Computer simulations of adsorption

Fig. 3.36 Segment density profiles from a Monte Carlo computer simulation of adsorption of a BAB triblock at a planar interface, where the hydrophobic B block is preferentially adsorbed (Balazs and Lewandowski 1990). Profiles are plotted for different A segment-surface interaction parameters, AS, with Xas = 0 and a chain length - 30 units.

Fig. 2. Computer simulations of adsorption in the case of four layers with equal values of the binding parameters. o is taken to be 100. Jantti s method proves to be useful in spite of the layer effect .

Bakaev V. A. and Steele W. A., Grand Canonical Ensemble Computer Simulation of Adsorption of Argon on a Heterogeneous Surface. Langmuir 8 (1992) 148. 

Computer simulation of adsorption on amorphous oxide surfaces... 

Thus, the surface of this amorphous carbon (which is a model of the surfaces of non-graphitized carbon blacks [23]) differs considerably from the surface of amorphous oxide and the main structural characteristics such as the C-C and 0-0 coordination numbers are also drastically different. Nevertheless, the adsorption properties of heterogeneous surfaces of various nongraphitized carbon blacks with respect to an inert adsorbate such as argon are not that drastically different and actually have many common features. We discuss these properties in the next section. Here we only use this fact to show that subtle structural differences of various models of amorphous oxide surfaces discussed above may be not that important for their adsorption properties in comparison to other factors such as indefiniteness of adsorption potential on oxide surfaces (see below). Because of its generality and in spite of its approximate character, the BS appears to be a convenient model for the computer simulation of adsorption on amorphous, and even more general (see Introduction) heterogeneous oxide surfaces. 

Bakaev, V. and Steele, W.A. (1992). Grand canonical ensemble computer simulation of adsorption of argon oh a heterogeneous surface. Langmuir, 8, 148. 

Computer simulations of adsorption isotherms for Ar on rigid homogeneous bundles predict the existence of three different phases in the first layer [49]. The simulations found that, at low temperatures, the film grows by the formation of successive lines or channels of atoms on the outer surface of the SWNTs. 

The methods of computer simulation of adsorption (and diffusion) in micro-porous solids were described in Chapter 4 a summary is given in Table 4.1. These techniques are now sufficiently well developed for physisorption that thermodynamic properties can be predicted routinely for relatively simple adsorbates, once the structural details of the host are known. Molecular mechanics using standard forcelields are very successful for zeolitic systems, which take into account dispersive interactions satisfactorily, but it is also possible to use higher level calculations. 

Figure 6 Aggregates at surfaces corresponding to perforated bilayers (only tail groups are shown) (a and aT) for H4T4 and full bilayer (b and bT) for H2T4. (Reprinted from J. Coll. hit. Sci., 313, X. Zhang, B. Chen, Z. Wang Computer simulation of adsorption kinetics of surfactants on solid surfaces 414 2007, with permission from Elsevier.)...

S. Murad, J. G. Powles. Computer simulation of osmosis and reverse osmosis in solutions. Chem Phys Lett 225A11, 1994 S. Murad. Molecular dynamics of osmosis and reverse osmosis in solutions. Adsorption 2 95, 1996. 

Garofalini, S.H. (1990) Molecular dynamics computer simulations of silica surface structure and adsorption of water molecules, J. Non-Cryst. Solids, 120, 1. 

This chapter is concerned with the application of liquid state methods to the behavior of polymers at surfaces. The focus is on computer simulation and liquid state theories for the structure of continuous-space or off-lattice models of polymers near surfaces. The first computer simulations of off-lattice models of polymers at surfaces appeared in the late 1980s, and the first theory was reported in 1991. Since then there have been many theoretical and simulation studies on a number of polymer models using a variety of techniques. This chapter does not address or discuss the considerable body of literature on the adsorption of a single chain to a surface, the scaling behavior of polymers confined to narrow spaces, or self-consistent field theories and simulations of lattice models of polymers. The interested reader is instead guided to review articles [9-11] and books [12-15] that cover these topics. 

The main goal of the molecular dynamics computer simulation of ionic solvation and adsorption on a metal surface has been to test the above model and to provide more quantitative information about the different factors that influence the structure of hydrated ions at the interface. Unfortunately, most of the experimental information about these issues has been obtained from indirect measurements such as capacity and current-potential plots, although in recent years in situ experimental techniques have begun to provide an accurate test of the above model. For a recent review of experimental techniques and the theory of ionic adsorption at the water/metal interface, see the excellent paper by Philpott. ... 

