Application of the Kirkwood-Buff theory to nonionic and ionic solutions
The Kirkwood-Buff theory is a general treatment of liquid solutions at molecular level. Its application to bath nonionic and ionic solutions has evoked great interest in recent years. The present thesis has two parts: the first part is about nonionic solutions; the second part is about ionic solutions. For the nonionic solutions, there are two related major topics in the thesis: (1) the examination of the hydrophobic interaction for the water-hydroorganic cosolvent mixtures; (2) the effect of solvent on the thermal transition of black copolymer polyoxyethylene - polyoxypropylene (PEO-PPO-PEO). For the first topic, the hydrophobic effect present in bath water-alcohol and water-ethylene glycol(EG), ethanolamine(EA), ethylenediamine(ED), and 2-methoxyethanol(ME) systems have been examined in terms of the Kirkwood-Buff integrals, G₁₁, G₂₂ and G₁₂ , which reflect overall intermolecular affinity water/water, cosolvent/cosolvent and water/cosolvent, respectively. The Kirkwood-Buff integrals show that n-alcohols behave in a way much more complicated than those bifunctional cosolvents and indicate that the alcohol-alcohol affinity in the water/alcohol mixtures (expressible by G₂₂) plays a key role in this complexity. However, the various intermolecular affinity coefficients in the water/EG EA, ED and ME mixtures exhibit, in general, "parity" or similar features and the hydrophobic effect is obviously less strong than appeared in the water/alcohol system. For the second topic, based on the knowledge extracted regarding mixed aqueous-organic solvents, solvent effects on thermal-induced transition of the black copolymer, PEO-PPO-PEO, has been investigated using DSC. The result is show that, in general, the transition temperature is lowered (from about 30°C in water to about 10° C in the mixed aqueous-organic solvents) at relatively low cosolvent mole fraction( i.e. xs≤ 0.1). Simultaneously, the enthalpy and cooperativity of the transition are also greatly reduced. These changes in the transition parameters may arise from a preferential solvation of each fragment of the black copolymer and intra- and inter- molecular hydrophobic effects. Solvent effects on the microstate transition of the black copolymer may be expected to be significant to understand analogous thermal transitions appearing in protein denaturations. For ionic solutions, the Kirkwood-Buff theory has been applied to derive the equation required to treat solvation problems of electrolytes. The equation derived may access the classical Debye-Huckel limiting law and can be further modified to yield a useful equation, which was shown applicable to model the activity coefficients of more than twenty 1:1 electrolytes in aqueous solutions over wide range of concentrations and temperatures with high precision.
- Sciences – Thèses