Mechanism and Modeling of Emulsion Polymerization: New Ideas and Concepts – 2. Modeling Strategies

Summary: Molecular modeling strategies offer new insights into the mechanism of heterophase polymerization. The capabilities of Brownian dynamic simulations are illustrated by means of studies regarding radical entry and exist as essential steps in emulsion polymerization. Interestingly, the results allow certain generalizations which were not possible with macroscopic deterministic modeling strategies.     

Modeling Cassie–Baxter State on Superhydrophobic Surfaces

The goal of this work is to study the Cassie–Baxter state on the microstructure hydrophobic surfaces. The dependence of the energy barrier on the drop size, contact angle, the gap between the pillars, and pillar width is investigated. We consider the drop in three dimensions using a numerical approach to minimize the free energy of the drop in any situations. Numerical results are obtained for the wetting of a hydrophobic surface textured with a square lattice of pillars. According to the results, we found that the curvature increases allowing the liquid to touch the surface below the posts as the drop loses volume or decreased the contact angle with fixed drop volume. In the situations we considered, the pillar diagonal length is very critical and sensitive to the details of the surface patterning when the drop volume is larger.     

Modeling and conformation analysis of β-cyclodextrin complexes

Summary A series of -cyclodextrin complexes containing various guest molecules was studied using computer-aided molecular modeling and conformation analysis techniques. The geometry of each complex was studied using crystallographic data. The positions of the glycosidic O4 atoms indicate that the -cyclodextrin molecules are elliptically distorted. This distortion can be related to the van der Waals volume of the guest molecules. This correlation is different for aromatic and non-aromatic guest compounds. Rigid body docking experiments demonstrated that in crystal structures the guest molecule occupies a position in the cavity of nearly minimum interaction energy when there are no other molecules having interactions with the guest molecule. From the crystallographic data several rules could be deduced which seem to determine the conformation of -cyclodextrin molecules in complexes. A procedure was developed to construct -cyclodextrin molecules that are able to encompass guest molecules having a given van der Waals volume.     

Kinetic Modeling of Plasma Methane Conversion Using Gliding Arc

Plasma methane (CH4) conversion in gliding arc discharge was examined. The result data of experiments regarding the performance of gliding arc discharge were presented in this paper. A simulation which is consisted some chemical kinetic mechanisms has been provided to analyze and describe the plasma process. The effect of total gas flow rate and input frequency refers to power consumption have been studied to evaluate the performance of gliding arc plasma system and the reaction mechanism of decomposition.Experiment results indicated that the maximum conversion of CH4 reached 50% at the total gas flow rate of 1 L/min. The plasma reaction was occurred at the atmospheric pressure and the main products were C (solid), hydrogen, and acetylene (C2H2). The plasma reaction of methane conversion was exothermic reaction which increased the product stream temperature around 30～50℃.     

Modeling the Chain-Length Differentiated Polymer Microstructure of α-Olefins

Summary: Due to a complex polymerization scheme, incorporating besides propagation, termination and transfer to monomer and chain transfer agents in addition intra- and inter-molecular transfer to polymer as well as β-scission, α-olefin (co)polymers feature a quite complex polymeric microstructure. It is demanding to design a kinetic model that describes these in a predictive manner in order to have a tool for computer-aided product design. The molecular weight distribution and branching indices together with the composition are the subjects of interest in this case. The latter quantities are often provided as being averaged over the molecular weight distribution. Modern coupled analytical techniques of size exclusion chromatography provide even more insight. The combination of size exclusion chromatography with fractionation techniques provide under adequate processing of the data branching indices and co-polymer composition differentiated with respect to chain-lengths. This contribution will inspect how good a model for predicting the chain-length differentiated co-polymer composition in high-pressure high-temperature ethene – vinyl acetate-co-polymerizations will coincide with analytical results of technical products.     

Modeling Biological Systems: The Belousov–Zhabotinsky Reaction

In this essay I examine the ways in which the Belousov–Zhabotinsky (BZ) reaction is being used by biologists to model a variety of biological systems and processes. The BZ reaction is characterized as a functional model of biological phenomena. It is able to play this role because, though based on very different substrates, the model and system modeled are examples of the same type of excitable medium. Lessons are drawn from this case about the relationships between the sciences of chemistry and biology.     

