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  • 1
    Electronic Resource
    Electronic Resource
    Adsorption Simulations of Small Molecules and Their Mixtures in a Zeolite Micropore (1994)
    s.l. : American Chemical Society
    Langmuir 10 (1994), S. 1257-1267 
    Details
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/la00016a046
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  • 2
    Electronic Resource
    Electronic Resource
    Theory and simulation of adsorption in a templated porous material: Hard sphere systems (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3006-3013 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An emerging strategy for controlling porosity in disordered materials is to employ a removable template during synthesis. We present here a theoretical description of adsorption in a templated porous material modeled as a collection of particles formed by an equilibrium quench of a binary mixture of matrix and template particles and subsequent removal of the template component. We show, using the replica method, that an adsorbed phase in the templated material is just the s=0 limit of a special s+2 component replica system. We present a set of Ornstein–Zernike equations relating the correlation functions of the matrix, template, and adsorbate components, solve these equations for the case of hard sphere interactions within the Percus–Yevick closure, and evaluate the system thermodynamics via the compressibility route. We also present a grand canonical Monte Carlo simulation of this model system and find good agreement between theory and simulation. We show that for systems of constant matrix+template volume fraction, templating always enhances adsorption and this enhancement is most pronounced when the template/matrix ratio is low and/or the template size is small. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480874
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  • 3
    Electronic Resource
    Electronic Resource
    Theory and simulation of the available volume for adsorption in a chain molecule templated porous material (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 4974-4981 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular templating offers a means of tailoring the pore space geometry of disordered materials. We present here a theoretical description of the available volume (porosity) for adsorption created by chain molecule templates. Our model material is a quenched, equilibrated hard-sphere/tangent hard-sphere chain mixture configuration with the chain molecules removed. We extend a diagrammatic theory [P. R. Van Tassel, Phys. Rev. E. 60, R25 (1999)], previously used for a hard-sphere template, to this system and obtain the required correlation functions from the polymer Percus–Yevick theory of a sticky two-point associating fluid mixture within an ideal chain approximation. We also apply Monte Carlo simulation. We find that the available volume increases with template length and that this is most pronounced for a small chain length (n≤4), a large template:matrix ratio, and a large adsorbate size. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1350442
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  • 4
    Electronic Resource
    Electronic Resource
    Enhanced saturation coverages in adsorption–desorption processes (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1483-1488 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Many experimental studies of protein deposition on solid surfaces involve alternating adsorption/desorption steps. In this paper, we investigate the effect of a desorption step (separating two adsorption steps) on the kinetics, the adsorbed-layer structure, and the saturation density. Our theoretical approach involves a density expansion of the pair distribution function and an application of an interpolation formula to estimate the saturation density as a function of the density at which the desorption process commences, ρ1, and the density of the depleted configuration, ρ2. The theory predicts an enhancement of the saturation density compared with that of a simple, uninterrupted random sequential adsorption (RSA) process and a maximum in the saturation density when ρ2=(2/3)ρ1. The theoretical results are in qualitative and semiquantitative agreement with the results of numerical simulations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480715
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  • 5
    Electronic Resource
    Electronic Resource
    Irreversible adsorption of macromolecules at a liquid–solid interface: Theoretical studies of the effects of conformational change (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7064-7073 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effects of particle conformational changes on the kinetics and saturation coverage of irreversible macromolecular adsorption at liquid–solid interfaces are investigated by computer simulation of a modified random sequential adsorption model. In this model, macromolecules (modeled as disks of diameter σα) adsorb onto a surface at a rate ka. Once adsorbed, the particles spread symmetrically and discretely to a larger diameter σβ at a rate ks. Adsorption or spreading events which result in the overlap of particles on the surface are not allowed. We investigate the effects of changes in spreading magnitude Σ (=σβ/σα) and relative spreading rate Ks (=ks/ka). We observe that the saturation coverage of spread particles decreases while that of unspread particles increases with spreading magnitude. This dependence is most pronounced for small spreading: the derivative of the surface coverage of both spread and unspread particles with respect to Σ diverges logarithmically when Σ→1. An increase in the rate of spreading increases the saturation coverage of spread particles while decreasing that of unspread particles. The dependence of the coverage on spreading rate is weaker than its dependence on spreading magnitude: a four order of magnitude change in Ks results in a factor of 2 change in the partial coverages. The coverage of unspread particles may become nonmonotonic in time for certain values of Σ and Ks. The total density of particles on the surface decreases and the average particle size increases with Ks, in accordance with recent protein adsorption experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468332
