| Description |
Mesophases are states of matter that have intermediate order between liquids and crystals. Lamellar, hexagonal, and gyroid mesophases are typically produced by block copolymers and surfactants that have two components that do not like each other but are connected by a chemical bond. Free particles that can arrange into mesophases have not yet been realized in experiments. The first goal of this dissertation is to design simple and robust interaction potentials between unbound particles that could form the same mesophases as block copolymers and surfactants. We achieved this through the design of binary mixtures in which the particles experience frustrated attraction. It has long been known that, in general, it is more difficult to nucleate the gyroid mesophase from the disordered liquid than the lamellar and hexagonal mesophases. We investigate the origin of this phenomena, and find that the slow nucleation of the gyroid from the disordered liquid is due to the extremely low temperature and entropy of melting of the gyroid. Zeolites are porous crystalline materials that form in the presence of surfactant structure-directing agents (SDA). The interaction of surfactants with the silicate precursors favors the formation of mesophases. We here demonstrate that mesophases can promote the nucleation and polymorph selection of model zeolites, investigate the mechanism of nucleation of a gyroidal zeolite from amorphous mixtures, and demonstrate that -depending on the temperature- it occurs in two steps with the gyroid as intermediate phase, or in one step. In the latter case, the mechanism is still not iv classical, as the critical nucleus for the formation of the zeolite is not a crystal but a mesophase. We further investigate the role of SDA molar fraction and size and the strength of tetrahedral interactions of the network former in the zeolite on the structure of the zeolite polymorph formed by the model mixtures. We find that the first two parameters result in a wide range of distinct zeolites, while the third results in only minor changes of the structure of the crystal, although -interestingly- results in the existence of more than one double gyroid mesophase. To our knowledge, this dissertation is the first to achieve the nucleation of zeolites from amorphous mixtures using molecular dynamics simulations. |
