Solid-state phase transition kinetics of organic molecules with the application of AFM

Understanding the kinetics and thermal behavior of materials are very important when the characteristics of materials can be significantly changed in the variation of temperature. For example, the solubility and bioavailability of drug molecules can be drastically changed upon the temperature-driven polymorphic transition. The decomposition rate of energetic materials determines the shelf life, stability and detonation properties. For the application of glassy and amorphous materials, crystallization from glass to crystalline phase must be suppressed. For phase transition materials, on the other hand, rapid crystallization process from liquid to crystalline phase is demanded for the high efficiency and low-cost solution process. In the traditional thermal analysis kinetic studies, conventional thermal analysis tools such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) have been used for measuring the kinetic and thermodynamic parameters and understanding the thermal behaviors of materials. Recently, in the development of nanotechnology and biotechnology, thermal analysis kinetic has been expanded to wide areas like characterization of nano and bio materials. Also, needs for developing new experimental techniques and simulation tools have increased for the development and application of novel materials.
This dissertation will focus on the phase transition kinetics of organic compounds in the solid-state using various crystalline forms (cocrystals, solvates and micro-islands crystals) of pharmaceutical and energetic materials. For the reliable kinetic analysis and understanding the underlying phenomena, we used atomic force microscopy (AFM) as a novel tool, combined with several bulk kinetic techniques such as DSC, TGA, IR spectroscopy and X-ray diffraction (XRD). One of topic addressed here is the kinetics of solid-state polymorphic transition (SSPT) process. In chapter 3, we used a nicotinamide/pimelic acid pharmaceutical cocrystal as a model system to understand the SSPT process under comprehensive consideration of structural, thermodynamic and kinetic aspects. Solvate formation/desolvation is also one of most important solid-state transition process encountered when developing novel pharmaceutical and energetic materials. In chapter 4, kinetics and transition mechanism of desolvation process of newly developed 1,2,4-trinitrotoluene (TNT)/aniline solvates was investigated. In chapter 5, we investigated the size-dependent kinetics and sublimation behavior of TNT islands using in situ AFM. The purpose of this work is to understand the phenomena such as sublimation, diffusion and recrystallization process, observed during the storage of organic energetic materials and to investigate how TNT islands size affects the sublimation rate and the activation energy of sublimation.