Modeling research in low-medium temperature geothermal field, Tianjin

The geothermal reservoir in Tianjin can be divided into two parts: the upper one is theporous medium reservoir in the Tertiary system; the lower one includes the basement reservoir inLower Paleozoic and Middle-Upper Proterozoic. Hot springs are exposed in the northern mountainand confined geothermal water is imbedded in the southern plain. The geothermal reservoir is in-cised by several fractures. In recent years, TDS of the geothermal water have gone up along withthe production rate increasing, along the eastern fracture zone (Cangdong Fracture and West Bai-tangkou Fracture). This means that the northern fracture system is the main seepage channel ofthe deep circulation geothermal water, and the reservoir has good connection in a certain area anddefinite direction. The isotopic research about hydrogen and carbon chronology indicates that themain recharge period of geothermal water is the Holocene Epoch, the pluvial and chilly period of20 kaBP. The karst conduits in weathered carbonate rocks of the Proterozoic and Lower Paleozoicand the northeast regional fracture system are the main feeding channels of Tianjin geothermalwater. Since the Holocene epoch, the geothermal water stayed at a sealed warm period. Thetracer test in WR45 doublet system shows that the tracer test is a very effective measure forunderstanding the reservoir's transport nature and predicting the cooling time and transportvelocity during the reinjection. 3-D numerical simulation shows that if the reinjection well keeps asuitable distance from the production well, reinjection will be a highly effective measure to extractmore thermal energy from the rock matrix. The cooling of the production well will not be a problem.     

Modeling of Fischer-Tropsch Synthesis in a Slurry Reactor with Water Permeable Membrane

Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins. In recent years, the abundant availability of natural gas and the increasing demand of olefins, diesel, and waxes have led to a high interest to further develop this process. A mathematical model of a slurry membrane reactor used for syngas polymerization was developed to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional slurry reactor. The carbon polymerization was studied from a modeling point of view in a slurry reactor with a water permeable membrane and a conventional slurry reactor. Simulation results show that different parameters affect syngas conversion and carbon product distribution, such as the hydrogen to carbon monoxide ratio, and the membrane parameters such as membrane permeance.     

Modeling of solid–liquid equilibria in naphthalene,normal-alkane and polyethylene solutions

A solid–liquid equilibrium (SLE) model is developed on the basis of an equation of state referred to as copolymer SAFT. This SLE model is demonstrated for hydrocarbon solutions containing totally and partially crystallizable solutes. Initially regressed and tested on the solubility data for naphthalene, normal-alkane, and polyethylene, this model is used in a sensitivity study to understand the effects of crystallizability, melting temperature, molecular weight, and pressure on solid–liquid and liquid–liquid transitions of polyethylene in subcritical and supercritical propane.     

Modeling of emulsion co- and terpolymerizations: Will it ever be possible?

In this paper some of the problematic aspects of modeling emulsion copolymerizations will be discussed, giving a retrospective and a perspective on the area. In order to describe the fundamental processes in emulsion polymerization, like entry and exit of radicals in emulsion copolymerizations, many basic kinetic and thermodynamic constants are needed but still lacking. It will be shown that in the past dramatically deviating parameters were applied in modeling emulsion copolymerization. The most important of these parameters will be discussed and some of the outstanding problems will be highlighted.     

Modeling of gas–solid equilibrium of binary systems aided by Frankenstein PSO

Binary systems containing supercritical CO₂ + hydrocarbons were used for modeling gas–solid equilibrium by a combined method including a thermodynamic model and a meta-heuristic algorithm. The Peng–Robinson (PR) equation of state was used in the classical solubility equation. In addition, Wong–Sandler (WS) mixing rules were used, and the van Laar model (VL) was included in order to evaluate the excess Gibbs free energy that appears in these mixing rules. Then, a variant of particle swarm optimization (PSO), called Frankenstein PSO (FPSO) was implemented for minimizing the difference between calculated and experimental solubility values. The results showed that the FPSO algorithm is a very powerful tool for parameter estimation on the PR-WS-VL model with good performance and accuracy, and considerably low deviations. Therefore, values calculated by the combined method (PR-WS-VL + FPSO) are considered accurate enough for physical and engineering calculations, among other uses.     

Is Modeling the PSD in Emulsion Polymerization a Finished Problem? An Overview

Significant progress has been made over the past 20–30 years in terms of the ability to develop and solve mechanistic models of emulsion polymerization processes, and in particular models for prediction of the particle size distribution. However, this does not imply that modeling of these economically important processes is by any means a “solved problem,” or that it is no longer necessary to perform fundamental research in this area. There are a number of areas where strong scientific work would increase the understanding of the process, including events in the aqueous phase, radical entry into growing particles, monomer partitioning, and especially the mechanisms and modeling of particle coagulation.

