Optical measurement of binary and multicomponent diffusion coefficients in aqueous solutions

Abstract

Diffusion coefficients on the volume-fixed frame, D$\sb{\rm v}$, for the binary systems KSCN-H$\sb2$O, NH$\sb4$Cl-H$\sb2$O, and (NH$\sb4$)$\sb2$SO$\sb4$-H$\sb2$O have been measured over the entire concentration range at 25.00$\sp\circ$C by Rayleigh interferometry. Density data were measured for all three systems. For KSCN-H$\sb2$O, isopiestic osmotic and activity coefficients, viscosity coefficients, thermodynamic diffusion coefficients, and limiting conductivity data were also obtained. Thermodynamic diffusion coefficients for NH$\sb4$Cl-H$\sb2$O and (NH$\sb4$)$\sb2$SO$\sb4$-H$\sb2$O are reported. Ternary volume-fixed diffusion coefficients (D$\sb{\rm ij}$)$\sb{\rm v}$ at 25.00$\sp\circ$C have been measured for the system NH$\sb4$Cl-(NH$\sb4$)$\sb2$SO$\sb4$-H$\sb2$O at total concentrations of 1, 2, 3 and 4 mol dm$\sp{-3}$ at solute ratios of 1:3, 1:1, and 3:1 by Rayleigh and Gouy interferometry. Values of (L$\sb{\rm ij}$)$\sb0$, the thermodynamic diffusion coefficients on the solvent-fixed frame, are calculated for this system from (D$\sb{\rm ij}$)$\sb{\rm v}$, measured partial molar volumes and approximate activity data. (D$\sb{\rm ij}$)$\sb{\rm v}$ at 25.00$\sp\circ$C have been measured by Gouy interferometry for the ternary system ($\alpha$-cyclodextrin)-(L-phenylalanine)-(H$\sb2$O) at four compositions at low concentration, and an equilibrium constant for complexation between $\alpha$-cyclodextrin and L-phenylalanine calculated from these data. (D$\sb{\rm ij}$)$\sb{\rm v}$ at 25.00$\sp\circ$C are also reported for the quaternary system sucrose-NaCl-KCl-H$\sb2$O at the composition c$\sb{\rm sucrose}$ = 0.25, c$\sb{\rm NaCl}$ = 0.5, and c$\sb{\rm KCl}$ = 0.5 mol dm$\sp{-3}$ as measured by Gouy interferometry. A reasonably detailed account is given of the theory of optical diffusiometric techniques.