A. Vergara et al., Multicomponent diffusion in crowded solutions. 1. Mutual diffusion in the ternary system poly(ethylene glycol) 400-NaCl-water, MACROMOLEC, 34(4), 2001, pp. 991-1000
The multicomponent approach in the description of molecular diffusion takes
into account the correlation of motion between solutes. Here it is shown t
hat this approach is necessary to describe correctly the flows of each comp
onent in concentrated solutions of macromolecules, defined "crowded solutio
ns". Microscopic intuitive considerations make clear this necessity also fo
r hypothetical uncharged hard particles. We present precise measurements of
mutual diffusion coefficients relative to five compositions of the ternary
system poly(ethylene glycol) (PEG) 400-NaCl-water, changing both the PEG a
nd salt concentrations. The values of the experimental diffusion coefficien
ts for this system seem to be dominated by an excluded volume effect. Our r
ecent predictive equations, proposed to evaluate the diffusion coefficients
in a ternary systems of hard sphere solutes, have been tested on the exper
imental data with reasonable success. The thermodynamic and gravitational s
tability analysis on the collected data is also reported. By changing the c
hoice of solvent constituent from water to PEG or NaCl, it is clear that th
e counter-flow related to the polymer flux in crowded solutions is due esse
ntially to the water and not to other constituents.