Hui Lu

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


1. A conductimetric technique has been used to study the thermal diffusion of dilute aqueous solutions of Me{dollar}\sb4{dollar}NBr, Me{dollar}\sb4{dollar}NIi, Et{dollar}\sb4{dollar}NBr, Et{dollar}\sb4{dollar}NI, Pr{dollar}\sb4{dollar}NBr, Pr{dollar}\sb4{dollar}NI, Pr{dollar}\sb4{dollar}NOH, Bu{dollar}\sb4{dollar}NCl, Bu{dollar}\sb4{dollar}NBr, Bu{dollar}\sb4{dollar}NI, Bu{dollar}\sb4{dollar}NSCN, Bu{dollar}\sb4{dollar}PCl, NaPh{dollar}\sb4{dollar}B, Ph{dollar}\sb4{dollar}PCl and Ph{dollar}\sb4{dollar}AsCl (Me = methyl, Et ethyl, Pr = propyl, Bu = butyl, Ph = phenyl). The enthalpies of transport of these salts, {dollar}H\sp*{dollar}, have unusual concentration dependences. For Me{dollar}\sb4{dollar}NBr and Me{dollar}\sb4{dollar}NI, {dollar}H\sp*{dollar} is almost constant. For the tetrabutylammonium salts, {dollar}H\sp*{dollar} passes through minima at high dilutions. {dollar}H\sp*{dollar} increases with concentration for the rest of salts. Only for Pr{dollar}\sb4{dollar}NOH does {dollar}H\sp*{dollar} decrease with concentration, which is the normal concentration dependence of {dollar}H\sp*{dollar} for dilute electrolytes.;2. The Soret coefficients of NaCl, KCl, Bu{dollar}\sb4{dollar}NCl and Ph{dollar}\sb4{dollar}PCl in dilute methanol solutions have been measured conductimetrically. The enthalpies of transport of NaCl and KCl in methanol were found to be larger than those for the same salts in water. The opposite behavior was found for Bu{dollar}\sb4{dollar}NCl and Ph{dollar}\sb4{dollar}NCl.;3. The Soret coefficients and enthalpies of transport have been determined for aqueous H{dollar}\sb3{dollar}PO{dollar}\sb4{dollar}, HIO{dollar}\sb3{dollar}, KH{dollar}\sb2{dollar}PO{dollar}\sb4{dollar}, K{dollar}\sb2{dollar}HPO{dollar}\sb4{dollar} and KIO{dollar}\sb3{dollar}. To interpret the results, equations have been developed for the enthalpy of transport of 1:1 weak electrolytes.;4. The thermal diffusion of aqueous sodium dodecylsulfate (NaDS) and sodium decanoate (NaDec) has been measured. The Soret coefficients jump by about a factor of three as the concentration of each salt is raised through the critical micelle concentration. The molar enthalpies of transport of completely dissociated submicellar NaDS and NaDec are about an order of magnitude larger than the corresponding quantities for the micellar form of the electrolytes, which can be understood in terms of ionic hydration.;5. The Soret coefficients of dilute aqueous solutions of the stepwise self-associating dyes methylene blue and methyl orange have been found to increase with concentration. An approximate treatment of the thermal diffusion of stepwise-associating solutes is developed to interpret the results.;6. A conductimetric technique for the determination of the Soret coefficients of ternary mixed electrolyte solutions has been developed. The technique has been used to measure the Soret coefficients and enthalpies of transport of aqueous NaOH + NaCl solutions. In aqueous NaOH solutions, NaCl diffuses to the warm plate of Soret cell instead of the cold plate as it does in water. The concentration dependence of measured Soret coefficients agrees qualitatively with theory.;7. Hydrolysis of aqueous Na{dollar}\sb2{dollar}CO{dollar}\sb3{dollar} produces NaHCO{dollar}\sb3{dollar} and NaOH. Conductimetric measurements of thermal diffusion of aqueous Na{dollar}\sb2{dollar}CO{dollar}\sb3{dollar} reveals that the NaOH diffuses more rapidly than NaHCO{dollar}\sb3{dollar}, leading to the accumulation of excess of NaOH (relative to NaHCO{dollar}\sb3{dollar}) at the cold plate. Binary solutions of Na{dollar}\sb2{dollar}CO{dollar}\sb3{dollar} therefore separate into ternary Na{dollar}\sb2{dollar}CO{dollar}\sb3{dollar} + NaOH and Na{dollar}\sb2{dollar}CO{dollar}\sb3{dollar} +NaHCO{dollar}\sb3{dollar} solutions under nonisothermal conditions.



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