     

A Method for Multiconformational Modeling of the Three‐Dimensional Shape of a Molecule

A method for multiconformational modeling of the threedimensional shape of a molecule is proposed that includes search for conformers, their optimum superposition, and analysis of spatial features of the resulting structure. The method allows one to determine features of various molecular conformations of compounds under study, to assess the contributions of conformers to particular properties of the substance, to evaluate the space occupied by the molecule, and to compare the average size of the multiconformational model of the molecule with the sizes of the most stable conformations. The potentials of the model are illustrated by density calculations for 137 organic liquids.     

Phase Equilibrium Modeling of Clathrate Hydrates of Carbon Dioxide + 1,4-Dioxine Using Intelligent Approaches

In this work, an adaptive neuro-fuzzy inference system (ANFIS) and a couple of fuzzy logic approach and genetic algorithms are utilized to serve robust inverse-based approaches for determination/prediction of the clathrate hydrate formation pressure of carbon dioxide in the presence of 1,4-dioxine, which is a most-widely implemented water “soluble” organic promoter. The gained outcomes prove the reliability and accuracy of the suggested ANFIS approach with the mean square error of 0.0034 and squared correlation coefficients of 0.9969. Thanks to the results generated by the aforementioned intelligent approaches, the models proposed in the current research contribute to high accuracy for the estimations of the phase equilibria clathrate hydrates of carbon dioxide +1,4-dioxane.      

Numerical Modeling of an RF Argon–Silane Plasma with Dust Particle Nucleation and Growth

A one-dimensional numerical model and simulation results are presented for a capacitively-coupled radio frequency parallel-plate argon–silane dusty plasma. The model includes self-consistently coupled numerical modules, including a plasma fluid model, a sectional aerosol model, and a simple chemistry model to predict rates of particle nucleation and surface growth. Operating conditions considered include 13.56 MHz frequency, 100 mTorr pressure, a 4-cm electrode gap, gas flow through the top electrode with a 30:1 ratio of argon to silane, and applied radio frequency voltage amplitude of either 100 or 250 V. In the higher voltage case two lobes of relatively large particles are formed by ion drag, while fresh nucleation occurs in the void between these lobes. It is shown that the reason that fresh nucleation occurs in the void involves an interplay among several coupled phenomena, including nanoparticle transport, the plasma potential profile, and trapping of silicon hydride anions that drive nucleation in this system.     

Xα–DV Modeling of Photoionization and Electronic Absorption Spectra of Cobalt tris–Acetylacetonate

Ionization energies, excited state energies, and oscillator strengths of electron–dipole transitions are calculated within the framework of the SCF–X–DV quantum–chemical model of the Co(HCOCHHCO)₃ model complex in order to interpret the photoionization and electronic absorption spectra of cobalt tris––diketonate. It is shown that the sequences of ionization and excitation energies calculated in the transition state approximation do not significantly differ from the sequence of energies estimated in the frozen MO approximation. The model absorption spectrum with a correction of 1.9 eV applied to the energy of the vacant ₄ ^* orbital is in good agreement with our gas–phase absorption spectrum of Co(acac)₃.     

Modeling current–voltage relationships of mixed conducting cathode materials for solid oxide fuel cells

In recent decades, high-temperature oxygen reduction reaction on mixed conducting cathodes were investigated intensively by many researchers. Computational approaches as well as electrochemical and spectroscopic studies have been made to elucidate the kinetics. Contribution of oxygen vacancy to the reaction rate was suggested in multiple reports, and plausible reaction pathways were proposed based on density functional theory (DFT) calculations. The picture of oxygen reduction reaction has become clearer in these years. However, there still is a discussion about a credible formula that represents the current–voltage relationships. Discrepancies are found among the reported data on the magnitude of the rate constant and on its dependencies on partial pressure and temperature. The difference is significant between a model electrode and a practical porous electrode. Comparison of the results suggests the existence of series reaction barriers, that is, the surface reaction and subsurface transport, which should be considered for consistent representation of the total electrode process.     

Analysis of the Glass-Forming Ability of Fe–Er Alloys,Based on Thermodynamic Modeling

The Fe–Er phase diagram and thermodynamic properties of all its phases are assessed by means of self-consistent analysis. To refine the data on phase equilibria in the Fe–Er system, an investigation is performed in the 10–40 at % range of Er concentrations. The temperature–concentration dependences of the thermodynamic properties of a melt are presented using the model of ideal associated solutions. Thermodynamic parameters of each phase are obtained, and the calculated results are in agreement with available experimental data. The correlation between the thermodynamic properties of liquid Fe–Er alloys and their tendency toward amorphization are studied. It is shown that compositions of amorphous alloys prepared by melt quenching coincide with the ranges of concentration with the predominance of Fe₃Er and FeEr₂ associative groups that have large negative entropies of formation.