Transport processes in binary and ternary mixtures containing water, triethylamine and urea. Part 1.—Intradiffusion and viscosity coefficients

Intradiffusion coefficients for each component of the binary system water + triethylamine, and of urea at trace concentrations (2 × 10–5 mol dm–3) have been determined at 5 and 15°C, i.e. below the lower consolute temperature of the system. In addition, intradiffusion coefficients for urea in the ternary system water + triethylamine + 0.2 mol dm–3 urea at 5 and 17.5°C have been measured. Limiting intradiffusion coefficients for triethylamine, urea, and tritium-labelled water in water are consistent with expectations based on a modified Stokes–Einstein equation, but water in triethylamine diffuses at about the same rate as triethylamine in triethylamine. This can be explained by assuming that water molecules are strongly bound to triethylamine in these circumstances. The intradiffusion coefficients of urea and water vary rapidly with changing triethylamine content, but maintain almost the same ratio. Intradiffusion coefficients of triethylamine also change markedly with concentration but in a different manner.Two semi-empirical equations relating the viscosity of a binary solution to the intra-diffusion coefficients of the two components have been tested with these data. One was reasonably successful in predicting the composition at which the viscosity reached its maximum.