Polyelectrolyte Diffusion in Convex Lens-induced Confinement (CLiC)

Understanding the transport and thermodynamics of polymers in confined spaces is helpful for many separation processes like water purification, drug delivery, and oil recovery. Specifically for water purification, typical membrane foulants are polyelectrolytes, which have been modeled using polyacrylic acid. Uncovering how these polyelectrolytes interact in confinement can reduce the fouling of organic membranes and will lead to better separation processes overall. We have determined the diffusion coefficient, D, of sodium polyacrylic acid (NaPAA) and dextran in Convex Lens-induced Confinement (CLiC) using differential dynamic microscopy (DDM). In this setup, the confinement ranges continuously from 0.085 – 21.7 µm. To increase the contrast, the polymers were fluorescently tagged. It was found that Dextran diffusion become slower in higher confinement, which is consistent with a change in hydrodynamic interactions. On the other hand, the diffusion of NaPAA in a high ionic strength solution (I ~ 160 mM), increased as the confinement became stronger. These findings indicate that polyelectrolyte diffusion changes in confinement and can lead to a better understanding of separation processes.