Investigations of the Mechanical and Hydrothermal Stabilities of SBA-15 and Al-SBA-15 Mesoporous Materials

MRS Advances ◽  
2016 ◽  
Vol 1 (35) ◽  
pp. 2453-2458 ◽  
Author(s):  
Dayton G. Kizzire ◽  
James Thomas ◽  
Sonal Dey ◽  
Hayley Osman ◽  
Robert A. Mayanovic ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Pore Size ◽  
Mesoporous Materials ◽  
High Surface ◽  
Md Simulations ◽  
High Energy ◽  
Hydrothermal Stability ◽  
Synchrotron Source ◽  
Stability Properties

ABSTRACTPeriodic mesoporous materials possess high surface to volume ratio and nano-scale sized pores, making them potential candidates for heterogeneous catalysis, ion exchange, gas sensing and other applications. In this study, we use in situ small angle x-ray scattering (SAXS) and molecular dynamics (MD) simulations to investigate the mechanical and hydrothermal stability properties of periodic mesoporous SBA-15 silica and SBA-15 type aluminosilica (Al-SBA-15) to extreme conditions. The mesoporous SBA-15 silica and Al-SBA-15 aluminosilica possess amorphous frameworks and have similar pore size distribution (pore size ∼9-10 nm). The in situ SAXS measurements were made at the B1 beamline, at the Cornell High Energy Synchrotron Source (CHESS). The mesoporous SBA-15 silica and Al-SBA-15 aluminosilica specimens were loaded in a diamond anvil cell (DAC) for pressure measurements, and, separately, with water in the DAC for hydrothermal measurements to high P-T conditions (to 255 °C and ∼ 114 MPa). Analyses of the pressure-dependent SAXS data show that the mesoporous Al-SBA-15 aluminosilica is substantially more mechanically stable than the SBA-15 silica. Hydrothermal measurements show a small net swelling of the framework at elevated P-T conditions, due to dissolution of water into the pore walls. Under elevated P-T conditions, the Al-SBA-15 aluminosilica shows significantly greater hydrothermal stability than the SBA-15 silica. Our MD simulations show that the bulk modulus value of periodic mesoporous SBA-15 silica varies exponentially with percentage porosity. Molecular dynamics simulations are being made in order to better understand how the pore architecture and the chemical composition of the host structure govern the stability properties of the mesoporous materials.

scholarly journals In Situ Stress Tensor Determination during Phase Transformation of a Metal Matrix Composite by High-Energy X-ray Diffraction

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1415 ◽  
Author(s):  
Guillaume Geandier ◽  
Lilian Vautrot ◽  
Benoît Denand ◽  
Sabine Denis
Keyword(s):  
Phase Transformation ◽  
Stress Tensor ◽  
Metal Matrix Composite ◽  
Matrix Composite ◽  
Metal Matrix ◽  
High Energy ◽  
X Ray Diffraction ◽  
Synchrotron Source ◽  
X Ray

In situ high-energy X-ray diffraction using a synchrotron source performed on a steel metal matrix composite reinforced by TiC allows the evolutions of internal stresses during cooling to be followed thanks to the development of a new original experimental device (a transportable radiation furnace with controlled rotation of the specimen). Using the device on a high-energy beamline during in situ thermal treatment, we were able to extract the evolution of the stress tensor components in all phases: austenite, TiC, and even during the martensitic phase transformation of the matrix.

In situ formed methyl-co-(bis-R) silsesquioxane based polymer networks with solvent controlled pore size distributions and high surface areas

2020 ◽  
Vol 4 (3) ◽  
pp. 851-861 ◽  
Author(s):  
Nai-hsuan Hu ◽  
Chamika U. Lenora ◽  
Timothy A. May ◽  
Nathan C. Hershberger ◽  
Joseph C. Furgal
Keyword(s):  
Pore Size ◽  
High Surface ◽  
Polymer Networks ◽  
Size Distributions ◽  
Surface Areas ◽  
Pore Size Distributions

Specific pore size distributions of synthesized methylsilsesquioxane-based network materials stem from a combination of the solvation of monomers and growing oligomers, as well as miscibility of water in tested solvents; enabling specific analyte uptake materials.