This chapter is organized as follows. The thermodynamics of the critical micelle concentration are considered in Section 3.2. Section 3.3 is concerned with a summary of experiments characterizing micellization in block copolymers, and tables are used to provide a summary of some of the studies from the vast literature. Theories for dilute block copolymer solutions are described in Section 3.4, including both scaling models and mean field theories. Computer simulations of block copolymer micelles are discussed in Section 3.5. Micellization of ionic block copolymers is described in Section 3.6. Several methods for the study of dynamics in block copolymer solutions are sketched in Section 3.7. Finally, Section 3.8 is concerned with adsorption of block copolymers at the liquid interface. 

Dickinson, E., and Euston, S. R. (1991a). Computer simulation of macromolecular adsorption. In Food Polymers, Gels and Colloids, Dickinson, E. (Ed.), pp. 557-563. Royal Chem. Soc., London. 

Many new adsorbents have been developed over the past 20 years including carbon molecular sieves, new zeolites and aluminophosphates, pillared clays and model mesoporous solids. In addition, various spectroscopic, microscopic and scattering techniques can now be employed for studying the state of the adsorbate and microstructure of the adsorbent. Major advances have been made in the experimental measurement of isotherms and heats of adsorption and in the computer simulation of physisorption. 

Framework Dynamics Including Computer Simulations of the Water Adsorption Isotherm of Zeolite Na-MAP. See also J.-R. Hill, C. M. Freeman, and L. Subramanian, in Reviews in Computational Chemistry, K. B. Lipkowitz and D. B. Boyd, Eds., Wiley-VCH, New York, 2000, Vol. 16, pp. 141-216. Use of Force Fields in Materials Modeling. The shell model is also discussed by B. van de Graaf, S. L. Njo, and K. S. Smirnov, in Reviews in... 

M. J. Bojan and W. A. Steele, Computer Simulations of the Adsorption of Xenon on Stepped Surfaces, Mol. Phys., in press. 

A. Vemov and W. A. Steele, Computer Simulations of Benzene Adsorbed on Graphite. 1. 85 K, Langmuir 7 (1991) 3110-3117 . 2. 298 K, ibid 2817-2820. References to experimental and other simulation studies of this system are contained in these papers. Also, A. Vemov and W. A. Steele Computer Simulations of Benzene Adsorbed on Graphite. 85 - 298 K, in Proc. 4 Int. Conf. On Fundamentals of Adsorption, ed. M. Suzuki, Kodansha Publishers, Tokyo, 1993, 695-701 M. A. Matties and R. Hentschke, Molecular Dynamics Simulation of Benzene on Graphite 1. Phase Behavior of an Adsorbed Monolayer, Langmuir 12 (1996) 2495-2500 2. Phase Behavior of Adsorbed Multilayers, ibid, 2501-2504. 

A. V. Vemov and W. A. Steele, Dynamics of Nitrogen Molecules Adsorbed on Graphite by Computer Simulation, Langmuir 2 (1986) 606-612 R. M. Lyndon-Bell, J. Talbot, D. J. Tildesley and W. A. Steele, Reorientation of N2 Adsorbed on Graphite in Various Computer Simulated Phases, Mol. Phys. 54 (1985) 183-195 A. V. Vemov and W. A. Steele, Computer Simulations of the Motions of N2 Adsorbed on the Graphite Basal Plane, in Proc. International Conference on the Fundamentals of Adsorption, ed. A. I. Liapis, Engineering Foundation, New York (1987) 611-618. 

W. A, Steele, Computer Simulation of Surface Diffusion in Adsorbed Phases, in Equilibria and Dynamics of Gas Adsorption on Heterogeneous Solid Surfaces, ed. W. Rudzinski, W. A. Steele and G. Zgrablich (Elsevier, Amsterdam, 1996), 451-486. 

D. Nicholson and N. G. Parsonage, Computer Simulation of the Statistical Mechanics of Adsorption, Academic Press, London, 1982... 

As soon as the expressions and constants in Eq. (4) are fixed one may proceed with calculation of the adsorption energy at a given point of adsorption space. However, to make such a calculation possible one has to know the positions of all the atoms of adsorbent relative to the given point. In other words, one has to know exactly the atomic structure of the adsorbent. This is what is in fact unknown for amorphous oxides. Although one can simulate the atomic structure at the surface of an amorphous oxide as described above, the reliability of the result can at present only be checked by comparison of prediction of adsorption properties with experimental data. But the calculation of adsorption properties (described below) includes, generally speaking, two unknowns the atomic structure of an adsorbent and the adsorption potential. This is the reason why the computer simulation of physical adsorption on amorphous oxides should be preceded by similar simulations on oxides with well defined crystalline structures. 

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