Computer simulation of fractal dimensions of fat crystal networks

The rheological properties of fat-structured products are determined by the microstructure of their fat crystal networks, which can be quantified by using microscopical and rheological techniques. Of particular interest to this study is the quantification of the fractal dimension of the network using these two techniques. Fractal dimensions determined by polarized light microscopy include box-counting, particle-counting, and Fouriertransform fractal dimensions, whereas the fractal dimensions determined by small deformation dynamic rheology exploit the dependence of the storage modulus on the solids' volume fraction. This work reveals that different microscopy fractal dimensions are sensitive to different microstructural factors within the fat crystal network, and thus have different physical meanings. The boxcounting fractal dimension, D _b , increases with increases in crystal size and area fraction of the fat crystals, whereas the particlecounting fractal dimension, D _f , is sensitive to the radial distribution pattern of fat crystals; and the Fourier-transform fractal dimension, D _FT, decreases with increasing crystal size. In the studies on the macroscopic physical properties of fat crystal networks, it is necessary to find the determining structural characteristics and then use the fractal dimensions that are most closely related.     

Influence of pH on the crystal structure of NiMoO4 nanomaterials and their supercapacitor performances

Three types of NiMoO₄ nanomaterials with different morphologies and crystal structures were synthesized by regulating the pH value of the precursor solutions. The corresponding electrochemical performances were also systematically measured. Very interestingly, with increasing of the pH value, the morphologies of NiMoO₄ nanomaterials changed from nanorods to nanosheets, and eventually became to nanoparticles. The NiO/MoO₃ (NiMo-7) sample, prepared at the pH of 7 in the precursor solution, exhibited highly interconnected porous structure, demonstrating much higher specific surface area and enhanced specific capacitance (1516 F/g) at 1 A/g. The assembled asymmetric supercapacitor NiMo-7//AC also delivered a high energy density of 50.13 Wh/kg at 749.9 W/kg and good cyclic stability with a capacity retention of 76% after 5000 cycles at 10 A/g. These results indicated that the NiMo-7 electrode has a very promising application prospect in electrochemical energy storage.     

Hybrid versus global thermostatting in molecular-dynamics simulation of methane-hydrate crystallisation

Molecular-dynamics (MD) simulations have been performed for the growth of a spherical methane-hydrate nano-crystallite, surrounded by a supersaturated water-methane liquid phase, using both a hybrid and globalsystem thermostatting approach. It was found that hybrid thermostatting led to more sluggish growth and the establishment of a radial temperature profile about the spherical hydrate crystallite, in which the growing crystal phase is at a higher temperature than the surrounding liquid phase in the interfacial region, owing to latent-heat dissipation. In addition, Onsager's-hypothesis fluctuation-dissipation analysis of fluctuations in the number of crystal-state water molecules at the interface shows slower growth.     

Computer simulation of the structure and electronic and detonation properties of energy materials

Computer modeling is used within the framework of the theory of density functional to determine the physical and chemical properties of a set of energy materials, which correlate with detonation parameters and sensitivity factors. There are two models of prediction of detonation parameters and sensitivity factors formulated for molecules and explosive crystals that satisfactorily correlate with the experimental data.     

Computer simulation of phase structure and mechanical properties of polymer mixtures

Computer programs have been developed to predict phase separation, flow-induced phase structure, and structure-dependent mechanical properties of binary polymer mixtures. The phase separation is simulated by solving a two-dimensional Langevin equation with Flory–Huggins free energy using the finite difference method under periodic boundary conditions. The change of phase structure due to flow is predicted by adding a shear flow term to the equation. By generating a finite element mesh from the calculated phase structure, the stress analysis is carried out for estimating the mechanical properties of the system using the finite element method. The elastic modulus and thermal expansion coefficient based on the phase structure were numerically investigated for various volume fractions and properties of components using the developed programs. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:807–813, 1998     

溶致液晶模板法制备纳米材料研究进展

主要综述了复合溶致液晶模板和真溶致液晶模板对于纳米材料结构的调控作用。首先讨论了不同复合溶致液晶体系制备介孔材料的方法,并总结了研究介孔材料形貌变化的最新理论成果;而对于真溶致液晶模板,则重点阐述了其对纳米颗粒、纳米棒、纳米线、纳米管和介孔材料的调控作用;最后展望了液晶模板法制备纳米材料的发展趋势。     