scholarly journals Dissolution Enhancement of Gliclazide Using pH Change Approach in Presence of Twelve Stabilizers with Various Physico-Chemical Properties

2009 ◽  
Vol 12 (3) ◽  
pp. 250 ◽  
Author(s):  
Roya Talari ◽  
Ali Nokhodchi ◽  
Seyed Abolfazl Mostafavi ◽  
Jaleh Varshosaz
Keyword(s):  
Dissolution Rate ◽  
Fine Particles ◽  
High Surface ◽  
High Surface Area ◽  
Chemical Properties ◽  
High Energy ◽  
Dissolution Enhancement ◽  
Ph Change ◽  
Fast Dissolution

Purpose: The micronization using milling process to enhance dissolution rate is extremely inefficient due to a high energy input, and disruptions in the crystal lattice which can cause physical or chemical instability. Therefore, the aim of the present study is to use in situ micronization process through pH change method to produce micron-size gliclazide particles for fast dissolution hence better bioavailability. Methods: Gliclazide was recrystallized in presence of 12 different stabilizers and the effects of each stabilizer on micromeritic behaviors, morphology of microcrystals, dissolution rate and solid state of recrystallized drug particles were investigated. Results: The results showed that recrystallized samples showed faster dissolution rate than untreated gliclazide particles and the fastest dissolution rate was observed for the samples recrystallized in presence of PEG 1500. Some of the recrystallized drug samples in presence of stabilizers dissolved 100% within the first 5 min showing at least 10 times greater dissolution rate than the dissolution rate of untreated gliclazide powders. Micromeritic studies showed that in situ micronization technique via pH change method is able to produce smaller particle size with a high surface area. The results also showed that the type of stabilizer had significant impact on morphology of recrystallized drug particles. The untreated gliclazide is rod or rectangular shape, whereas the crystals produced in presence of stabilizers, depending on the type of stabilizer, were very fine particles with irregular, cubic, rectangular, granular and spherical/modular shape. The results showed that crystallization of gliclazide in presence of stabilizers reduced the crystallinity of the samples as confirmed by XRPD and DSC results. Conclusion: In situ micronization of gliclazide through pH change method can successfully be used to produce micron-sized drug particles to enhance dissolution rate.

scholarly journals Molecular Dynamics Simulation of 2-Benzimidazolyl-Urea with DPPC Lipid Membrane and Comparison with a Copper(II) Complex Derivative

Membranes ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 743
Author(s):  
Georgios Rossos ◽  
Sotiris K. Hadjikakou ◽  
Nikolaos Kourkoumelis
Keyword(s):  
Molecular Dynamics ◽  
Lipid Membrane ◽  
Membrane Damage ◽  
Md Simulations ◽  
High Energy ◽  
Biological Properties ◽  
Complex Compounds ◽  
Phospholipid Bilayer ◽  
Dynamics Simulation ◽  
Benzimidazole Derivatives

Benzimidazole derivatives have gained attention recently due to their wide pharmacological activity acting as anti-inflammatory, hypotensive, analgesic, and anti-aggregatory agents. They are also common ligands in transition metal coordination chemistry, forming complex compounds with enhanced biological properties, especially in targeted cancer therapy. A key issue to understand anti-tumour effects is drug permeability through cellular membranes, as poor permeability outcomes can avert further futile drug development. In this work, we conducted atomistic molecular dynamics (MD) simulations and biased MD simulations to explore the interactions of 2-benzimidazolyl-urea with a phospholipid bilayer (dipalmitoylphosphatidylcholine, DPPC) together with a previously synthesized copper(II) complex compound. The aim was to study the permeability of these compounds by assessing their free energy profile along the bilayer normal. The simulations indicated that both the ligand (2-benzimidazolyl-urea, BZIMU) and the complex show a similar behaviour, yielding high energy barriers for the permeation process. However, with increasing concentration of BZIMU, the molecules tend to aggregate and form a cluster, leading to the formation of a pore. Clustering and pore formation can possibly explain the previously observed cytotoxicity of the BZIMU molecule via membrane damage.

