Short-range order in disordered phases using neutron diffraction

• Autores: Muriel Rovira Esteva
• Directores de la Tesis: Luis Carlos Pardo Soto (dir. tes.), Josep Lluís Tamarit Mur (dir. tes.)
• Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2014
• Idioma: inglés
• Tribunal Calificador de la Tesis: Elvira Guàrdia i Manuel (presid.), Carlos Cabrillo García (secret.), Jean-François Moulin (voc.)
• Materias:
  • Física
    • Física molecular
      • Estructura molecular
    • Química física
      • Física del estado liquido
    • Física del estado sólido
      • Estados no cristalinos
• Enlaces
  • Tesis en acceso abierto en: TDX
• Resumen

  • Neutron diffraction is a powerful technique that allows to probe the structure of disordered phases across a variety of length scales. However, due to the inherent complexity of these disordered hases, the analysis of the information contained in the experimental data is not obvious. In this work, a few alternative methods are presented that allow to make the most of the neutron diffraction measurements as well as the molecular configurations obtained from molecular dynamics simulations or data modelling. They mainly consist in a Bayesian approach to fit the molecular structures measured with neutron diffraction, and a multidimensional analysis of the molecular structure probability distribution functions obtained from simulations or data modelling techniques, instead of the standard averaging over many variables. These methodologies are then applied to the structural investigation of several disordered systems in order to answer a series of open questions: the origin of the liquid-liquid transition in trans-1,2-dichloroethene (C2Cl2H2), the extreme fragility of 1,1,2,2-tetrachloro-1,2-difluoroethane's orientational glass (F-112, C2Cl4F2), the local density paradox in carbon tetrachloride (CCl4), and the roles of steric and electrostatic interactions in the short range order of the liquids of quasitetrahedral molecules, particularly trichlorobromomethane (CBrCl3) and dibromodichloromethane (CBr2Cl2). Additionally, a concise summary of the theoretical framework for neutron diffraction of disordered systems, as well as the practicalities of the experimental setup and the necessary data treatment, are also included to provide interested researchers with a self-contained overview on the topic.