The effect of salt on the chemical potential of neutral macromolecules determined by ternary diffusion coefficients

Diffusion of macromolecules in aqueous solutions is important for many laboratory, biological, and manufacturing applications. However, aqueous solutions containing macromolecules often contain other additives. An important feature of these multicomponent mixtures is the macromolecule-additive interaction. Due to this interaction, the additive concentration gradient can induce macromolecule diffusion and vice versa. This phenomenon is known as coupled diffusion and is described by multicomponent diffusion coefficients. This thesis reports the experimental investigation of multicomponent diffusion coefficients for the Poly(ethylene glycol)-KCl-water ternary system at 25°C using Rayleigh interferometry. These coefficients were used to determine PEG-salt interaction. Furthermore, isopiestic experiments were performed to demonstrate that multicomponent diffusion yields accurate thermodynamic parameters. Fundamentally, this work has provided a significant contribution to the connection between diffusion and thermodynamics. Moreover, significant coupled diffusion between PEG and KCl was observed due to a large PEG hydration. Thus, PEG concentration gradients can be used to induce diffusion of other molecules in water for potential applications in controlled-release and micro-fluidic technologies.