Recently there has been a great deal of attention in the oilfield industry focused on the phenomenal properties of viscoelastic surfactants (VES). The interest is motivated by their applications as switchable smart fluids, their surface tension, and their thickening and rheology enhancement in aqueous solution. Surfactant molecules in solution are known for their ability to assemble spontaneously into complex structures. Under certain thermodynamic conditions, temperature and electrolyte concentrations, wormlike micelles are formed. These micelles share similar equilibrium and dynamic properties with polymer solutions, However, micellar chains can break and recombine spontaneously which make them part of the more general class of living polymers. It is vital to understand the properties of viscoelastic wormlike micelles with regard to their flow in porous media. The overall objective of this study is to establish a better understanding of counterion effect on behavior of VES. The dependence of macroscopic properties on intermolecular interactions of complex fluid systems such as VES is an enormous challenge. To achieve our objective, we use first-principle calculations and molecular dynamics (MD) simulations to resolve the full chemical details in order to study how the structure of the micellar and solution properties depends on the chemical structure of the surfactant head group (HG) and type of counterion. In particular, we run simulations for different structures in gas-phase and aqueous solutions together with their salt counterions at room temperature and atmospheric pressure. For this purpose, we consider four types of surfactant HG (anionic, cationic, betaine and amidoamine oxide) together with the most common ions present in the acidizing fluid of a carbonate reservoir such as Ca2+, Mg2+, Fe2+, Fe3+, Mn2+ and Zn2+, Cl-, OH- and HS-. Hydration of ions as well as interactions with surfactant the HG are studied using density functional theory (DFT). The results give important insight into the links between molecular details of VES HG structure and observed solution properties. This study proposes for the first time the possible mechanisms that explain the exotic behavior of VES at high Fe(III) concentration. Also, our MD simulation suggests that distribution of chloride ion around surfactant molecules is responsible for their viscosity behavior in HCl solution. We believe that our results are an important step to develop more systematic procedures for the molecular design and formulation of more effective and efficient VES systems.

In this study, all possible mono, di and trinitro-substituted triazine compounds as potential candidates for high energy density materials (HEDMs) have been investigated by using quantum chemical treatment. Computational chemistry is a valuable tool for estimating the potential candidates for high energy density materials. Geometric features and electronic structures of these nitro-substituted triazines have been systematically studied using ab initio and density functional theory (DFT, B3LYP) at the level of 6-31G(d,p), 6-31+G(d,p), 6-311G(d,p), 6-311+G(d,p), cc-pVDZ. Detonation performances were evaluated by the Kamlet-Jacobs equations based on the calculated densities and heats of formation. It is found that 2G derivative with the predicted densities of 1.9 g/cm3, detonation velocities of 9.43 km/s, and detonation pressures of 40.68 GPa may be novel potential candidates of high energy density materials (HEDMs). Moreover, thermal stabilities were investigated by calculating bond dissociation energies (BDE) at B3LYP/6-311G(d,p) level. Detailed molecular orbital (MO) investigation have been performed on these potential HEDMs.

In this study, the effect of surface crystallography on hydrogen molecule adsorption properties on FeTi surfaces is presented. Furthermore, the substitutional adsorption of 3d-transition metals on (001), (110) and (111) surfaces of FeTi is studied. Using ab initio pseudopotential methods, the adsorption energies of hydrogen and 3d-transition metals are calculated. In substitutional adsorption of 3d-transition metals, Fe-terminated (111) and Ti-terminated (001) surfaces, are found to express the lowest adsorption energies. The adsorption energy versus adsorbed elements&rsquo / curves are very alike for all the surfaces. According to this, going from the left to right of periodic table, the adsorption energies increase first. The maximum energy belongs to Cr, Mn and Fe for all the surfaces. Then a minimum is observed in Co for all the surfaces and after that the energy increases again. Adsorption energies of atomic and molecular hydrogen are calculated on high symmetry sites of surfaces. As a result, top and bridge sites came out to be the most stable positions for molecular and atomic hydrogen adsorption, respectively, for (001) and (111) surfaces in all terminations. In (110) surface / however, 3-fold (Ti-Ti)L-Fe and 3-fold (Ti-Ti)S-Fe hollow sites express the lowest adsorption energies for molecular and atomic hydrogen, respectively. Considering the minimum adsorption energy sites for hydrogen molecule and atom, a path of dissociation of hydrogen molecule on surfaces is represented. After that by fully relaxing the hydrogen molecule on the surface and using CI-NEB method the activation energy for hydrogen dissociation is calculated. So it has been found that on Fe-terminated (111) and FeTi (110) surfaces the dissociation of hydrogen molecule happens without activation energy. Meanwhile, the activation energy for Fe-terminated (001) surface and Ti-terminated (001) surface, is calculated to be 0.178 and 0.190 eV, respectively.

