Microstructure computer simulation

A special mention is in order of high-resolution electron microscopy (HREM), a variant that permits columns of atoms normal to the specimen surface to be imaged the resolution is better than an atomic diameter, but the nature of the image is not safely interpretable without the use of computer simulation of images to check whether the assumed interpretation matches what is actually seen. Solid-state chemists studying complex, non-stoichiometric oxides found this image simulation approach essential for their work. The technique has proved immensely powerful, especially with respect to the many types of defect that are found in microstructures. 

O. Yanagisawa, A. Almansour, K. Matsugi, T. Hatayama. Computer simulation for sohdified microstructure prediction of spheroidal graphite cast iron of the Fe-C-Si system. J Jpn Inst Met 50 1101, 1996. 

One of the major difficulties in developing theories of the rheology of coagulated or flocculated dispersions is that the microstructures of the aggregates are nonequilibrium structures under shear. Understandably, the rheology of such dispersions is history dependent, as we have seen above, and requires computer simulations and nonequilibrium statistical mechanics for proper study. 

H. J. Jou et al., Computer simulations for the prediction of microstructure/property variation in aeroturbine disks, Superalloys, Warrendale, PA pp. 877-886 (2004)... 

We hope to have demonstrated that computer simulation of transport and transformation processes on digitally reconstructed multi-phase media can be beneficial to practical chemical engineering applications. We believe that as chemical engineering becomes more product-oriented, the need to model phenomena that control material microstructure formation will gain in importance. We hope that this chapter will provide a useful starting point for those who wish to familiarize themselves with the relevant computational techniques. 

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. 

In some cases, one is interested in the structures of complex fluids only at the continuum level, and the detailed molecular structure is not important. For example, long polymer molecules, especially block copolymers, can form phases whose microstructure has length scales ranging from nanometers almost up to microns. Computer simulations of such structures at the level of atoms is not feasible. However, composition field equations can be written that account for the dynamics of some slow variable such as 0 (x), the concentration of one species in a binary polymer blend, or of one block of a diblock copolymer. If an expression for the free energy / of the mixture exists, then a Ginzburg-Landau type of equation can sometimes be written for the time evolution of the variable 0 with or without flow. An example of such an equation is (Ohta et al. 1990 Tanaka 1994 Kodama and Doi 1996)... 

FIGURE 27.7 Computer simulations of microstructures of (a-d) PZT and (e-h) SrTiOs thin-film cross sections illustrating microstructural evolution at various times during the transformation to the perovskite state. Lighter colors associated with intermediate phase darker colors associated with the perovskite phase. 

GCMC simulations, provided that the model of the adsorbent microstructure used in the simulations is sufficiently realistic. In the next section we describe a computer simulation algorithm which can be used to investigate this issue further. 

Computer simulation of the tweed microstructure induced during a ferroelastic phase transition. Green indicates ares of the crystal in which the order parameter is positive, and red indicates areas in which it is negative. Yellow areas are domain boundaries in which the order parameter is close to zero. 

Fig. 3. Computer simulation results using a time-dependent Ginzburg-Landau approach, showing the microstructural evolution after a temperature jump from the lamellar phase to the hexagonal cylinder phase for a moderately asymmetric diblock copolymer. The time units are arbitrary. (Reprinted with permission from Polymer 39, S. Y. Qi and Z.-G. Zheng, Weakly segregated block copolymers Anisotropic fluctuations and kinetics of order-order and order-disorder transitions, 4639-4648, copyright 1998, with permission of Excerpta Medica Inc.)...

Rheology and Microstructure of Interfaces Stabilized by Mixed Proteins and Surfactants A Computer Simulation Study... 

Pugnaloni, L.A., Ettelaie, R., and Dickinson, E. Computer simulation of the microstructure of a nanoparticle monolayer formed under interfacial compression, Langmuir, 20, 6096, 2004b. 

Substantial interest has been raised in the problem of the structure and dynamics of suspensions in shear hydrodynamic fields. ° ° The experiments showed that both shear-induced melting and shear-induced ordering can be observed at different particle volume fractions and shear rates. The nonequilibrium microstructure of the suspension under shear can be investigated in these experiments and compared with the predictions from analytical theories and computer simulations. 

Computer simulation of the deformation of microstructural models based on the kinetic theory of deformation, as in the work of Termonia et al [94-99], Bicerano et al [100] and Zaitsev et al [101], appears to be a more promising approach than the development of simple... 

Only the final product of the process (19.10), that is, molecular hydrogen (H2, HD, and D2), can be detected by online mass spectrometry. However, the catalyst microstructure may be reconstructed by the computer simulation, since the gas evolved remembers the surrounding hydrogen atoms in the environs Had and Dad atoms serve as peculiar markers of reactions (19.11) and (19.12) and thereby define on which site—either anodic or cathodic—they appear. The location of reactions (19.11) and (19.12) at specific site ensembles seems to be probable, taking into account a heterogeneity (structural, chemical, and energetic) of the real catalyst surface. This could be reconstructed from the H2, HD, and D2 distribution in the gas. 

Montaudo, M.S., Ballistreri, A., and Montaudo, G., Determination of Microstructure in Copolymers. Statistical Modeling and Computer Simulation of Mass Spectra, Macromolecules, 24, 5051 (1991). 

Notably two important tools need to be in place to speed up progress in emulsification with microstructured systems, the first one being computer simulations that allow for detailed investigation of formation mechanisms, as also illustrated in the key research finding sections on T-shaped junctions and microchannels. This allows for fast evaluation of various process parameters without the need of elaborative... 

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