Phase transitions and mesophases in molecular liquids and solutions: spectroscopic and imaging studies.

QC Physics;QD Chemistry

Findlay, Joanna Edyta ; Wynne, Klaas

University:University of Glasgow

Department:School of Chemistry

关键词: Liquid, crystal nucleation, liquid-liquid phase separation, water, liquid phase-separation-induced crystal templating, ice, fluff-like water crystals, liquid-liquid transition, LLT, order parameter, triphenyl phosphite, polarity, fluorescence, coumarin 153, perylene, n-butanol, liquid crystal, LC, rippled lamellar liquid crystal, frustration of crystallisation, FLIM, phase-contrast microscopy, confocal Raman microscopy, polarisation microscopy.;   

Others  :  http://theses.gla.ac.uk/8531/7/Microsoft%20Word.pdf

来源: University of Glasgow

【 摘 要 】

Liquids are the primary medium for chemical and biological reactions. Phase transitions can give rise to phase separation through nucleation or spinodal decomposition. This phase separation may be the reason behind structure in many liquids, which then has an effect on more practical processes. Mesoscopic (1 nm-1 μm) structuring of the liquid in the neighbourhood of a second critical point associated with a liquid-liquid transition (LLT) can cause anisotropic diffusion, which greatly affects the wetting properties of the liquid. It may also segregate reactants and products, affecting reaction rates and outcomes. Some examples of processes, which may be affected by this, include the synthesis and preparation of pharmaceutical drugs (which is sensitive to liquid structure, phase separation, and nucleation), preparation of nanometre scale materials, electrochemistry, dye-based solar cells, separation technology, and heterogeneous catalysis.This thesis concentrates on advancing of the understanding of some of the phase transitions and mesophases occurring in liquids. The first two chapters are introductory and the remaining chapters describe original research.Chapter 3 describes our studies on crystal nucleation in the presence of a liquid-liquid phase separation. The subjects of these studies were two binary liquid systems: nitrobenzene-hexane and water-1,2-trans-dichloroethylene. Our discovery of template-less asymmetric water crystals (water fluff), which we were able to reproduce repeatedly, strongly suggests that, despite common belief, high driving force does not necessarily lead to ill-defined crystalline forms. We also propose that crystal templating induced by liquid-liquid phase separation might be a general phenomenon, not limited to water.In Chapter 4 we explore one of the most interesting and challenging postulates in the field of liquid science, that is the existence of more than one isotropic liquid states in a single-component liquid at constant temperature and an LLT between these different states. By employing a number of experimental techniques, some of them not previously used to study this subject, we provide a new evidence for the existence of the LLT in triphenyl phosphite (TPP). Furthermore we answer an important and fundamental question of what is the order parameter characterising the LLT in TPP. Finally, Chapter 5 shows how our investigations into the existence of the LLT in n-butanol led to the conclusion that the observed phenomenon is in fact a transition between a supercooled isotropic liquid and a liquid-crystalline (LC) state. The LC is in general considered a form of matter “in between” the liquid and the crystal. However, the LC phase in n-butanol geometrically frustrated the formation of the stable crystalline phase. This frustrated phase can be seen as a template for similar ordering in other molecular liquids and is likely to be essential in their supercooling and LLTs.