(192h) What Is a “Hydrophobic” Solute? a Detailed Examination of Driving Forces for Adsorption of Small, Neutral Solutes at Chemically Patterned Interfaces

While essential to life, water is also a valuable, critical component in the production of both energy and man-made materials. With global population growth, water demands will increase significantly, making recovery of water from waste-streams an essential to human life and the global economy. An efficient, cost-effective route towards meeting this demand is through membrane-based purification strategies. However, significant improvements will be necessary to meet projected global growth, in particular in terms of developing improved membrane materials for preventing fouling and allowing for selective recovery of potentially valuable contaminants. We begin to address this goal through a computational design strategy that couples detailed molecular simulations with genetic algorithm optimization. Specifically, we optimize the affinity of small, neutral solutes for model interfaces by adjusting chemical patterning of exposed surfaces. Affinities of solutes are decomposed in a detailed manner to pick apart specific contributions to binding, which we can show is driven largely by an increased ability of solvent to accommodate a solute at an interface compared to in bulk solution. Surprisingly, polar solutes adsorb to both predominantly methylated and hydroxylated surfaces, which precludes the use of common metrics, such as solvation or octanol-water transfer free energies, to predict adsorption. We directly show that chemical repatterning of a surface to reduce affinity is tied to reducing the “space” available to accommodate a solute at an interface. Finally, we demonstrate that specific patterns of charged surface moieties can flip this contribution to binding from highly favorable to unfavorable, allowing for large shifts in binding affinity at fixed material composition, which further emphasizes the central role of chemical patterning in designing membrane materials.