Influence of the fuel structure on the flame synthesis of carbon nanomaterials

Carbon nanomaterials (CNMs) were grown on nickel-coated stainless-steel mesh grids using a combustion synthesis method. Three fuel feedstocks of dissimilar chemical structures, ethylene, ethyl benzene and ethyl alcohol, were burned at fuel-rich equivalence ratios to generate disparate combustion products. The chemical compositions of these products were assessed to identify and contrast the species that contribute to the growth of CNMs. The generated CNMs were characterized using SEM and TEM. Each set of conditions produced a distinct distribution (bi-modal or mono-modal) of CNMs, including carbon nanotubes and carbon nanofibers, both of varying diameters and lengths. The effects of combustion-generated light aliphatic hydrocarbons and light aromatic hydrocarbons on CNM growth and structure were ascertained. It was found that ethylene and ethyl alcohol generated tubular CNMs under all tested conditions, whereas ethyl benzene generated only small amounts of CNMs and under much more limited conditions. It was also determined that concentrations of aliphatic species, notably methane and acetylene, at mole fractions as low as 500 ppm have a thickening effect on the resulting CNMs. Linear correlations were found between the concentrations of these species and the mean diameter of the CNMs.     

Computer simulation of structure and properties of crosslinked polymers: application to epoxy resins

In this work, a methodology has been developed for construction of atomistic models of crosslinked polymer networks. The methodology has been applied to low molecular weight water soluble epoxy resins crosslinked with different curing agents that are being considered for use as a primer coating on steel. The simulations allowed the crosslink density and the amount of free crosslinking sites in the coatings to be predicted. Shrinkage of the resin upon curing was reproduced by the simulation. In addition, the barrier properties of the model coatings were estimated. The interface between an inorganic substrate and cured epoxy resin has been constructed and the strength and molecular mechanisms of adhesion have been revealed. The developed methodology has a potential to significantly impact on the design and development of new coatings with improved barrier and adhesion properties.     

Computer simulation of network formation processes,structure and mechanical properties of polymer networks

The possibilities offered by computer simulation for the investigation of polymer networks are discussed. Instantaneous crosslinking can be simulated by fixing the conformation of a set of linear macromolecules. Equilibrium crosslinking requires a complete rearrangement of the conformation after formation of each crosslink. The conformations of the lattice models of polymer networks with certain topologies can be constructed using a Monte Carlo procedure for obtaining the equilibrium configurations of the junction points, and the methods of generating conformations of polymer chains with fixed end-to-end distances. The deformational properties of polymer networks, taking into account the finite length of chains, can be investigated by the use of a model of interacting junction points, quasi-particles. The way of investigating the entanglement effects and the interchain interactions are proposed. Polymer chain mobility may be simulated by the molecular dynamics of the ‘pearl necklace’ model. Destruction processes in polymer networks can be simulated by a Monte Carlo method if the breakage of a strand connecting two junction points is regarded as an elementary event.     

Investigation of sol-gel derived nanomaterials with a hierarchical structure

The basic processes of self-assembly in sol-gel technologies during the formation of network nanomaterials with a hierarchical structure have been considered. The gas-sensitive fractal structures have been prepared in systems based on dioxides of tin and silicon. The formation of a structure of nanocomposites has been studied using atomic force microscopy and electron microscopy methods. The gas-sensitive properties of nanomaterials have been investigated. A method for diagnosing objects with a hierarchical structure based on metal oxides has been proposed.     

Computer simulation of injection molding

The injection-molding process consists of three consecutive stages: filling, packing, and cooling. In order to obtain some insight into the phenomena involved in the process, and particularly in order to evaluate the moldability of certain resins and to predict the microstructure and properties of products molded therefrom, a number of workers have employed a variety of techniques based on mathematical simulation of the process. Mathematical simulation involves writing the relevant continuity, momentum, and energy equations governing the system, with appropriate boundary and initial conditions representing the prevailing conditions in the cavity and delivery channels. In order to obtain meaningful solutions to the above equations, detailed information is required regarding the thermodynamic, thermal, and rheological properties of the resin. Moreover, the prediction of the microstructure and ultimate properties of the molded article requires a knowledge of the morphological, crystallization, and orientation phenomena that take place under the influence of the thermo-mechanical history experienced by the resin. The complexity of the equations involved results in the utilization of a number of simplifying assumptions and the resort to computer simulation and numerical solutions of these equations. A variety of numerical schemes based on finite difference and finite element methods has been employed by various researchers.     

Computer simulation of stiff-chain polymers

A review of studies on the computer simulation of the phase behavior of various stiff-chain polymer systems is presented. Methods for calculating phase diagrams of a polymer solution in a computer experiment are discussed, including the methods of extended ensembles, entropic simulation, and the Wang-Landau algorithm to obtain the density-of-states function. The authors’ original results on studying the intramolecular orientational and spatial ordering of monomer units in a single stiff-chain macromolecule in the bulk and near a planar adsorbing surface by means of the Wang-Landau algorithm and using the bond-fluctuation lattice model are presented. Corresponding state diagrams are presented for these two cases. For systems of multiple chains, the phenomenon of nematic liquid-crystalline ordering in semi-dilute solutions in the bulk and in a planar layer is considered, and the phase diagrams for these cases are presented. A survey of the published data on some other promising directions of investigation of stiff-chain polymer systems is presented.     

