Phase diagrams of microscopic models for nematogenic mixtures

• Ano de defesa: 2023
• Autor(a) principal: Oropesa, William Gabriel Carreras
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: biaxial nematic structures; dipolar nanoparticles; Landau-like multicritical points; liquid crystals; microscopic models; modelos microscópicos; cristais líquidos; nanopartículas dipolares; estruturas nemáticas biaxiais; pontos multicríticos de Landau
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/43/43134/tde-22062023-115855/

We employ different extensions of the mean-field Maier-Saupe model with discrete orientational states to study the phase behavior of statistical models for nematogenic mixtures. More specifically, we study two problems: (i) dilution effects on liquid crystals and (ii) binary mixtures of nematogens and dipolar nanoparticles. For the dilution problem, the phase behavior of the systems is investigated in terms of the strength of the isotropic interaction between anisotropic objects, as well as the degree of biaxiality and the concentration of those units. We obtain phase diagrams with isotropic phases and stable biaxial and uniaxial nematic structures, various phase coexistences, many types of critical and multicritical behavior, such as ordinary vapor-liquid critical points, critical end points, and tricritical points, as well as distinct Landau-like multicritical points. For the problem involving dipolar nanoparticles, we have an extra parameter, the strength of the interaction between objects of different nature. We obtain phase diagrams with reentrant biaxial structures, ordinary dipolar-richdipolar-poor critical points, tricritical points, Landau multicritical points, and various other types of critical behavior. We present a perturbative calculation to study the effects produced in the liquid-crystal host when doping with small amounts of dipolar particles. For both problems, our results widen the possibilities of relating the phenomenological coefficients of the Landaude Gennes expansion to microscopic parameters, allowing an improved interpretation of theoretical fittings to experimental data.