Molecular dynamics simulations for CL-20/TNT co-crystal based polymer-bonded explosives

2017 ◽  
Vol 16 (08) ◽  
pp. 1750072
Author(s):  
Qiang Cao ◽  
Ji Jun Xiao ◽  
Pei Gao ◽  
Shen Shen Li ◽  
Feng Zhao ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Pair Correlation ◽  
Md Simulations ◽  
High Energy ◽  
Binding Energies ◽  
Polymer Binders ◽  
Polymer Bonded Explosives ◽  
Dynamics Simulations ◽  
Theoretical Results ◽  
Crystal Compound

Molecular dynamics (MD) simulations were carried out to study the polymer-bonded explosives (PBXs) where the explosive base was the well-known high energy co-crystal compound, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazaisowurtzitane/2,4,6-trinitrotoluene (CL-20/TNT), and the polymer binders were fluorine rubber (F[Formula: see text], fluorine resin (F[Formula: see text], polyvinyl acetate (PVAc) and polystyrene (PS), respectively. The binding energies, pair correlation functions (PCFs) and mechanical properties of the PBXs were reported. According to our theoretical results of binding energies, the compatibility of the PBXs is predicted to be in the following order: CL-20/TNT/PVAc[Formula: see text] CL-20/TNT/F[Formula: see text] [Formula: see text] CL-20/TNT/PS [Formula: see text] CL-20/TNT/F[Formula: see text]. The binding energies of the PBXs on three crystalline surfaces, (100), (001), (010), of the CL-20/TNT co-crystal were also compared: CL-20/TNT(100)[Formula: see text]CL-20/TNT(001)[Formula: see text]CL-20/TNT(010) for F[Formula: see text], F[Formula: see text], and PS; CL-20/TNT(001)[Formula: see text]CL-20/TNT(100)[Formula: see text]CL-20/TNT(010) for PVAc. The PCF analysis reveals that there exist H-bonds between H and O, F, and N atoms on all three interfaces and among all H-bonds, N H-bond has the fewest number. For the CL-20/TNT co-crystal, the moduli can be reduced by adding a small amount of the polymer binders but the ductility can be prolonged only by F[Formula: see text] and F[Formula: see text].

Thermal Conductivity of Sol-Gel Amorphous Mesoporous Silica Thin Films: Molecular Dynamics Simulations Versus Experiments

2011 ◽  
Author(s):  
Thomas Coquil ◽  
Laurent Pilon
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Mesoporous Silica ◽  
Pore Size ◽  
Amorphous Silica ◽  
Sol Gel ◽  
Md Simulations ◽  
Silica Matrix ◽  
Simulation Cell

This study reports non-equilibrium molecular dynamics (MD) simulations predicting the thermal conductivity of amorphous mesoporous silica. The heat flux was imposed using the Muller-Plathe method and interatomic interactions were modeled using the van Beest, Kramer and van Santen (BKS) potential. First, simulations were validated against results reported in the literature for dense quartz and amorphous silica. The BKS potential was found to significantly overestimate the thermal conductivity of dense amorphous silica and results depended on the length of the simulation cell. Then, highly ordered pores were introduced in an amorphous silica matrix by removing atoms within selected areas of the simulation cell. Effects of the simulation cell length, pore size, and porosity on the thermal conductivity were investigated at room temperature. Results were compared with predictions from commonly used effective medium approximations as well as with previously reported experimental data for films with porosity and pore diameter ranging from 20% to 48% and 30 to 180 Å, respectively. Predictions of MD simulations overestimated the experimental data and agreed with predictions from the coherent potential model. However, MD simulations confirmed that thermal conductivity in sol-gel amorphous mesoporous materials was independent of pore size and depended only on porosity.

Synchrotron Characterization of Texture and Stress Evolution in Ag Films

2007 ◽  
Vol 1027 ◽  
Author(s):  
Aaron Vodnick ◽  
Michael Lawrence ◽  
Bethany Little ◽  
Derek Worden ◽  
Shefford Baker
Keyword(s):  
Real Time ◽  
Driving Forces ◽  
Texture Evolution ◽  
High Energy ◽  
Fiber Texture ◽  
X Ray Diffraction ◽  
Synchrotron Source ◽  
The Individual