Computer simulation of urethane formation

Computer model calculations have been used to simulate the reaction of polyoxypropylene triol with hexamethylene diisocyanate. Various molecular weight distributions and degrees of polymerisation are used in the calculation. The effect of side reactions is investigated and compared with experiment. Good agreement for both cyclisation and gel points is found for bulk and concentrated solutions. The model can be used to simulate random polycondensation reactions with a reliability approaching that of experiments, and it gives crucial results that cannot be obtained in any other way.     

Computer simulation of the polydispersive sol coagulation process

This work reports on a computer‐simulated investigation of the coagulation rate for a system comprising spherical sol and coagulant particles. The discussed experiment positively verified the functioning of the simulated coagulation system, where the aggregation process proceeds in line with the particle‐cluster model as a rapid and perikinetic coagulation process that satisfies the Smoluchowski equation. The rate of the simulated coagulation process satisfies kinetic equations for both first‐order and second‐order reactions. Selected concepts and models of the coagulation theory have been also verified. © 2012 Canadian Society for Chemical Engineering     

Computer simulation on the self-assembly of associating polymers

We present the results of Monte Carlo simulations of self-assembly in melt of pseudo-block copolymer formed through the association of associating polymer chains with attractive end-groups (sticker sites). Complexities of the phase structures result from these pseudo-block copolymers strongly depend on parameters, such as attractive interaction strength between two stickers and chain length of associating polymers. The weak, intermediate and strong interactions between two stickers lead, respectively, to the macro-separated, disordered and ordered lamellar phase structures. The ordered lamellar phases formed by these pseudo-block copolymers are more stable than that formed by pure diblock copolymers. Pseudo-block copolymers with shorter associating polymer chain prefer to form ordered lamellar phase and that with longer associating chain tend to form disordered phase.     

Computer simulation of wastewater treatment plant

The computer simulation of wastewater treatment systems is finding increasingly wide application. Simulation studies of complete municipal waste treatment plants have been successfully accomplished. This paper describes an attempt to simulate the operation of the Kitchener, Ontario, Waste Treatment plant taking data from the last six months of 1975. It is shown that, provided some parameter values are taken from the actual plant, it is possible to closely match the mean monthly performance of the system. Steady-state mathematical models of the major waste treatment units are presented together with a discussion of the structure and operation of the SEPSIM computer program. Detailed cost relationships for a complete municipal waste treatment plant are also shown.     

Computer simulation of high-discharge-rate battery systems

Simulations were carried out for a proposed two-dimensional high-discharge-rate cell under load with an interelectrode gap of the order of 100 m. A finite difference program was written to solve the set of coupled, partial differential equations governing the behaviour of this system. Cell dimensions, cell loads, and kinetic parameters were varied to study the effects on voltage, current and specific energy. Trends in cell performance are noted, and suggestions are made for development of cells to meet specific design criteria. Modelling difficulties are discussed and suggestions are made for improvement.Nomenclature A surface area of unit cell (cm²) - A _k conductivity parameter (cm^{2 –1} mol^–1) - b Tafel slope (V) - c concentration (mol cm^–3) - c ₀ concentration of bulk electrolyte (mol cm^–3) - D diffusivity (cm² s^–1) - D _h lumped diffusion parameter (J s cm^–2 mol^–1) - D _s lumped diffusion coefficient (A cm² mol^–1) - E rest potential of electrode (V) - F Faraday constant (96 500 C mol^–1) - i current density (A cm^–2) - I total current for unit cell (A) - i ₀ exchange current density (A cm^–2) - N flux of charged species (mol cm² s^–1) - R gas constant (8.314 J mol^–1 K^–1) - R _ext resistance external to cell () - t time (s) - T temperature (K) - t ₀ transference number - u mobility (cm² mol J^–1 s^–1) - V volume of an element in the cell (cm³) - V _ext voltage external to cell (V) - z charge on an ion - _c concentration overpotential (V) - _s surface overpotential (V) - conductivity (^–1 cm^–1) - stoichiometric coefficient - electric potential in solution (V)     

Computer simulation of granule microstructure formation

The diagenesis (porous microstructure evolution) of granules formed by a layering growth mechanism in a wet granulation process has been modelled. The model includes the packing of primary particles with a given size and shape distribution, and the deposition, spreading, and solidification of binder droplets within the growing granule. The dependence of granule porosity on the binder/solids ratio, primary particle size and morphology, and the rates of binder spreading and solidification has been investigated. The results are presented in the form of structure maps relating volume-averaged microstructure parameters with dimensionless groups including the ratio of droplet spreading and solidification times and the mean time between particle collisions. These graphs can guide the selection of process operating conditions or formulation ingredient properties required to obtain a particular granule microstructure.