered materials such as Vycor glass …
Studies Of A Lattice Model Of Water Confined In A Slit Pore, Peter A. Monson, J. -C. Liu, Frank Van Swol
Studies Of A Lattice Model Of Water Confined In A Slit Pore, Peter A. Monson, J. -C. Liu, Frank Van Swol
Peter A. Monson
We describe an extension of the Bell−Salt lattice model of water to the study of water confined in a slit pore. Wall−fluid interactions are chosen to be qualitatively representative of water interacting with a graphite surface. We have calculated the bulk vapor−liquid phase coexistence for the model through direct Monte Carlo simulations of the vapor−liquid interface. Adsorption and desorption isotherms in the slit pore were calculated using grand canonical ensemble Monte Carlo simulations. In addition, the thermodynamic conditions of vapor−liquid equilibrium for the confined fluid were determined. Our results are consistent with recent calculations for off-lattice models of confined water …
Further Studies Of A Simple Atomistic Model Of Silica: Thermodynamic Stability Of Zeolite Frameworks As Silica Polymorphs, Peter A. Monson, S. M. Auerbach, M. H. Ford
Further Studies Of A Simple Atomistic Model Of Silica: Thermodynamic Stability Of Zeolite Frameworks As Silica Polymorphs, Peter A. Monson, S. M. Auerbach, M. H. Ford
Peter A. Monson
We have applied our previously reported model of silica based on low coordination and strong association [ J. Chem. Phys. 121, 8415 (2004) ], to the calculation of phase stability of zeolite frameworks SOD, LTA, MFI, and FAU as silica polymorphs. We applied the method of Frenkel and Ladd for calculating free energies of these solids. Our model predicts that the MFI framework structure has a regime of thermodynamic stability at low pressures and above ∼ 1400 K, relative to dense phases such as quartz. In contrast, our calculations predict that the less dense frameworks SOD, LTA, and FAU exhibit …
Calculation Of Free Energies And Chemical Potentials For Gas Hydrates Using Monte Carlo Simulations, Peter A. Monson, S. J. Wierzchowski
Calculation Of Free Energies And Chemical Potentials For Gas Hydrates Using Monte Carlo Simulations, Peter A. Monson, S. J. Wierzchowski
Peter A. Monson
We describe a method for calculating free energies and chemical potentials for molecular models of gas hydrate systems using Monte Carlo simulations. The method has two components: (i) thermodynamic integration to obtain the water and guest molecule chemical potentials as functions of the hydrate occupancy; (ii) calculation of the free energy of the zero-occupancy hydrate system using thermodynamic integration from an Einstein crystal reference state. The approach is applicable to any classical molecular model of a hydrate. We illustrate the methodology with an application to the structure-I methane hydrate using two molecular models. Results from the method are also used …
Wetting Of Rings On A Nanopatterned Surface: A Lattice Model Study, Peter A. Monson, Fabien Porcheron
Wetting Of Rings On A Nanopatterned Surface: A Lattice Model Study, Peter A. Monson, Fabien Porcheron
Peter A. Monson
We perform mean-field density functional theory calculations on a lattice model to study the wetting of a solid substrate decorated with a ring pattern of nanoscale dimensions. We have found three different liquid morphologies on the substrate: a ring morphology where the liquid covers the pattern, a bulge morphology where a droplet is forming on one side of the ring, and a morphology where the liquid forms a cap spanning the nonwetting disk inside the pattern. We investigate the relative stability of these morphologies as a function of the ring size, wall-fluid interaction, and temperature. The results found are in …