AbstractReal-time in-situ synchrotron x-ray diffraction measurements were performed at the Cornell High Energy Synchrotron Source to characterize both the texture evolution and stresses within the individual texture components of Ag films during recrystallization. As deposited films had a nearly perfect (111) fiber texture. During isothermal anneals, stress and texture were characterized in real-time as the texture evolved into a strong (001) fiber. An Avrami analysis of the evolving texture fractions yielded very different activation energies for films on different barrier layers, suggesting different governing mechanisms were responsible for secondary grain growth. The strains were used to test a common model for texture prediction that assumes the same strain within each texture component. It was found that secondary (001) grains were able to grow primarily strain free. Selection for this strain energy minimizing orientation occurred during the nucleation process during which texture interactions play an important role. By using these real time measurements, we are able to show that driving forces for texture transformations in metal films may not be as simple previously described.

scholarly journals Quick X-ray reflectivity using monochromatic synchrotron radiation for time-resolved applications

2018 ◽  
Vol 25 (3) ◽  
pp. 706-716 ◽  
Author(s):  
H. Joress ◽  
J. D. Brock ◽  
A. R. Woll
Keyword(s):  
Synchrotron Radiation ◽  
Film Growth ◽  
Sample Surface ◽  
High Energy ◽  
Time Resolved ◽  
Synchrotron Source ◽  
X Ray ◽  
Area Detector ◽  
Monochromatic Synchrotron

A new technique for the parallel collection of X-ray reflectivity (XRR) data, compatible with monochromatic synchrotron radiation and flat substrates, is described and applied to thein situobservation of thin-film growth. The method employs a polycapillary X-ray optic to produce a converging fan of radiation, incident onto a sample surface, and an area detector to simultaneously collect the XRR signal over an angular range matching that of the incident fan. Factors determining the range and instrumental resolution of the technique in reciprocal space, in addition to the signal-to-background ratio, are described in detail. This particular implementation records ∼5° in 2θ and resolves Kiessig fringes from samples with layer thicknesses ranging from 3 to 76 nm. The value of this approach is illustrated by showingin situXRR data obtained with 100 ms time resolution during the growth of epitaxial La0.7Sr0.3MnO3on SrTiO3by pulsed laser deposition at the Cornell High Energy Synchrotron Source (CHESS). Compared with prior methods for parallel XRR data collection, this is the first method that is both sample-independent and compatible with the highly collimated, monochromatic radiation typical of third-generation synchrotron sources. Further, this technique can be readily adapted for use with laboratory-based sources.

scholarly journals A survey of algorithms for transforming molecular dynamics data into metadata for in situ analytics based on machine learning methods

2020 ◽  
Vol 378 (2166) ◽  
pp. 20190063
Author(s):  
Michela Taufer ◽  
Trilce Estrada ◽  
Travis Johnston
Keyword(s):  
Machine Learning ◽  
Molecular Dynamics ◽  
Drug Design ◽  
High Performance ◽  
Molecular System ◽  
Md Simulations ◽  
Ligand Docking ◽  
Learning Methods ◽  
Machine Learning Methods

This paper presents the survey of three algorithms to transform atomic-level molecular snapshots from molecular dynamics (MD) simulations into metadata representations that are suitable for in situ analytics based on machine learning methods. MD simulations studying the classical time evolution of a molecular system at atomic resolution are widely recognized in the fields of chemistry, material sciences, molecular biology and drug design; these simulations are one of the most common simulations on supercomputers. Next-generation supercomputers will have a dramatically higher performance than current systems, generating more data that needs to be analysed (e.g. in terms of number and length of MD trajectories). In the future, the coordination of data generation and analysis can no longer rely on manual, centralized analysis traditionally performed after the simulation is completed or on current data representations that have been defined for traditional visualization tools. Powerful data preparation phases (i.e. phases in which original row data is transformed to concise and still meaningful representations) will need to proceed data analysis phases. Here, we discuss three algorithms for transforming traditionally used molecular representations into concise and meaningful metadata representations. The transformations can be performed locally. The new metadata can be fed into machine learning methods for runtime in situ analysis of larger MD trajectories supported by high-performance computing. In this paper, we provide an overview of the three algorithms and their use for three different applications: protein–ligand docking in drug design; protein folding simulations; and protein engineering based on analytics of protein functions depending on proteins' three-dimensional structures. This article is part of a discussion meeting issue ‘Numerical algorithms for high-performance computational science’.

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