Aromatic hydrocarbons constitute an important fraction (~20%) of total volatile organic compounds (VOCs) in the urban atmosphere. A better understanding of the aromatic oxidation and its association in urban and regional ozone and organic aerosol formation is essential to assess the urban air pollution. This dissertation consists of two parts: (1) theoretical investigation of the toluene oxidation initiated by OH radical using quantum chemical and kinetic calculations to understand the mechanism of O3 and SOA precursors and (2) experimental investigation of atmospheric new particle formation from aromatic acids. Density functional theory (DFT) and ab initio multiconfigurational calculations have been performed to investigate the OH-toluene reaction. The branching ratios of OH addition to ortho, para, meta, and ipso positions are predicted to be 0.52, 0.34, 0.11, and 0.03, respectively, significantly different from a recent theoretical study of the same reaction system. Aromatic peroxy radicals arising from initial OH and subsequent O2 additions to the toluene ring are shown to cyclize to form bicyclic radicals rather than undergoing reaction with NO under atmospheric conditions.Isomerization of bicyclic radicals to more stable epoxide radicals possesses significantly higher barriers and hence has slower rates than O2 addition to form bicyclic peroxy radicals. At each OH attachment site, only one isomeric pathway via the bicyclic peroxy radical is accessible to lead to ring cleavage. Decomposition of the bicyclic alkoxy radicals leads primarily to formation of glyoxal and methyl glyoxal along with other dicarbonyl compounds. Atmospheric aerosols often contain a considerable fraction of organic matter, but the role of organic compounds in new nanometer-sized particle formation is highly uncertain. Laboratory experiments show that nucleation of sulfuric acid is considerably enhanced in the presence of aromatic acids. Theoretical calculations identify the formation of an unusually stable aromatic acid-sulfuric acid complex, which likely leads to a reduced nucleation barrier. The results imply that the interaction between organic and sulfuric acids promotes efficient formation of organic and sulfate aerosols in the polluted atmosphere because of emissions from burning of fossil fuels, which strongly impact human health and global climate.

AgCdO is one of the most widely used contact materials in the world because of its outstanding performance. Nevertheless, due to environmental considerations, it will soon be completely forbidden by European environmental directives. Therefore, finding a good substitute is of crucial importance. Electrical arc erosion plays a crucial role in the reliability and life of power switching devices. Depending on the contact material's behavior in response to an electrical arc, surface damage can induce severe changes in contact material properties that will impact the power switching device's functioning. Consequently, electrical arc effects and consequences on the contact material surface are of first importance. In this context, we have focused our research activities on the following axes. First of all, in order to better understand AgCdO (Current contact material in aerospace industry) and AgSnO₂(Potential candidate to AgCdO substitution) arc erosion behaviors, arc erosion experiments, where the power switching devices have been subjected to different numbers of arc discharges, have been realized. Further, a general macroscopic electrical contact arc erosion model valid for low and high currents was developed. To compare model results to experimental data, this model describes the complete breaking process of electrical contacts and gives the total amount of material removed after one breaking operation. In parallel, arc erosion experiments on AgCdO power switching devices have been conducted at high currents (0 -> 1000 A) in order to validate the arc erosion model. Next, using the general arc erosion model, the properties having the greatest influence on the electrical arc erosion process have been determined through simulations on silver contact material. At this stage, ab initio calculations were needed to obtain ranges of variation of certain silver contact material properties. Finally, an investigation of the trends of changing local contact material on these identified material properties was performed. This study composition of AgSnO₂was based on ab initio calculations for two different oxide compositions of AgSnO₂. These will allow us to give directions to aid the design of a good substitute for AgCdO, and therefore, to complete the main objective of this research work.

In this thesis we have investigated the correlated ground state properties of polymers by applying wave-function-based ab-initio quantum-chemical methods such as the Hartree-Fock approach, the full configuration interaction method (FCI), coupled-cluster (CC) and Moller-Plesset second-order perturbation (MP2) theory. The polymers we have studied are the boron-nitrogen polymers, i.e., polyiminoborane (PIB) and polyaminoborane (PAB), the lithium hydride chain and the beryllium hydride polymer as well as the polymethineimine (PMI). The optimized structural parameters, cohesive energies, polymerization ernergies, relative stabilities of isomeric forms and some band structure results are presented. The results demonstrated that quantum chemical ab initio methods can be applied successfully to infinite systems like polymers, although such calculations are still far from being routine.

La zirconolite est une des matrices envisagées pour le confinement des actinides mineurs dans le cadre du stockage des déchets en site géologique profond. Cependant, dans ces conditions, après plusieurs milliers d'années, l'eau peut arriver au contact du colis de déchets et être radiolysée lors de la désintégration des radionucléides. Au cours de cette thèse, nous avons donc étudié les effets de la radiolyse de l'eau, induite par des particules chargées (alphas ou protons), selon deux géométries, sur la livixation d'une zirconoloite synthétique, de formule Ca0,8Nd0,2ZrTi1,8Al0,2O7, où Nd simule la présence des actinides mineurs. Les irradiations externes ont été réalisées sur des zirconolites saines et amorphisées, dans l'eau pure ou en présence d'ions complexants. La dissolution de l'échantillon a été évaluée via le relâchement des cations constitutifs. La production de H2O2 radiolytique a également été mesurée. Le comportement du matériau a été évalué par calculs ab initio.

Ce travail comporte deux partie, l'une de développement méthodologique, l'autre concerne l'étude ab-initio, par une méthode de spectroscopie de fragments immergés dans un bain, des composés Sr(14-x)Ca(x)Cu(24)O(41).<br /><br />Le travail méthodologique propose une généralisation et systématisation du calcul du potentiel de Madelung ainsi qu'une simplification de la méthode de calcul ab-initio permettant un gain de ressources sans perte de précision.<br /><br />L'étude des composés Sr(14-x)Ca(x)Cu(24)O(41) (x=0 et x=13.6) montre l'influence des modulations structurales incommensurables des deux sous-systèmes (chaînes et échelles de spins) sur la physique de basse énergie des composés (dimérisation, ordre anti-ferromagnétique). Des modèles t-J+V ont été déterminés à partir des calculs ab-initio en fonction des paramètre incommensurables.

Thèse doctorat : Instrumentation et analyses avancées : Lille 1 : 2000. / Résumé en français et en anglais. Bibliogr. p. 173-189.

Reprodution de : Thèse de doctorat : Physique des matériaux : Lyon 1 : 2006. / Titre provenant de l'écran titre. 138 réf. bibliogr.