How Does Charge Impact Surface Hydrophobicity?

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• Camille Bilodeau, University of Virginia
• Monday 02 June 2025, 14:00-14:30
• Zoom: https://zoom.us/j/92447982065?pwd=RkhaYkM5VTZPZ3pYSHptUXlRSkppQT09.

If you have a question about this talk, please contact Isaac Parker.

Molecular-scale hydrophobicity plays a key role in many important interfacial phenomena ranging from adsorptive separations and fouling to colloidal assembly and protein aggregation. While macroscopic hydrophobicity can be experimentally measured using a simple contact angle, hydrophobicity at molecular length-scales is difficult to quantify and depends on surface chemistry and patterning in unintuitive ways. In this work, we investigate the relationship between charge and hydrophobicity by studying a series of model patterned hydrophobic and charged surfaces. To measure the “hydrophobicity” of the surface, we use two different views of hydrophobicity. First, we apply Indirect Umbrella Sampling (INDUS) an enhanced sampling technique that directly measures the free energy of cavity formation. Second, we perform spatial umbrella sampling to obtain a free energy of binding of two model hydrophobic solutes, a gold nanoparticle functionalized with an alkyl thiol SAM and a model hydrophobic protein, hydrophobin. We show how our definition of hydrophobicity is sensitive to how we define hydrophobicity and discuss the theoretical basis for connecting adsorption energetics to de-wetting thermodynamics. Using these methodologies, we find that different positively charged groups (i.e. ammonium versus guanidinium) impact hydrophobicity differently due to their differences in geometry, partial charge distribution, and number of hydrogen bond donor sites. We additionally find that charged group spacing plays a major role in modulating hydrophobicity, with specific “sweet spot” distances being associated with maximizing hydrophilicity. This work lays a foundation for connecting dewetting calculations to adsorption as well as for understanding how charged group chemistry and patterning impact hydrophobicity.

This talk is part of the Lennard-Jones Centre series.

This talk is included in these lists:

• Hanchen DaDaDash
• Lennard-Jones Centre
• Zoom: https://zoom.us/j/92447982065?pwd=RkhaYkM5VTZPZ3pYSHptUXlRSkppQT09

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