Thermodynamics and Structure of Plate-Like Particle Dispersions

Abstract: Popular Abstract in English Most people see chemistry as an abstract and complicated subject because it deals with species that can not be seen with bare eyes. But if one think about it, chemistry is everywhere! Chemical processes happen all around you and inside you everyday : there is chemistry in the human body where proteins play a great role, in shampoo bottles, the toothpaste, in the cement that is used to build houses. Then it should not come as a surprise that so much effort are put into understanding chemical processes. So what are those invisible species that chemistry is dealing with ? I can say with few doubts that everyone have heard about atoms and molecules (the latter being an assembly of atoms). Atoms and molecules are not always neutral species, i.e, they can carry an electrical charge (in this case atoms turn into ions). This transition from a neutral to a charged species can occur when the species are put into a solvent (like water). This is the case for example with salt that dissolves in water and form ions. Examples of molecules that becomes charged in an solvent are numerous : proteins, virus, polyeletrolytes ... But why is this electrical charge so important ? Like for magnets, where a positive pole will attract a negative one, the species will start to interact according to their charge. Among other factors like the shape of the particles, the role played by the charges in chemical processes is fundamental. Physical chemistry focuses on the understanding of the behavior of such small particles (called collo\"idal particles) in solution. Nevertheless, down to this scale, the experimental study of collo\"idal dispersions is not trivial. In this context computational chemistry happens to be very useful. By the use of mathematical and physical models, one tries to simulate the results obtained by experiments and this way one can access properties that are not obtainable by other means. Hence, it is a complementary technique to experiments. This thesis deals with simulations, using Metropolis Monte Carlo method, of mineral particles. In a first project I investigate how the number of charges on mineral particles varies when emerged into a salt solution. In a second project the influence of the charge carried by the particles in the formation of the gels and liquid-crystals is studied. One of the striking result is the discovery of new liquid crystal phases which could lead to the development of new materials. Finally I studied the growth of nanoplatelets and their interaction in conditions comparable to the one encountered in cement paste.