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical studies of the available volume for adsorption in a random quenched and depleted disordered medium (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 9530-9534 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The use of a removable template during synthesis of a disordered porous material can result in a material of greatly differing pore structure. We present here a theoretical study of the influence of a template on the material's available volume. We model the material as a medium formed by quenching and depleting an equilibrium fluid and develop a theoretical method by which the available volume for adsorption in this model material may be investigated. This method makes use of the known relationship between the direct correlation function and the available volume. An analysis of the diagrams contributing to the available volume shows that two types of field points are present: those corresponding to the density of the medium following depletion (ρ) and those corresponding to the density of the original quenched fluid (ρq). A perturbation term to the available volume is derived that accounts for the diagrams containing ρq field points. The resulting expression contains only the direct and total correlation function; these quantities are known exactly for a hard sphere system within the Percus–Yevick approximation. Using this approach, we show that for materials of a given density, those formed by depletion can possess available volumes enhanced by up to an order of magnitude. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475249
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  • 7
    Electronic Resource
    Electronic Resource
    Adsorption and energetics of xenon in mordenite: A Monte Carlo simulation study (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3029-3037 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Grand canonical Monte Carlo (GCMC) simulations were used to calculate energy contour maps, isodensity surfaces and adsorption isotherms of xenon in purely siliceous mordenite at 300 K using previously published potential parameters. Then, in order to understand the effect of aluminum content, Al-containing mordenites were modeled by adding the appropriate negative charge to each of the oxygen atoms in the mordenite framework and by inserting Na+ ions at fixed extra-framework positions previously identified from x-ray crystallographic data. GCMC simulations were again performed using these structure models. Both main channel and sidepocket xenon adsorption were observed in all mordenite structures. The sidepockets were found to be only singly occupied whereas the main channel allowed multiple occupancy. Sidepocket xenon adsorption became more favorable when cations (and aluminum) were introduced. In the main channel, xenon adsorbed into localized sites that were distributed in an octahedral arrangement within each unit cell with two apices in front of opposing sidepockets. These sites remained at the same location over the entire range of loading (0–16 Xe/unit cell) and cation (and aluminum) content. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470492
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  • 8
    Electronic Resource
    Electronic Resource
    A kinetic model of partially reversible protein adsorption (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 761-770 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a kinetic adsorption model for proteins that accounts for the experimentally observed properties of partial reversibility and surface induced conformational change. Particles (proteins) are modeled as disks that adsorb sequentially and without overlap at random positions onto a surface. Following adsorption, a particle can either desorb or spread symmetrically to a larger size. If the latter occurs, it remains adsorbed irreversibly. Both of these events obey first order kinetic rate laws. We derive analytical results in the asymptotic regime and report Monte Carlo results for shorter times. This model yields adsorbed phases that are more dense than those predicted by models of purely irreversible adsorption. We attribute this densification to a fluid structure that is quite liquidlike. We show that a number of experimentally observed kinetic behaviors can be reproduced with this model and that it is in good quantitative agreement with recent experiments. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473164
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  • 9
    Electronic Resource
    Electronic Resource
    Open-system Monte Carlo simulations of Xe in NaA (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 8919-8928 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The grand canonical ensemble Monte Carlo method is used to determine the adsorption isotherm, energy, entropy, occupancy distribution, and density distribution of Xe atoms adsorbed in zeolite NaA, which is modeled as a single alpha cage and as a network of connected cages. The isotherms exhibit multiple plateaus, indicating the existence of certain favored loadings. These plateaus can be predicted by considering constant loading energy and density distributions found previously. A linear regression method of determining the constant loading entropy of Xe atoms is presented. The entropy is a smooth function of loading, which suggests that the structure of the adsorbed Xe is also smoothly varying. The pressures needed to obtain complete loading are quite large and beyond the range of conventional experiment. However, the simulated isotherm and occupancy distribution compare well with the available experimental data. Structural modifications of NaA in the form of cation removal are investigated. A cation-poor model NaA adsorbs fewer Xe at low chemical potential due to its smaller electric field, but has a larger overall adsorption capacity due to its greater accessible volume.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464451
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  • 10
    Electronic Resource
    Electronic Resource
    New lattice model for adsorption of small molecules in zeolite micropores (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 925-934 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new adsorption model is developed for small molecules in zeolites whose form is based on features revealed by molecular simulation. Adsorption is assumed to occur onto a 3-D polyhedral lattice, and both the energy and entropy of the lattice sites are accounted for using a statistical mechanics approach. Energetic interactions are described by an Ising model with both 2- and multibody nearest-neighbor in-teractions. Entropic interactions are included by an adsorption site volume term which accounts for the loss of traslational freedom associated with lattice crowding.The model is applied to a system of small molecules (xenon, methane) adsorbed in idealized zeolite NaA, where adsorption has been shown by computer simulation to occur on finite, cuboctahedral lattices (Van Tassel et al., 1992). The model quantitavely predicts the simulated isotherm over the entire pressure range. Comparison is made with a Langmuir model and a van der Waals gas model which, although valid at low pressures, fail at high pressures due to overestimation of translational entropy and inaccurate portrayal of sorbate-sorbate interaction energy.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400603
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