The Chemical Reactions In Water/AOT/Oil Microemulsions

This thesis studied the equilibrium thermodynamics and kinetics of chemical reaction in W/O microemulsion droplets by UV-vis spectrophotometer, and then discussed the difference and relation of the reactions between in microemulsion droplets and the bulk water. It is the first time to investigate the kinetics of synthesis of nanoparticles in microemulsion by spectrum analysis method of the three wavelengths. The nanoparticles were characterized by transmission electron microscopy (TEM). The main content is the following:1. The absorbance measurements of CV ((4, 4', 4"-tris(dimethylamino) triphenylmethy chloride or crystal violet) in W/O microemulsion with surfactant AOT (sodium bis(2-ethlhexyl) sulfosuccinate) at seven temperatures were carried at 580nm. An association model that the reaction between crystal violet and AOT takes place in the interfacial layer between water and surfactant was used to analyze the experimental data to obtain the association equilibrium constants (K) and association ratios (n) of CV and AOT for various temperatures. It was estimated that about up to 72% CV in water/AOT/isooctane microemulsion and 69% CV in water/AOT/decane microemulsion were associated by AOT, which resulted in a significant reduction of the effective concentration of CV and retarded the reaction of alkaline fading of CV in the microemulsion. Decreasing the molar ratio ω favors the association of CV and AOT at fixed temperature. The values of thermodynamics functions of association Gibbs free energy (Δ_rG_m), enthalpy (Δ₄H_m), and entropy (ΔpS_m), were calculated from the association constants at various temperatures. The results show the reactions of CV and AOT both in water/AOT/isooctane microemulsion and in water/AOT/decane microemulsion are endothermic and entropy promoting, and the effect of entropy of the association reaction is larger than the effect of enthalpy. Both the association enthalpy and the association entropy of CV and AOT in water/AOT/isooctane microemulsion are larger than that in water/AOT/decane.2. The kinetics of alkaline fading of crystal violet has been studied inmicroemulsion systems of water/AOT/isooctane and water/AOT/decane at seven temperatures. Through monitoring the change of absorbance of CV at the wavelength of 600nm in the course of reaction, the pseudo first order rate constants were obtained from which the apparent second order rate constants (ki) were then calculated. The actual rate constants k and activation energy are calculated on the basis of the association equilibrium constants of CV and AOT and the apparent second order rate constants at various temperatures. It has been found that the actual rate constants k of the alkaline fading of CV change as co and temperatures in two microemulsion systems above, and the relation of Ea and co is obtained. The effect of nonpolar solvents of isooctane and decane on the kinetics of CV alkaline fading has been discussed.3. It is successful to apply the spectrum analysis method of three wavelength to the reaction of K.3Fe(CN)6 and C0CI2 in the block water and water/AOT/isooctane. Through monitoring the change of absorbance at the wavelength of 410nm, 420nm and 440nm in the course of reaction at 298K, the concentration of reactant K3Fe(CN)6 at various time were obtained from which the apparent second order rate constants {ki) were then calculated. The result shows that the reaction rate of K.3Fe(CN)6 and C0CI2 in water/AOT/isooctane microemulsion is slower than that in the bulk water, and ki decreased as the co increased. The influence of the reaction kinetics on the size and morphologies of nanoparticles in microemulsions were discussed.