| Abstract
| - The multicomponent approach in the description of molecular diffusion takes into accountthe correlation of motion between solutes. Here it is shown that this approach is necessary to describecorrectly the flows of each component in concentrated solutions of macromolecules, defined “crowdedsolutions”. Microscopic intuitive considerations make clear this necessity also for hypothetical unchargedhard particles. We present precise measurements of mutual diffusion coefficients relative to fivecompositions of the ternary system poly(ethylene glycol) (PEG) 400−NaCl−water, changing both the PEGand salt concentrations. The values of the experimental diffusion coefficients for this system seem to bedominated by an excluded volume effect. Our recent predictive equations, proposed to evaluate the diffusioncoefficients in a ternary systems of hard sphere solutes, have been tested on the experimental data withreasonable success. The thermodynamic and gravitational stability analysis on the collected data is alsoreported. By changing the choice of solvent constituent from water to PEG or NaCl, it is clear that thecounter-flow related to the polymer flux in crowded solutions is due essentially to the water and not toother constituents.
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