Solvation of ions, surfactants and polymers at interfaces and in confinement
Douwe Jan Bonthuis
ITPCP, TU Graz
16:15 - 17:15 Tuesday 14 March 2023 TUG In contact with aqueous solutions, many interface types spontaneously acquire a surface charge through deprotonation, adsorption of charged species, or both. Moreover, modification of surface properties by polymer adsorption is a widely used technique to tune interactions in experiments such as nanopore sensing. Understanding the combined effects of ions, polymers and surfactants on aqueous solutes is of paramount importance for our understanding of a wide range of geological, electrochemical and biochemical processes. I will discuss two systems where the combination of experiments with molecular simulations provide detailed insights in these fundamental interactions.
At partially deprotonated surfaces in water, ions screen the surface charge, and interfacial fields break the centro-symmetry near the surface, which can be probed using second-order nonlinear spectroscopy. We use sum-frequency generation (SFG) spectroscopy to probe the symmetry-breaking of water molecules at a charged silica surface in contact with alkaline metal chloride solutions. Use molecular dynamics simulations, we are able to interpret the experimental results on the basis of the underlying molecular structure of the interfacial layer.
Using microfluidic experiments and Monte Carlo simulations, we investigate how the ionic current noise through solid-state nanopores reflects the adsorption of short, neutral polymers to the pore surface. In particular, the power spectral density of the current noise shows a characteristic change upon the reversible adsorption of polymers, the magnitude of which is strongly dependent on both polymer length and salt concentration. Comparison with the Monte Carlo simulations provides direct access to the molecular interaction potential.
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